^r6U HARVARD UNIVERSITY -^ Library of the Museum of Comparative Zoology 3-t\/A - Prov o Brigham Young University Scienc Bulletin THE PEREGRINE FALCON IN UTAH, EMPHASIZING ECOLOGY AND COMPETITION WITH THE PRAIRIE FALCON MUS. COMP. ZOOl- L/BRARY SEP 24 1973 HARVARD byUNJVERSlTY Richard D. Porter and Clayton M. White in collaboration with Robert J. Erwin BIOLOGICAL SERIES— VOLUME XVIII, NUMBER 1 JUNE 1973/ISSN 0068-1024 BRIGHAM YOUNG UNIVERSITY SCIENCE BULLETIN BIOLOGICAL SERIES Editor: Stanley L. Welsh, Department of Botany, Brigham Young University, Provo, Utah Acting Editor: Vernon J. Tipton, Zoology Members of the Editorial Board: Ferron L. Andersen, Zoology Joseph R. Murdock, Botany WiLMER W. Tanner, Zoology Ex officio Members: A. Lester Allen, Dean, College of Biological and Agricultural Sciences Ernest L. Olson, Director, Brigham Young University Press The Brigham Young University Science Bulletin, Biological Series, publishes acceptable papers, particularly large manuscripts, on all phases of biology. Separate numbers and back volumes can be purchased from University Press Marketing, Brigham Young University, Provo, Utah 84602. All remittances should be made payable to Brigham Young University. Orders and materials for library exchange should be directed to the Division of Gifts and Exchange, Brigham Young University Library, Provo, Utah 84602. Brigham Young University Science Bulletin THE PEREGRINE FALCON IN UTAH, EMPHASIZING ECOLOGY AND COMPETITION WITH THE PRAIRIE FALCON by Richard D. Porter and Clayton M. White in collaboration with Robert J. Erwin BIOLOGICAL SERIES— VOLUME XVIII, NUMBER 1 JUNE 1973/ISSN 0068-1024 Frontispiece. Male (tierce!) Peregrine Falcon on rock in front of eyrie (Table 1, site 7); it is clutching a young American Avocet ( Recurvirostra amcricuna), that was fed to tlie young falcons, c. New York Times Co., 1971. Photo by R. D. Porter, 1952. TABLE OF CONTENTS ABSTRACT 1 INTRODUCTION 1 GEOGRAPHIC DISTRIBUTION IN UTAH 2 Historic Records 2 Specimen Records 2 Nesting Records 2 Postnesting Season and Winter Records 9 DENSITY DISTRIBUTION OF PEREGRINE EYRIES IN UTAH 12 TOPOGRAPHY. CLIMATE, AND PLANT COVER IN UTAH 13 ECOLOGICAL DISTRIBUTION OF UTAH PEREGRINES 14 Climate 14 Altitude '. 15 Habitat Niche 15 Nesting Sites 19 Cliff Orientation 19 Rock T)pe, Cliff Size, and Eyrie Height 19 Hunting Sites 21 Food Niche 28 NESTING BEHAVIOR IN UTAH 32 History of Nesting at a Wasatch Mountain Eyrie 32 Egg Laying 38 Incubation 41 PEREGRINE DECLINE IN UTAH 41 Climatic Change Hypothesis for Peregrine Decline 42 Pesticide Hypothesis for Peregrine Decline 44 Pesticide Syndrome in Utah Peregrines 44 Residues of Pesticides in Peregrine Prey Species 46 Mosquitocide Usage in Utah 46 Disease Hypothesis for Peregrine Decline 47 Human Activity Factors in the Decline of the Peregrine 47 FACTORS INFLUENCING PEREGRINE DISTRIBUTION AND ABUNDANCE IN UTAH 48 Water, Food, and Nesting Sites as Limiting Factors 49 Interspecific Competition during Nesting Season 50 Some Factors Modifying Competition and Success 51 Competition with the Prairie Falcon for Food 52 Competition with the Prairie Falcon for Eyrie Sites 55 Directional Exposure Preferences 55 Height Preference for Cliffs and Eyrie Sites 56 Eyrie Type Preferences 56 Size Preference for Nesting Area 58 Aggressive Interactions between Peregrines and Prairie Falcons 59 Date of Egg Laying as a Competitive Factor 61 Reproductive Potential as a Competitive Factor 62 PLEISTOCENE AND PREHISTORIC PEREGRINE AND PRAIRIE FALCON DISTRIBUTIONAL RELATIONSHIPS 62 Pleistocene Distributional Records 62 Post- Pleistocene Distributional Records 63 Lake Bonneville and Peregrine Distribution in Utah 63 SUMMARY AND CONCLUSIONS 65 Addendum 70 ACKNOWLEDGMENTS 70 APPENDIX —ADDITIONAL HISTORY OF DDT USAGE AS A MOSQUITOCIDE IN UTAH 70 LITERATURE CITED 71 THE PEREGRINE FALCON IN UTAH, EMPHASIZING ECOLOGY AND COMPETITION WITH THE PRAIRIE FALCON by Richard D. Porter^ and Clayton M. White^ in collaboration with Robert J. Erwin^ ABSTRACT This study was undertaken to record the known history of the Peregrine Falcon ( Faico peregrinus) in Utah as we have been able to construct it from both the hterature and from our original research that extends over about a 30-year period in the state. The present total population of the peregrine in Utah is possibly only 10 percent of what it has been in historic times. In an effort to find explanations for the decline, we have explored hypotheses of ch- matic changes, impact of pesticides, disease, and human disturbances. We conclude that pesticide contamination and climatic changes mav have been the major reasons for their de- cline in Utah. A general background of the geographical and ecological distribution of the species in Utah is provided as are also details of its nest- ing behavior from some Wasatch Mountain eyries. Our data suggest that its nesting density along the Wasatch Mountains was about the same order of magnitude as nesting densities in other regions of North America that are gen- erally considered more favorable to the pere- grine. We have considered some of the environ- mental factors that may limit the species in Utah and especially its relationship with a congener, the Prairie Falcon {Falco mexicanus). We con- clude that the peregrine may live jointly with the Prairie Falcon with a minimum of intra- specific competition. We present evidence which suggests that the peregrine has been in Utah since the late Pleistocene and that it has had a long history of sympatric existence with the Prairie Falcon. INTRODUCTION Breeding populations of the Peregrine Falcon (Falco peregrinus) have declined sharply over much of its historic range in North America and Europe during the last two decades. Although this decline has been well documented for many areas (Hickey, 1969), little has been published on the status, past or present, of the species in the Great Basin, especially as a breeding bird in Utah, an area encompassing 84,916 sq miles (219,932 km-). We wish, therefore, to place on record our obscr\'ations of the peregrine in Utah from data collected over the past .30 years. In presenting these data, it is our purpose to : ( 1 ) describe the ecological distribution of the species in the state, (2) delineate the ecological factors which may have Hmited its distribution and breeding success there, (3) describe its food and habitat niches, (4) discuss its competition with related species, especially the Prairie Falcon (Falco mexicanus), and (5) compare its present levels of population with those formerly known, since peregrines in Utah have not been immune to the decline that afflicted its populations else- where. Because the known active eyries of this species in the state are now only about 10 per- cent of those known to have been present earlier in the century, another of our objectives is to (6) discuss and evaluate the factors which may have led to the near extirpation of this species in the state. ^Present address: Bureau i>f Sport KiOieries and Wildlife. Inteniiountain Forest and Range Experiment Station, Federal Building, Rm B2, West First North, Provo, Utah 84t)()l ^Department of 7,ooIogv. Brigham Young University. Provo, Utah 84(i02 '892 East 3250 North, Ogden, Utah H+404- Bricham Young Univehsity Science Bulletin GEOGRAPHIC DISTRIBUTION Historic Records The percgriiu' was not mentioned in the or- nithological literature for Utah until 1871, when it was reported by Allen (1872) to prey on waterfowl about the marshes of the Great Salt Lake near Ogden. He found it to be common there in September. The next to mention the presence of the species was Henshaw (1874), who with Yarrow, collected 600 specimens of birds representing 165 species on a trip from Salt Lake City to St. George between July and De- cember 1872. The peregrine was considered by Henshaw to be a rather common resident in Utah and to nest in the state. Henshaw's later account (1875) mentions only an observation of this species by Allen (1872) in the vicinity of Ogden, thus opening to question the source of his data supporting the status of the species in Utah. The lack of observations by Allen (1872) of the Prairie Falcon in the Great Salt Lake Val- ley and the complete absence of this species in his account of the birds encountered in Kan- sas, Colorado, Wyoming, and Utah is difficult to understand, since the peregrine apparently was noted at all but two of Allen's collecting localities and a specimen (young bird) was ob- tained by him (ibid.) at Fairplay (South Park), Colorado Territory. Did Allen ( ibid. ) overlook the Prairie Falcon or did he consider all large falcons to be peregrines? Nevertheless, his ob- servations of the peregrine along the Great Salt Lake marshes probably were accurate, as the species has been seen there many times since then. Although Ridgway ( 1S74, 1877) found the Prairie Falcon to be common in the rocky canyons of the Wasatch Mountains and a rare breeder along cliffs of canyons and valleys in Salt Lake Cit)' and neighborhood in 1869, he apparently made no observations of the pere- grine in Utah. Several earlier naturalists and explorers (Fremont, 1845; Stansbury, 1852; Baird, 1852; and Remy and Brenchley, 1861) also failed to mention the presence of the pere- grine in Utah. Specimen Records Specimens from both the arctic tundra pop- ulation (F. ;;. timdriu.s) and the more southern population ( F. p. amitttm) have been taken in Utah during the winter months. A specimen of the tumhius race, identified b)' C. M. White (CMW), was found shot and wounded by R. Vem Bullough on 15 December 1956, near Famiington Ba\-, Davis County. (For a dis- cussion of peregrine systematics, see White, 1968b.) A male specimen of unknown racial affinity was collected by Wolfe ( 1928 ) near St. George, Washington County, on 5 February 1926. John Hutchings (Bee and Hutchings, 1942) collected a specimen of anattan (sensii lata; western sub- group) (CMW) near Pelican Point, Lake Moun- tains, Utah County (date not given, Woodbury, Cottam and Sugden, unpubl. ms, indicate speci- men was taken alive, 2 August 1935). Five specimens (Twomey, 1942)— a male, molting into adult plumage; an adult female, collection date not given; and three males, collected on 23 April and 5 and 23 August in 1935 at the Ash- ley Creek marshes, Uintah County— were as- signed to the race anatinn {scnsu lato; western subgroup) (CMW). Woodbury et al. (unpubl. ms) record the following additional specimens by countv: Box Elder, at Bear River marshes, specimens taken 1 Julv and 6 September 1914; 14 September 1915; '2-, 4 September 1947 (UU). Iron, near Cedar City, 12 May 1936 (Chicago Field Mus.; LBB), anatum (sensu lato; western subgroup) (CMW). Uintah, Ashley Creek marshes, a young male in 1937 (Carnegie Mus.). Washington, Zion Canvon (Zion National Park), 16 July 1939 (Zion Park Museum) anatum (sensu lato; u-estern subgroup) (CMW). Additional specimens of F. p. anatum (sensu lato; western subgroup) have been examined by C. M. White for Emerv Count)', two speci- mens, July; and Salt Lake Countv, two speci- mens, Januar)' and November. Nesting Records Historically, the peregrine is known to have nested in 13 counties of Utah and is suspected of nesting in at least three others. Figure 1 shows the pattern of known and suspected breeding distribution in Utah, and Table 1 gives their known histories in the state. The first recorded eyrie for the state was an observation by Johnson (1899), who in May 1898, found three \oung peregrines in a shallow cave under an overhanging rock of an 80-foot (24 m) cliff [Land Rock] in Lake Mountains, west of Utah Lake, Utah Count)', and five eggs Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah m UTAH Fig. 1. Pattern of known and suspected breeding distribution of the Peregrine Falcon in Utah. Letters for the regions and numbers correspond to those on Table 1. The hne running nearly vertically through the center of the state separates the Great Basin from the Colorado River Basin. The west face of the Wasatch Moun- tains bisects area A and is encompassed within the northern and southern boundary of the area. Lightly stippled area between regions A and B delimits the Great Salt Lake Desert, although there are also other areas of salt flats at the southwest edge of the Great Salt Lake that are not classified within the confines of the desert. Bricham Young University Science Bulletin Table 1. Peregrine eyries in Utah. Eyrie site numbers and letters for regional areas correspond with those given in Figure 1. Site No. First Located and Subsequent History Last Known to be Active Date Observer Date Observer 1 2' 3 4 9 10 11 12 13 1898 1940 1939-42 1935 ca. 1926-27 1939-42 1954 1956 1940s 1939-42 1939-42 1943 ca. 1900-20? 1939-42 1943 1939 1939-42 1950 1955 1939-42 1939-42 1940s 1951 14 ca. 1900-20 1926-27 1939-42 1940s 15 1930 16 1943 1940s 17 1930s 1940s 1950s 1967 18 1930s 1939-46? 19 1930-32 20 1946-? A — Great Basin Region — Surrounding Utah and Great Salt lakes, and North Central Utah H. C. Johnson (1899) R. G. Bee (field notes) Nelson (1969)° Bee and Hutchings (1942) L. R. Wolfe (in letter) Nelson (1969)° Porter et al. (unpubl. ms) C. M. White Morlan Nelson (pers. comm., 1971) Boyd Shaeffer ( pers. coinin. ) Nelson (1969)° Nelson (1969)° R, D. & R. L. Porter R. J. Erwin, J. F. Poorman (unpubl. data) Trcganza ( in Woodbury et al., unpubl. ms) Nelson (1969)° R. D. Porter & R. ]. Erwin (unpubl. data) Morlan Nelson (pers. comm., 1971) Nelson (1969)° C. Wilson (pers. comm.) Lorin Carsey (pers. comm.), one young female taken for falconry Nelson (1969)° Nelson (1969)° Boyd Shaeffer (pers. comm.) reported eyrie to have been found and photographed in tlie 1930's by a different party R. D. Porter and Jack Hagan (unpubl. data), birds seen, eyrie not located Treganza ( in Woodbury et al., unpubl. ms) L. R. Wolfe ( in field notes of R. G. Bee), seen carrying food toward cliffs, and Wolfe (1928) Morlan Nelson (pers. comm., 1971) Boyd Shaeffer (pers. comm.), took young from eyrie Dr. Harold Austin (pers. comm.) R. D. & R. L. Porter, and R. J. Erwin (unpubl. data) Boyd Shaeffer (pers. comm.) Clyde Ward ( pers. comm. ) Boyd Shaeffer (pers. comm.) C. 'M. White (unpubl. data) Del Diamond (pers. comm.) Clyde Ward (pers. comm.) Morlan Nelson ( pers. comm. ) Clyde Ward (pers. comm.) Boyd Shaeffer (pers. comm.) Marcus Nelson? Early H. G. Johnson (field notes 1900s of R. G. Bee) 1940 R. G. Bee (field notes) Nelson (1969) 1957-58 C. M. White (unpubl. data) 1953 R. J. Erwin (unpubl. data) 1969 C. M. White (unpubl. data), single bird 1956 C. M. White (unpubl. data ) 1952 R. J. Erwin (unpubl. data) 1968? Clyde Ward 19.54 Clyde Ward 1969 H.' Austin and L. Wakefield one adult seen. 1930-32 Clyde Ward (pers. comm.) Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah Table 1 ( Continued ) 21 (SNV)= ca. 1926-27 22 (SNV) 1939-4S 23' 1942 24 1942 25 ca. 1939 26 1969 27 (SNV) 1960 28 1961 29 (SNV) 1916 & 1936 30 (SNV) 1958 1959 31 (SNV) 1953 32 1958 33 (SNV) 1958-59 34 1937 35 (SNV) 1935-? 1965-66 36 (SNV) 1961 37 1936 38 1939 39 (SNV) 1963 40 (SNV) ca. 1926 L. R. Wolfe ( ill field notes of R. G. Bee) Morlan Nelson ( pers. comm., 1971) 1970 C. M. White (unpubl. data) B — Great Basin Region — Great Salt Lake Desert 1959-60 C. M. White and Gary D. Lloyd (unpubl. data) H. Webster (letter, 1961) H. Webster (letter, 1961) C — Central Utah, eastern edge Great Basin, western Colorado River Basin (Plateau) Gunther and Nelson ( in Woodbury et al., unpubl. ms.) C. M. White (unpubl. data) 1969 G. G. Musser, A. D. Stock, and C. M. White (unpubl. data) White and Lloyd (1962) 1964 D — Colorado Plateau and Navajo Country Woodbury and Russell (1945) 1961 edge R. J. Erwin (unpubl. data) 1962 R. D. Porter (unpubl. data) Behle (1960) G. L. Richards (pers. comm.), saw fledged young C. M. White (pers. comm. from M. Hopkins, unpubl. data) E — Uinta Basin and Upper Colorado River Basin Twomey (1942) 1961 Twomey (1942) E. Peck, W. Pingree, and J. Gaskill (pers. comm.) F — Southwestern Utah, edge Great Basin; and Virgin River Valley C. M. White (unpubl. data) C. M. White and G. D. Lloyd (unpubl. data) C. M. White and G. D. Lloyd (unpubl. data), pair seen in area G. D. Lloyd (unpubl. data), adult in general area G. L. Richards (pers. comm.), at nearby locahty C. M. White and G. Worthen (unpubl. data) W. S. Long ( breeding female collected ) Grater (1947) Wauer and Carter (1965) Wolfe (1928) 1961 G. M. White (unpubl. data) 1962 C. M. White and G. D. Lloyd (unpubl. data), an adult in area 1964 Wauer and Garter (1965) 1966 C. M. White (unpubl. data), lone adult seen JMay be an alternate site for number 1: located only 2 or 3 miles (3.2 or 4.8 km) from site number 1, but nearly 40 years later. -SNV, (suspected, but not verified) adults were observed at these localities, but eyrie sites not actually located; although adult birds have been >cen one nr nir>re time^, m the authors' opinions, the sites need further verification. The validity of these sites is probable. ■The eyrie proper is about 0-5 mile (0.8 km) into Nevada. "These sites are the ones referred to by Nelson (1969); their locations were commimicated to us in a letter from Nelson dated 25 April 1969. on the same ledge on 30 March 1899 (Figs. 1-5; Table 1, site 1). While circling Utah Lake, John- son (ibid) noted Long-billed Curlew (Ntimenius americamts) , snipes (Capella gallinago), bitterns (Botaurus lentigino.nis), and a goodly number of ducks of various species which probably served as a food supply for the peregrines. Bee and Hutchings (1942) report finding a nest containing four fresh eggs on a ledge over- looking Utah Lake, (5 miles south of the Land Rock site) near Pelican Point in the Lake Moun- tains, 20 May 1935 (Fig. 1, Table 1, site 3). Thev collected the adults to verify identification. Local residents report that peregrines had been observed nesting there for many years ( ibid. ) . A visit to the sites on 22 April 1950 by R. D. Por- ter and R. J. Erwin revealed no indications of recent occupancy. In recent years lime mining Bhicham Young Univehsity Science Bulletin Fig. 2. Land Rock, west side of Utah Lake; location of first known peregrine eyrie site in Utah. It is a marginal site, which in some recent years has been occupied by Prairie Falcons. Note scrubby nature of vegetation in foreground. Photo by Kim Despain, 197L operations have destroyed the Pehcan Point site (Fig. 6) and Prairie Falcons have occasionally occupied the Land Rock site. Nelson ( 1969 ) located 9 or 10 eyries ( in letter, 25 April 1969, Nelson gave 9 eyrie loca- tions) in the area surrounding the Utah and Great Salt lakes during the period 1939-1942. This area included parts of Box Elder, Weber, Davis, Salt Lake, Utah, and Tooele counties. Treganza (in letter, 5 January 1930; Woodbury et al., unpubl. ms) found the species breeding on the cliffs fronting the lake from Brigham to Ogden [at least four eyries overlooked the Bear River Marshes in the 18 miles from Ogden to Brigham City (Woodbury, pers. comm., in White, 1969b)]. Although he located nests, he was unable to negotiate the cliffs; one was over 1,000 feet (305 m) high (Fig. 7). Females were col- lected off the nests, but precise nesting data were not obtained. Gunther and Nelson (Woodbury et al., un- publ. ms) noted the species nesting at a site in the Great Basin Desert of west central Utah during the nesting season (vear not given). Gun- ther (Woodbury et al., unpubl. ms) saw the species at a large reservoir in Wasatch County in the summer of 1938. Fig. 3. Utah Lake and adjacent habitat as presently seen from atop the Land Rock eyrie site; marshes former- ly were more extensive than today and came closer to the eyrie. Photo by Kim Despain, 197L Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah Fig. 4. A view of Land Rock eyrie showing nature of terrain and vegetation. Photo by Kim Despain, 1971. Grater ( 1947 ) recorded peregrines at Angel's Landing in Zion Canyon, Washington County, from March to August 1939, where adults fre- quently were seen carrying food to a high ledge on the face of the peak. On 16 July 1939 (the more precise dates from Woodbury et al., un- publ. ms ) a young female, only a few weeks old, was accidentally killed in the canyon (Figs. 1 Fig. 5. A different view of the Land Rock eyrie show- ing terrain. Flat area formerly contained some marsh habitat. Photo by Kim Despain, 1971. and 8, Table 1, site 38). Wauer and Carter ( 1965 ) reported this site to be active as late as 19&4. In the Uinta Basin, Twome)' ( 1942) re- ported an inaccessible eyrie about 40 feet (12.2 m) up on a deep shelf of a cliff, east of the Green River, near Venial ( Fig. 1; Table 1, site 34), Uintah Count)'. Actions of the adults indicated that young were in the nest and im- mature birds were seen at the Ashley Creek marshes in early August and in the vicinity of Jensen from August through September. G. L. Richards ( pers. comm. ) saw a pair in the marsh- es in 1961, the most recent evidence of activity at this eyrie. In southern Utah, single falcons were seen at Kanab, Kane County, on 28 April 1935, and 6 April 1947, and two were recorded along Kanab Creek on 20 May 1947 (Behle, Bushman, and Greenhalgh, 1958). Behle (1960) also noted the species near the Colorado River at Dewey on 21 May 1953 (Fig. 1; Table 1, site 31), and in Glen Can\'on on 6 August 1958. Peregrines were seen several times in July and August at Navajo Mountain, San Juan County, by Woodbury and Russell ( 1945) in 1936, and by C. M. White and G. D. Lloyd (unpubl. data) in 1960 and 1961 (Fig. 1; table 1, site 29). White and Lloyd (1962) reported on the predation of young peregrines which had not yet fledged from an eyrie in the Colorado River Basin (Figs. 1, 9, and 10; Table 1, site 28). Bricham Young University Science Bulletin Fig. 6. Pelican Point eyrie site (Table 1, site 3, Fig. 1) showing lime mining operation, which in recent years destroyed the nesting cliff. Photo by Kim Despain, 1971. ^-\/'- JS^w"-*^^ Fig. 7. Treganza noted a pair of peregrines nesting on the distant 1,000 ft. (305 m) cliff in the early 1900s, but he was unable to reach the eyrie site (Woodbur)' ct al. unpubl. ms). Photo by R. J. Erwin, 1971. Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah ■mm.- '■ ■ I ' -^ '"''J\A A: ■4-J^ it^ .a#tr- :^ Fig. 8. Angel's Landing, Zion Canyon. Cliff in center where Grater (1947) saw peregrines nesting high on face of peak (Fig. 1, Table 1, site 38). Photo by Grant, 1 September 1929, Courtesy U. S. National Park Service. Postnesting Season and Winter Records The species is present in the state through- out the year (Woodbury, Cottam, and Sugden, 1949). Postbrceding adults, immatures, migrants, and wintering falcons congregate near marshes where a plentiful supply of food is available, especially near the marshes of the Great Salt Lake (Woodbury, Cottam, and Sugden, unpubl. ins). At the Bear River marshes, for example, records extend back to 1915, when Alexander Wetmore found the peregrine to be a regular and frequent visitor after mid-July (ibid.). The Christmas bird censuses taken loy Vanez T. Wil- son et al. (in Bird Lore 42, 1940; Audubon Magazine 43-48, 1941-1946; and Audubon Field Notes 1-24, 1947-1970) at the Bear River Migra- tor\ Waterfowl Refuge, indicate that the spe- cies wintered there in small numbers until the early 1960s (Fig. 11). The greatest number of peregrines seen during the seven- to eight-hour censuses was seven, in 1940. The Christmas bird counts at the Bear River marshes were exception- ally consistent from one vear to the next begin- ning in 19.39 through 1960 as regards the number of participants. th(> area covered, and the party hours afield. .Vdditionallv, V. T. Wilson directed and participated each year until 1960, after which other observers were involved and a greater area was covered, although the number of party hours afield remained essentially the same. Tlie racial affinity of specimens taken at the Bear River marshes between 1 July and 28 September (anatum, sensu lato; western sub- group), suggest that most of the postbreeding and fall peregrines in these marshes were from local eyries. The steady decline in the numbers of peregrines recorded at the Bear River marshes during thi' Christmas bird counts (ibid.) from 1939 to the early 1960s (Fig. 11) closely cor- responded with the decline in the number of ac- tive eyries in the area surrounding the marshes. This correspondence suggests that most pere- grines wintering in the marshes of Great Salt Lake probably were from local breeding popu- lations, although they also mav have been from some other sharply declining population of the anatum race. It is probable that only a small percentage of these wintering birds were from the arctic populations (F. p. twidrius), because arctic birds normally winter farther south, and because the arctic populations were not known 10 Bricham Young University Science Bulletin to have declined between 1939 and the late 1960s. Peregrines also have been reported on Christ- mas bird counts both at Ogden and Salt Lake Cit)' over the past 30 years. In addition, they have been recorded at Parowan, Iron County, on 27 December 1963 (Audubon Field Notes 18; 1964) and at St. George, Washington County, on 1 January 1969 (Audubon Field Notes 23; 1969). Cliristmas bird count data for the areas other than the Bear River marshes are either too spotty or are too heterogeneous in their method of collection to be evaluated statistically. The peregrine was recorded at Clear Lake State Waterfowl Management Area by R. Wil- liams on 16 September 1939, and by Gunther Mi:^^'^5«^-»i Fig. 9. Peregrine cliff in desert of Colorado Plateau, reported by White and Lloyd (1962) (Fig. I, Table 1, site 28). Distance from the rock at point A to the eyrie ledge at point B is 70 ft (21.3 m). Poplar trees (Popidus fremotitii), along a water course in foreground (C) are 40-50 ft (12.2- 15.2 m) in height. Photo by J. B. Piatt, May 1971. and Nelson on 24 October, 10 November, and 4 December 1941 (Woodbury et al., unpubl. ms), indicating that the species winters at other marshes as well as at those near the Great Salt Lake. Members of arctic populations (F. p. tundrius) apparently utilize Utah's marshes both as stopping places during migration and, spar- ingly, as wintering grounds. This is suggested by Lincoln's ( 1933 ) report of a peregrine banded as a juvenile at King's Point, Yukon Territory, within the geographic range of tundrius on 30 July 1924; by its recovery at Duchesne, Du- chesne Countv', Utah, on 20 February 1925; and by the collection in December of the pre- viously mentioned specimen of tundrius from Famiington Bay. Late summer sightings, which could repre- sent either resident birds or early migrants, have been recorded from several other areas. Twomey (1942) reported peregrines at Hill Creek, 40 miles (64.4 km) south of Ouray, Uintah Coun- ty, on 5 August [1935?], at Strawberr)' Reser- voir, Wasatch County, on 17 August [1935?], and Bchle ( 1960) recorded the species at Glen Can- von near Wahweep Creek, Mile 17, on 6 August 1958 and at 10,500 feet (3,200 m) on the north slope of Mt. Ellen, Henry Mountains, on 8 September 1957. Finally, a subadult was seen near Park City, Wasatch County, in late August 1959 (M. Nelson and F. Welch, pers. comm. ) . Fig. 10. Two-day-old young and an addled egg on nesting ledge at desert eyrie in Colorado Plateau (site 28) shown in Figure 9. Photo by G. D. Lloyd and C. M. White, 10 June 196L Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 11 y=.38l+(-.OI4X) Fig. 11. Linear regression analysis of the number of Peregrine Falcons recorded per party hour, during Christ- mas bird counts at the Bear River Migratory Waterfowl Refuge between 1939 and 1970. Each circle represents the observations for one Christmas bird count. Downward trend is statistically significant (p<0.01). This analysis suggests that the peregrine had essentially disappeared as a wintering bird in the Bear River marshes by 1965. 12 BnicnAM Young University Science Bulletin DENSITY DISTRIBUTION OF PEREGRINE EYRIES IN UTAH Utah's desert climate should seem to be a significant barrier to the nesting of the pere- grine, yet we have compiled a list of about 40 eyries in the state (Table 1), which appear to have been active at one time or another. On the basis of density, if all 40 eyries were active simultaneously, there would be about 2,123 sq miles (5,499 km-) per eyrie site. If the 11 sus- pected but unverified eyries (SNV, Table 1) are excluded, the density would be reduced to one eyrie site for every 2,928 sq miles (7,584 km=). Density of peregrine nesting sites in Utah appears to be directly related to the availability of food and suitable cliffs for nesting. The im- portance of these two factors to the distribution and density of the peregrine in the state will be discussed separately in a later section. Eyrie sites usually were situated near marshes, lakes, or rivers, where there was a plentiful supply of prey species. Where the nesting habitat was ex- tensive, such as in the area of the Great Salt Lake ( Fig. 1, Table 1 ), eyrie sites were clustered around the marshes in a pattern conforming to the availability of nesting sites (Fig. 12). Else- where in the state, where suitable habitat is greatly restricted, each eyrie site usually was located many miles from its closest known neigh- bor (Fig. 1). The density of peregrine eyries in Utah, ex- clusive of the area surrounding the Great Salt Lake (4,500 mi-; 11,655 km-), is one site per 4,232 sq miles ( 10,962 km-), if the 19 additional- ly known and suspected eyries were all active simultaneously. If the 10 suspected eyries in the remainder of the state are excluded, the aver- age area per nest site would be 8,935 sq miles (23,142 km-). There were 20 known eyries in the area surrounding the Utah and Great Salt lakes (Fig. 1, Table 1, e}rie sites, 1-20). This is exclusive of eyrie site 22 (Table 1) which is outside of the region. One other probable eyrie is suggested by the presence of adults on each of several visits by L. R. Wolfe ( field notes of R. G. Bee) to one other site (site 21, Table 1). If all 20 known eyries were active concurrently, there would have been one eyrie site for about every 225 sq miles (583 km-) in an area cover- ing about 4,500 scj miles (11,655 km-), sur- rounding and including the Utah and Great Salt lakes (Fig. 1, Table 1). The average distance between 13 eyries ( sites 5, 7-10, 12-19, Table 1) located along 130 linear miles (209 km) of the west face of the Wasatch Mountains from the south end of Utah Lake to the north end of the Great Salt Lake was 10.0 linear miles ( 16.1 km). The closest eyries to each other were about 2 miles ( 3.2 km ) apart and the Fig. 12. Looking east from the peregrine's hunting habitat at a large Utah marsh toward its nesting habitat along the escarpment of the Wasateh Mountains. Two pairs of peregrines ami tliree pairs of frairie FiJcons nested on the portion of the ejiffs seen in tlie distanee and both species utilized tlie marshes. Photo by R. J. Erwin, August 1971. Biological Sehies, Vol. 18, No. 1 PEREcniNE Falcon in Utah 13 farthest were 20 miles (32.2 km) apart. How- ever, since cliffs make up only about 25 miles (40 km) of the 130 linear miles, including side canyons (estimated from U. S. Geological Sur- vey topographic maps), peregrine eyries, on the average, were only about two miles (3 km) apart on the cliff sections of the mountain. Sev- eral additional eyries near the western edge of Utah Lake and the eastern and southern edges of the Great Salt Lake were not included because they did not fall in a direct line with the 13 eyries mentioned above. It is possible that populations of the pere- grine were substantially greater prior to arrival of the first white settlers than historically, con- sidering the apparent abundance of food that was available in nearby marshes, the number of cliffs which appear to be suitable (but which lia\'e not been known to harbor peregrines ) , and the probable lack of human disturbance. Population densities of the magnitude of those occurring around the Great Salt Lake seeminglv did not differ greatly from some of those present in other regions of North America where the environment is considered more con- genial to the peregrine. For instance, Herbert and Herbert (1965) recorded nine eyries along 55 miles (88.5 km) of the Hudson River (eight on the west side) for an average of 6.1 miles (9.8 km) per eyrie. Berger and Mueller (1969) found 14 eyries along a 198.4-mile (319 km) stretch of upper Mississippi River for an average of 14.2 miles (22.8 km) between eyries. White and Cade ( 1971 ) recorded a peregrine density along the Colville River in 1967-1969 to be one pair per 8.3 miles (13.4 km) above Umiat Mountain and one pair per 3.7 miles (6.0 km) below Umiat Mountain, giving an overall average of 6.03 river miles (9.7 km) be- tvveen eyries. The distance between active eyries ranged from 0.4 miles (0.64 km) to 27 miles ( 4.3.4 km ) . There were 32 nesting pairs of pere- grines along 183 miles (294 km) of the Colville River in Alaska in 1952, 40 pairs in 1959, and 27 pairs in 1967, for an average distance in miles between eyries of 5.7, 4.6, and 6.8 (9.2, 7.4, and 10.9 km), respectively (Cade, I960; White and Cade, 1971). The average distance between 19 eyries along 172 miles (277 km) of the Yukon River in Alas- ka was 9.3 miles (15 km) (range, 2.75-31 mi; 4.4-49.9 km) in 1951 and 10.1 miles (16.3 km) (range, 2-31; 3.2-49.9 km) in 1966 (Cade, White, and Haugh, 1968). Cade, White, and Haugh (1968) believed that the peregrine probably was never more common along the Yukon than in 1966. For the Aleutian Islands, White, Emison, and Williamson ( 1971 ) found the average distance between peregrines defending territories to be about 5.8 miles (9.3 km) (range, 0.81-21 mi; 1.3-34 km) for Amchitka Island, similar densi- ties on Rat and Semisopochnoi islands, and ec|ual or perhaps greater densities on Kiska Island (M. Nelson, pers. comm., 1971). On the other hand, no locality in Utah had populations approaching the densities found in several other regions. Hickey (1942), for exam- ple, in a local area of the eastern United States, reported five pairs of peregrines on 7 miles (11.3 km) of escaqiment. In Great Britain, Rat- cliff e ( 1962 ) found three pairs residing along a linear distance of 1,000 yards (914 m) of sea chff, and 15 pairs along a 17-mile (27.4 km) distance. The highest densities known are for the Queen Charlotte Islands, where five to eight pairs of falcons utilized a linear distance of a mile (1.61 km) of sea cliff (Beebe, 1960). Hickey (1942) listed 19 pairs of peregrines in an area of about 10,000 sq miles ( 25,900 km^ ) around New York City, for an average of one pair for evers' 526 sq miles (1,362 km-). Cade ( 1960 ) estimated a probable density of 200 and 300 sq miles (518 and 777 km') per pair in the Colville and Yukon river systems, respec- tively, and one known pair per 2,000 sq miles (5,180 km-) in the Yukon countr\'. Bond ( 1946 ) considered the peregrine to be common along the western coast of the United States and Baja, Mexico, where there was an average of less than 2,000 sq miles (5,180 km=) per known pair. Judging from the data presented above, the peregrine was relatively common in the area of the Great Salt Lake and uncommon elsewhere in Utah. TOPOGRAPHY, CLIMATE, AND PLANT COVER IN UTAH Utah is in a region of generally high inland plateaus and mountains which have been dis- sected by numerous canyons and dotted with manv lakes and inland valle\s. A chain of moun- tains and high plateaus beginning at the comer of Wyoming and extending southwest\vard ap- proximately two-thirds of the length of Utah separate the major part of the state into the Colorado and Great Basin drainage areas (see Fig. 1 ) . The elevation of this central mountain 14 BniGHAM YouNO Univeksity Science Bulletin chain ranges from 9.000 to 12,000 feet (2,743- 3,658 m). Tlie Wasatch Mountains make up the northern third of the central cliain ( to the south- em end of Utah Lake) and high plateaus the remainder. Nearly all of Utah west of the central moun- tain chain lies in the Great Basin and contains the entire drainage of ancient Lake Bonneville, of which Utah, Sevier, and Great Salt lakes are remnants. The Great Salt Lake, which is about 83 miles (134 km) long by 51 miles (82 km) wide, has fluctuated in area from 2,400 sq miles (6,216 km-) in 1870 to 950 sq miles (2,461 km-) in 1961 (Nelson, 1969). It contains high concen- trations of salts (about 25 percent) comprising principally sodium chloride and sodium sul- fate. Utah Lake, which is about 23 miles (37 km) long and 15 miles (24 km) wide, is fresh water. Water comprises nearly three percent of Utah's area due mainly to these lakes. The low- lands on the floor of the basin range from 4,200 to 5,550 feet (1,280-1,692 m) in elevaHon. Just west of the Great Salt Lake lies the Great Salt Lake Desert, one of the most formidable deserts in North America. In its greatest length and width it exceeds 150 by 60 miles (240 by 97 km) (see Fig. 1). Tlie eastern half of the state is in part of the Colorado Plateau or Colorado River Basin. The Colorado River Basin is bordered on the north by the high Uinta Mountains, some peaks of which exceed 13,000 feet (3,962 m), and con- tains the Uinta Basin immediately south of the mountains and the eanvonlands farther south. It is dissected from north to south by the Green and Colorado rivers. The basin floor ranges in elevation from about 4,300 feet to 6,000 feet (1,311-1,829 m). The Virgin River Basin, in southwestern Utah, is about 2.250 feet (686 m) in elevation. Because Utah lies in the rain shadow of the high coastal ranges, it is one of the drier regions in North America, with an average of onlv 4 to 10 inches ( 10.2-25.4 cm ) of annual precipita- tion in the desert lowlands. The precipitation generally increases with an increase in altitude and may reach 30 to 50 inches (76.2-127.0 cm) annually in the higher mountains. Daily and seasonal temperatures in Utah vary widely. The summer maximum may exceed 100°F. The rela- tive humidity is extremely low and the evapora- tion rate is high. The desert lowlands are dotted with salt desert shrubs consisting chiefly of greasewood (Sarcobatus vermiculatus) and shadscale (Atrt- plex confertifolia) in areas below 5,.500 feet ( 1,676 m) in elevation, and sagebrush (Artemisia tridentata) in areas higher than 5,500 feet (1,676 m) throughout much of the Colorado Plateau and the Great Basin. This low scrubby vegeta- tion ranges from several inches to several feet in height. Desert scrub, consisting predominantly of mesquite (Prosopis glandtiliflora) , creosote bush ( Larrea divaricata ) , and black brush ( Coleogtjne Tamosissima ) , occurs in the southern desert of southwestern Utah. The more arid foothills in the Great Basin and Colorado Plateau, which receive 10 to 15 inches (25.4-38.1 cm) of rainfall annually, are covered with pinon-junipcr forests (Pinus and Jimipems). 10 to 30 feet (3.0-9.1 m) in height. Foothills receiving 16 to 20 inches (40.6-50.8 em) of rainfall are covered with a variety of scrubbv trees and bushes called chaparral, con- sisting of oak (Qiiercus), maple (Acer), service- berry (Amelancliier), mountain mahogany (Cer- cocarpus), mountain laurel (Ceanothus), and manzanita (Arctostaphtjlos). Above the foot- hills lie montane forests of spruce (Picea), fir (Abies), and aspen (Populus tremnloides) . The aforementioned data on relationships between precipitation and vegetation are modified from Woodbury and Cottam (1962). Utah's numerous mountain ranges, its ex- tensive plateaus, and its high cliffs and mesas supply a plentitude of suitable nesting sites for birds of prey. The low scrubby vegetation of its foothills and desert lowlands provides the extensive hunting areas preferred by the larger falcons. ECOLOGICAL DISTRIBUTION OF UTAH PEREGRINES Climate The peregrine, as represented by a cosmo- politan assortment of geographically variable races, has adapted to a wide variety of environ- mental conditions. This is true also for the ana- tum race, which ranges from the tree line of the North American Arctic south sparingly into northern Mexico and the southern tip of Baja California. In Utah, the peregrine has been known to nest in the Great Salt Lake Desert, one of the more arid regions known to be in- habited by this cosmopolitan species. At Wen- dover, for example, the monthly rainfall for the critical breeding period of March through July averaged onlv 0.44 inches (1.12 cm) over a 49- vear period; the mean monthlv temperature Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 15 ranged from 42° F (6°C) in March to 79°F (26°C) in July (U. S. Dept. of Commerce, 1965). Bond ( 1946) tells of peregrines nesting in the hot, arid climates along the lower Colorado River in California, in northeastern California, and eastern Oregon. Climate along the Wasatch Mountains of Utah, where the peregrine historically attained its maximum density in the state, is more mod- erate. Here (Salt Lake City) the monthly rain- fall for March through July averaged 1.03 inches (2.62 cm) over a 32-year period; the monthly temperature ranged from 40°F (4.4°C) in March to 77°F (25°C) in July (U. S. Dept. of Com- merce, 1965). Figures 13-15 delineate some of the climatic extremes associated with nesting peregrines in Utah. The hythergraphs given in Figure 13 are composites of the mean monthly extremes of daily temperature (for record period) and the mean monthly precipitation for weather sta- tions near 18 known peregrine eyries distrib- uted throughout Utah. Tlie breeding period, March through August, is indicated also. Tlie composite hythergraphs are constructed the same as those given by Twomey (1936) and Linsdale ( 1937 ) , except that these authors used mean nionthlv averages of daily temperature rather than extremes (data from U. S. Dept. of Commerce, 1965). In Figure 14 we have plotted the monthly a\'erage of the daily minimum temperature against the monthly average of the daily maxi- mum relative humidit>' (from readings taken at three-hour intervals, 1965 through 1969) and the monthly average of the daily maximum tempera- tures against the monthly average of the daily minimum relative humidity for Salt Lake City ( U. S. Dept. of Commerce, Local Climatol. Data 1965-1969). Figure 15 gives a composite of the mean number of days per month that the precipitation was equal to or exceeded 0.1 inch (0.25 cm) and the mean number of davs per month in which the temperature was equal to or exceeded 90°F (.32.2°C), averaged for the 18 stations util- ized in Figure 13 (data from U. S. Dept. of Commerce, 1965, [for record period]). We used the extremes of climate since they, more than means, are likelv to influence the general distribution of a species. According to Odum (19.59:116-117): . . . temperature exerts a more severe limiting effect on organLsm.s when moishire conditions are extreme, that is, either very high or very low, tlian wlien such conditions are moderate. Likewise, moisture plays a more critical role in the extremes of temperature. It is at the environmental extremes that the evolutionary processes for a species are most pronounced in regards to the development of new limits of tolerance. By comparing the cli- matic extremes at the periphery of the ecologi- cal range of a species, such as the peregrine in Utah, one may gain an insight into the climatic factors which may hmit its range. Altitude For western North America, Bond's data ( 1946 ) indicate that the peregrine rarely nests above 5,000 feet (1,524 m) in elevation, with a few nesting up to 10,000 feet (3,048 m) in California. However, many of the 18 eyries cited by Enderson (1965) for Colorado were above 5,280 feet (1,610 m), while the majority of them were above 6,000 feet (1,829 m) (En- derson, pers. comm.), with one eyrie in a high mountain region of Colorado, situated at an elevation of 12,000 feet (3,658 m) (Thomas D. Ray, pers. comm.). It may be that the habitat requirements of the peregrine are best satisfied in Colorado at these higher elevations. The paucity of eyries known to Bond ( 1946 ) to be at the higher elevations may be due, in part, to the difficulties encountered in reaching and search- ing the cliffs. Nelson (1969) reported that peregrines in Utah nest at elevations up to tree line, between 6,000 and 7,000 feet (1,829 and 2,134 m). The only eyrie in Utah exceeding 6,000 feet (1,829 m), that is known to us, is at an elevation of 6,700 feet (2,042 m) (Table 1, site 36), but two are at 6,000 feet (Fig. 1, Table 1, sites 22 and 37), and the elevations of four others approach 6,000 feet (Fig. 1, Table 1, sites 26, 28, 35, 38). One suspected eyrie site, however, is at an ele- vation of 8,500 feet (2,591 m) (Fig. 1, Table 1, site 29) and another is at 9,750 feet (2,972 m) (Fig. 1, Table 1, site 27), suggesting the possi- bility that if higher areas were searched, others would be found. The mean elevation of pere- grine eyries in Utah is about 5,000 feet (1,524 m) (Table 2). They ranged from 3,360 to 6,750 feet (1,024-2,057 m), with a prepon- derance of eyries (89 percent) between 4,000 and 6,000 feet (1,219 and 1,829 m) in eleva- tion, and with nearly 50 percent of them at elevations between 4,500 and 4,999 feet (1,372 and 1,524 m). A frequency distribution of the elevations of Utah eyries is given in Table 2. Habitat Niche The habitat niche of the peregrine may be divided into two parts: (1) the cliff or substrate upon wliich it lays its eggs and rears its young 16 Bhicium YdUNC University Science Bulletin 100- 2C>- 10- - Maximum oV 0 ■M- 4- M NIMUM I I I I I I I I 2 3 0 12 Inches of Precipitation Fig. 13. Composite hythcrj^raph for 18 stations situated near known peregrine eyries in Utah. Mean total monthly precipitation is represented in inches and mean monthlv extremes of temperature (daily ma.\i- mum and minimum, for record period) are represented in degrees F; they were constnicted the same as those given by Twomev (1936) and Linsdale (1937), except that these authors used mean monthly temperatures (U.S. Dept. Commerce, 1965). The diagonalK lined area depicts the climatic conditions for the egg-laying and incubation period (March-May); the stippled area represents the hatching and nestling period (May and June); the vertically lined area shows the fledging period (June-August). Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 17 IOOt SO- SO' UJ S60- Q -50- LlI a: <40- Ixl a. ^30' 20-- 10- - 0' MIN TEMP : MAX REL HUM ■'• K. MAX TEMP-. MIN REL HUM 1 I I I I I I I 0 10 20 30 40 50 60 70 Percent of Humidity -I 80 90 100 I'ig. 14. Climographs for Salt Lake City. Utah. Daily maximum temperatures (averaged monthly for years 1965-1969), represented in degrees F are plotted against the mean daily minimum relative humidity for the same period; and the mean daily minimum temperatures for the same period are plotted against the mean daily maximum relative humidity. Humidit)- vahies were average from the maximum and minimum readings, taken at .3-hour intervals for 196.5 through 1969 (U.S. Dept. Commerce, Local Climatological Data). Num- bers beside points designate month.s of the year. 18 Bhigham Young University Science Bulletin 3a 25- 20 o o < Q 10- N=I8 Mean- EXTREMES / / / -r- ^^ \ •4- Mar Apr May Jun MONTHS Jul Aug 30 25 20 15 \0 O Al i^^--^^ N=I8 Mean Extremes a;:^' —(I ^•~. I 0^ ,^^ Cv. ^/S^"^^'^93B3a ^^K^ I b. £ \ &/\ A Fig. 16. Directional facings of Peregrine Falcon and Prairie Falcon eyries in Utah, both in areas of sympatry and in areas of allopatry. The values in the outer ring are for the peregrine; those in the inner ring are for the Prairie Falcon. The directional relationships shown here were statistically significant at /; <0.01 (X" test; calculated .\= value, 7.37, 1 df) for the Prairie Falcon and p<0.05 (X=test; calculated X= value, 4.48, 1 df) for the Peregrine Falcon. situated on cliffs composed principally of four types of rocks: limestone, nine e\'rics; sandstone, nine eyries; quartzite, six eyries; and volcanic rock, three eyries. One additional eyrie each was located on volcanic agglomerate, granite, and metamorphic gneiss. According to Hickey (1942), the height of the cliff is involved in the species' fidclit) at the eyrie site over many generations of occupancy, and this concept is supported h\- Ratcliffe ( 1962, 1969) in Great Britain; iMsclu-r (1967) has dis- cussed the concept for eyries elsewhere in Eu- rope. Hickey (1942), on the basis of height and c()ntinuit\' of use, classified cliffs in the eastern United States into three classes. Bond (1946) believes Hieke\"s (op. eit. ) classification to bi' an oversimplification in the western United States. Peregrines in Utah selected a wide variety of e\ rie sites. .-Mthough the histor\- of occupancy of indi\'iduai eyries in Utah is largely unknown, there is some evidence to support Hickey's ( op. cit. ) hypothesis, at least in regards to height. I']\rie sites on the low, marginal cliffs were the first to be abandoned in Utah, whereas several Biological .Series, Vol. 18, No. 1 Pereghine Falcon in Utah 21 that were situated high up, on massive cliffs that were difficult to climb, have the longest histories of occupancy. A frequenc\' distribution of heights of cliffs which supported nesting peregrines in Utah are gi\'en in Table 3. These cliffs ranged from 40 to 400 feet (12.2-122 m) in height. The mean height of 21 such cliffs in Utah was 178 feet (.54.3 m). An additional cliff, first noted by Treganza earlv in this centur)' and reported by \\'oodburA- et al., (unpubl. ms), was in excess of 1,000 feet (304.8 m) in height (Figs. 1 and 7; Table 1, site 8). We excluded it from our cal- culations so as to not disturb unduly the more normal range of heights (see footnote. Table 3). For 14 evries the distance from the base of the cliff to the evrie site averaged 105.5 feet (32.2 m) and ranged from 28 to 330 feet (8.5-100.6 m). These measurements do not include the talus slope and mountain side. If these distances were included, the values given above would be considerably higher for most sites, especially those on the escaq^mcnt of the Wasatch Mountains. Ratcliffe (1962) has dis- cussed the importance of the steep slopes as a relevant factor in attracting peregrines to the cliff. From the brink of the cliff to the eyrie sites below, the distance averaged 68.6 feet ( 20.9 m ) and ranged from 12 to 250 feet ( 3.7- 76.2 m ) for 13 e\ries. The values given here for cliff heights aver- age somewhat higher than those reported by Cade (1960) for "the Yukon River in Alaska, and by White and Cade (1971) for the Colville River. Distances from the base of cliffs to the nest sites in Utah, however, averaged nearly twice those reported by Cade ( 1960) in the Arc- tic. Hunting Sites Marshes apparently play an important role in the breeding ecology of the peregrine in Utah (Figs. 12, 17, and 18), because nearly all peregrine eyries are situated near them. We measured the distances from each of 20 known eyrie sites in the Great Salt Lake and Utah Lake valleys to the closest nonflowing surface water, to the closest marsh 320 acres (130 ha) or larger, and to the closest marsh with no re- gard to size. The surface areas of the closest nonflowing water and the size of the closest marsh were also determined. Measurements were taken from U.S. Geological Survey topographic maps which were constructed from aerial photo- graphs taken between 1945 and 1956; they are summarized in Table 4. Of the 4,.500 sq miles (11,655 km=) sur- rounding and including these two lakes, marshes covered about 100 sq miles (259 km-), while open water comprised about 1,443 sq miles (3,737 km=). With exclusion of the Utah and Great Salt lakes, with their surface areas of about 138 sq miles and 1,661 sq miles (358 km- and 4,302 km-), respectively, the surface area of water would be 80 sq miles (207 k-m"). If the three large impoundment lakes (surface area, about 55 mi"; 142 km-) at the Bear River Table 3. Frequency distribution of heights of cliffs containing Peregrine Utah and the vertical distances of eyrie sites above bases of the cliffs. Falcon and Prairie Falcon eyries in Distance CLIFFS EYRIES Distance in Peregrine Prairie Peregrine Prairie in Feet n Percent n Percent n Percent n Percent meters 0-24 0 0.0 1 2.3 0 0.0 10 19.6 0.0-7.5 25-49 1 4.5 11 25.0 3 21.4 19 37.3 7.6-15.1 50-74 1 4.5 10 22.7 3 21.4 8 15.6 15.2-22.8 75-99 4 18.2 8 18^2 3 21.4 7 13.7 22.9-30.4 100-124 4 18.2 5 11.4 0 0.0 2 3.9 30.5-37.9 125-149 1 4.5 0 0.0 1 7.1 0 0.0 38.0-45.6 150-199 3 13.6 3 6.8 0 14.3 2 3.9 45.7-60.9 200-249 1 4.5 2 4.5 0 0.0 1 2.0 61.0-76.1 250-299 1 4.5 1 2.3 1 7.1 1 2.0 76.2-91.3 300-349 2 9.1 2 4.5 1 7.1 0 0.0 91.4-106.6 350-399 1 4.5 0 0.0 0 0.0 0 0.0 106.7-121.8 400-449 2 9.1 0 0.0 0 0.0 0 0.0 121.9-137.0 450-499 0 0.0 0 0.0 0 0.0 1 2.0 137.1-152.3 500 > 1 4.5 1 2.3 n 0.0 0 0.0 152.4> Totals: 22 99.7 44 100.0 14 99.8 51 100.0 X 178.0 ft" 101.7 ft 105.5 ft 64.2 ft (54.3 m) (31.0 m) (32. ,2 m) (19.6 m) Range: 40--400 ft 7-500 ft 28-330 ft 2, .5-450 ft (12.2-121.9) (2.] 1-152.4 m) (8.,5-100.6 m) (0.76-1.37.2 m) •Excludes one ground nestcr and one eyrie on a 1.000 ft ( ^On m) cliff. 22 Bricham Young University Science Bulletin I \ Fig. 17. Saltgrass (Distichlis stricta) marsh at Ogden Bay Refuge, Black-necked stilts (Himantopus mexicantis), a prey species of the peregrine, in the foreground. Photo by R. D. Porter, 1953. Fig. 18. View to the west toward Promontory Mountains from Ogden Bay Waterfowl Management Area. Marshes in foreground are typical of those adjacent to Great Salt Lake from which peregrines and prai- ries nesting along the Wasatch escarpment and adjacent mountains obtained their major food source. Photo 1)V R. J. Erwin, August 1972. Biological Series, Vol. 18, No. 1 Pehecrine Falcon in Utah 23 Table 4. Distances from peregrine e)rie sites in the Great Salt Lake Valley and Great Basin De.sert to open, nonflowing water and marsh liiinting areas and the size of these areas in relation to distance (measured from U.S. Geological Sursey topographic maps which were constructed from aerial photographs taken be- tween 1946 and 1956). Values in parentheses represent metric equivalence in kilometers or hectares. MARSHES SURFACE WATER' Mi. to Mi. to Number of Mi. to closest Acres in Mi. to closest acres in closest marsh > closest closest water > closest Area & Sta- marsh 320 acres marsh water 320 acres water tistic ( km ) (130 ha) (ha) (km) (130 ha) (ha) Wasatch Mountains ( Utah & Great Salt Lake valleys) n 19 19 17= 19 19 14' x±SD 3.3 ±2.6 7.6±5.1 17.5 ±20.6 2.5+2.0 5.2±4.3 59.6 ±344 (5.3 ±4.2) (12.2±8,2) (7.1±8.3) (4.0 ±3.2) (8.4±6.9) (24.1 ±13.9) Range 0.19-9.7 0.19-18.6 3.7-82.6 0.10-6.7 0.10-13.6 1.2-188.8 (0.31-15.6) (0.31-29.9) (1.5-33.4) (0.16-10.8) (0.16-21.9) (0.49-76.4) Desert, Great Basin n 3 3 3 3 2* 3 x±SD 1.3 + 1.3 1.3 + 1.3 7,302 ±10,396 1.7 + 2.0 4.0 406 ±701 (2.1±2.1) (2.1±2.1) (2,955 ±4,207) (2.7 ±3.2) (64) (164 + 284) Range 0.19-2.8 0.19-2.8 640-19,281= 0.19-4.0 4.0-4.0 1.0-1,216 (0.31-4.5) (0.31-4.5) (259-7,803) (0.31-64) (6.4-6.4) (0.40-492) 'nonflowing waters; lakes and ponds, -excludes Iwo large marshes, one 5,598 acres {2,2G() hal, the other 1,114 acres (-lol ha), ^closest water to five eyries was either Utah Lake or Great Salt Lake; hence, they were excluded. Mata for one desert eyrie, which was nearly 100 miles (Ifil km) from large bod,y of water, was excluded. ^Nelson (19(36) gives 4,700 acres (1.000 ha) for Clear Lake Water- fowl Management .\rea, but topographic maps show an additional 14,5-Sl acres (5,901 ha), contiguous with the management area, and a total of 53,000 acres (21.449 ha) are shown within about 20 miles radius of the Clear Lake e.vrie, Refuge were also excluded, the amount of sur- face w'ater would be reduced to 25 sq miles (65 km-). If both surface waters, exclusive of the Utah and Great Salt lakes, and marshes were divided equall\- by the 20 known peregrine eyries for the area, each pair of birds at these evries would use prey species from 4.0 sq miles ('10.4 km-) of water.'S.O sq miles (13.0 km=) of marsh, and 9.0 sq miles (23.3 km-) of the two combined. Nelson ( 1966), on the other hand, re- ports that there are 234 sq miles (606 km=) of managed marshlands surrounding the Great Salt Lake (see Fig. 19), to which may be added several sq miles of unmanaged marshes con- trolled bv duck clubs. The disparitv between Nelson's measurements and ours probablv is due to the fact that we used onlv marsh areas as shown on topographic maps and excluded mud flats and water, whereas Nelson's measurements probabU' include all lands and water within the Waterfowl Management Areas. Marshes were the dominant features near three eyries in the Great Basin desert (Figs. 1 and 20, Table 1, sites 4, 23, and 25), and Twome\- (1942) reported the use of the Ashley Greek marshes by peregrines nesting in Uintah Gount)-. The desert eyrie in the Colorado Plateau reported by White and Lloyd (1962) was by a river (Fig. 9). Figure 21 gives an aerial view of a river site in the desert of northern Arizona, tspical of those in parts of Utah, and Figures 22 and 23 show marshes near eyrie sites in the Great Salt Lake Desert. Peregrines nesting along the Wasatch es- carpment traveled long distances to obtain shore and marsh birds, which made up the bulk of the food items found in their nests (Table 4), and the marshes where they hunted were rather extensive. In general, the Great Basin desert eyries were closer to marshes and to open water than were the Wasatch escarpment eyries ( Table 4 ) . One marsh supporting an eyrie in the Great Salt Lake Desert is onlv about a square mile (2.6 km-) in extent, and is only about a mile (1.6 km) from the eyrie (Fig. 20). It is about the same size as the Ashley Creek marsh (Stewart Lake Waterfowl Management Area, Nelson, 1966) near the eyrie found by Twomey ( 1942 ) . The marsh at one other e^'ric in the Great Salt Lake Desert covers about 2^4 square miles (5.8 km-) and is less than a mile from the e\rie site. An additional eyrie site (Woodbury et al., unpubl. ms) was 2.8 miles (4.5 km) from a marsh that covered over 30 square miles (78 km-') (Table 4). The surface area of fresh water at two of the desert sites is only a few acres in extent (Fig. 23), whereas that at the additional site was about 2 square miles (5.2 km-) in extent. Of the 40 eyries and suspected eyries in Utah for which we have data, three were along rivers with marshes, streams, or lakes; five were 24 Bricham Young Universiti- Science Bulletin GRANTSVlLLfc Fig. 19. Distrihiition of maiuigcd marshlands concciitratnl aniviiul tlu- Cr^at Salt Lake region. Photo by per- mission of Utah Oivisioii of Wildlife Resources, in Nelson, 1960. Biological Series, Vol. 18, No. 1 Pehegrine Falcon in Utah 25 ^^j"-*' Fig. 20. View across a marshy area adjacent to an eyrie in the Great Basin at the edge of the Great Salt Lake Desert. R. D. Porter is standing in foreground ;ind is about 1 mile (1.6 km) east of the eyrie shown in Figure 44. Photo by R. J. Erwin, August 1972. Fig. 21. Aerial view of a river eyrie site in the desert of northern Arizona typical of those in southeastern Utah. View looking NNE. Peregrines nested on the canyon wall on the right hand side of tile photo. Photo by G. D. Lloyd, 1960. 26 Bricham Young University Science Bulletin along major rivers; 25 were near marshes with lakes and streams; five were along streams only; and there was one each near a marsh and a lake only. All but two of the 21 eyries near the Great Salt Lake were adjacent to a stream, which usual- ly comprised the closest source of water. The smaller passerine birds associated with the streamside vegetation provided the peregrines with a source of food which frequently was within the immediate area of the eyrie. The marshes originate from desert springs, from the overflow of rivers and creeks, from deltas at the junctions of rivers and lakes, and in more recent times, from artificial damming of streams or from the fomiation of ponds re- sulting from the drilling of wells. Bulrush (Scir- pus sp. ), saltgrass {Distichlis stricta) (Figs. 17 and 18), and cattail (Tijpha sp. ) (Fig. 12) are the principal plants in these marshes. The marshes supply food for peregrines dur- ing all seasons of the year, but are especially im- portant during nesting season. The presence of an abundant food supply in the marshes at Og- den Ba\' undoubtedly was the major ecological factor responsible for the groundnesting of a peregrine there. Several easily accessible eyries that were mentioned by Beebe (1960) in the Queen Charlotte Islands mav have been due to an abundant source of pre)' and to the absence of mammalian predators. The combination of marshes adjacent to suit- able cliffs for nesting may be considered an "ecological magnet" (Hiekey, 1941) for the pere- grine in Utah, especially along the Wasatch es- carpment, where extensive marshes border the Utah and the Great Salt lakes. Here, marshes are formed at the deltas of three major rivers that flow into the lake (Fig. 19). Typical of M i^' '>-%'^ Fig. 22. Eyrie site near the eastern limits of the Great Salt Lake Desert. The eyrie, when first located by Porter in the early 19.5()s, was on a small cliff in the left foreground which does not show in this photo be- cause it was removed to make a road bed. The peregrines were last .seen using the cliffs near the top right of the photo. Prairie l'"alc()iis also used the same eyrie that was last used by the peregrines at least three years after the peregrines were last seen there. Photo by K. J. Krwin, August 1971. Biological Sebies, Vol. 18, No. 1 Peregrine Falcon in Utah 27 their vegetation is that at the delta of the Weber River (Ogden Bay), which, from salt flats to river channels, consists mainly of glasswort (Salicornia sp. ), saltgrass, alkali bulrush (S. pahi(losus). hardstem bulrush (S. acutiis), cat- tail (T. latifoJia and T. angustifolia) , and sago pondwecd (Potamogeton pectinatus) (Nelson, 1954). For a more comprehensive description of plant ecology in Utah marshes, see Nelson's ( 1954 ) studies of a marsh near the Great Salt Lake ( Ogden Bay ) and Bolen's ( 1964 ) discus- sion of a spring fed marsh in the Great Salt Lake Desert (Fish Springs). Numerous remains of nine species of water- birds, including grebes, ducks, rails, avocet, gulls, and terns, from anthropological sites at the northwest side of the Great Salt Lake, some dating back at least 8,350 years (Hai^per and Alder, in press ) , suggest that marshes were pres- ent in the Great Salt Lake valley long before the arrival of the white man. Some of the early hunters and explorers to enter the valley re- ported the presence of numerous waterfowl and shorebirds. Father Escalante, who visited Utah Lake in 1776, wrote that the lake "abounds in man\' kinds of fish and in geese and waterfowl" (Harris, 1909). Osborne Russell, a trapper, saw "miriads of Swans, Geese Brants, and Ducks which kept up a continuous hum day and night . . ." at Bear River marshes on 2 April 1842 (Haines, 1955). Fremont (1845), who visited the Bear River Delta on 3 September 1843, men- tioned the thunderous noise made by multitudes of waterfowl in the marshes and described the area as being covered with rushes and canes. Captain Stansbury (1852) made similar observa- tions on 22 October 1849 from a vantage point on the east side of Promontory Point. He re- corded that ". . . thousands of acres, as far as the eye could reach, were covered with them [water- fowl]. . . ." Fremont (1845) reported that "the stillness of the night [8 September 1843] was en- livened by millions of waterfowl," this time at the mouth of the Weber River near Little Moun- tain; and on 9 September he reported that the shallow delta of the river was "absolutely cov- ered with flocks of screaming plover." Stansbury ( 1852 ) noted innumerable flocks of ducks, geese, white swan, and long-legged plover around the shallows at the mouth of the Jordan River on 4 April 1850. It is probable that the "plover" were mostly American Avocet {Recurvirostra americana). Black-necked Stilt (Himantopus viexicarms). and Willet {Catoptrophorus semi- pahnattis) . Vegetation at the river sites was comprised mostly of cottonwoods {PopuJus fremontii in the Lower Sonoran desert areas; P. angustifolia in the Upper Sonoran areas) and willows (Salix exigua was most frequently present, with S. hitea, S. gooddingi, and S. caudata occasionally present also). Other plant species known to oc- Fig. 2.3. View from hilLsiile below eyrie in Figure 22, Brackish marsh can be seen in the midgroiind, and salt flats from the Great Salt Lake can be seen in the background. Photo by R. J. Erwin. August 1971. 28 Brigham Young University Science Bulletin cur with the cottonvvoods and willows include: squawbush (RIius trilohata), wildrose {Rosa sp. ), tamarix (Tamarix ramosissimu) , Joshua tree (Clistoyucca hrevifolia), box elder (Acer ne- gundo ) , ash ( Fraxinus sp. ) , baccharis ( Baccharis emonji), hackberrv (Celtis douglasii), and even scrub oak {(^)uercus gambelii). Tlie presence or absence of the latter species is dependent upon altitude, latitude, and local ecological conditions. Food Niche Little has been published on the diet of the peregrine in the intermountain region. Wet- more's ( 1933:49-50) account of the hunting tac- tics of the peregrine on the Bear River marshes has been quoted elsewhere ( Bent, 1938 ) . It is re- peated here because it gives a remarkedly vivid picture of the peregrine in its native haunts along marshes of the Great Salt Lake earlier in the present century. The birds [falcx)ns] at rest perched in low willows, or on logs or bits of drift, where tliey had clear view of the teeming bird life about them. Wlien hungry, they dashed across the open flats at high speed, striking ruthlessly at any birds that appeared, from small s;md- pipers to large ducks. Their appearance in the air was always the signal for chattering cries of akirm from blackbirds and avo- cets that put all tlieir bird neighbors on the watch. These warnings had little effect, however, as the duck hawk, killing practically at will, was truly despot of this realm. I have seen this falc-on dash through closely massed flocks of flying sandpipers, striking out two or three with as mimy thrusts of the claws, allowing each bird to drop and then wheeling swiftly to seize the falling prey in mid-air before it reached the ground. Again, I liave seen one in a stoop, swift almost ;is light, knock a redhead duck to the ground, where it landed with a broken wing and other injuries. On one occasion a pair of duck hawks harried a help- less nighthawk, stooping at it playfully until one in passing gave it a f[uick squeeze with one foot. It then ;Ul()wed the nighthawk to fall, when it was seized by the other duck h;uvk. Tlicn the pair flew away, and the one with the booty at intervals dropped it, so that it could be seized in air by its mate. Food items found in several Utah eyries are summarized in Tables 5 and 6. We collected 107 individual prev items representing 20 species of birds and at least one species of mammal from two eyries along the escarpment of the Wasatch Mountains between 1943 and 1957. The Ameri- can Avocet was represented in the greatest num- bers ( Fig. 24 ) . It, the Mourning Dove ( Zenai- I"ig. 24. Avoccl at nest. This species was the most important food species found in the eyries of the pere- grine in the valley of tin; Great Salt Lake and also the most fre(iuent shorebird species in the eyries of the Prairie Falcon in the same localit)-. I'hoto by R. J. Erwin, 8 Jiuie 19.59. Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utaii 29 Table 5. Prey species in Peregrine Falcon and Prairie Falcon eyries in areas of sympatry along the escarpment of Utah's Wasatch Mountains', facim' the marshes v( the Great Salt Lake. Prey species Weight class in grams" Duck sp. (yng. )' Killdeer ( Charadrius lociferous ) Willet ( Catotrophorus semipalmatus ) Greater Yellow-legs ( Totanus melanoleucus) Long-liillcd Dowitcher ( Limnodromus scolopaceus) Sanderling (Crocethia alba) American Avocet ( Rccurvirostra americana ) Black-necked Stilt ( Himantopus rncxicnnus ) Wilson's Phalarope ( Stcganopus tricolor ) Franklin's Gull ( Lurus pipixcan ) Shorebird and Gull Subtotal California Quail ( Lophortijx californiciis) Ring-necked Pheasant {Phasianus colchicus) Gallinaceous Bird Subtotal Mourning Dove (Zetuiidura macroura) Rock Dove {Coluniba livia) Dove Subtotal Red-shafted Flicker (Colaptcs cafer) Western Kingbird (Tijranrws vcrticalis) Homed Lark (Eremophila alpestris) Scrub Jay (Aphelocoma coeridescens) Robin (Tiirdui- migratoriiis) Bohemian WiLwving (Bombi/cilla garrula) House sparrow (Passer domcsticus) Western Meadowhvrk (Sturnclla ncglecta) Redwinged Blackbird (Agelaius phocniceus) Brewer's Blackbird ( Euphagus cijanoccphalus ) Unidentified blackbird Green-tailed Towhee (Chlorura chlorura) Rufous-side Towhee ( Pipilo en/throphthalmus) Passerine Subtotal Big brown bat (Eptcsicus fuscus) Unidentified bat 150 106 203 165 86 63 281 152 58 295 198 807 115 318 137 42 29 77 82 56 26 89 54 68 61 30 .37 n Peregrine Percent of total Falcon Percent of biomass 3 2 2.80 1.87 2.75 1.29 10 9.35 12.38 3 2.80 3.02 2 1.87 1.05 Prairie Falcon n Percent of Percent of total biomass 22 20.56 1 0.93 6 5.61 1 0.93 50 43.92 13 12.15 5 4.67 18 16.82 8 7.48 0.93 1.87 1.87 9 8.41 4 3.74 3 2.80 5 2 4.67 1.87 37.10 0.93 2.12 1.80 59.69 9.12 9.70 18.82 6.69 0.47 0.99 0.68 4.89 1.32 1.24 1.86 0.37 28 26.16 11.82 18 1 0.93 0.11 10 2 1.87 0.12 9 18 1 1 2 40 2.63 11.84 6.58 1.32 7.89 21 27.63 1 1.32 2 2.63 3 3.95 2 2.63 1 1.32 3 3.95 1 1.32 1 1.32 1 1.32 9.21 11.84 23.67 1.32 1.32 2.63 52.63 2.60 8.26 8.79 0.55 14.60 32.20 1.71 13.97 15.68 1.99 2.75 4.74 1.19 0.36 0.25 4.97 2.03 13.87 0,59 0.53 0.64 23.24 30 Bricham Young Univebsity Science Bulletin Table 5 (Continued) Uintah groiintl squirrel {Cilelius trrmatus) 250 _ _ _ 2 2.63 4.33 Rock siniirrel 696 _ _ _ 2 2.63 12.04 (Citellus variegatus) Unidentified ground 400 _ _ _ 1 1.32 3.46 squirrel (Citellus sp) Meadow mouse 60 _ _ _ 1 1.32 0.52 ( Microtus sp ) Mammal 3 2.80 0.23 6 7.90 20.35 Subtotal Totals 107 99.98 20 species 100.00 76 100.01 21 species 100.00 'Mo.':t prey itcni^ for both species origmated Irom the Peregrine Falcon and Prairie Falcon eyries at site 7 (Table 1, Fig. 1); hence, ior the most part, they represent prey species from n common resource. 'Weights of all avian species, with exception of tlie common pigeon, were obtained from Porter, Bushman, and Behle (impubl. ms); the value for the common pigeon w.is obtained from Roxie I.ayboume. of the U. S. Bureau of Sport Fishencs and Wildlife; weights of mammalian species were estimated from those given by Hall I194C). Those of xmidentified bats, ground squirrels, and young ducks were esti- mated by the authors. ^Weight of the young ducks is estimated; voimg pintails iAnas titutti) not vet feathered were in the peregrine e\Tie on 13 and 14 June 19+7. dura macruura), Willct (Fig. 25), Western Mead- owlark ( Sturnella neglecta ) , Red-shafted Flicker {Colaptes cafcr), Wilson's Phalarope {Stegano- piis tricolor). Rock Dove {Columha livia), and two species of blackbirds (Agelaius phoenicetts and Euphagus cijanocephalus) made up nearly 79 percent of the food items at the eyries. How- ever, in both total biomass (59.7 percent) and in numbers (4.3.9 percent), the shorebirds com- prised the largest segment of the diet, of which the avocet (37.5 percent biomass) (also see White, 1963) and Willct (12.4 percent biomass) were by far the most frequent. Tliis is probably a reflection of the availabilit)' of shorebirds in the Great Salt Lake marshes. Aside from being common, both avocet and Willet ma\' have some conspicuous behavior that makes them easv to capture and that accounts for the numbers taken b\' the falcons. Tinbcrgen ( 1940 ) has shown that various behavioral pecu- liarities of certain passerine birds enhance their vulnerability to predation, and F. and J. Craig- head (1956), based on the study of the food remains at 20 peregrine eyries, have suggested that the flash patterns of meadowlarks, redwings, and the Blue |a\ {Cijanocitta cristata) and the eonspieuous Hight of flickers ma\' increase the vuliKTability of these species to predation by the peregrine. This hypothesis may be applicable to the Willet and avocet, both of which have con- spicuous flash patteiTis. Mourning l^oves and Rock Doves were im- portant columbiforme items ( hS.S percent of bio- mass and 16.8 percent of total items). Passer- ines, woodpeckers, and bats were represented in smaller numbers and biomass (Table 5). The use of bats for food by peregrines has been reported from Texas by Stager ( 1941 ), and desert nesting Shaheen Falcons ( Falco pelegri- nokles hahtjloniciis) of the Middle East, which are either peregrines or are very closeh' related to them (Vaurie, 1961; White, 1968b; Brown and Amadon, 1968), reportedly hunt bats at dusk (Dementiev, 1951 and 1957). In Indonesia, Mees (1949) reports that wintering tundra fal- cons seem to be specialized for feeding on bats. He saw one falcon kill seven bats one after an- other. Fischer ( 1968 ) reports that the subspecies of peregrine (F. ;}. ernesti) indigenous to Indo- nesia also hunts bats. Fig. 25. Willet {Catoptrophortis scvtipahiatus) on nest. The Willet was an important prey species in pere- grine cvries of the CJreat Salt Lake Valley. This species is inconspicuous while on nest but in fUght it, like the stilt and avocet, shows a striking flash pattern. Photo by R. J. Erwin 19.59. Biological Series, Vol. 18, No. 1 Pehecrine Falcon in Utah 31 Table 6. Prey species in two Peregrine Falcon eyries in Utah's desert (sites 4 and 28, Table 1, Figs. 1, 9, and 22).* C = Colorado Plateau, GB = Great Basin. Weight class in grains No. Percent of total Percent ot biomass Chukar {Alectoris graeca) (C)'" American Coot (Fulica americana) (GB)°" Mourning Dove {Zeimidura macroura) (C, GB) Common Nightliawk (Chordeiles minor ) (GB)°° Ash-throated Flycatcher {Myiarchus cincra'icens) (C)"" Sav s Phoebe ( Sayrnis saya ) ( C ) ° ° Horned Lark { Eremophila alpcslris) (C, GB)"" Pinon Jay {Gijmnorhinus cyanocephala) (C)°° Western Meadowlark (Sturnella ncglccta) (GB) Yellow-headed Blackbird ( Xanthocephahis xanthocephalus) (C)" Redwinged Blackbird {Agelaiits phocniceus) (C, GB) Lark Sparrow (Chondestes grammacus) (GB)"" Unidentified Passerines (C) Passerine Subtotal Desert Totals 520 1 5.26 26.52 365 1 5.26 18.60 115 2 10.53 11.73 62 1 5.26 3.16 29 2 10.53 2.96 21 1 5.26 1.07 29 3 15.79 4.44 116 1 5.26 5.92 89 1 5.26 4.54 92 3 15.79 14.07 54 2 10.53 5.51 29 1 5.26 1.48 14 73.68 39.99 19 99.99 100.00 'Sro fonttinte for Table 5 •'Not recorded in Wasatch Moiinlain eyries (see Table 5). Eyries adjacent to the Great Salt Lake con- tained no full-grown waterfowl despite the abun- dance of waterfowl in the adjacent marshes, al- though the peregrine has been observed eating or pursuing full-grown ducks of several species during the breeding season. These include the Gad\\all ( Anas strepera ) ( observed 5 May 1938, field notes of R. G. Bee), a teal (H. Austin, pers. comm.), a teal on 10 April 1948 at Ogden Bay (Porter), and the Redhead {Aijthya ameri- cana) (Wetmore, 19.33). Calvin Wilson (pers. comm.) has watched peregrines from an eyrie in the Wasatch Mountains eating Ruddy Duck (Oxytira janmicensis) , Cinnamon Teal {Anas cij- anoptera). Pintail (Anas acuta), and American Coot {Fulica americana) on dikes of a nearby marsh. R. J. Erwin (unpubl. data) flushed a peregrine from the side of a highway in Grand County in April 1958, where it had just cap- tured an adult Mallard {Anas platjtrhynchos). Cade, White, and Haugh ( 1968), on the other hand, found that waterfowl constituted nearly 50 percent (biomass) of the food items in the eyries of the Alaskan taiga peregrine (F. p. anatum, sensu lata). Utah peregrines are smaller, however, than those of interior Alaska. The absence of ducks in the Wasatch Mountain ey- ries mav possibly be explained on the basis of the weight of the prev item in relation to the distance that peregrines must earn,' it to their evries. A full-grown duck may be too heavy for peregrines to carry the several miles from the Great Salt Lake marshes to eyries along the Wasatch escarpment. Shorcbirds were not present in two desert eyries. One e\rie was located near a marsh in 12 species the Great Basin and the other near a river in the desert of the Colorado Plateau. The avail- ability of a variety of marsh and shorcbirds to the peregrines at the desert eyries in the Great Basin (Table 6) accounts for the presence of the coot. The coot in the Great Basin desert eyrie probably came from a pond (desert spring) which was only about 1,200 yards ( 1,097 m ) from the eyrie site. Since its weight (400 g) is about the same as that of a duck, it is possible that its absence from the Wasatch Mountain eyries may have been for the same reason that ducks were missing from these eyries. The small sample-size of food items probably accounts for the absence of shorcbirds in this desert eyrie. At a Wasatch Mountain eyrie, observed by R. D. Porter (site 7, Table 1) for the first two weeks after hatching, only one, and at most, two, prey items were found each day in the nest; these usually consisted of Redwinged Black- birds, Mourning Doves, Willets, and meadow- larks. But as the nesting season progressed, a greater number of species and items were brought to the nest. On 28 June 1952, for ex- ample, about three weeks after hatching of the young falcons, the female returned with a young Willet at 11:00, a robin-sized bird at 11:50, and an unidentified item at 17:20. The male re- turned with a young avocet at 15:20 and a leg of a young avocet at 15:45. The next day the male brought a Wilson's Phalarope to the nest and the female an avocet. Other items found in the nt^t on 29 June were Scrub Jay ( Aphelo- coma coerulescens) , unidentified blackbird, big brown bat {Eptesicus fuscus) and one adult and one immature Wilson's Phalarope. Of the shore- 32 Brigham Young UNrvERsiTY Science Bulletin birds brought to the young at this eyrie (site 7, Table 1) during the years it was observed, 33 percent were partially fledged young of the sea- son. Peregrines nesting along the face of the Wasatch Mountains traveled several miles to obtain the marsh and shorebirds (Table 4); other species were obtainable much closer to the eyries. Despite the peregrine's reported antipathy to capturing food on or near the ground (Bond, 1936a), mammalian prey species such as the brush rabbit (Sijlvilagus bachmani) (Bond, 1936c), rats [Rattus sp.) (White, et al, 1973), and certain gallinaceous birds (ptamiigan, Lagopus sp.) '(Cade, I960; White and Cade, 1971 ) also are taken for food occasionally. Bond ( 1946 ) reported that peregrines commonly brought Horned Larks to their small young. The Homed Lark, which is essentially a ground- dwelling species, is one of the most abundant birds in Utah's salt desert scrub vegetation. It was present in peregrine evries in both the Colorado Basin and Great Basin deserts of Utah (Table 6). Much of the desert lowlands and foothills of Utah are vegetated with desert scnib and with pigm\' conifer forests, respcctivelv, yet the pere- grine was not known to nest far from water in those areas where the Homed Lark of necessity would have been an important item in its diet. Javs (ApliclocoDia and Gymnorliinus), king- birds {Tyranmis), Ash-throated Flvcatcher [Miiiarclius cinerascens). Lesser Nighthawks, Red-shafted Flickers, Robins, Mourning Doves, and Black-throated Cra\' Warbler (Dcndroica nigrescens). some of which are kTiown to be used as prev bv the peregrine, are available in the pig- mv forests, vet the peregrine nests in these areas only when water or marshes are nearby. A more intensive study of the peregrine's food habits in Utah during nesting season un- doubtedh' would have revealed a much wider variety of prey species, especially the smaller passerines. In terms of biomass, however, the smaller species of birds probably would not have altered appreciably the percentages of each categor)' of birds. The abundance of doves in Utah eyries is not surprising, despite the availability of marsh and shorebirds, since the domestic pigeon has been found to be a favorite prey species of the peregrine, not only in the eastern United States, but also in many other areas of the peregrine's cosmopolitan distribution (Hickey and Ander- son, 1969). The Utah peregrines utilize a wide variety of prev species (at least 29 species, see Tables 5 and 6) during the nesting season, and in this respect their diet is more comparable to that of populations elsewhere in North America than to tliat of populations in the Queen Charlotte Is- lands, where Beebe (1960) found them limited mosth' to one and not more than four prey spe- cies during the nesring season. On Amchitka in the Aleutian Islands, White, Emison, and Wil- liamson ( 1973, in press ) list 32 species in the peregrine's diet, most of which were found in the nests, and comprised principally marine birds, waterfowl, gulls, and shorebirds. Shore- birds were represented frequenth' in the eyries of peregrines along the Colville River of Alaska (White and Cade, 1971). Cade, White, and Haugh ( 1968) reported 49 prev species in eyries located in the taiga zone of the Arctic, and Cade (1960) found 21 species in nests located in the tundra zone. NESTING BEHAVIOR IN UTAH History of Nesting at a Wasatch Mountain Eyrie Eyrie sites of the Peregrine and Prairie Fal- con at a chff on the escarpment of the Wasatch Mountains (Table 1, site 7; Fig. 26) were ob- served by R. D. Porter, R. J. Erwin, and others from 1943 through 1952, exclusive of two war years, 1944 and 1945. We obtained data at this cliff on interspecific competition between the two species and on productivity, incubation peri- ods, and rcproduetive failure for the peregrine, all of wliieh will be discussed under s(>parate headings. The cliffs were composed of quartzite and faced westerly along the west-facing escarpment of the mountains and southerK- along a south- facing edge of a side canyon. Peregrines were first noted there on 3 April 1943, the year the cliff was first under our observations, by R. J. Erwin and J. F. Poorman, and again that year by J. F. Poorman and R. L. Porter on 15 April. A nest containing three eggs was found on 26 ,\pril. Prairie Falcons were also first noted at this cliff in 1943. A summary of the reproductive history of the peregrines at this site is given in Table 7. The phvsical characteristics of the var- ious peregrine and Prairie Falcon sites utilized during the period of studv are given in Table 8. The photographs represented by Figures 27-39 were taken in 1947, 1948, and 1952. In 1949 the peregrines defended a nesting Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 33 Fig. 26. A cliff along the escarpment of the Wasatch Mountains which contained eyries of both the Peregrine Fal- con and tlie Prairie Falcon (Table 1. site 7). The Peregrine Falcons used site A-3 in 194.3, 1952, and 1953; site B in 1946 and 1947; and site C in 1948 and 1951. The Prairie Falcons used site 2 in 1948; site A-3, 1949; and site 1, to the north (not shown in photograph) of site A-3, in 1943 and 1950. Sites B and C faced south, sites 1, 2, and A-3 faced west. Photo by R. J. Envin, 1972. ledge, which contained two nest scrapes, but apparently laid no eggs. They defended several sites on the cliff in 1950 but with less tenacity than usual. Although they made 20 to 25 scrapes along several hundred feet of ledge, no eggs were found. Between 4 March and early June the cliffs were searched for an eyrie 10 times without success. The behavior of the birds sug- gested the presence of a nest at numerous places along the cliff. However, each new section of chff was defended with nearly equal spirit. In 1952, the two young at site A (Fig. 26 and Tables 7 and 8) were measured and weighed from date of hatching until 13 August. They were removed from the nest on 5 July. R. J. Erwin banded three young peregrines at the 194.3 site in 1953. He obtained no informa- tion on egg number or occurrence of Prairie Falcons. A new female peregrine nested at alternate site A in 1952. She still had some immature ,0^' •t V Fig. 27. Five-egg clutch of Peregrine Falcon (eyrie site 7-B, Table 1, 1947). Note the wood rat {Neo- toma sp. ) scat on ledge and about the eggs. Photo by R. D. Porter. 34 Brigham Young University Science Bulletin Fig. 28. Female peregrine entering eyrie. Photo by R. D. Porter and R. J. Erwin, 1948. Fig. 29. Female peregrine settling down over nestling.s which are only a few days old (Table 1, site 7, alt. .site C). Photo by R. D. Porter and R. J. Erwin. 1948. Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 35 Fig. 30. Female peregrine brooding young. Note addled egg. Photo by R. D. Porter and R. J. Erwin, 1948. Fig. 31. Female peregrine with young, in defensive attitude. Photo by R. D. Porter and R. J. Erwin, 1948. 36 Bricham Young University Science Bulletin ». Fig. 32. Female peregrine feeding young. Photo by R. D. Porter and R. J. Erwin, 1948. \^1\ V u^ « t-'' Fig. 33. Female peregrine feeding young which were nearly 3 week.s old (eyrie site 7, alt. site B, Table 1). Photo by R. D. Porter, 1947. Biological Series, Vol. 18, No. 1 Peregrine F.alcon in Utah 37 A - Fig. 34. Young peregrines at approximately 4 weeks of age (eyrie site 7, alt. site C). Photo by R. D. Porter and R. J. Erwin, 1948. Fig. 3.5. Young peregrines about 6 weeks of age, nearly old enough to fledge (eyrie site 7, alt. site C). Photo bv R. D. Porter, 1947. 38 Bhicham Young University Science Bulletin Table 7. Reproductive history of the peregrines at a Wasatch Figs. 26-29). Mountain eyrie ( site 7, see Tables 1 and 8, and Alternate EGGS NESTLINGS Probable Incubation Other site Dates date of period Dates dates of Year location recorded No. 1st egg (in days) No. hatched record Misc. Data 1943 A 26 April 3 - ^37 (3rd egg) 3' unknown 31 May 1946 B - - - unknown 4 unknown 26 June Young nearly fledged, two taken 1947 B 26 April 17 May 3 5? 21-22 April 35-37 (3rd egg) 3 unknown 31 May Downy young 1948 C 16 April 19 April 27 May 3 4 5 11-12 April 42-44 (3rd egg) 39-41 (4th egg) 4 28-29 May 29 May 29 June 5 July 17 July 5 eggs, 1 pipped 27 May; 4 young -|- 1 addled egg, 29 May 4 young, 2 taken' young fledged' young full grown' 1951 C 2 May 3 May 13 May 19 May 3 3 2 0 unknown 0 -^ 1952 A 29 April 1 May 27 May V V 3 29 April 37 (cggl) 0' 2 4 June 5 June, 07:00 5 June 2 eggs pipping 1 hatclied, 1° nearly hatched 31 May 3 - 2 7 June both hatched 1 June 3 - 1953 A - - - - unknown 3 - ^Three young were about ready for flight when two were taken for falconry s-iinetime in early July. -29 June: 4 young, 2 males, 2 females; females taken for falconry; oldest male, tail half grown, flew from nest. 5 July: I young male, still on nest ledge, flew at approach of observer, first male to leave nest on rock above nest. \7 July: females taken from nest about full grown. ^Marked with a numeral 1 in India ink. ^Two eggs pipping, one with small bole (egg 1), other barely dented, young peeping inside both eggs, loudest in egg marked with numeral 1 ; marked egg weighed 47 g, other pipped egg, 50 g, and impipped egg, 48 g. ^Shell around abdomen and legs; it probably hatched on 6 June; third egg addled. feathers (see Figs. 36-38), and was undergoing a molt as evidenced bv the fact that on 28 June the upper surface of the wings had just begun to molt into the adult plumage. The molt on the back (capital and spinal feather tracts) and the lower breast (ventral tracts) was nearly com- plete, while that of the primaries and rectrices had only begun. The capital tracts of the head were only partially molted. While the female was in flight, it was noted that at least one pri- mary was missing on each wing as well as at least one retrix on each side of the tail. The plumage condition of this bird indicates that she probably was no more than three years of age. Records of breeding peregrines while still in their immature plumage are not common. Beebe (1960) noted no instances of mated pairs in immature plumage, or even in plumage show- ing traces of immaturity, in a rather large sample of pairs along the northwest Pacific Coast. However, Herbert and Herbert (1965) pointed out two instances of immatiux'-plum- aged females occupying an eyrie, neither of which was found to lay eggs. Hickcy (1942) reported on three immature, one-vi-ar-old fe- males that failed to lay eggs and a fourth that brooded a clutch of t\vo eggs, making a total of only one first-year f(-male out of .34 falcons over a two-year-period in New York. A report by Herbert of two females believed by him to be two-vear-old birds, both of which laid only two eggs in different )ears, also was mentioned by Hickcy ( 1942). White and J. R. Haugh (pers. ol)ser. ) found one female, out of 17 pairs breed- ing on the Yukon River in 1966, that was essen- tially still in the streaked brown immature plum- age. Therefore, it was thought to be but one year old. She laid Uvo fertile eggs, one of which hatched. Egg Laying At the alternate site A eyrie (Table 1, site 7) egg la\ing began between 12 and 29 April ( 1943-1952) as estimated by counting back from known dates certain eggs were laid (Table 7). Published records for the state range from about 22 March (counting back from 30 March as given by Johnson, 1899) to the second or third week in NIa\- (counting back from 20 Ma\' given by Bee and Hutchings, 1942). The first' egg of a three-egg clutch found by White and Lloyd (Table 1, site 28) was probably laid around 6 Ma\', as indicated by the date of hatching. At the aforementioned e\rie in the Wasatch Moun- tains (Table 1, site 7), 3.8 (\ggs (range .3-5) on the average were laid per year during the five Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 39 ..v;-^ Fig. 36. A view of female peregrine with unmolted immature plumage. Her two young are about 3 weeks old (eyrie site 7, alt. site A). Photo by R. D. Porter, 1952. Fig. 37. Same female as in Fig. 36. This bird is c(;rtainly not more than three years old because of the amount of immature plumage retained. Note tiiat most of the tail, secondary wing feathers, and greater wing coverts are immature feathers. Photo by R. D. Porter, 1952. 40 Bhigham Young University Science Bulletin Table 8. Physical characteristics of eyrie sites at a cliff in the Wasatch Mountains (Table 1, site 7, see Figs. 26-39) used by botli peregrines (Pe) and Prairie Falcons (Pr). Values in parentheses represent metric equiva- lents. Approx. dist. Dist. Eyrie Dia. in ft (in) Species' Cliff Eyrie Ledge Ledge below Nest nest Depth from and height. height, length. width. overhang. area scrape. .soil, Alt. site A year ft ft Direct inches inches inches ft= inches inches site to site used (m) (m) facing (m) (m) (m) (m=) (m) (m) A-3= 0 Pe 1943 110 85 W 72 62 20 7.42 6.9 2 1952 (34) (26) (1.8) (1.6) (0.,51) (0.69) (0.18) (0.051) 1953 Pr 1949 B 320 Pe 1946 135 90 S 120 60 18 6.45 - - (98) 1947 (41) (27) (3.0) (1.5) (0.46) (0.60) C 350 Pe 1948 135 90 S 156 48 35 6.55 6.4 (107) 1951 (41) (27) (4.0) (1.2) (0.89) (0.61) (0.16) - 1' 300 Pr 1943 110 (91) 1950 (34) - w - - - - - 2' 55 Pr 1948 110 95 w 61 90 21 21.8 - 2 (17) (34) (29) (1.5) (2.3) (0.53) (2.0) - (0.051) M^rairie Falmiis wrie not reinrded in 1**47. 1952. and lOji, were seen, bul no nest was found in 1951. 'All values were obtained by direct measurements at eyrie sites; all other values given in the table, except cliff and ej-rie heights, distances between e>Tie sites, are approximations from photographs, using a peregrine's egg or the adult peregrine as a unit of measurement. ^Exact e>xie site was not reached. years that eggs were found (see Fig. 27), and 2.4 of the eggs (range 0-4) on the average hatched. The eyrie produced a total of 19 young during the seven years it was known to have been active, for an average of 2.7 young per year. Although the number of fledged young was not ascertained, no )Oung were known to have died in the nest. Eight young, however, were removed for falconr>' when nearly fledged. These values approach those for the peregrine Fig. .38. A close-up of same female as in Fig. 36. Photo by R. D. Porter, 1952. Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 41 in eastern North America, where Hickey (1942) found the average clutch size to be 3.72 and the average number of downy young to be 3.0. For western North America, Bond (1946) re- ported an average clutch size of 3.7 and Cade ( 1960 ) recorded an average of 2.7 eggs per clutch in northern Alaska and 3.1 eggs per clutch in other locations in the Arctic. Incubation The eggs are laid usually at two-day inter- vals, and occasionallv at three ( Cade, 1960; Her- bert and Herbert, 1965; Dcmandt in Fischer, 1967). On the Hudson River, incubation gener- ally began on the fifth day with the laying of the third egg and averaged 32-33 days from time of commencement until the hatching of the last egg (Herbert and Herbert, op. cit. ). The incubation period is detennined best by check- ing the time between the last egg laid and the last \oung hatched (Nice, 1954), providing that all eggs hatch. Although the incubation period in the peregrine is said to be 28-29 days (Witherby, et al, 1939; Dementiev, 1951; Herbert and Herbert, 1965), there is still some unccrtainb." regarding its exact length, as sug- gested also by Nelson ( 1972), who believes it to be closer to 32 to 34 days in F. p. pealei. If the incubation period for the fifth egg is 28 to 29 davs, and not more than two days elapse be- tween the laving of each egg, the period be- tween la\'ing of the fourth egg and the hatching of the fifth egg would be 30 to 31 days; be- tween the la\ing of the third egg and the hatch- ing of the fiftii, .32 to 33 days; between the second and the fifth, 34 to 35 days; and between the first and the fifth egg, 36 to 37 days. In four-egg clutches, the intervals between the lay- ing and hatching of the third and fourth egg would be 30 to 31 days; between the second and the fourth egg, 32 to 33 days; and between the first and fourth egg, 34 to 35 days. For three-egg clutches, the intervals between the laving of the second and third eggs would be 30 to 31 days; and between first and third eggs, 32 to .33 days. If, as reported b\' Nelson (ibid.), the incubation period is 32 to .34 days, 4 to 6 additional days must be added to each of the above values. At the Wasatch Mountain eyrie (Tables 1 and 7, site 7), the incubation period in 1947 and 1952 was close to that given by Nelson ( op. cit. ) for pealei. In 1948, however, it seemed to have lasted abnormally long. The period from laying to hatching was about 40 days (39 to 41) for the fourth egg and at least 42 days (42 to 44) for the third egg, which is about 10 days longer than that expected using the 28 to 29 day period. This could be explained if the first clutch was destroyed within a day or so after the fifth egg was laid and if the first egg of a new clutch was laid a day or two later. This would increase the observed incubation period by about 10 davs. This phenomenon has been reported in captive American Kestrels {Falco sparverius) (Porter and Wiemeyer, 1972). In 19.52, the period between the laying and hatching of marked egg number one was about 37 days. It likely was laid the day it was first found or the day before. Unfortunately, the period of 36 to 37 days corresponds closely to the expected incubation period for the first egg of a five-egg clutch, if the incubation period is 28 to 29 days, as well as that expected for the first egg of a three-egg clutch if the incubation period is 32 to .34 days. Tlie 32- to 34-day period seems to fit our data better than does the 28- to 29-day period. Addi- tional observations are needed to resolve this problem. Two da\'s elapsed between the pipping of the first egg to hatch and the fourth egg to hatch (a fifth egg did not hatch) in 1948. Only one day elapsed between pipping and hatching of egg number one in 1952 and the same was probably true of the second egg as well. This appears to agree with Hall's (1955) observation in 1943 on the Sun Life peregrines, which hatched two eggs on each of t\vo succes- sive days. Porter and Wiemeyer (1972) reported a two-dav interval between the hatching of the first and the last egg of five-egg clutches of captive kestrels. The kestrels frequently began incubation wath the laying of the fourth egg. Unlike the peregrines of the lower latitudes, those in the Arctic reportedly initiate incubation with tlie la\ing of the first egg (Cade, 1960; Dementiev, ■ 1951). Cade (1960) reported as much as a week's difference between the ages of the youngest and oldest nestlings in four-egg clutches in the Arctic. PEREGRINE DECLINE IN UTAH The peregrine in Utah, as elsewhere in the United States and in Europe (Hickev, 1969), declined precipitously in the past two decades. To our knowledge, only two or three of the 29 eyries known to occur in Utah over the past several decades are still active. Nelson (1969) 42 Bhigham Young University Science Bulletin reported that before 1942, 50 percent of the "9 or 10" (9, Nelson, pers. comm. 1969, see Table 1) eyries located by him between 1939 and 1942 around the Great Salt Lake were taken over bv Prairie Falcons, and by 1948 onlv three or four of them were left. White (1963), how- ever, noted that five of these eyries (Table 1, sites 4, 7, 8, 10, and 13) were still active as late as 1952, and two additional eyries (sites 17 and 18) are known to have been active in 1952 (C. Ward, pers. comm.), indicating that some of them were overlooked b\' Nelson (1969) or else previously unoccupied eyries were reactivated later. However, White's (1969b) report of the occupancN' by peregrines in 19.54 of an eyrie which earlier in the ccnturv' ( 1927) was used by Prairie Falcons (Wolfe, 1929) suggests that the reverse situation also may have taken place. The usurpation of peregrine eyries by Prairie Falcons nia\' not have been permanent, as sug- gested bv our observations of the two species utilizing one another's eyries in Utah. Nelson (1969) indicates that he was unaware of the utilization of alternate nesting sites by the pere- grine between 1939 and 1942, which increases the possibility that some of the peregrine loca- tions believed to have been taken over by Prairie Falcons at that time were still being utilized by peregrines nesting at alternate eyries. By 19.56, onlv four of the 20 known eyries along the Wasatch Front were active. No young have been known to fledge from an\' of these eyries since then (White, 1963), although one adult was seen at each of two eyries in 1969 (Table 1, sites 8 and 18), and a third is report- edly still active. Onh' two or three eyries were believed to have been active by 1969 in the entire state, which represents only about 10 percent of the total known to occur earlier. On the other hand, there are vast areas in Utah with seemingl)' appropriate ecological condi- tions that have remained virtuallv unexplored for falcons. It is possible that 10 or more eyries exist in these areas. It is interesting to note that the eyries in the more remote parts of Utah remained active nearly a decade longer than did those in the more populous and more intensive- ly c>iltivat(>d areas. Climatic Change Hypothesis for Peregrine Decline Nelson (1969) has hypothesized that the re- duction in numbers of active eyries in Utah was caused by a combination of rising average temperature and drasticalK' reduced precipita- tion, starting about 1870. He suggested that these changes resulted in the dr\ing up of small lakes and ponds and the lowering of the surface water areas of larger lakes, causing a critical reduction in the habitat for the prey species of the peregrine in Utah and in other areas of the northwestern United States. According to Nelson (ibid.) b\' 1961 the drought gave way to more moderate conditions resulting in habitat changes more suitable to the peregrine. Besides the drought conditions reported by Nelson (1969), river waters were diverted for irrigation and the vegetation adjacent to the marshes was overgrazed by livestock (Behle, 1958). By 1910, thousands of once productive acres of heavily vegetated marshlands along the shores of the Great Salt Lake, with their smaller lakes, ponds, and channels of frt^h water, became mud flats with stagnant pools of alkaline water. Ultimately these changes caused the death of thousands of ducks, shorebirds, and marshbirds due to botulism (Wehnore, 1915, 1918; Behle, 1958). It was not until after the completion of the Bear River Migraton' Water- fowl Refuge between 1932 and 1935 and tlie Ogden Bav and Fannington Bay refuges in about 1941 that these marshes regained much of their former vitality and productivity. Some changes took place as late as the early 19.50s in the marshes fm-ther removed from the lake. Weller, Wingfield, and Low (1958), for example, recorded a drastic change in the size of the Knudson Marsh, four miles west of Brig- ham City, Utah, between 1950 and 1955. They attributed the changes to a deepening of the water channel entering Bear River Refuge, an increased demand for irrigation waters, a below average rainfall between 1952 and 1954, and overgrazing bv cattle. The change in size of the Knudson Marsh resulted in a decline of one- third in the number of species and two-thirds in the number of birds nesting there. Bv 1960, the total acreage of marshland in Utah was reduced bv nearly 50 percent ( Smith, 1961) of the 1,174,400 acres (475,279 ha) known to exist originally (Low, 1966). Smith (1961) reported the existence in 1960 of 600,000 acres (242,820 ha) of wetland habitat in Utah of variable value to wildlife. Of this acreage, 83,000 (33,590 ha) were owned bv the U.S. Fish and Wildlife Service and 60,()00 (24,282 ha) were owned and operated by the State Fish and Game Department. The remaining acreage was in private ownership, either as managed clubs or as unmanaged natural wetlands. Un- fortunately, the effects of these environmental changes on the peregrine were never docu- mented adeHjuatelv. Morlan Nelson (Hickey, 1969: 96) has sug- gested that in 1965 there was only enough Biological Series, Vol. 18. No. 1 Peregrine F.alcon in Utah 43 habitat left in tlie Bear River marshes to sup- port one pair ot peregrines. This would seem to he an underestimation, since we know of several evrie sites in the western United States where peregrines have bred successfully adjacent to marshes much smaller and much less productive than are the Bear River marshes. In discussing the decline of the peregrine in Utah. Nelson (1969) indicated that the pere- grines nesting in 1939 at the Ul site (site 11, Table 1 ) adjacent to the Bear River Migratorv Bird Refuge did not return to nest by 1941 be- cause the drought dried up their hunting sites. So that we might critically assess Nelson's im- plication, we measured the extent of the marshes and open waters within a fi\e-mile ( 18 km ) radi- us (if tlu' Ul e\ rie, using U. S. Geological Sur- \e\' topographic maps (aerialh- photographed, 1953-19.56). The resulting measurements tend to weaken Nelson's argument, since there were still 16.6 sq miles (43 km-) of marsh and 5.8 sq miles ( 15 km- ) of open water within the five-mile radius. Moreover, the Bear River Ref- uge, with its extensive marshes, was only seven miles away. However, this is based on the as- sumption that these marshes did not increase appreciabh' in size between 1941 and 1956. We cannot comment on the latter premise because we have no infomiation on the extent of these marshes for the earlv 1940s. Since we consider the cliff at the Ul site to be marginal in terms of accessibility to humans and predators, we believe that human disturbance may have been the major factor causing the abandonment of this evrie, although habitat change and competition with the Prairie Falcon probablv played a subordinate role. Further evidence which tends to weaken Nelson's climatic change h\pothesis was ob- tained from Noland F. Nelson, manager of the Ogden Bay State Waterfowl Management Area. Nelson spent man\ hours at the Bear River and Ogden Bav marshes prior to the completion of the refuges. He noted that there was not a dearth of shorebirds and marshbirds at these marshes before the dikes were constructed (N. F. Nelson, pers. comm., 1971) and that the de- velopment of the Ogden Bav area increased the numbers of nesting and migrant shorebirds (Nelson, 1954). Nevertheless, he does believe that the shorebird populations at Ogden Bay have declined in the past several years (N. F. Nelson, pers. comm., 1971). Furthermore, it is of interest to note that Noland Nelson observed fewer peregrines at Ogden Bay in the 1950s than in the i940s. He saw them there occasionallv in the 1940s (Nel- son, 1954), but rarely after the early 1950s (N. F. Nelson, pers. com., 1971). The occasional ob- servation of peregrines at Ogden Bay during the 1940s is about all one would expect, con- sidering that these marshes were supporting at most only three pairs of active eyries during these years. These observations correspond with the reduction of breeding pairs along the Wa- satch escarpment between 1940 and the 1950s. The Great Salt Lake has been subject to major cyclic fluctuations in size twice historical- ly, and perhaps many times in the past several thousand vears. Early historical evidence indi- cates that in 1850, when the Great Salt Lake was first sur\'eyed bv Captain Howard Stans- bury, it was much reduced in size compared to earlier and later reports. James Clvman, who with a parts' of trappers first circumnavigated the Great Salt Lake in a bullboat in 1826, wrote the following in his journal on 1 June as he passed through the Great Salt Lake Valley in 1846 on a trip east from California. proceeded ne.irlv ea,st to the point of a liigh mountain [Oquirrh Mountains] that Bound.s the Southern part of the greate salt lake I observed that this lake like all the rest of this wide spread Sterility ha.s nearly wasted away one half of its surface since 1825 [1826] when I floated around it in mv Bull Boate and we crossed a large Bay of this lake with our horses which is now dry . . . (Koms. 19.51:36). Four \ears later when the lake was sur- veyed bv Stansbur\' (1852), it covered 1,750 sq miles (4,433 km-) '(Powell, 1879). By 1S69, the lake had increased in size to 2,166 sq miles (5,610 knr) (ibid.), and bv 1870 to 2,400 sq miles (6.216 km-) (Bue, 1963 in Nelson, 1969). By 1961, the Great Salt Lake had receded to an unprecedented low (950 mi-; 2,461 km-) fol- lowing several decades of drought (ibid.), and b\' 1971 it had risen about seven feet (2.1 m) above its historic low, with a surface area of 1,461 s(i miles (3,784 km') (U.S. Geol. Survey, 1971). Powell (1879) considered the lake to be at its highest level in 1869, which exceeded a level to which it had long been subjected, and that its old mean area was 1,820 s(( miles (4,714 km-). A drawing of the lake in 18.50 by Stansbury (Powell, 1879) is a near duplicate of the size and shape of th(> lake shown on U.S. Geological Sur\'ey topographic maps constructed from photographs taken in 1953. Anthropologi- cal studies in Utah b\' Antevs (1948) and Har- per and Alder (in press) and the studies of Blackwelder (1948) suggest that the lake prob- ably was subjected to fluctuations in size many times prior to written history; this will be taken up in more detail imder a separate heading. Despite these periods of drought and their corresponding changes in aquatic habitat, the 44 BmciiAM YouNo University Science Bulletin peregrine persisted until the late 1950s. Although the relationsiiip between the changes in climate and coneoiiiitant ilnetuations in tlie size of the lake and the effects of these changes on peregrine populations of the area may never be fully un- derstood, it is clear that never before had these populations been so adversely influenced by the actixities of man as in the past century. Data from Utah Lake also do not seem to fully support Nelson's (1969) hypothesis. Data on the fluctuations of water surface and com- promise le\els have been plotted for the period 1883 to 1960 (from several sources, including Bureau of Reclamation and Utah State Fish and Game). The lake oscillated around the compro- mise level (4,488.95 ft; 1,. 368.2.3 m) between a plus and minus five feet (1.5 m) through 1925. Between 192.5 and 19.30, the lake remained around the minus five-foot (1.5 m) level, and starting in 1930 the lake level gradually lowered to its lowest level, slighth below minus 10 feet (.3.0 m), in 19.34 and 1935. There was a slow regain, remaining near the minus five-foot ( 1.5 m) level through the mid-1940s, until it reached above the compromise le\el in 19.52. However, the lake has remained below the compromise level since then. At its lowest level ( 1934-35) about .37 percent of the surface area was lost (data through D.A. White from the Utah Lake Research Shition). PresumabK many marshes around the i-dgc- of the lake dried up during this low period^ thereby reducing shorebird and water bird habitat. However, this may not be a totally satisfacton' index to the availability of marshes. Man\- areas fomierly covered by water l)ut appareiitl>- dr\ during the low water years, such as Provo Bay, were fed b\ springs and doubtless maintained some habitat for the prime avian pre\ species. Some of these areas were situated opposite acti\-e peregrine eyries. Thus, tlie impact of tlie drought \ears on peregrines is difficult to evaluate. Even so, it is clear that it was not until well after the drought years and after the 19.50s that some of the eyries around Utah Lake became inacti\e (Table 1, sites 17 and 18, for example). As mentioned earlier, tlie nunilxT n) pere- grines wintering in the marshes adjacent to the Great Salt Lak(> declined steadilv from 1939 (;><0.01, linear regression analysis), the vear Nelson ( U)69) located his first e\ ries in Utah, until the early 1960s when tlie species disap- peared as a resident in tlie iiiaishes (Fig. 1 \). The decline correlated closely in tiiiu- with the aban- dcmment of local eyries. The desertion of some e\ries during the early 194()s and perhaps earlier in the centun' is explainable on the ba.sis of Nel- son's (ibid. ) cliniatie change hypothesis. How- ever, the magnitude of the decline which fol- lowed later in the decade and on into the late 195()s is not, since management methods by then iiad brought about stabilit\ to the marshes and a concomitant increased population of prey spe- cies. If climate had been the sole cause of the decline in Utah, one should have expected the reactivation of e\ries b\- the early 1950s fol- lowing the development of the migratory water- fowl lefuges in Utah, yet this did not happen. ( Additionalh', a reported increase in nesting peregrines since 19.39 in Arizona at the expense of tlie Prairie Falcon is still unexplained [Phil- lips, Marshall and Monson, 19641.) We do not ciuestion thi' \alidity of Nelson's (op. cit. ) climatic change hypothesis for Idaho and elsewhere in the Northwest, where peregrine food producing marshes and waters disappeared. We do believe, however, that the more penna- nent nature of the Great Salt Lake marshc^s great- l\- lessened the impact of these climatic changes in Utah, resulting in the abandonment of a few marginal e\ries (Table 1, sites 11 and 25) that were situated near smaller and less pemianent marshes or that were located on small, relative- l\ accessible cliffs. Howe\'er, the number of e\ries, if anv, that disappeared prior to Nel- son's (1969) 19.39-1948 observations in Utah is not known. Furthermore, a 10-year reversal of the prolonged drought of the preceding half centurv \\'hich purporti'dl\ caused the peregrine decline has not \et resulted in an appreciable recolonization of old e\ lie sites or the estab- lishment of new sites. Nelson ( op. cit. ) also suggested that Utah's peregrines ina\- have made altitudinal adjust- ments during periods of drought to compensate for the changes in climate. Our data show no in- ilication whatever of shifts in the species nesting populations from lower tn higher elevations (see Table 2). On!\ one known eyrie (site 36, Table 1) and two suspected e\ ries (sites 27 and 29, Table 1) in I'tah weii' above 6.000 feet (1,829 m) in elexatioii. Two oi these were known earlier in the eentun (early 1900s and middle 19.3()s). whereas the third is of more re- cent iibseixation in an area that was not investi- (fated l)i(ili)L;ieall\ earlier in the eentur\'. Pesticide Ilvpothesis for Peregrine Decline Pesticide Si/;u/ro(»ic in Utah Fere possibility tli.it pesticides max ha\-e been iinohed during the later stages oi the decline. Biological Series, Vol. 18, No. 1 Pehegiune Falcon in Utah 45 Abnomial boha\ior and increased reproduc- tive failure were recorded at several Utah e\rii's durins; tlie period follo\vinproductive abnormalities Iiave been duplicated experimentalK' in the American Kes- trel (Porter and Wi<'me\ cr, 1969), the Mallard (Heath, Spann, and Kreitzer, 1969), and Black Duck (Ana.s- ruhripes) (Longcore, Samson, and Whittendale. 1971) b\' giving them low dietaiy levels of organochlorine pesticides. The mode of action of these chemicals on avian reproduc- tion has been investigated (Peakall, 1969, 1970, 1971; Bitman, Cecil, and Fries, 1970), and the effects of DDT on the structiue and chemistry of the eggshell are now being studied ( McFar- land, Garrett, and Nowell, 1971; Longcore et al., 1971). Experimental studies which indicate that DDT dekns oxidation in the Bengalese Finch (Loncluira striata) (Jefferies, 1967) and also in American Kestiels ( Porter and Wiemeyer, un- publ. data), suggest that this phenomenon may have occurred in wild peregrines as well. The la\'ing date of th(> first egg in 1952 at eyrie number 7 (Tables 1 and 7) (29 April) was two and one-half weeks later than in 1948 (approxi- mately 11-12 April), and a week later than in 1947 (about 21-22 April). However, this may be a reflection of the change in females that was known to lunc taken place at the e\rie in 1952, or of an adjiistment to ;i change in weather, rather than to a pesticide-induced delav in ovu- lation. Direct mortalit\ of adult birds due to DDE- poisoning cannot be discfuuited as a factor in the decline of the peregrine, since Porter and Wie- mever (1972) have demonstrated that dietary le\'els of onlv 2.S ppm (wet weight basis) /;,//- DDE were letlial to S p(ic(>nt ol male cap- tive American Kestrels after one xcar on dosage. The effects were most pionounced duiing molt and immediatelv follow ing nesting seasoTi— a pe- riod when the fat ev'ele of the kestrel was at its lowest point. Thev ha\'e also shown (Porter and Wieme\-er, in preparation ) that kestrels dosed at both low (0.28 ppm dieldrin; 1.4 ppm DDT) and high (0.84 ppm dieldrin; 4.7 ppm DDT) (wet weight basis) dosage levels of DDT and dieldrin in combination are more susceptibli- to death following stress of weather than are non- dosed kestrels. Residues of Pesticides in Peregrine Prey Species We will now consider the quantity of or- ganochlorin(> pesticides in the tissues of some of the peregrine's pre\' species in Utah, since many of the principal pre\' of the peregrine are known to contain high levels of these chemicals. Cade, White, and Haugh (1968), and Ender- son and Berger (1968), for instance, determined that DDT, DDD, DDE, and dieldrin were present in greater (|uantities in the tissues of migrant sandpipers than in an\- other of the peregrine's pre\' species in the .Arctic. Somc^ con- tained DDE in their tissues in cjuantities of suf- ficient magnitude* to be cause for concern (see Porter and Wiemeyer, 1969. and Wiemc\cr and Porter, 1970). ■ DDE is considered to be the most inimical to avian reproduction of the metabolites of DDT. Relatively high DDE residues were present in the eggs and in tissues of Short-billed Dowitch- ers {Limnodromus griscits), Killdeer (Cltarad- rius vociferus), American .\\'ocets and Rlaek- neeked Stilts in California (Keith and Hunt. 1966). Surprisingly liigh residues of /),//-DDE ( expressed in average and extreme ppm. wet weight basis ) were found in the eggs ot Black- necked Stilts (4.92, range 1.0-13.7), American Avoccts (4.43, 1.5-12.0)', and Franklin's (inlls (0.92, 0.5-2 2) collected at the Bear River marsh- es in 1968 (unpubl. data, Dc>nver Wildlife Re- search Center). The whole bodv tissues ol two Lesser Yellowlegs (Totaiius flavipes) contained (m the average 10.95 (range 5.1-16.8) ppm /).//- DDE (wet weight basis); four Long-billed Dowitchers {Liinnodromus scoloj)a(cus), 13.25 (0.7-49.20); one avoeet, 3.4; nine Whit(>-faced Ibis (Plegadis chihi), 2.55 (0.1-6.5); and three Marbled Godwits (Limosa fedoa), 6.04 (0.1.5- 17.8). Dieldrin in the tissues of these birds ranged from 0.1-0.86 ppm in the ibis, 0.2 ppm in the Lesser Yellowlegs, 0.0.5-0.50 ppm in the godwits, and 0.6.8 ppm in the avoeet. Many of the DDE values are greater than the 2.8 ppm (wet basis) of l^DE that caused eggshell thinning ( Wiemc^-er and Porter, 1970) and adult mortality (Porter and Wiem(>yer, 1972) in .American Kestrels. Residues of PCB's were found in foui- of the dowitchers and two of the \(41owle^s. The\ axeraged 3.75 ppin (1. -5-10.0) and 4.5 ppm (3.0-6.0), respectively. Mosiiuilocidc I'sagc in Vlali The chemical DDT was used as a mos(|uito- eide in the marshes along the Great Salt Lake as eari\ as 1947 in Weber (Ogden Ba\- State Waterfowl Managemc-nt .Area) (Benge and Fronk. 1970) and Box Elder eountic-s ( K. L. Josephson. pers. eonnn., 1971 ) and on an experi- Biological Series, Vol. 18, No. 1 Peregrine Falcon in Ut^vh 47 mental basis in Salt Lake County (Salt Lake City Mosquito Abatement District) in 1945 (Graham and Rees, 1958). This chemical was used at Ogden Bay until 1961, at which time the use of parathion was initiated (Benge and Fronk, op. cit. ). Davis County probably began the use of DDT in 1951 or 1952, since mosquito control was initiated there in 1951 (Stewart, 1954; Nielson, 1962). The quantities of DDT used in the early \'ears probably were not great, since it was applied bv means of foggers and hand-operated sprayers. However, beginning in 1949, DDT was applied to the extensive marshes bordering the Great Salt Lake by means of air- craft (for additional history of mosquitocide usage in Utah, sec Appendix. The utiliza- tion of DDT increased with the use of air- planes as a vehicle for application. It is inter- esting to note that reproductive failure in the peregrine was most pronounced in the vcars coincident with, and immediately following, the initiation of aerial spraying, although this may be an unrelated coincidence. Between 1947 and 1961 many thousands of pounds of DDT were deposited on agricultural crops, and more importantly, directly on the marshes and waters in the Great Salt Lake Valley where nesting peregrines obtained much of their food. The quantities applied by mosquito abate- ment districts were greatest along the marshes of the Great Salt Lake, where no peregrine eyries are known to have been active after 1957, and least in Utah County, where several pere- grine eyries apparently remained active until the late 1960s. Data on the (juantities of organochlorine in- secticides used for agricultural purposes in the area surrounding the Utah and Great Salt lakes were unavailable to us, but chlorinated hydro- carbon pesticides probably were used in large quantities, judging from a recent surv'ey of pesticides in Utah (VVarnick, 1971). However, they were applied to farm crops, farm animals, and buildings, and not directly on the marshes where the peregrine obtained its food. Unfor- tunatelw little is known regarding the move- ments of these chemicals from agricultural lands to the marshes. We have no direct evidence linking these chemicals with the sharp reduction in active peregrine e\ries along the Wasatch Mountains during the critical years between 1945, when the chemicals were first used, and 1957, when the species was last known to breed in the area. Nor do we know the extent of the environmen- tal contamination at that time bv other chemicals such as the polvchlorinated biphenyls (PCBs). We do not know the effects of PCBs on raptor reproduction, although some PCBs (1245) in small dietary concentrations do not seem to affect reproduction in Mallards, Pheasants (Pha- siantis colcliicus) (Heath et al., 1972), and Ring Doves (Streptopelia risoria) (Peakall, 1971) in the same way as does DDE. We can only speculate regarding the resi- dues of chlorinated hydrocarbons present in the tissues of either the peregrine or its prey species during the period of its decline in Utah. Most of the peregrine's prey species were migratory in nature. Thus, part of the insecticide residues acquired by them were from areas other than Utah and the Great Salt Lake valleys. We are unable, therefore, to establish an absolute cause and effect relationship between the quantities of chlorinated hydrocarbons used and the decline of the peregrine in Utah, although one is sug- gested by the experimental, ecological, and be- havioral evidence which we have presented. Disease Hypothesis for Peregrine Decline White (1963) referred to 27 cases of botu- lism (Clostridium botuJinum) in peregrines that were found in the Great Salt Lake marshes be- tween 1943 and 1958. Ralph B. Williams (pers. comm., 1972) also found several affected pere- grines on marshes around Utah Lake in the mid-1940s. The disease was most prevalent be- tween late July and early October, and it ap- peared to affect adults more than young, and females more than males. Botulism undoubted- ly has taken its toll of peregrines during the past several decades and perhaps, sporadically, for many hundreds of years. Its effects, histori- cally, on the local peregrine population cannot be assessed because the fluctuations in numbers of active peregrine eyries in Utah are not known. We cannot evaluate the effects of botulism tox- ins combined with those of pesticides, since knowledge of the effects of pesticides on the susceptibilit)' of birds to various diseases and the interactions of botulism toxins with the chlorinated hydrocarbons arc poorly understood. However, any mortality of adult birds due to disease during periods of reproductive failure would tend to accelerate the decline. Human Activity Factors in the Decline of the Peregrine A number of human activities, besides the agricultural practices already mentioned, may have adversely affected the peregrine in Utah, particularly in combination with the inimical effects of organochlorine pesticides, botulism poisoning, and changes in the climate. (See an 48 Bricham Young University Science Bulletin earlier analysis by White (1969b) of tlit- effect of human pressures. ) The impact of nest robbing, which started earlier in the centurv with egg collecting and later in the centur\-, starting about 1939, with the utilization of the nestlings for falconry, are difficult to evaluate, although there is no evi- dence that these activities per se were respon- sible for the sharp increase in abandoned eyries in the state. Some peregrine eyries in Europe were robbed of their young for many hundreds of years without apparent harmful effects ( Fi- scher, 1967; Ratcliffe, 1969). Photography at eyrie sites also may have caused some birds to abandon their eyries, al- though to our knowledge onl\' one nest in Utah (Table 1, site 7) was harassed in this way and the eyrie site was known to have been active subsequently. The reported collection of an adult falcon from the Pelican Point eyrie (Table 1, site 3) in 1935 (Bee and Hatchings, 1942) apparently had little impact on this eyrie, since it was still occupied as late as 1939 (notes of R. G. Bee). The removal of the adults from evrie site 4 (Table 1) in 1957 or 195S b\ a falconer probably hastened the abandonment of that eyrie by only a few years, since what seems to us to have been the pesticide syndrome was already in strong evidence there. The cliff at Pelican Point (site 3. Table 1, Fig. 6) became a limestone quarr\' in recent years and the evrie site was destroyed, as was an eyrie site in southwestern Utah (site 37, Table 1). Lower portions of the cliff near one of the most inaccessible peregrine e\ries in the state (Table 1, site 8) were blasted away dur- ing tlie 1960s. .Some of the earlier observations of peregrines in Utah were near this site. A bird was noted there in 1969 ( C. M. White), but not in 1971 (R. J. Erwin). A recreation area, establislicd after 196(S, is situated below one eyrie in east-central Utah (Table 1, site 2S). When the e\rie was visited in Mav 1971, several motore\cle clubs were us- ing the area as a point of rendezvous and all day and night the roar of motorcycles echoed through the can\()n. Although fresh excreta was seen along a ledge nnming adjacent to the old e\rie site, no falcons were seen in two da\s of observations. This eyrie had shown evidence of the pesticide syndrome as early as 1961, how- ever. The extent of the damage to the above site is not known. Depredation oi the species 1)\ hunters is a mortality factor which is frequently overlooked. Utah's marshes, which in the past were fre- (juented b\ peregrines in the fall and winter, have been used by increasingly greater numbers of waterfowl hunters in recent years. This is es- pecialK true of areas around the Great Salt Lake since the establishment of state and federal waterfowl refuges between 1930 and the early 1940s. Often hunters kill raptors and other birds indiscriminatelv. This could be a contributory factor to the peregrine decline, since peregrines fre(iuenting the marshes during hunting season probably were from local eyries. However, the significance of depredation by hunters is diffi- cult to assess since the peregrine is noted for its abilitN' to withstand this type of persecution and destructive treatment bv man (Ferguson- Lei's, 1957; Cadc>, White, andHaugh, 196S; Rat- cliffe, 1962, 1969). In the past two decades, the construction of human dwellings on the high foothills of the Wasatch Mountains below certain eyrie sites may have had an adverse affect on these eyries (sec White, 1969b), and the effects of the activi- ties at a nearby rifle range on one such eyrie also ari' unknown. Oni' can only spcx'ulate what the construction of homes near eyrie sites will do to these sites, since there is already a precedent set for peregrines nesting above railroad tracks, on bridges, and in heavilv populated urban centers (Hicke), 1942; Olivier, 19.5.3). The ex- tent to which some individuals of the species persist, despite the presence of human popula- tions near their e\ries, is illustrated b\' the pere- grines at one e\ rie that tolerati-d for o\-er a centurv the acti\'ities of a \ illage of two hundred peopli' at tlie base of the cliff th;it housed the falcon evrie (TTiekey. 1942). To sum up, pollution, shooting, nest site and hiibitat destruction, human disturbance, and climatic changes ha\i' contributed singlv and jointK' to the near demise of the peregrine in Utah. Of these, ]Dollution ;md climatic change appear to have played the dominant roles. FACTORS INFLUENCING PEREGRINE DISTRIBUTION AND ABUNDANCE IN UTAH To more lull\ understand tlu' various fac- tors involved in I lie distribution of tin- peregrine in Utah prior to its catastrophic decline, we ha\(' .ttteniptcd to examine the impact on tlu' species of \arinus ecological factors, both past and present. Biological Series, Vol. 18, No. 1 Peheghine F.alcon in Ut.\ii 49 Water, Food, and Nesting Sites as Limiting Factors Bond (1946) lias reported that in the west- ern United States tlie peregrine seldom nested more than one half mile (0.8 km) from uater in which to bathe. Exceptions to Bond's ( ibid. ) observations are icw. Gabrielson and Jewett (1940), for example, tell of a pair that nested in Oregon on an isolated rock far from water ( 11 mi.; 17.7 km., Bond, 1946), and Tliom- as Ra\' (pers. comm. ) located an active eyrie far from water in arid western New Mexico. The peregrine's affinit)' for free water prob- ably is associated more uith its needs to bathe and to obtain food than \\ith its needs to drink. Bartholomew and Cade (1963) point ont that the larger predator^' birds obtain adecjuate quan- tities of water from their food under most cir- cumstances. They cited instances of several fal- cons, including the peregrine, maintaining weight for man\ months without free uater. Beebe (1960) concluded that because 11 of 1.3 young peregrines taken from nests in the Pacific Northwest and raised in Denver died of deh\ dration, humidit\' rather than nearness of free water was perhaps a critical factor in brood success in areas of the West other than the Northwest Pacific coast. Since these nestlings died despite ha\'ing been supplied with drink- ing water, Beebe (ibid.) Inpothesized that pere- grines were more or less restricted to nesting sites near water because of high humidit\' rather than the presence of free water. An important cjuestion appears to be whether or not the young mentioned by Beebe were ac- climatized to tht' cool, humid climate of the Northwest before being transferred to the arid intcmiountain area. Nelson (pers. comm., 1971) has suggested that these birds may have died of malnutrition rather than dehydration. He raised and trained one of them and encountered no difficult\- uith deln dration. Other nestling peregrines from British Columbia and the Aleu- tian Islands, similarly transferred to Utah, have not been affected in this manner. Nestlings taken from Utah evries have not appeared to suffer greatl)' from delndration nor has there been any evidence of moisture loss among young peregrines cared for in the nest ])\' their parents. This affinity for high humidit\-, if it exists, mav be an inherited physiological characteristic of the pealei race, which is less pronounced in the peregrine populations of the arid Intennoun- tain \\'est (see also. White. 196Sb, for further documentation of this problem). Furthemiore, other populations of falcons, such as those of the Shaheen, exist and breed in the deserts of the Middle East under the harshest conditions known (Bartholomew and Cade, 1963). Food availability appears to be a major cri- terion influencing the distribution and abun- dance of the peregrine in arid regions of the West. Density and distribution of peregrine populations in Utah appear to correlate best with the abundance of the food supply. Pere- grine populations are most dense in the area surrounding the Utah and Great Salt lakes where the preferred prey species, particularly shorebirds and marshbirds, are most abundant. Here, the marshes have historically supplied food for 10 to 20 eyries during a single nesting period. Hunting areas for isolated pairs of pere- grines elsewhere in the state were supplied by smaller, less extensive marshes or by narrow tongues of streamside vegetation. Usually, iso- lated pairs survived and reproduced where ade- quate food was available. Food availability apparcnth' is an important factor in the distribution and abundance of the peregrine in more humid and mesic regions as well as in arid regions. Beebe (1960) has at- tributed an unusually high breeding density of peregrines in British Columbia to the extremely high concentrations of four or five species of colonial seabirds occurring there. These small pelagic birds apparcnth' were especially suited as pre\' species for the peregrine. Ratcliffe (1962) considered the geographic variation of food supph' as the most obvious factor associated with population density of the peregrine in Great Britain. He has correlated size of territory and density' of peregrine popula- tions in Britain with the nature of the food supply. The same factor generally appeared to be operative in Utah, although peregrine density in the Great Salt Lake Valley of Utah probably was not limited by the size of the prey popula- tions. However, the species may be limited by the distance (up to 17 mi, 27.4 km; Table 4) it must fly to reach the marshes where it obtains its preferred prey species. Peregrines ma\- select easily accessible nest- ing sites in areas containing an abundance of suitable prey species, as occurs in the Queen Charlotte Islands (Beebe, 1960). Such sites are seldom utilized in areas containing less favorable food supplies. This is illustrated in Utah by the occurrence of the ground-nesting peregrines at Ogdcn Ba\'. Hick(>\- (1942, 1969) considered the cliff on which per(>grines nest as the dominant feature of their ecological niche. He considered extremely high cliffs as "ecological magnets" which at- tract peregrines regardless of nesting success. 50 Brigham Young Univkhsity Science Bulletin Cade (1960), on the other hand, has argued that the ability of the pair to breed effectively is a result of a strong pair bond, and that the strength of the bond is a more important con- sideration than the size of the cliff. He argued that the pair bond would be dissolved and that the evrie would become inacti\e indefinitely if both the male and female disappeared from the eyrie. Ratcliffe (Hickey, 1969), in support of Hickey (1942, 1969), has cited examples of several eyrie sites which were consistently reoc- cupied following the deaths of both adults. This also has been noted in the Arctic b\- White ( un- publ. data). (See Fischer, 1967 for additional documentation. ) In Utah, selection of e\rie sites by pere- grines is associated with the avai]abilit\' of suit- able sites near a readily available supply of preferred prey species. The preferred prey spe- cies usually are closely associated with a marsh or stream. These two factors combined, then, constitute the most important aspect of the pere- grine's nesting econonn in the state. Interspecific Competition During Nesting Season Cade (1960) has discussed competition be- tween the jieregrine and the Cvrfaleon (Falco riisticohis). White and C:ade (1971) have dis- cussed competition among several species of raptorial birds in the Arctic, and White (1968b) has discussed this problem as concerns peregrine distriliution and its relation to large congeners over broad distributional areas. These papers give a valuable basis for the evaluation of the competition between the peregrine and other raptors whose range and habitat in Utah are svmpatrie. In our discussion of interspecific competition, we prefer the more restricted defi- nition of the tenn "interspecific competition" as given b\' Birch (1957) and as discussed by Cade (1960). Tliat is, competition results when more than one species re(|uires a resource that is in short supply. Competition for food and/or nesting sites between the peregrine and other species of rap- tors, particularls' the Prairie Falcon and the Golden Eagle, ma\' be factors contributing to the relati\'e paucity of peregrines in the arid Inter- mountain West. Where relati\-el\- abundant, the Colden EagU- ma\' be a eoinpetiti\e factor limiting the density of the peregrine in the more arid regions of Utah. Bond (1946) has watched the peregrine strike at Golden Eagles and R. J. Erwin and J. F. Poonnan (impubl. notes) have made a simi- lar observation in Utah. Dixon (19.37) tells of one instance when a pair nt Golden Eagles in California usurped a cliff that had been occupied by peregrines for years. Tlie eagles persistently outfought the peregrines, forcing them to leave. Cade ( 1960 ) found that the peregrine was quick- er and more persistent in its attacks on Golden Eagles than on any other raptor discussed. Rat- cliffe (1962, 196.3)' reported that in man\- dis- tricts in Scotland, where there is a surplus of suitable cliffs, the densit\' of Golden Eagles is high while the densities of the peregrine and the Common Raven (Corviis corax) are low. In these situations apparently the eagle replaced the peregrine as the chief nesting predator in the Scottish Highlands. In Utah, peregrines and eagles were found nesting concurrentK' on the same set of cliffs only once. The eagles nested one mile ( 1.6 km) (Morlan Nelson, pers. comm., 1971) from ac- tive peregrine and Prairie Falcon eyries (see Nelson, 1969), but on the opposite side of the mountain (north). Tlu- eagles apparentK' foraged northwardh , while the peregrines foraged south- wardly. No aggression was noted between the eagles and the falcons (Nelson, pers. comm.). A cliff formerly occupied b\ peregrines in Utah (site 15, Table 1) contained an active Golden Eagle's nest in the spring of 1971, and the pres- ence of two old eagle nests ( R. J. Erwin) sug- gests a long period of occupancy bv the eagles. The cliff also had been occupied b\' as man\- as tliree pairs of Prairie Falcons simultaneously during some oi the intervening \'ears (Nelson, pers. cdinm., 1971). The food habits of the eagle and peregrine are sufficicnth' diverse in Utah so as to negate a strong competition for food. Additionally, the eagle seems to attain its greatest abundance in the more arid regions of the state, wIktc it more liki'K' would compete with the Prairie Falcon for nesting sites than with the peregrine, al- though the abundance of eagles in the deserts of Utah may be one of the reasons whv the piTegriiu' seldom occurs there. This latter postu- lation, liowevi'r, appears unlikeK' because of an absence of the ft)od niche preferred b\' the peregrine. The Common HaNcn lias lieen shown bv White and C^ade (1971) to compete rather ex- tensiveh with G\ rfaleons for nest sites in the Arctic, though it seems to ha\e only limited competiti\e effect on Arctic peregrines using the same cliffs. In Utah, where the raven is com- mon, onK three cliffs with peregrines were known to house ravens. Like the situation in the .Arctic. ra\('ns probably had "no" effect on Utah peregrines, although Porter observed peregrines at site number 4 pursuing ravens on 8 .April 19.51 |{;i\(iis ina\. howe\('r. h.ivc a considerable Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 51 modihing effect on Prairie FaIcon.s, a.s wall be discussed in a later section. ( See also Ratcliffe, 1962, for a c-onsideration of raven-peregrine in- teraction in Great Britain. ) The Prairie Falcon ( Fig. .39 ) , on the other hand, is more closeh' related plu'logenetically, is more similar in size, and is more equivalent in ecological function to the peregrine, than is cither the eagle or raven. Hence, it likely would be a more serious competitor of the peregrine and it probabK would be a more important factor limiting peregrine populations in areas of sympatr\'. The Prairie Falcon is a true desert falcon. It undoubtedly evolved in the arid West, and therefore is probabK- better adapted than is the peregrine for Utah's arid environment. The Pere- grine Falcon is separated from the Prairie Falcon and the Cyrfalcon at the subgeneric level. The two species are of similar size, although the peregrine is somewhat heavier than the I-'rairie Falcon (Sei' Table 9 and Webster, in Beebe and Webster, 1964). The peregrine, which is nearh' cosmopolitan in its geographic distribution, has a breeding range which completely overlaps that of the Prairie Falcon geographicallv but not ecologi- callv. The Prairie Falcon breeds from central British Columbia, southern Alberta, southern .Saskatchewan, and North Dakota, south t(j Baja California, and northern Mexico (Sec AOU Checklist of N. Am. Birds, 1957). The pere- grine is most abundant north of its zone of svm- patry with the Prairie Falcon. According to Bond (1946), the Prairie Fal- con ma\' be quite common up to 6,000 or 7,000 feet (1,829 or 2,1.34 m) in suitable localities and at elevations where trained Prairie Falcons, with their much greater surface to weight ratio, clear- ly outflv trained peregrines, which are their su- periors at sea level. Morlan Nelson (pers. comm. 1971), who has tested Bond's (1946) hypothesis on several occasions with captive falcons, con- siders that it is more a matter of individual varia- tion within both species than it is a factor of elevation. Actual contact between the two species oc- curs where their ecological niches overlap. To our knowledge, there is no locality in Utah where peregrines nest which is not also inhabited bv Prairie Falcons, but not the reverse. The peregrine's proclivity to nest near water or marshes where both its food and nesting re- quirements are met is not shared by the more euryecious Prairie Falcon which may fulfill these requirements both near water and in the desert many miles from water. As discussed previously, the several pere- grine e\ries found in the deserts of Utah were situated within easy access of marshes, desert springs, ponds, streams, or rivers. Perhaps this reflects the differences in hunting methods and food habits of the two species, as well as the proclivitv of the peregrine to bathe in water as discussed by Bond (1946) and Cade (1960). Both species can be dust bathers in captivity (Nelson, pers. comm.), although the Prairie Falcon is less dependent on water than is the Peregrine Falcon. Some Factors Modifying Competition and Success Before examining the kinds of competition that may affect Utah peregrines, a general dis- cussion is in order. There are many ways that falcons can exploit their respective environments. Their success, that is, the total number of young that become breeding adults in the next generation, depends upon the effectiveness of this exploitation. Frequently ecologists use the terms "gen- eralist" and "specialist" to describe a species in terms of the manner in which it utilizes certain resources. Most frequently this pertains to the manner in which the food or habitat niche is exploited, or to the modes of hunting certain species of prey. Although the specialist has a narrower habi- tat tolerance, it usually compensates b\' being more competitive (see, for example. Cade, Table 9. Weights ( in gram,s ) of Peregrine Falcons and Prairie Falcons from various North American populations. Species and MALES FEMALES Population n X range n X range PEREGRINE FALCONS (White. 1968a & b) F. p. tundrius' F. p. anatumr PRAIRIE FALCONS' (Enderson, 1964) 12 5 15 610.9 678.0 554.0 550-647 67.5-682 500-635 19 5 31 952.0 1,038.0 863.0 825-1,094 870-1,201 760-975 'Weights are from adult birds. -From population in western United States. 52 Bhk;ham Young Univebsity Science Bulletin 1960). When the optimal requirements for the speciahst are present, it tends to eapitahze on or "monopoHze" the resources or conditions to receive maximum benefit, often to the ex- clusion of the generalist or other specialists. It is the existence of a specific or optimal set of conditions that allows the specialist to be suc- cessful. The generalist might also successfully exploit the precise conditions. However, because of competition with the specialist, it may alter the manner in which it uses the conditions by partitioning the resource, or it mav be forced into suboptimal conditions because of the domi- nance of the specialist. In the absence of the specialist, the generalist obtains even greater benefit by the use of the specific combination of resources or conditions that the specialist would have used. The generalist tends to be more widespread geographicail\' and often more common than the specialist. Moreover, when two closely re- lated species with similar ecological niches oc- cupy the same geographic area, one tends to assume the role of the "specialist" and the other th(> role of the "generalist," depending upon their individual needs. G\'rfalcons, for instance, are specialists on the Arctic Slope of .'\laska, where thev have specific nesting requirements and where thev specialize on ptannigan for food, while the sympatric peregrine is the generalist, having rather broad reciuirements for nesting and feeding (White and Cade, 1971). The G\ rfaleon seemingK has the adxantage and ap- pears to outcompcte the peregrine for certain resources. However, because the peregrine is a generalist, it has less precise requirements and therefore is able to occur over a much broader geographic range in Alaska, such as the taiga regions. Then, too, it is probabK more numer- ous when considering its entire range. Even though the j^eregrine is probably a generalist o\er much of its cosmopolitan range, it becomes a specialist in the Aleutian Islands, where it has a narrower food niche consisting mostK of marine birds of tlie famih' Alcididae and of the order Procellariiformes. Thus, the role of the species is modified In the conditions in a given localih'. Prairie Falcons ha\'e been thought of as spe- cialists liecause the\' are al)le to exploit \('ry arid climates where a limited number of food species are present. They often occur where other large falcons arc unable to survive. Be- cause they are able to concentrate on the prey species most a\ailable, Prairie I-'aleons mav have a ratlier highK specialized food niche, especial- ly in the more arid regions w^here a limited number of food species occur. Their abilit\ to "specialize" on what is a\ailable enables them to live successfulh' in a wide variety of eco- logical situations. If one considers the Prairie Falcon's entire geographic and ecological range, it is narrowly selective in its exploitation of the climatic condi- tions a\'ailablc to it (i.e. a near obligate of xeric conditions), but it is broadh' selective in its ex- ploitation of food and n(-sting sites. Additionally, where the geographic ranges of the two species o\'i'rlap, Prairie Falcons are much more common than art" peregrines. Because of the Prairie Fal- con's seemingly narrow climatic tolerance dur- ing the breeding season, climate ma\' be a major factor limiting its geographic distribution. Peregrines, imlike prairies, are broadl\- selec- tive in their exploitation of climatic conditions over their entire geographic range. However, tlie\' are narrowly selective in their exploitation of food and nesting sites in the arid West where the\- must compete with the s\mpatric Prairie Falcon. Moreover, the\' are much less common than are Prairie Falcons, where the ranges of the two species are svmpatric. Their specialized food rcHiuiremi'nts (generallv "water-t\ pe " birds) and restrictive methods of capturing pre\ (not prone to capture prey on the ground), are the major factors limiting the expansion of their geographic and ecological ranges in Utah and probabK else\\here in the arid West. The presence of surface water in the arid West ma\' dramatically alter the environment. For certain species it may even act as a limiting factor. Water creates a food niche which ap- parenth is optimal for the peregrine, providing an abundance of aquatic birds in these local- ized areas. Hence, the peregrine does better in the presence of surface water. This is especially evident at the margin of the species' ecological range in the arid parts of Utah. With the pres- ence of these "oases" of acjuatic habitat in an otherwise unexploitable enxironment, the pere- grine assumes the role of specialist: and, where the peregrine and piairie occur together in Utah, the prairie seemingK' assumes the role of the "generalist." The broad spectnmi of food, habi- tat, and nesting sites which the prairie selects overlajis and surpasses the reciuirements of the peregrine. The requirements of the peregrine are more limited and restrictive, \ I't it may do bet- ter competitiwlv than its congener when the optimal conditions pre\ail. (Competition \\ itli the Prairie I'alcon for Food Where the two species occur together along the escarpment of the Wasatch Mountains and adjacent to the Croat Salt Lake, their food ap- Biological Series, Vol. 18, No. 1 Peheghine F.\lcon in Utah 53 pears to be quite similar (Table 5), although there are some marked differences. In this re- gion of joint occupancy, the Prairie Falcon uti- lizes a much wider \arictA' of vertebrate species than docs the peregrine. As illustrated in Table 5, the Prairie Falcon is more prone to feed on ro- dents and on ground-dwelling birds, such as ([uail, pheasants, meadowlarks, and passerine l)irds in general, and is less inclined to feed on pigeons, doves, and flickers than is the pere- grine (also see Bond, 1936a, b, and c). Prairie Falcons also feed on reptiles. For in- stance, at one Prairie Falcon eyrie in the Great Basin, not far from a peregrine e)ric, adults were observed carrying large whiptail lizards ( Cnemidophorits sp. ) to the eyrie. The Prairie Falcon exploits a different food resource in thi- allopatric parts of its geographic range than in those that are sxmpatric with the peregrine. A case in point is the high plateau countr\- of Utah NNW of the Uinta Mountains ( 6,800' feet ele\ation; 2,073 m ) where only the Prairie Falcon occurs, although one would expect peregrines also to occup)' the habitat. Food items taken from several nests between 1961 and 1964 in this region of allopatry consisted of 61 percent mammals, about 90 percent of which was the Uintah Ground Squirrel ( CifeUus armatus), although another species of ground squirrel, a chipmunk {Eiitamias sp. ), and a vole (Slicrottis sp. ) also occurred. Birds made up the remaining .39 percent, with Mourning Doves being the principal avian food, though the Brew- er's Blackbird (Euphaniis aianoccpJwhis). Flick- ers ( Colaptcs sp. ), Horned Larks, Starling (Sfi/r- ntis vidp^aris). and the Mountain Bluebird {Sialia cttrrticoidcs) also occurred. Thus, about 75 per- cent of the total food uas made up of t\\'o spe- cies, one mammal and one bird. In this case, and those cited bv Enderson (1964), with an ab- sence of peregrines in both localities, the Prairie Falcon tended to fill the role of a "specialist" in food habits; and to a large extent the species was mammi\-orous (mammal-eating). (See Bond, 1936b). The avivorous (bird-eating) peregrine, on the other hand, consumes few mammals and fewer, if any, reptiles. Ground-nesting birds and rodents are im- portant items in the diet of the Prairie Falcon in areas other than Utah. For example, Enderson (1964) found remains of the ground-nesting Horned Lark and of the Richardson's ground sc|uirr(>l (Cifelhis richardsonii) most often, and sometimi's exclusi\el\-, in the nests of Prairie Falcons in eastern W\oming and Golorado. Og- den (1971) considered the Townsend's ground sfiuirrel (CiteUus fotcnsei-tdi) to be the most important food species, followed by Homed Larks, Meadowlarks, and whiptail lizards in Prairie Falcon eyries along the Snake River of southwestern Idaho. The antelope ground squirrel (Citcllits Icucurus) was also present, but in smaller numbers. The Horned Lark was also a staple item in the winter diet of Prairie Falcons in Utah and in the prairies of Wyoming, Colorado, and New Mex- ico, where it influences the falcon's seasonal movements and distribution (Enderson, 1964). An overlap in the food niches of the pere- grine and Prairie Falcon is evident in the area along the Wasatch Mountains (Table 5). In terms of biomass, aquatic birds comprised the largest categoPi' of prey species in the Wasatch Mountain eyries of both species, but the\- were much more predominant in the eyries of the peregrine than in those of the Prairie Falcon. The a\ocet was the major aquatic species in the e\ ries of both falcons (see Frontispiece and Fig. 39). The importance of the avocet as a pre\ species of the Prairie Falcon was apparent also at two e\ries in the Great Basin, northwest of Great Salt Lake, where the adult Prairie Falcons brought avocets and Antelope Ground Squirrels to their young almost exclusively in 1962 (C. M. White, unpubl. data) and commonly in 1969 (P'att, 1971). This, however, was in the apparent absence of competition with the pere- grine. The presence of the avocet in the diets of lioth species is probabK- a reflection of the local abundance of this shorebird and the ease with uhich it may be captured. The avocet likely did not represent a resource in short supph' and undoubtedh' was an important item in the diet of the peregrine long before the first white settlers arrived in the western United States. In 1S71 Allen (1872) found it \-ery abundant along the shores of Great Salt Lake, where he noted flocks containing several thousand indi- viduals from 1 September to 8 October, and a quarter of a century earlier (4 April 1850), Stansbury (1852) observed innumerable flocks of long-legged ]ilo\ers, many of which probably were avocets, Willets, and stilts. The avocet predated uhite man in the Great Salt Lake area 1)\ man\' thousands of years, as evidenced b\' its presence among the bird remains dating l^aek nearh- 8,500 \ears B.P. in the early strata of Hogup Gave, just north of the Great Salt Lake (Harper and Alder, in press). Tlie White-faced Ibis was an additional marshbird upon which both species of falcons apparenth preyed. Wcller 't al. (1958) indi- cated that the peregrine killed White-faced Ibis in the Knudson marshes near Brigham Gity, 54 BnicnAM YouNO Univfusitv Science Bulletin and R. D. Porter (unpuhl. data) ohscrvt-d a Prairie Falcon feeding on an ibis at the Bear River marshes on 5 June 1951. Since the ihis was not found in the evries of either species, it was prol)ahl\- too heavy for the falcons to carry to their eyries. The weight of an adult female ibis as determined by Porter et al. (unpubl. ms) is 517 grams, whereas the weights of two adult female avocets average 281 grams. In Prairie Falcon eyries along the Wasatch Mountains, shorebirds, passerines, rodents, and gallinaceous birds were nearlv equally repre- sented; whereas in the e\ries of the peregrine, shorebirds predominated and gallinaceous birds and rodents were absent (Table 5). The ducks present in the eyri(«i of the Prairie Falcon (Table 5) were about half grown and probably inca- pable ot (light. Hence, the\ probabK were either captured on the water or on the ground and were sufficiently light in weight that thev could be carried hv the falcons. We have no data for comparison of the food habits of the peregrines nesting in the desert (Table 6) with those of desert-nesting Prairie Falcons in the same region. A comparison of this kind is needed to fulh' evaluate the compe- tition for food by the two species. Cade (1960) found that the overlap in food species of the peregrine and Gvrfalcon were least in the areas of contact and greatest in areas where ranges were not s\mpatric. A comparison of this kind between the peregrine and Prairie Falcon would be difficult to make, since in Utah the Prairie Falcon occurs in the same geographic area as the peregrine. Nevertheless, one would expect ,« ^ F"ig. 39. Prairie Falcon feeding its voung a downy avocct (peregrine site 7, alt. prairie site 2, see Fig. 26). Photo l>v W. 1. Erwin and' IL I). Porter, 1948.' liroLoc-.iCAL Sf.hies, Vol. 18, No. 1 Pehegrine Falcon in Utah 55 less latluT than more overlap in food habits in areas of allopatry than in areas of contact. The isolated jieregrine's evrie in Oregon, which was situated far from water (Gabrielson and Jcwett, 1940), contained birds usually preyed upon by Prairie Falcons, and an adult peregrine at an eyrie in Zion Canyon was observed by Grater to carrv a squirrel into a crag (Woodbury et al., unpubl. nis). In Utah, then, the Prairie Falcon has a wider versatility in taking prey species than does the peregrine, which would seem to lessen the com- petition between the two species for food. Hence the role played by the Prairie Falcon in Utah is similar to that of the peregrine in the .\rctic (Cade, I960; White and Cade, 1971), and that played bv the peregrine in Utah is similar to that of the Gvrfalcon in the Arctic. According to White and Cade (1971), there is no evidence to suggest that density of breeding peregrines is influenced in anv way by availa- bilits- of food in the Colville valley of Alaska. This generally is not applicable to the peregrine in Utah, but in the region surrounding the Great Salt Lake it is difficult to surmise how the density of tlic peregrine could have been limited b\- availabilit\ of food, considering the super- alDundance of prey species in the Great Salt Lake marshes. Nevertheless, extensive distances from (•\rie sites (Table 4) to hunting sites in the marsh mav have limited their density. Competition with the Prairie Falcon for Eyrie Sites Directional Exposure Preferences In Utah the peregrine's preference for cliffs \\ith northerh^ or easterly exposures (Fig. 16) would tend to lessen the competition for nest- ing sites between it and the Prairie Falcon if the Prairie Falcon had a preference for south-facing cliffs similar to that reported for Colorado and Wyoming by Enderson (1964). We investigated this hypothesis by examining the directional fac- ing of the 49 evrie sites of the Prairie Falcon in Utah for which we had available data. As shown in Figure 16, 69.4 percent of these evries faced south and west and 30.6 percent faced north and east. This relationship was statistically signifi- cant at ;)<0.0I (X' test; calculated X- vahu07.37, 1 df). Conversely. 70.4 percent of 27 )ieregrine evries in Utah faced north and east and 29.6 per- cent faced south and west, and this relationship was significant at /><0.05 (X- test; calculated X' value, 4.48; 1 df). When the two species nested in close juxta- position on the same set of cliffs, as at site 7 in the Wasatch Mountains, the Prairie Falcon seemingly selected the sites more exposed to the afternoon sun (west-facing sites) than did the peregrine (see Histor)' of Nesting at a Wasatch Mountain Evrie, Table 7 and Fig. 26). As a gen- eral iTilc, the Prairie Falcon eyries on the escarp- ment of the Wasatch Mountains were situated directly on the west face, whereas those of the peregrine, as discussed previously, usually were on cliffs in the side canyons with northerly or easterly exposures. For example, three of the Prairie Falcon eyries were situated on west-fac- ing cliffs (see Figs. 26 and 39-42). At each of these sites, peregrines had been seen in the side canyons, although not always concurrently with the nesting of the Prairie Falcon (sites 7, 8, and 16, Table 1). In 1943, a Prairie Falcon nested in one of the canyons (near peregrine site 16, Table 1), but at a west-facing site in an easily accessi- ble Red-tailed Hawk's nest. Morlan Nelson (pers. comm., 1971) noted a similar orientation between the evries of the two species at the Ul site in northern Utah (site 11, Table 1), where he observed the two species in aerial combat (Nelson, 1969). The peregrine eyrie was on a ledge facing east and the Prairie Fal- con evrie was in a pothole (cave-like recess) in the side of the wt^st-facing cliff, less than half a mile away (1,320 ft; 402 m; Nelson, pers. comm., 1971). Potholes probably provide greater pro- tection from the hot afternoon ra\s of the sun than do exposed ledges. These data suggest that both species may se- lect eyrie sites on the basis of directional expo- sure to the sun, and that such a preference by these two species tends to lessen competition be- tween them for eyrie sites. Nevertheless, this jihenomenon needs further investigation, both in Utah and elsewhere, since some studies sug- gest that the Prairie Falcon in some parts of its range selects evrie sites on the basis of availabil- ity of suitable cliffs rather than directional fac- ing. For example, Leedy (1972) investigated the directional facing of 49 Prairie Falcon eyries in Montana during 1970 and 1971 and compared them u'ith the directional facing of the available cliffs. He found that 72 percent of the eyries faced south (33 percent) or east (39 percent), 8 percent faced north, and 20 ]iercent faced west. Of the 45 available cliffs in Leedy 's study area, 71 percent faced south (31 ]icrcent) or east (40 percent), 7 percent faced north, and 22 percent faced west— a near duplication of the directional facing of tlu> eyrie sites. Similarly, Tyler (1923) reported that most Prairii' Falcon eyries exam- ined by him in southem California had northern exposures because in the region where he made his observations the north ends of the ridges 56 BniGiiAM Young University Science Bulletin broke off abniptl\' into cliffs that faced north. Nevcrtliclcss, a few of his e\rics were on west- facing cHffs; one was on an cast-facing cliff; and none were on south-facing cliffs. Height Preference for Cliffs and Eyrie Sites The I'rairie Falcon in Utah ma\' use nesting sites of a quality inferior to those normally used bv the peregrine in Utah. Judging from Bond's (1946) observations, this ina\' be typical of the behavior of the two species wherever their geo- graphic ranges overlap. Three of nine Prairie Falcon eyries found in Utah bv Porter and Erwin between 1950 and 1952 were at locations that were easily accessible to both humans and mammalian predators. Two were situated in potholes, one of which was lo- cated onh' 30 inches (76.2 cm) from the base of a small sandstone cliff and the other was onh- 36 inches (91.4 cm) from the base and 48 inches (121.9 cm) from the top of an outcropping of limestone. A third e\rie was located in 194.3 by R. L. Porter and J. F. Poorman in an old Red- tailed Hawk's nest that was situated on a small pinnacle of rock which required no climbing to reach. One found in 1958 bv F. Welch and G. L. Richards was on a large rock about 15 feet (5 m) above the ground and 6 feet (2 m) below the top of the rock. It probablv could have been reached by a good climber without the aid of a rope. In southwestern Utah the Prairie Falcon has nested in a stick nest in the top of a 20-foot (6 m ) juni- per tree (Jtmipcnis sp. ) (^^'illiams and Matteson, 1948). In Utah peregrine evries were a greater dis- tance from the base of the cliffs, on the average, than were those of the Prairie Falcon. They were on higher cliffs, on the average, and the\' were on relativelv more inaccessible ledges than were the eyries of their congener (Table 3). Moreover, the peregrine evries averaged a greater distance below the brink of the cliff (x= 68.6 ft. 21 m; range, 2.5-250 ft, S-76 ni; n = i;3) than did those of the Prairie Falcon (x= 2.5.3 ft, 7.7 ni; range, 4-175 ft, 1-53 m; n = 41). The average height of the Prairie Falcon e\- ries in Utah (64 ft; 20 ni) was grc;iter than that recorded by Enderson (1964) in Colorado and Wyoming (.34.7 ft; 11.1 m), and less than that re- ported bv Leedv (1972) in Montana (80 ft; 24.4 m). The average cliff height of 101.7 feet (31 m) for the Prairie Falcon in Utah is nearly twice that recorded b\' Enderson (1964) for this species in Colorado and W\-oining, and iibout 25 feet (7.6 m) less than that recorded In Leedy (1972) in Montana. Table .3. which compares the heights of cliffs and eyrie sites ot the Prairie l-'iileon \\'ith those of the peregrine, illustrates the difference in height preferences between the two species. The more marginal sites, including those on the smaller or more accessible cliffs at sites such as 1, 3, 11, and 20 (Table 1), probablv were aban- doned b\- the peregrine earlier in the century. Both their sizes and locations made them mar- ginal sites. Several investigators (Hickey, 1942; Ratcliffe, 1962) have indicated that the marginal sites were the Hrst to become inactive following the advent of earlv settlers. Eyrie Type Preferences Till' Piairie Falcon uses a wider variety of nesting situations than does the peregrine (see Figs. .39-45). For example, nearly half (45.8 per- cent) of 72 Prairie Falcon nesting sites in Utah were in potholes and crevices (Figs. 42-44) in the face of a cliff, whereas onlv a third of them (31.9 percent) were on an open ledge of a cliff (Fig. 39). An additional third of the e\ries were in the Fig. 40. Tlic Prairie Falcon eyrie that was .situattii on .111 old Common Haven'.s {Corvus corax) nest and was later leelaiined by the raven. Note the ac- cumulation of fecal material and detritus suggest- ing that the e\rie Ii;ul been used by the falcons for a long period of time (evrie site faces southwest). Photo bv W. D. Porter, 1951. Biological Series, Vol. 18, No. 1 Pehecbine Falcon in Utah 57 Fig. 41. Raven'.s nest built upon prairie eyrie (shown in Fig. 40). Photo by R. D. Porter, 1951. nests of other species of raptors and Common Ravens, which suggests that these species ma}' be beneficial to the Prairie Falcon b\' providing additional nesting sites. Table 10 gives the kind of nesting situations used bv Prairie Falcons in Utah. Sometimes these competitors may preempt their old nests from the Prairie Falcon. An oc- Table 10. Percentage use of various categories of eyrie sites bv Prairie Falcons in Utah ( see photos by Wolfe, '1928)' Kind of Site Usage n of eyrie types Percent Potholes= 26 36.1 Open cliff ledges Crevices 23 7 31.9 9.7 Stick nests Red-tailed Hawk's on cliff face 16 7 22.2 9.7 Common Raven's on cliff face' Tree nests Golden Eagle's on cliff face 5 2 1 6.9 2.8 1.4 Unknown species of hawk Totals 1 72 1.4 99.9 'From unpuliHshed data of authors, ficldnotcs of R. G. Bw. A B, Boyle, ana R. J. Envin, and from ornithological literature for the stale. ^Five or 6,9 percent of the eyries were in old ravens' nests lo (ated witliiii potholes. 'IncliidinB the five that were in old ravens' nests within pot holes, a total of 10 or 13.8 percent were in old ravens' nests. currence of this kind took place at an eyrie in Weber County observed by Porter and Erwin. The falcons were using an old raven's nest which apparentlv had been occupied for many vears bv falcons, since it was almost entirely buried in excrement (Fig. 40). Without the old raven's nest as a base, a falcon's eyrie would have been impossible. When fir'st located on 5 June 1950, five fully grown young were present in the nest. The following year the eyrie contained three. fresh eggs on 7 April. When it was next visited on 8 Mav, a raven flushed from the eyrie site, exposing six raven eggs in a newlv constructed stick nest over the old prairie eyrie (Fig. 41). The whereabouts of the previous tenants was not de- termined. Peregrines apparently were more restrictive in the selection of their eyrie sites. They used prcdominantlv open ledges or shelves which usu- alh were under an overhung portion of the cliff (See Figs. 26-38). Only two Utah eyries, to our knowledge, were situated in potholes on the sides of cliffs [sites 4 (alternate) and 23, Table 1 (See Fig. 44]. We have no evidence of a beneficial relationship between the peregrine and other cliff-nesting species similar to that previously discussed for the Prairie Falcon. Both species of falcon apparently prefer to nest under overhangs. Although our data on the >--■< V ^5*^ Fig. 42. Prairie Falcon eyrie in crevice on face of west- facing cliff. Peregrines nested up side canyon (site 8, Table 1 ) . Much of the wood in the crevice was carried there by wood rats ( Neotoma sp. ) . Photo bv R. D. Porter, 1951. 58 Bhicham Young Univehsitv Scmknt k Hi'i.letin Fig. 43. .\ cliff used alternately i)y I'rairie Falcons anil ravens. Nesting site is situated in a pothole similar to that shown in I'igure 4(1 Cliff is less than 2 miles ( 2.6 km ) from the peregrine eyrie shown in Figure 22, and this cliff may also have hecn used historically hy peregrines. Photo hx l\. J. Erwin. August 1972. Prairie Falcon arc incomplete in thi.s regard, all but one of 36 Prairie Falcon eyries in Colorado and Wvoming reported 1)\' Ender.son (1964) were directh' ovcrhinm li\ a |iortioii of tiie clifl. Size Preference for Nesting Area The Prairie I'"alcon appears to he less selec- tive than the peregrine in the size of its nesting or egg-laying area. White (nnpnbl. data), for in- stance, ohserved a Prairie I'alcon nesting in a pothole that was appart>ntl\ too small for a large family of \()inig because, Ix'fore the vonng had fledged, all but one were forced from the c\rie to an unlimelv death on the talus below (Figs. 45-46). This nest was used for fi\e consccutix'c years. The female laid five eggs each vear and each vear onl\ one \ onng fledged. The e\Tie was then abandoned. We have also, however, seen prairies successfulh' fledge large broods from ledges e(|ual to or smaller than the site men- tioned above. The aforementioned Prairie Falcon e\rie in Weber Coimt\ that was taken over b\' ravens liad a total, nesting area of only about 310 sq inches (2,000 cm'-) (measured from photographs). A Prairie Falcon e\rie in Box Elder Comity, found bv Erwin, was in a crevice in the face of a cliff wiiich was onlv 20 inches (51 cm) wide at the point whcr(> the eggs were laid. The crc\'ice was over 80 inches in depth (ca. 200 cm) and nearlx high enough for a man to stand in (mea- sured from a photograph). In the Wasatch Mountains, peregrines usual- ly laid their eggs on wider ledges with a relative- Iv more spacious nesting area (fref|uentl\' with grass on them) than did the Prairie I'alcon. The area and or volume available for nesting on open ledges and \\ ithin potholes used as evrie sites in Utah are gi\en in Tables 9 and 11. The average available nesting area for peregrine e\ries in Utah is uearK' tvvice that of prairie cvries (Table II). The wider variabilit\' in size and height of the Prairie Falcon's nesting siti's would appear to be advantageous to the Piairie Falcon in its eom|)e- tition with the peregrine. If the better qualit\- sites were alread\ utilized, one of lesser qualitv. BiOLOcic.\L Series, Vol. 18, No. 1 Peregrine F.\lcon in Utah 59 Table 11. Size of area available for nesting at Prairie and Peregrine Falcon eyrie sites in Utah." Types of sites and PRAIRIE FALCONS PEREGRINE FALCONS units of measure n X range n X range POTHOLE SITES Avail, nest, area sq feet 5 11.6 8.0 -18.8 - — — — sq meters 5 1.1 0.74- 1.7 - — — — N'olume of potholes cubic feet 4 20.2 9.0 -43.7 - — — ■ — cubic meters 4 0.6 0.3 - 1.2 - — — — LEDGE AND POTHOLE SITES, combined sq feet sq meters 8= 16.3 2.2 -38.8 7' 27.8 10.0-52.0 8' 1.5 0.2 - 3.6 7' 2.6 0.9- 4.8 kI R, J Envii 'Data were collected between 1943 and 1972 by R. D. Porter, C .M While peregrine eyrie site 7. ^Two of the eyrie sites were alternate sites at site 7 (Table 1); one was used in common with peregrines. ^Data are from toiu different eyrie sites, including tliree alternate eyrie sites at site 7 (Table 1. figs. 2(i-VI r.ilile 8 for nuiie detailed data on and possibly not suitable for peregrines, could be used, thus giving additional pairs of Prairie Falcons the opportunity to nest. Prairie Falcons nesting in the more arid desert areas of Utah frequentlv use sites which probably would not be used b\' the peregrine. Aggressive Interactions between Peregrines and Prairie Falcons Nelson's (1969) reported decline in active peregrine eyries around the Great Salt Lake probably involved the use by Prairie Falcons of abandoned peregrine evries (Nelson, pers. comm., 1971), and as mentioned earlier, the peregrine also is known to have occupied an eyrie which earlier in the ccntur\ was used by Prairie Fal- cons (see White, 1969b). No direct competition between the two spe- cies for nt>sting sitt^ was recorded during the \ears that the earlier mentioned Wasatch Moun- tain evries (Table 1, site 7) were under observa- tion by Porter and Erwin, despite the fact that the e\'rie sites were only about 300 feet (91 111) apart (Figs. 22 and 23), and that the pere- grines frequenth- flew within 100 yards (91 m) or so of the prairie's evrie. Neither of the eyries were visible from the other (see Fig. 22). White and Cade (1971) found peregrines and Gyrfal- cons nesting on the same cliffs simultancousb and succc>ssfully. They postulated that perhaps peregrines and Gvrfalcons can coexist in close ju.xtaposition if their nests are not visible to one another and if their schedules or routes of going to and from their nests to hunt are different. Other instances of amicable interspecific co- existence between the peregrine and the prairie have been reported. Bond (1946), for example, tells of the two species nesting peaceably on!\ a few hundred feet apart. Pettingill and Whitney (1965) noted the nesting of a pair of peregrines and prairies 400 yards (366 m) apart in South Dakota without apparent conflict. French (1951) found the tvvo species nesting 200 )ards (183 m) apart, but not in view of each other. He watched the peregrines attack the prairies at least three times, but only during one of several visits to the eyrie. It is possible that his disturbance of the prairies at their eyrie helped provoke the attack by the peregrines. Lanner Falcons {Falco biara- Fig. 44. Cliff in Great Basin desert (site 23, Table 1 ) . Peregrine eyrie was situated near the horse- shoe-shaped depression, "pothole," at the center of the cliff indicated by arrow. Photo by R. J. Erwin, August 1972. 60 HiiiGHAM Young Univehsitv Science Bulletin Fig. 45. Prairie Falcon cvrie in pothole on side of sandstone cliff. Photo hv Gar\- D. Llovd and C. M. White, 1958. inicus) and peiegiint's in Sicily have been re- ported b\' Mel).s (in Fischer, 1967) to nest only 50() meters apart w itli no apparent conflict chn- ing the nesting period. On the other hand. Nelson (1969) watched a pair of Prairie Falcons in aerial comliat witli a pair of peregrines in Utah near the nesting site of the latter (Tal)le 1, site 11); the two pairs nested about one-fourth mile (402 m) apart (Nel- son, pers. conim., 1971). In discussing the aerial battles between the two species. Nelson (1969), indicated tliat the Prairie Falcons seemed to win them. Later in the paragraph he writes, "The battles were not definite and alwaws ended in sort of a draw, with observers deciding that the Prairie Falcons won." lie also noted that al- though the Prairie Falcons iiad command of tlie air, when the two species parted the\' returned to their respective sites. Hence, he did not con- sider the aggression to result in the abandon- ment of cvrics b\- cither species. Webster (in Bcebe and Webster. 1964) gives a vivid account of an aerial attack in Colorado bv a female I'rai- rie Falcon on a peregrine presumabb cariv ing food to its \oimg in which the Prairie Falcon roblied tlie peregrine of its pre\ . The Prairie Falcon nested nearb\ , but the location of the Fig. 46. Young Prairie Falcon in pothole eyrie illus- trated in Fig. 43. Plioto bv Gary D. Lloyd and C. M. White, 1958. peregrine's e\rie was not ascertained b\ the ob- si'i^ver. Not all encounters between the two species are won 1)\ Prairie Falcons. Ogdcn (1972) sighted an adult female peregrine along the Snake River of southwestern Idaho on .31 March and 6 April 1972. Although unmated, she forced a pair of Prairie Falcons to abandon their estab- lished territor\ and clutch of eggs following about two weeks of conflict between the two species (Ogden, pers. comm., 1972). The female peregrine remained and defended the cliff through the remainder of the nesting season and on several occasions she made reproductive over- tiues toward male Prairie Falcons (ibid.). Richard Fvfe (pers. comm., 1972) made an observation similar to Ogden's on 11 April 1972 in Alberta, C^anada. A pair of Prairie Falcons was well es- tablished and the female was about to la\' eggs in a "iiothole" e\rie on a high dirt river bank at the time that the female peregrine arrived at that cvrie on 1 1 April. The male pei-egrine pre- ceded her arrival b\ a few day.s. Within a mat- ter of hours on the da\- of her arrival, the pere- grines had dri\-en the prairies awa\' and usurped the i)()th()!c. Despite these obser\ations of conflict, both sjiecies are able to establish and hold an e\rie site in close proximit\' to its congener. The near e(|Malit\ in size and strength betweeti the two Biological Series, \'ol. 18, No. I PERECniNE Falcon in Utah 61 species seems to recliKv their dominance over each otlier. This is unlike the competition be- tween the peregrine and the Gvrfalcon in the .Arctic, \\here the larger and stronger Gyrfal- eon, due to its earlier nesting and superioritv to the peregrine in aerial combat, is able to es- tablish and hold the most propitious nesting sites (Cade, 1960). Both peregrines and prairies mav use one another's alternate nesting sites, the availabilitv of which ma\' enable the two species to nest in closer pro.\imit\' to each other than would two pairs of peregrines or t\\-o pairs of Prairie Falcons. Mebs (in Fischer, 1967) reported a similar relationship between the Lanner Falcon, a near ecological i'(|ui\'alent of the Prairie Fal- con, and the peregrine in Sicih . A nesting cavity (hole) under his observation for three years was occupied in 1957 b\ lanners and in 1958 and 1959 b\' peregrines. In some instances, tlu' Prairie Falcon ina\' occupy sites which otherwise would be used bv additional pairs of peregrines— as well as the reverse— thus possibh' limiting each other's breeding density. Each species is known to maintain distances between exries in j^arts of its geographic range not occupied b\ the other species which are much less than the distances between their evries along the Wasatch escarpment. Few of the distances, however, averaged less than the distance between the alternate nesting sites used b\ the peregrine and Prairie Falcon at site 7. Hickev (1942), for example, mentions that two pairs of peri'griius nested only a half mile (805 m) apart in Canada, and Ratcliff (1962) gives an instance in Great Britain of four pairs breeding on a mile (1.6 km) stretch of cliff. White and Cade (1971) found peregrines nesting a quarter of a mile (1.40 km) apart in the Arctic, but this was the exception, not the rule. Beebe (1960) noted fi\e to eight pairs nesting on a linear mile (1.6 km) of cliff in the Queen Char- lotte Islands, the highest density known for the peregrine. The highest Prairie Falcon densit\", to our knowledge, is along the Snake River in south- western Idaho, where in 1971 Ogden (1971) found 74 acti\e nest locations along a 53 mile (85.3 km) stretch of river, for an average of 1.4 occupied areas per linear mile (1.6 km). The e\Tie sites averaged less than one mile (1.6 km) apart (one pair/3,771 ft; 1,149 m). Date of Egg Laying as a Competitive Factor We have observed in Utah that the Prairie Falcon generalK' initiates egg la\ing earlier in the spring than does the peregrine, and Nelson (1969) also noted this relationship between the two species. In Utah, peregrines have initiated egg laxing as earh as 22 March and as late as the second week in May. We have records of Prairie Falcon clutches in the Great Salt Lake area containing three eggs on 7 April, four eggs on 10 .'^pril (R. L. Porter and J. F. Poonnan, unpubl. notes), and five eggs on 22 April. Newly hatched young were present on 13 May; \oung capable of flight were pres- ent on 10 June. A nest in extreme northern Utah found by Erwin in 1969 contained fully fledged \oung on 1 June. Woodbury et al. (unpubl. ms) recorded 51 sets of eggs from Tooele, Salt Lake, and Utah counties collected from 3 March to 15 June 1939. The average date of collection for 16 of the clutches, for \\-hich sufficient dates are available, was 20 April (range: 3 April-22 May). This did not, however, represent the dates of the laying of the first eggs. Wolfe (1928) records complete clutches of Prairie Falcon eggs in Utah from 5 to 20 April. The average nesting date for 36 records in I'tah Count\' was 18 April (range: 3 March-15 June) (data from Bee and Hutch- ings, 1942). An earlier nesting date would give the Prairie Falcon first choice of eyrie sites. We have yer\' little precise information for Utah on the arrival dates of either species at their eyrie sites, although White has seen Prairie Falcons at cliffs where e\rie sites were situated in Februarx' and earh March and Porter has re- corded them at a nesting cliff in the west desert of Utah as early as 3 Februar\- (1953) (Porter, Bushman and Behle, unpubl. ms). Wolfe (1928) noted the first appearance' of Prairie Falcons in the Salt Lake Valley about the middle of March, and earlier farther south. He indicated that in some of the warmer valleys many of the falcons probabh' remain during the entire win- ter. Morlan Nelson (pers. comm., 1971) has seen this species at its desert eyries in Utah the year around. He believes that only the young leave the area of the nesting site (ibid.), although Enderson (1964) recorded the earliest arrivals in northern Colorado on 22 Februar}- in 1961 and observed that most adults became associated with the cliffs b\- mid-March. Judging from the observation of adult male peregrines at exries the year around in New Mexico (T. Smylie, pers. comm., 1971), it is (|uite possible that peregrines remain at or near some of the Utah e\ries the year around, [>ar- tieularly the desert sites. Paul Newey (pers. comm., 1952) observed peregrines chasing his l^igeons near the Wasatch Mountains during 62 BiucHAM Young Univehsity Scieni:k IUu.i.ktin the last week in January 1950 and again on 18 Februar\ 1950. The falcons were probably from a nearb\- eyrie. The nesting cliff was climbed on 25 February b\' R. D. and R. L. Porter, but no falcons were seen. Both pere- grines and Prairie Falcons, howe\c'r, were seen b\' 4 April. Re|)roductive Potential as a Competitive Factor The Prairie Falcon appears to have a greater reproductive potential than does the peregrine. This, however, among other things such as food availabilit\- and winter niortalit\' of \oung, may be a reflection of the greater vulnerability of the Prairie Falcon's eggs and \oung to predation due to its selection of evries at sites which are more easily accessible to predators. The average clutch size for the Prairie Falcon is 4.5 for .55 completed clutches in Wyoming and Colorado (I'lnderson. 1964), 4..'3 for 20 nests in western Montana (Leeds', 1972), 4.25 for 31 eyries along the middle Snake River in Idaho (Ogden, 1971), and 4.35 for the 65 clutches from the Utah e\ries in the present stud\ . These are compared with an average clutch size of 3.8 for peregrines in Utah, 3.7 for peregrines elsewhere in the United States (Hickey, 1942; Bond, 1946), and 2.9 for peregrines in northern Alaska (Cade, 1960). PLEISTOCENE AND PREHISTORIC PEREGRINE AND PRAIRIE FALCON DISTRIBUTIONAL RELATIONSHIPS Although Nelson's (1969) climatic change hypothesis probabh' is not the complete answer to the recent reduction in active eyries in Utah, it has a great deal of merit on a long-term basis. Perhaps the peregrine's present distribution in Utah can be elucidated best bv an examination of tlu> possible distribution of the peregrine and prairie falcon during prehistoric and Pleistocene times. Pleistocene Distributional Records Botii tlu' peregrine and tlie Prairie Falcon are known from late Pleistocene deposits in western North America (Howard, 1962b; Miller, 1943). Hence, both species probabh' were pres- ent in Utah during the late Pleistocene. White and (>ade (1971) suggest that the peregrine ma\- have originated in midlatitude regions of Ein-asia, then spread northward into the Arctic, and from there into North America (White 1968b). The Prairie Falcon apparently evolved in situ in western North America. Both species were ]iresent in the Los Angeles area of California conlem]ioraneousl\' (Howard, 1962b) throughout much of the late Pleistocene period covered by fossils found in the La Brea Tar Pits. The fossils in tlicse pits are believed to range from 5.()()() to 10,000 sears old (Berger and Libln-, 1966; Ho, .Marcus, and Berger, 1969; and Downs and .Miller, 1971). Pit 16 contained fossils of three each of both the peregrine and the Piairic I-'aleon. I'ossil wood from two depths, 6'/2 and 12 feet (2-3. 7m), in this pit has been dated back > 40,000 years bv radiocarbon dating (Berger and Libbw 1966). The occurrence of these two species together in this and other pits (Howard, 1962b) suggests a long association between the two species. Since there is, however, a considerable \aria- tion in the ages of the fossils from the various pits and from the various depths of each pit, and since the greatest depths have not alwax's yield- ed the oldi'st fossils (pit 9, Berger and Libb)', 1966), the exact age of the peregrine fossils is not known. In addition, Howard's (1962b) pub- lished account of the fossils present in the vari- ous pits does not indicate the depths from which the fossils were obtained nor if the fossils of the two species discussed here intermixed with- in the same depth. Therefore, a more definitive interpretation regarding the duration of a s\m- patric association between the two species and the age of their fossil remains must await car- bon dating of the actual peregrine and Pniirie Falcon fossils. Additional speeiinens of tlie Prairie Falcon from Pleistocene deposits are known from Smith Creek Cave in Nevada (Howard, 1952), from Rock\- Arro\() (Wetmore, 1932) and Howell's Ridge C;ave (Howard, 1962a) in New Mexico, from Lubbock Reservoir in Texas (Brodkorb, 1964), and from Nuevo Leon in Mexico (Miller, 194.3). Specimens of the peregrine also have been found at Potter Creek Cave and at McKittrick in California (Miller, 1911 and 1927). Shelter Cave in New Mexico (Howard and Miller. 1933), and at American Falls in Idaho (Brodkorb. 1963). Vertebrate fossils from the late Pleistocene American Falls bed B, wlu're this latter speci- men apparently originated, have been dated as having an age greater than 29,700 B. P. (ibid.). Biological Series, Vol. LS, No. 1 Peregrine Falcon in Utah 63 Post-Pleistocene Distributional Records The Prairif Falcon was distributed widely durinc; prehistoric times. It is known from Ore- gon (Miller, 1957; i-\ rie sites that were acti\c' during recent times nia\' ha\'e had long histories of activity sonu' perhaps, (>ven extended back into Lak(> Honne\ille tim(>s. This possibilitx seems especial- In' plausible when one considers the relative re- ei'ne\' of some of the later pluvial periods. Thus, tlie relationship between tlii' Prairie Falcon and peregrine |in)babK extends back maTi\' thou- sands ot years, which ma\ be a factor in the relati\"i- compatibilitN of the two species. Biological Sebies, Vor.. 18, No. 1 Peheghine Falcxjn in Utah 65 Data piivsentcd pre\iousl\' regarding the coii- temporaneit\' of the two species at Rancho La Brea; tlie occiirrenci' of the peri'grine in a lossil bed at American Falls. Idalio, dating back to at least 29,700 \ears B. P. (Brodkorb^ 1963); tiie presence of both species at anthropological sites just south of the Great Salt Lake (Steward. 1937; Black Hock C^avc); and the climatic and environ- mental evidences from Hogup Ca\e in northern Utah ( Harper and Alder, in press ) tend to coi- roborate this supposition. The lack of aggression between them also suggests a long sympatric relationship. White and Cade (1971) believe that tradi- tional use of an eyrie site will in the long run reduce the total impact of intolerant behavior and promote stability in the peregrine popula- tions of the Arctic. If so, a long history of oc- cupancN' at Utah evries probablv would have en- hanced the peregrine's competitive position with the Prairie Falcon and thus strengthened the peregrine's hold on its oj^timal e\rie sites. SUMMARY AND CONCLUSIONS Utah's rugged topograph)' and ecological variabilitv is conducive to its inhabitation by a wide varietx' of raptorial species. This includes the Peregrine Falcon, which now has \irtuallv disappeared as a breeding bird in the state. Although sparselv distributed throughout Utah, the species apparentlv found conditions especialh' suitalile for nesting in the environs of the Great Salt Lake and Utali Lake valle\s, where its nesting sites in the adjacent mountains were within fhing distance of a plentitude of preferred pre\' species which inhabited the marshes and shorelines surroundinst in the des- ert many miles from water. In the zone of con- tact between the two species, its selectivit\' in habitat and food encompasses and exceeds that of the peregrine. The zone of contact between the two species appears to be restricted onl\' bv the paucit\- of suitable nesting habitat adjacent to an adequate supply of food for the peregrine. Where the\- occup\- the same habitat their diets are somewhat different, thus mitigating the possibility of strong competition for food, al- though where they nested side bv side in the Great Salt Lake Valley their food niches did overlap considerabh-. Both species preved rather extensivcK- on the same two |)re\' species, the avocet and Willet, which probably was a re- sponse to the abundance of these two shorebirds. In general, the Prairie Falcon was much less selective in its food requirements in the area surrounding the Great Salt Lake than was the peregrine in the same area, and it was more prone to supph-ment its diet with rodents, ground nesting birds, and reptiles. Thus, in this respect, it ap(X'ared to have an adaptive ad- vantage over the peregrine. Competition between the two species for food did not appear to ha\e been an important factor in controlling their relative densities along the escarpment of the Wasatch Mountains, especialK when pojiulations of avocets, Willets, and other s|X'cies of shorebirds were sufficiently large to support them both. We have no data regarding the food niches of the IVairie Falcon in the zones of contact between the two species at riviT sites in the Biological Series, Vol. 18, No. 1 1'ereghine Falcon in Utah 67 desert. However, we would expect a greater overlap in the avian prey of the food niches of the two species in these areas due to the ehmina- tion of a great portion of aquatic birds from the diet of the peregrine (see Gabrielson and Jewett, 1940). Our data, however, suggest that the ex- tensi\'e utilization of rodents, particulail\' ground squirrels {Citcllus sp.), by the Prairie Fakvn in the desert areas would tend to k'ssen the im- pact of the competition between the two con- geners for a\ian pre\ in those regions. In regions of Utah where the populations of the peregrine were greatest, pairs of Prairie Fal- cons and peregrines ne'sted much closer together than did pairs of peregrines or pairs of prairies. Tlie two species sometimes e\'en used one another's alternate nesting sites. When they nest- ed close together, their nesting sites were not known to be visible from one another. Although thev were observed in aerial combat, neither species appeared to be able to consistently dis- lodge its congener from its nesting site. Our data suggest that both species select e\Tie sites on the basis of availabilit\', but when given a clioice thev seemingly select them on the basis of directional exposure to the sun. The peregrine shows a preference for north- and east-facing cliffs, and the Prairie Falcon shows a preference for south- and west-facing cliffs. This relationship between the two species needs additional investigation to further test its valid- itv in Utah and to test its applicability elsewhere in the arid West. The Prairie Falcon was less selective than was the peregrine in its choice of nesting sites, sometimes selecting sites which were seemingly shunned hv the peregrine. The former species, for example, utili/ed sites that were located on smaller ledges with a smaller total nesting area, as well as sites located on lower cliffs nearer the base of the cliff or otherwise more easily ac- cessible to humans and to maniinalian predators, than did the latter species. Furthermore, ravens which are common in Utah, seemingh' alter the nesting habitat in a beneficial way for Prairie Falcons b\ proxiding additional nests that are frequenth" used b\' the falcons, whereas the pere- grine apparently is little affected by the pres- ence of ra\'ens. The Prairie Falcons initiated egg laying ear- lier in the season, thus giving them first choice of nesting sites; and on the average they laid larger clutches than did the peregrine. Tlie Prairie Falcon is a true desert species. It apparently evolved in the arid environment of western Xortli .America, and as expected, in its association with the peregrine it appears to be the dominant competitor in the following ways: (1) it has a greater reproductive potential than does the peregrine, based on its larger clutch size; (2) it is less selective than is the peregrine in choice of nest sites and thereby has more nesting situations to choose from; (3) it lays earlier in the season than does the peregrine; thus it mav have first choice of cliffs and evrie sites; (4) it shows less selectivity in its choice of prey species as food for its young; consequently it has a wider range of species to choose from, including birds, mammals, and reptiles; and (5) because of its selection of prev species other than birds, it is not as obligate to open water for food, nor is it as obligate to open water for liathing, and thus it may nest many miles from water. The Prairie Falcon, then, would appear to have a marked adaptive advantage over the peregrine, especially in marginal areas where the peregrine's ecological tolerance is restricted and wluTC the peregrine's preferred food and/ or nesting sites are in short supply. The Prairie Falcon's adaptive advantage over the peregrine ma\' contribute to the restriction of the pere- grine to the more optimal aquatic habitats near streams and marshes where food and nesting sites are not in short supply, and where the peregrine competes successfully with its con- gener. Some of the reasons the peregrine in Utah is able to compete successfully with the Prairie Falcon for food and quality nesting sites may be: (1) the relative tolerance of the two species for each other while nesting close together; (2) the utilization of one another's alternate eyries, coupled with the inabilitv of either species to consistently gain a dominance over the other in aerial combat, although recent observations by Ogden (1972) and R. Fyfe (pers. comm.) suggest that the peregrine may occup\- the most propitious sites because it is capable of forcing the Prairie Falcon from them; (3) the possibk- partitioning of the mating cliff with each species having distinct preferences for dif- ferent t\|ies of nesting sites or a wide variability in acceptable nesting situations. There is, for ex- ample, tlu' peregrine's preference for open ledges and the Prairie Falcon's acceptance of a wide range of nesting situations, illustrated by its use of potholes in the face of the cliff, open ledges, and old stick nests of other raptorial species. The pothole e\'ries probabK enhance the survival prospects of voung reared on west- facing cliffs and probably offer greater protec- tion from predation than do the open ledges; (5) a variation between the two species in the size 68 Bricham Young University Science Bulletin of the nesting area and in the height of the chffs and eyrie sites; (6) the presence, in abundance, of the prey species preferred bv the peregrine in areas of Utah wlieri' tlie peregrine was most common, witli partial partitioning b\' the two species of their food niches; and (7) tlie pere- grine's fidehty to the cliff. We have Inpotlu'si/ed tliat the peregrine probably invaded the intennountain region dur- ing a pluvial period of the Pleistocene, when the environmental conditions favored the peregrine in its competition with the Prairie Falcon. More- over, tlie iincient Pleistocene Lakes Bonneville and Provo undoubtedly presented the peregrine with both an abundance of food and a suffi- ciency of nesting sites. Fossil remains of pere- grines from the La Brea Tar Pits dating back 40,000 \ears or more and from American Falls in Idaho dating back nearly 30,000 years sup- ]5ort this hvpothesis. There ma\' have been times during the cooler pluviiil periods when the geographic ranges of the two species were mutualh' cxclusi\e, at least in some localities of Utah. During the drier inter- pliuials, the Prairie Falcon probabh' took over nesting sites no longer tenable to the peregrine. However, the peregrine probabh' persisted at those sites where the ecological conditions were most propitious to its sur\iyal and where it gradually adapted to the more arid condition of the interpluvial. as is the present case. The pere- grine is noted tor its fidelit\' to certain cliffs over man\' generations of breeding birds. Traditional occupanc\' ma\ not be the rule with the Prairie Falcon. Finally, one would expect that the longer the existence of a svmpatrie relationship between two closeh' related congeners, the more exten- sive would be the partitioning of their resotirces and the greater the reduction in the conflict be- tsveen them. The partitioning of the resources between the peregrine and prairie seems to be sufficientK di'fined to suggest that this phe- nomenon lias been in operation for a consider- able period of time. The low level of interspecif- ic aggressiyeness as well as the paleontological records suggest that the relationship between the two species is probably of long standing. Fluctuations in |ieregrine populations con- comitant with fluetu;itions in height and length of the shoreline of the I^leistocene lakes prob- abh' luive ])een of natural occurrence down through the ages. Peregrine populations possibh' have been declining slowh in I'tah o\er the past several centuries eoneurrent with a general amelioration of climate and accompaining re- duction in suitable habitat based on climatic and biotic e\'idenee from Tlogup Cave dating back 8,5(X) vears, while popuhitions of the Prai- rie l^'alcon may have slowK expanded to fill the \'oid as suggested by Nelson (1969). Evidence that the southern extremit\' of the peregrine's geographic range historicalh' shifted northward along with an associated shift ;dti- tndinalK' (Nelson, 1969) has not been demon- strated for Utah. With the drastic decline in the species' breeding populations that is pres- ently taking place throughout North Amer- ic;i, ;i Inpothesis of this kind is difficult to test. A general cooling trend in Utah and elsewhere in the Northwest which started about 1961, how- ever, should result in more suitable ecological conditions for the peregrine. The extent to which old eyrie sites are recolonized should be a test of the validitN' of Nelson's (1969) climatic change liN'pothesis for the peregrine decline in the west- ern United States. The presence of the peregrine at desert sites on the peripher^• of its ecological range as late as 1959-60 in the Great Basin (Table 1, site 23) and the earl\- 1960s in the Colorado Plateau (Table 1, site 28) emphasizes the species's abilit\' to adapt and its tenacity for survival. The competitive roles of the peregrine and the Prairie I'alcon appiu'i'ntK' change according to locality, based on a\'ailability of food and nesting sites, and on the behavior and ecology of the rajitorial species with which thev must compete. For example, in the Arctic the Pere- grine Falcon is a gi'iieralist, both in terms of its selection of nesting sites and in regards to troph- ic relationships with its competitors (White and Cade, 1971); there, this species utilizes a wide variety of food, which is not a restricti\e aspect of its econoniN in the Arctic, and a broad selec- tion of nesting sites. Its chief competitors in the Arctic are the Common Ra\'en, the Cxifalcon. and th(> Rough-k'gged Ilauk (Biitco Ias. Conse()uentI\'. the peregrine utili/es "mar^inid " sites where it ma\' ha\'e to compete with the rough-legs. Apparenth', how- e\'er. the iK^regrine is capal)le of usurping the I'oiigh-lcgs's nest. In addition, the two species ma\' joint K' occu|)\' the same cliffs, thus lessen- ing the competition between them. White ;md Cade (1971) believe that .since ravens and pere- ounty sprayed 3,000 acres (1,214 ha) by air- craft in 1953 (Stewart, 1954). Aerial spraving greatlv increased in 19.54, according to Graham and Rees (19.58). In that year tlie Salt Lake City district (Collett, 1955) aerialh- treated 12,128 acres (4,908 ha), of which 2,286 acrc^ (925 ha) were in cooperation with the Davis County MAD. Insecticides used by the Salt Lake City MAD in 19.54 were DDT in number 2 fuel oil, DDT and water emulsion, and hepta- chlor emulsion in water; DDT was applied at the rate of two gals per acre (19 l/ha), contain- ing 0.4 lbs (181 g) of DDT; heptachlor was ap- plied at the rate of 0.06 lbs/acre (67 g/ha) for lai-vae and 0.08 lbs/acre (90 g/ha) for adults (Collett, ibid.). The Weber County MAD spra\ed over 10,000 acres (4,047 ha) by air in 1952 and 19,825 acres (8,023 ha) in 19.53. DDT was applied at 0.2 lbs/acre (224 g/ha) for 15,812 acres (6..399 ha) and at 0.4 lbs/acre (448 g/ha) for 1,793 acres (726 ha) in 1953, for a total of 3,880 lbs (1,760 kg) of DDT applied to 17,605 acres (7,124 ha) of marsh and pasture lands (Fronk, 1954). In 1954 Weber County aerially treated Biological Series, Vol. 18, No. 1 Peregrine Falcon in Utah 71 13,300 acres (5,382 ha) at 0.1 to 0.4 llxs of DDT per acre (112-448 g/ha) (Fronk and Jenne, 1955), while Box Elder Count\' .similarly sprayed 5,000 acres (2,02,3 ha) (Josephson, 1955). ' An abatement district was not operative in Utah Count\ nntil 1963, and the chemicals used were Bavtex, parathion (both in pastures), and DDT (where residues were considered to be no problem) (Davis, 1964). DDT was not used b\' the South Salt Lake Count\' district. Hepta- chlor was used in this county starting with the inception of the MAD in 1953 (Graham and Rees, 19.58; Graham in letter). It was applied at 0.04 lbs per acre (45 g/ha). Dieldrin was used extensively in this district also at the same concentrations as heptachlor. Other districts then began using heptachlor, and by 1958 it became as commonly used as DDT (Graham and Rees, 1958). Malathion and parathion were used in 1956, and parathion became the insecti- cide preferred by the Salt Lake County MAD in 1957 when resistance to heptachlor developed in the mosquitoes (Graham and Rees, 1958). B\' 1962 nearly all mosquito abatement districts in Utah had abandoned the use of DDT because pastures, milk, and food were becoming polluted with residues, and by 1970, only Box Elder Count)' was still using DDT. LITERATURE CITED Allen, J. A. 1872. Notes on an ornithological recon- naissance of portions of Kansas, Colorado, Wyoming, and Utah. Bull. Mus. Comp. Zool., 3(6):113-183. Antevs, E. 1948. The Great Basin with emphasis on glacial and postglacial times. III. Climatic changes and prewhite man. Bull. Univ. Utah 38(20), Biol. Ser. 10(7):167-191. A.O.U. 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N., and R. D. Porter. 1970. DDE thins eggshells of captive American Kestrels. Nature 227 (.52.59): 737 -738. Williams, R. B., and G. P. Matteson, Jr. 1948. Wyoming hawks. Wyoming Game and Fish Dept., Bull. No. 5, Cheyenne, Wyoming, 84 p. WiTiiERHY, H. F.. C. R. Jourdain, N. F. Ticehurst, AND B. W. Tucker.' 19.39. The handbook of British birds. Vol. 3, H. F. and G. Witherby. London, 399 p. Wolfe, L. R. 1928. The breeding Accipitres of Utah. Oologists" Record 8(4):90-102. . 1929. Collecting rent from falcons and ravens. Oologist, whole no. .501. 4fi(2):16-20. WooDiuHV, A. M., AND H. N. Russell, Jr. 1945. Birds of the Navajo country. Bull. Univ. Utah. .35(14), Biol. Ser. 9(1): 1-160. Woodhuhv, a. M., C. Gottam, and J. W. Suoden. 1949. Annotated checklist of the birds of Utah. Bull. Univ. Utah .39(16), Biol. Ser. ll(2):l-40. . The birds of Utah. Unpublished Ms. (de- posited with Lynn Hayward. Brigham Young Uni- versity ) . Wf)oi)HURY. A. M.. AND G. Gottam. 1962. Ecological studies of birds in Utah. Univ. Utah Biol. Ser. 12(7):V + 28 p. ^./l//4 - 'f'f^ro^o^ Brigham Young University Mus. coMP. zoou Science Bulletin NOV 51973 u'OTicOLOGICAL SURVEY OF THE ALGAE OF HUNTINGTON CANYON, UTAH by Lorin E. Squires Samuel R. Rushforth Carol J. Endsley BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 2 JUNE 1973/ISSN 0068-1024 BRIGHAM YOUNG UNIVERSITY SCIENCE BULLETIN BIOLOGICAL SERIES Editor: Stanley L. Welsh, Department of Botany, Brigham Young University, Provo, Utah Acting Editor: Vernon J. Tipton, Zoofogy Members of the Editorial Board: Ferron L. Andersen, Zoology Joseph R. Murdock, Botany WiLMER W. Tanner, Zoology Ex officio Members: A. Lester Allen, Dean, College of Biological and Agricultural Sciences Ernest L. Olson, Director, Brigham Yoimg University Press The Brigham Young University Science Bulletin, Biological Series, publishes acceptable papers, particularly large manuscripts, on all phases of biology. Separate numbers and back volumes can be purchased from University Press Marketing, Brigham Young University, Provo, Utah 84602. All remittances should be made payable to Brigham Young University. Orders and materials for Ubrary exchange should be directed to the Division of Gifts and Exchange, Brigham Young University Library, Provo, Utah 84602. Brigham Young University Science Bulletin AN ECOLOGICAL SURVEY OF THE ALGAE OF HUNTINGTON CANYON, UTAH by Lorin E. Squires Samuel R. Rushforth Carol J. Endsley BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 2 JUNE 1973/ISSN 0068-1024 TABLE OF CONTENTS ABSTRACT 1 INTRODUCTION 1 REVIEW OF SELECTED ALGAL STUDIES IN UTAH S DESCRIPTION OF THE HUNTINGTON CANYON DRAINAGE 6 GEOLOGY 6 CLIMATE AND VEGETATION ZONES 12 DESCRIPTION AND USES OF HUNTINGTON CREEK 15 DESCRIPTION OF SAMPLING SITES 17 LAWRENCE ( SITE 1 ) 17 HIGHWAY 10 BRIDGE (SITE 2) 17 PLANT SITE ( SITE 3 ) 17 BEAR-RILDA CAMPGROUND (SITE 4) 19 TIE FORK POND (SITE 5) 20 STUART FIRE STATION (SITE 6) 20 BEAR CANYON ( SITE 7 ) 20 METHODS 22 PHYSICAL AND CHEMICAL MEASUREMENTS 22 Temperature 22 Turbidity 22 Water Chemistry 22 PHYTOPLANKTON 22 Net Plankton 22 Naimoplankton 24 PERIPHYTON 24 VISIBLE BENTHIC ALGAE 26 FLORISTIC SAMPLING 26 RESULTS AND DISCUSSION 26 LAWRENCE ( SITE 1 ) 26 HIGHWAY 10 BRIDGE (SITE 2) 31 PLANT SITE ( SITE 3 ) 33 BEAR-RILDA CAMPGROUND (SITE 4) 39 STUART FIRE STATION (SITE 6) 44 BEAR CANYON ( SITE 7 ) 50 TIE FORK POND (SITE 5) 51 ALGAL FLORA OF HUNTINGTON CANYON 55 ACKNOWLEDGMENTS 57 APPENDIX I— NET PLANKTON, NANNOPLANKTON, PERIPHYTON, AND VISIBLE BENTHIC ALGAL TABLES 57 APPENDIX II— ALGAE COLLECTED FROM HUNTINGTON CANYON OCTOBER 1970— MARCH 1972 .... 84 LITERATURE CITED 86 AN ECOLOGICAL SURVEY OF THE ALGAE OF HUNTINGTON CANYON, UTAH by Lorin E. Squires/ Samuel R. Rushforth/ and Carol J. Endsley' ABSTRACT A quantitative and ecological study of the algae of Huntington Canyon, Emery County, Utah, was conducted from March 1971 to April 1972. Net plankton, nannoplankton, periphyton, and visible attached algae were studied. Cer- tain physical and chemical parameters in the waters of Huntington Creek and a small pond along its course were also measured. Huntington Creek contains a wide diversity of genera and species of algae. Diatoms are the main constituent of the flora of this stream throughout the year. Hydrurus foetidus is preva- lent in Huntington Creek from late winter to early summer, and filamentous blue green algae abound in the summer and fall. Cladophora glomerata, Oedogonitim sp., and Cham vulgaris are abundant in the creek beyond the mouth of the canyon. Most plankton in Huntington Creek originate on the substrate and in reser- voirs on the left fork. Huntington Creek is a cold, fast-flowing, hard-water mountain stream, and the algal flora of this creek is typical of such a habitat. INTRODUCTION In October 1970 a study of the algae of Huntington Canyon, Emery County, Utah, was initiated ( Fig. 1 ) . The need for this study stems from the construction of a coal-fired power- generating station and a 30,000 acre-foot reser- voir by Utah Power and Light Company. The generating station is located in lower Hunting- ton Canyon approximately 12 miles northwest of Huntington, Utah, on land formerly owned by the Utah State Division of Wildlife Re- sources and the Bureau of Land Management (Fig. 2). The Peabodv Coal Company will sup- ply coal for the generating station from a mine 2.5 miles southwest of the station, and the elec- tricity will be transmitted south to the Four Comers area and north to Camp Williams (Draft Environmental Statement, 1971). When completed, the station will consist of four gen- erating units. The first unit will generate 430 megawatts of electricity and will be operational in 1974. Thereafter, one unit will be completed during each of three four-year periods. Upon completion, the station will be capable of gen- erating 2,000 megawatts of electricity. The four generators will be cooled with water taken from Huntington Creek. To insure Fig. 1. Index map area. of the Huntington Canyon study ^Department of Botany and Range Science. Brigliain YounK University, Provo. t'l.ili ^f4(l02 Bricham Young University Science Bulletin Fig. 2 Mouth of Huntington Canyon on tlio eastern edge of tlie Wasatch Plateau. The Utah Power and Light Company Generating Station is located at the right center. Photographed Feb. 7, 1972. that a continuous supply of water will be avail- able, a new reservoir, called E'ectric Lake, will be constructed on the right fork of Huntington Creek approximately 20 miles upstream from the generating station near the mouth of Bear Canyon, Emery County, Utah (Fig. 3). The reservoir will be approximatelv 4.5 miles long and 215 feet deep at the dam (Fig. 4). It will store water from the spring nmoff, which will be released as needed during the summer and fall months. A paved road will allow access to the reser%oir, and public recreational facilities will be provided. Initial impact of this project on the environ- ment of Huntington Canyon will result from the following four factors : ( 1 ) the construction Biological Sehies, Vol. 18, No. 2 Algae of Huntington Canyon, Utah Fig. 3. Locality of the dam for Electric Lake on the Right Fork of Huntington Creek below Bear Canyon. Photographed Nov. 16, 1970. Bricham Young University Science Bulletin Fig. 4. Upper drainage of the Right Fork ol Huntjiigtoii Creek. Flat Canyon is at the lower right and James Canyon is at the left center. Photographed Nov. 16, 1970. of the generating station itself, which neces- .sitates extensive excavation and will infringe on the winter deer range; (2) the scarring of the mountainside during the construction of the dam and the relocation of approximately 15 miles of road through heavily forested regions; (3) the flooding of approximately 4.5 miles of prime fishing stream on the right fork of Hun- tington Creek, which currently serves as spawn- ing grounds for brown and cuttliroat trout; and (4) the destruction of watersheds along the patli of the power lines. Other less obvious effects may occur, espe- cially in the aquatic environment, which often Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah becomes a repository for chemical and physical pollutants entering via effluents, drainage from surrounding lands, and directly by rain and snow. The silt load in the creek is an important factor, especially during construction periods, causing abrasion and erosion which can be detrimental to the stream ecosystem. Also, the release of reservoir water into Huntington Creek may cause temporary or permanent temperature, chemical, and/ or nutrient changes which will affect the ecological balance of the biota of tlie stream. Because of the possible environmental effects of this project, the Center for Health and En- vironmental Studies at Brigham Young Univer- sity, with primary funding from Utah Power and Light Company, undertook a comprehensive study of the aquatic environment of the Hun- tington Canyon region in September 1970. The initial goal of this study was to gather data on physical, chemical, and biological parameters, which may be used to determine future changes in this ecosystem. Algae are important in such an environmen- tal impact study inasmuch as they are extremely responsive to changes in the environment and thus indicate changes and fluctuations that may occur. For instance, Blum (1957) found a marked change in the benthic algal flora as pollution outfalls entered the Sahne River, Mich- igan. Foerster and Corrin ( 1970 ) observed that the presence or absence of certain algae enable one to determine the condition of the water in which they are normally found. Palmer ( 1961 ) stated that a knowledge of the algal population of rivers both quantitatively and qualitatively is important if one is to assess their true value in the ecosystem. Pahner ( 1961) fmther stated that "... it can be important to know the algal population of a river before any major change is made in the use of the stream. Also, we need to know the algal population of rivers through- out the year and not merely for the simimer months." This paper reports the initial algal studies of Huntington Creek. Future comparative studies will be made during and after construction and operation of the power plant-reservoir complex. The initial goal of this study was to obtain an overall picture of the entire aquatic algal flora rather than one specific part. Therefore, sampling included water chemistry, quantitative analysis of phytoplankton and attached algae, and a floristic survey. Plankton are interpreted in this study as all organisms found in the open water (Kofoid, 1^)8), and only chlorophyll-bearing phytoplank- ton (Welch, 1935) are considered in this paper. Phytoplankton are divided into net plankton (those forms large enough to be retained by a 67-//,m mesh plankton net) and nannoplankton (those forms which can pass through the net). Nannoplankton are of primary importance in this study, since diatoms, the dominant algae in most rivers (Rice, 1938), are included in this group. Sampling of the attached algae included bo£h microscopic periphyton, defined by Young (1945) as that assemblage of microscopic or- ganisms growing upon free surfaces of sub- merged objects in water, and the visible at- tached algae. Floristic sampling was done to determine the composition and distribution of the algae of the canyon. REVIEW OF SELECTED ALGAL STUDIES IN UTAH Aquatic research in Utah has not been ex- tensive, although it has included several ecologi- cal and pollution studies. One significant con- tribution was made by Clark (1958), who stud- ied the phytoplankton of the Logan River in the Bear River Range of the Wasatch Moun- tains. Clark's results were valuable for com- parison with those of the present study, since the two streams are similar in size and certain other characteristics. A companion study to that conducted by Clark was completed by McCon- nell (1959), who estimated the algal productiv- ity of the Logan River from chlorophyll extracts of the algae growing on the river bed. Samuelson ( 1950) completed a study which illustrated man's influence on the algal floras in two mountain streams in the Wasatch Moun- tain Range east of Salt Lake Valley, Utah. He observed that hvestock grazing and recreation severely damaged the aquatic ecosystem in Emigration Canyon as compared to that of Red Butte Canyon. Another pollution study (Quinn, 1958) dem- onstrated that organic wastes from the effluent of a sugar beet factory were detrimental to the algal flora of the Jordan River in Salt Lake County, Utah. Currently, an algal floristic and ecological investigation is being conducted along the en- tire length of the Provo River (Lawson, pers. comm. ) . This study will establish the algal com- munities in the river and their responses to man's use of the drainage area. More investigations have been conducted Bricham Young University Science Bulletin on insects than on algae in Utah streams. These studies are valuable, since they often include information on the algae in the ecosystem being studied and give general information concerning biological responses to environmental stresses. One such study was conducted by Smith ( 1959 ) , who included algal samples in his macroinverte- brate study of the Weber River in north central Utah. His results showed that siltation from watershed misuse, habitat destruction from dredging, and stream bottom exposure resulting from irrigation diversion were more destructive to the aquatic biota than organic pollution. An earlier study by Dustans ( 1951 ) on the Provo River also discussed the effects of dredg- ing on aquatic life. He mentioned reduced photosynthesis, loss of marginal vegetation, and the loss of diatoms, desmids, and filamentous al- gae as primary contributing causes to the re- duction of insect benthos in dredged stream channels. A pollution studv was conducted in central Utah on the Price' River (Miller, 1959). Al- though this river, like Huntington Creek, drains the Wasatch Plateau, it is of little value for com- parison with the present study, since the ex- treme silt load in the Price River and organic pollution contributed by towns through which it passes severely restrict biological life. Mil- ler found only rare and limited amounts of Cladophora sp. and Chaetophora elegans in the river and a noteworthy absence of aquatic vas- cular plants. Work has also been done on the plankton of ponds, reservoirs, and lakes of Utah. These studies include the following: Piranian's (1937) report on the plankton of the Bear River Migra- tory Waterfowl Refuge; Chatwin's (1956) study of the vertical distribution of phytoplankton in Deer Creek Reservoir, Wasatch County, Utah; Pratt's ( 1957 ) investigation of plankton periodi- city in Salem Lake, Salem, Utah; and Longley's ( 1969) discussion of the phytoplankton associa- tions in Flaming Gorge Reservoir. The infor- mation provided by these and similar studies is valuable in understanding stream environ- ments and communities, since lentic environ- ments normally exert a definite strong influence on the streams that drain them. Since several reservoirs presently occur on the Huntington Creek drainage, and a new one (Electric Lake) is under construction as of 1972, their manage- ment and algal populations need to be con- sidered as factors affecting the physical and bio- logical parameters of Huntington Creek itself. Mention should also be made of some im- portant taxonomic references concerning Utah algae. The most significant contribution in this regard was made by Dr. Seville Flowers who published mimeographed keys to the common algae of Utah (n.d., a) and to the blue green algae of Utah, (n.d., b). Flowers has also re- ported on the nonvascular plants of various re- gions of the state ( 1959, 1960 ) . Two other taxo- nomic studies are those by Norrington (1925) and Coombs (1964) of the Wasatch and Uinta Mountains, and the Western Uinta Mountains, respectively. DESCRIPTION OF THE HUNTINGTON CANYON DRAINAGE Geology Huntington Creek is one of many streams that drain the Wasatch Plateau of central Utah. This plateau is the northernmost of the plateaus of Utah and is situated in the central part of the state between 30 and 40 degrees north latitude and 111 and 112 degrees west longitude. It merges northward with the higher land of the Uinta Basin and is separated from the Fish Lake Plateau to the south by a 20-mile-vvide erosional depression. The Wasatch Plateau, which rises to elevations of 11,000 feet above sea level and 5,000 to 6,000 feet above Castle Valley on the east and Sanpete Valley on the west (Spieker and Reeside, 1925), is essentially a tableland 90 mik^ long and 20 to 30 miles wide (Figs. 5-6). Strata in the plateau are mostly Late Cretaceous and Early Tertiary in age and lie flat or dip at moderate angles. Re- sistant rocks alternate with those less resistant, giving cliff, bench, and slope profiles much like those of the Colorado Plateau (Spieker and Billings, 1940). Castle Vallev on the east is of erosional origin. The western edge of this valley exhibits a sharp profile, since the eastern edge of the Wasatch Plateau drops abruptly through horizontal strata from one formation to another ( Fig. 2 ) . Sanpete and Sevier Valleys, west of the plateau, arose from down folding and fault- ing, with the western front of the plateau itself being a great monoclinal flexure. Otlu^ faults nnming through the plateau have created ir- regularities in stratigraphy, and erosion has carved canyon, cliffs, and gullies throughout the area (Dutton, 1880). The eastern slopes of the Wasatch Plateau are dissected bv deep, rock\' gorgt»s with fast- flowing streams similar to lower Huntington Biological Series, Vol. 18. No. 2 Algae ok Huntington Canyon, Utah Fie 5 North central portion of the Wasatch Plateau sliowing the Huntington Creek drainage. Left Fork of Huntington Creek is at A, Right Fork of Huntington Creek is at B, Nuck Woodward Canyon is at C, North Hughes Canyon is at D and Candland Mountain is at E. Photographed i-eb. 7, 197Z. Creek The eastern face of the plateau consists of the eastern slopes of the plateau. The San of sharp cUffs of Starpoint sandstone and rough Rafael River drains into the Green River, which erosion of the uppermost layers of Mancos in turn feeds the Colorado River. Streams of shale. From the mouth of Huntington Canyon, the western slope of the Wasatch Plateau dram Castle Vallev extends eastward toward the San into the San Pitch and Sevier rivers. Rafael River (Fig. 7), which collects the waters Spieker and Billings (1940) described the of Huntington Creek and other drainage waters stratigraphy and thickness of each formation Bricham Young Univehsity Science Bulletin > Fig. 6. Eastern edge of the Wasatch Plateau and Lower Huntington Canyon looking eastward toward the San Rafael Swell. The Left Fork of Huntington Creek is at the lower right, the right fork is at the lower left and Tie Fork Canyon is at A. Photographed Feb. 7, 1972. of the Huntington Canyon section of the Wa- .satch Plateau as follows: Paleocene Flagstaff limestone. Gray, tan, white limestone, with minor amounts of shale and sandstone; lacustrine 300-500' Upper Cretaceous and Paleocene North Horn formation. Buff, gray, red sandstone, gray to variegated shale, conglomerate, some limestone; flood- plain and lacu,strine in origin Upper Cretaceous Price River formation. Upper member: Gray sandstone and conglomerate with minor amounts of shale 2000' 600' Castlegate sandstone member: Massive, cliff-forming gray sandstone, coarse grained to conglomeratic 300' Blackhawk formation. Medium-tcnfine- grained buff and gray sandstone, gray shale, coal 1500' Starpoint sandstone. Massive, cliff- forming buff sandstone, medium-to- fine grained; marine 450' Mancos shale. Gray marine shale (only uppermost pat^ exposed in area described) 4000' -\- The upper portion of the Huntington Creek drainage (Fig. 8) is mostly North Horn sand- stone and shale with glaciated cirques, moraines, and widened valleys with outwash deposits of Biological Series, Vol, 18, No, 2 Alcae of Huntington Canyon, I'taii Fig, 7, Mouth of Huntington Canyon looking across Castle Valley toward the San Rafael Swell, Photographed Feb, 7, 1972, Pleistocene age (Spieker and Billings, 1940). Most cirques occur in Joe's Valley Graben, a vertically displaced fault block in the central part of the plateau. This graben averages 2.5 miles wide and extends south for 60 miles from the north central part of the plateau (Spieker and Billings, 1940). Most glaciers issued east- ward from the western edge of the plateau into the graben valk'\-, often coalescing to form large sheetlike moraines. Stream notches in many of these moraines have been dammed in recent years to foma storage reservoirs, such as Cleve- land and Huntington reservoirs. The left fork of Huntington Oeek drains the northern part of tliis graben and the slopes that rise from it. The headwaters gather from Spring, Lake, Rolfson, and Staker canyons, flow across the graben valle\ , and descend through a rocky gorge approximatel)' 3,000 feet deep (Spieker and Billings, IMO).' The headwaters of the right fork of Hun- tington Creek arise north of the termination of Joe's Valley Graben, which ends at Cleveland Reservoir. The right fork origmates in narrow rocky canyons in the Price River sandstone but flows early into Blackhawk sediments where the stream channel widens into a broad U- shaped valley (Fig. 9). This valley remains prominent to Bear Canyon, where it narrows again to a V-shaped mountain gorge (Fig. 10). This flat-bottomed valley was created by lateral erosive cutting by glaciers in this canyon. 10 Bricham Young University Science Bulletin "Xfea. Fig. 8. Geologic map of part of the Wasatcli Plateau, Utah (after Spieker and Billings, 1940). Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 11 Fig. 9. Glacier cut U-shaped valley in the upper drainage of the Right Fork of Huntington Creek. Northern end of Joe's Valley Graben is at the upper right. Photographed Nov. 19, 1970. 12 Bricham Young University' Science Bulletin Fig. 10. Deep gorges of Huntington Canyon. Pole Canyon (A), Left Fork (B), Horse Creek Canyon (C), Tie I^ork Canyon (D). Photographed Feb. 7, 1972. Climate and Vegetation Zones Tlie upper part of the drainage of Hunting- ton Creek exists under semihumid montane con- ditions, with 30 to 40 inches of precipitation annually (Draft of Environmental Statement, 1971). A large snowpack accumulates in this region in the winter, creating a high spring runoff supphing ground water which feeds local springs throughout the year. Aspen-snow- berr\- ( Populus tremttloides-Stjinphoricarpos vac- cinoides) associations are scattered throughout this upper drainage with populations of sub- alpine spruce ( Picea engelmannii ) on the north- other slopes and in the open valleys (Figs. 11- 12). Wet meadows and willows are common along gendy flowing streams and in pockets formed from Pleistocene glaciation. Lower Huntington Canyon exhibits a semi- arid climate with approximately 12 inches of precipitation amuially. Pinyon-juniper [Pinus monopJiyUa-Junipcrus osteosperma) and sage {Artemesia tridentata) communities are the dominant vegetation types here, with cotton- woods (Populus angustifolia) often hning the streams in the canyon bottoms (Fig. 2). em slopi^ and sagebrusli-grass communities on Castle Valley is flat and arid with a few scattered small towns. It provides some pasture Biological Series, \'ol. 18, No. 2 Algae of Huntington Canyon, Utah 13 Fig. 11 . North Hughes Canyon looking northeast from the Right Fork of Huntington Creek toward the Book Cliffs (in the background) showing spruce-aspen forest cover. Photographed Nov. 16, 1970. 14 Bricham Young University ScitNCE Bulletin xtrancous suspended matter from the water. The filters were cleaned using distilled water, and the resulting suspension centrifuged. The excess water was carefully decanted, and the pellet was resuspended in 5 ml of standard formalin-alcohol-acetic acid (FAA) to preserve it or in 5 ml of distilled water, if counting was done immediately. Nannoplankton were counted using a Pal- mer nannoplankton counting slide (Palmer and Maloney, 1954). This slide is designed for use with high power dr\' microscope objectives and allows for higher magnification and resolution necessary to identify and count nannoplankton genera. All nannoplankton observations and counts were made at 400x. An ocular micrometer was used to measure a 0.25-mm width on the Palmer slide, and the algae encountered in four transects of this width were counted across the diameter of the slide. From the four counts, an average count per transect was then computed. In most cases a new aliquot was used for each count, and the samples were always thoroughly mixed before the alicjuot was taken to maximize the chances for uniform distribution of the sus- pended organisms. Furthermore, averaging the number of algae c^ncounterc^d in four transects increased the probability of obtaining an accurate representa- tion of algae actually found in the river and reduced abnormal values due to clumping. The number of algae encountered in each transect was tallic^d separately as a check on the preci- sion of the counts, and, in most cases, relatively little variation occurred between the four counts. As mentioned previoush'. all diatoms were in- cluded in these nannoplankton investigations, as well as algal forms too small to be adequately retained in the plankton net. Since the original sample was taken directly from the river, net plankton forms were encountered during nanno- plankton enumeration. These were not included in the nannoplankton computations, although they did provide a check on net plankton studies. Turbidity was a noteworthy problem during nannoplankton investigations since most sus- pended particles were retained by the filters. Silt and sand particles, which were especially prevalent during the spring lainoff, often ob- scured the algal specimens and made it neces- sary to dilute samples to 10 ml, 15 ml, or 20 ml. In rare eases, higher dilutions were necessar)'. Pemianc^nt diatom slides were made from the nannoplankton samples from September 1971 to March 1972 so that a permanent record of the plankton flora would be available. Methods have been described by Weber (1970) and Patrick et al. (1954) to count diatoms and char- acterize diatom floras from prepared slides. Such studies may be undertaken at a future date, and the slides are also valuable to compare with future collections. All diatoms were mounted in Pleurax (Hanna, 1949). This mounting medium has a very high index of refraction (1.770) and greatly facilitates resolution. Periphyton Sampling of the periphxton community has received the attention of many workers in recent Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 25 years, and many variations in sampling methods have been attempted. Sladeckova (1962) sum- marized techniques ajid materials developed in periphyton work. Recent trends have been to submerge artificial substrates at study sites to obtain both a qualitative and quantitative con- cept of periphyton communities from studying the algae that become attached to these sub- strates. Materials such as wood, slate, concrete, asbestos, asbestos cement, various sheet metals, plastics, celluloid, st\'rofoam, and glass have been used. However, smooth glass is most wide- ly used and has given accurate results. Patrick et al. (1954) found that by using glass slides for sampling periphyton they were able to sample 75% to 85% of all species obtained by other collections, and 95% of those species with more than eight individuals per sample. Dor ( 1970 ) compared glass slides with basalt and limestone substrates in Lake Tiberia in Israel and found that production on slides was 73% of that produced on natural substrates. Odum (1957) found that succession of algae on glass slides was similar to that on Sagittaria plants. In general, Whitf ord and Schumacher ( 1963 ) found that colonization on glass slides was simi- lar to that of rock substrates, although it was somewhat different from colonization observed on hving plants. Under certain conditions, glass may be sur- passed by styrofoam as a colonization substrate for periphvton, especiallv diatoms. Holm and Hellerman'(1963) found that at 16° and 25°C, both substrates gave reprcsentarive colonies; but at 3°C, diatom species diversity on the glass was reduced as much as 40% while the sts'rofoam continued to support a representative flora. However, Dillard (1966) reported glass to have higher diatom populations at both high and low temperatures. The means of attaching slides to the sub- strate has also resulted in the development of many devices. Butcher (1932), who did a pio- neer river study using glass slides to sample periphvton, used a frame attached to tlie river bed to support his slides. Patrick ct al. (1954) developed a special apparatus for holding slides in the water which they called the Catherwood diatometer. This apparatus consists of a plastic rack with attached floats so that it can be sus- pended at desired depths in the water. Slides are placed vertically in the rack, which allows diatoms to colonize the slides and concurrently reduces silt deposition. Weber and Raschke (1970) described a similar apparatiis with styro- foam floats as a standard periphyton sampler for pollution surveillance. In Huntington Creek the current is extremely swift during runoff and quite low in tlie summer and fall. In addition, the stream and canyon are heavily used by campers, picnickers, and fishermen; and a periphyton sampling device such as described above is impractical. Consideration has also been given to the length of time the slides should be left in the water. Patrick et al. (1954) found two weeks to be optimum, since by that time diatom diver- sity had been established and longer periods had been allowed for excessive silt and debris deposition. Newcombe (1949), on the other hand, suggested 25 days to be the optimum time period. Patrick et al. (1954) found that the accumulation of debris and other organisms on the slides over a long time period made them less favorable for diatom growth, and the more adapted species actually crowded others out. However, a longer time period allows dominant species to become well established on tlie slides, and this may actually be an advantage in aid- ing an understanding of relationships between periphyton and the periphyton-influenced plank- ton assemblages. Newcombe (1949) discussed the advantages of vertical placement of the slides versus hori- zontal placement, claiming the latter to be best since production was higher and the results were more reproducible. However, Hohn and Hellerman ( 1963 ) reported no appreciable dif- ference due to slide placement, and since silt accumulation on horizontal slides presents a problem, vertical placement is often used. Peri- phvton slides in the present study were oriented both horizontally and vertically, and no appre- ciable difference in silt accumulation or diatom populations was observed. Periphyton sampling techniques used in the present studv were similar to those used by Whitford and Schumacher (1963). Clean 1" x 3" microscope slides were fastened to a length of copper or stainless steel wire by means of electrician's tape. The slides were then secured in the river bv fastening the wire to submerged sticks, large stones, or other convenient objects. Generally, the slides were allowed to drift free- Iv in the current. Four slides were placed in the water at each site monthly and retrieved the fol- lowing month. Both sides of the slides were cleaned with distilled water in the laboratory, and the attached algae were preserved in 10 ml of FFA until counting could be done. Samples were counted using a Palmer counting slide, and procedures similar to those used in counting nannoplankton were followed, except that all algal forms encountered were identified and re- corded. 26 Bricham Young University Science Bulletin In computing the algal totals, an average number of individuals per transect across the Palmer slide was made from four individual counts. Periphyton were computed in number per cm-. This counting method was used because it is the most precise commonly used method (Sladeckova, 1962) and it correlated with the nannoplankton procedures, thus allowing the establishment of accurate relationships between periphyton and plankton assemblages. Difficult)' was often encountered due to ex- cessive silt deposition on the slide, which ap- parently was entrapped by mucilage secreted by the algae. Dilutions beyond 10 ml were often necessary for accurate counting, although dilu- tions were kept as low as possible. Data presented from periphyton studies were obtained from counts on slides taken as much as possible from one specific location at each site. These data characterize the general peri- phyton flora of the area but certainly are not representative of every available ecological con- dition. Slides submerged at site 1 were sus- pended in slow, evenly flowing water. Those at site 3 were in deep fast-flowing water. Shdes from site 4 were in a deep hole where the water was quiet and in a shallow riffle. Slides from site 6 were in a shallow riffle, and slides from the pond (site 5) were submerged just below the water surface in still water. Visible Benthic Algae Visible benthic algae, including such forms as Cladophora, Chara, and Hydrurus were sampled following the methods of Blum (1957) and Dillard (1966), combining quadrat and line transect methods for studying plant com- munities. Transects were chosen across the stream at right angles to the current flow in areas displaying average growth conditions. The percent coverage of the substrate by each genus encountered was estimated in alternating 10-cm by 25-cm plots along this transect. Macroscopic benthic algae were always most abundant in riffles, and so one or more representative tran- sects of a riffle were taken at each study site. At sites 1 and 2 slow water also supported sig- nificant algal growths. Transects were run in these slow water areas as well as in riffles at these sites, and the results were averaged to give a figure representative of the site as a whole. From data gathered it was possible to calcu- late cover, composition, and frequency of each genus on the stream substrate. The frequency percent for each genus was obtained by dividing the total number of quadrats in the transect into those quadrats in which each genus occurred. The cover percent for each genus was deter- mined by assigning coverage classes (Dauben- mire, 1968) to the estimation of each genus re- corded in the field and then averaging the mid- points of these coverage classes. From the cover percentage, the percent composition of the total communitv represented bv each genus was de- termined bv dividing the total cover into the cover of each genus and multiplying by 100. This method of estimating cover in each quadrat gave more accurate information than Blum's (1957) method of onlv recording the presence or absence of a species beneath the plots. Where the water was deep and swift, this sampling method was not applicable. Turbid waters also hindered its use, altliough a glass jar submerged in the water enhanced visibility. Floristic Sampling Samples were taken from rocks, twigs, sand, and macroscopic vegetation at fourteen sites along the creek. Seven of these sites corresponded with the seven quantitative sites; and the other sites represented ponds, backwaters and other areas where algae were found growing. Floristic sampling began in October 1970 and continued throughout the study. Tlie algae in these samples were identified to species in the laborator)-. Samples of man\- filamentous algae were pre- served in FAA solution, and pennanent diatom slides were made. RESULTS AND DISCUSSION Each site in this study was chosen to repre- sent a unique ecological habitat. Consequently, each site was studied with the view in mind to characterize the complete alga! communitv' and ecological parameters found under each set of conditions. The following discussion therefore treats the algolog\' and ecology' of each site of the studv area. Lawrence (Site 1) The algal flora at Lawrence is dominated by macroscopic species including Cladophora glomerata, Oedogonhim sp. and Chara vulgaris and bv many diatom genera. Cladophora glom- erata was first recorded from floristic samples in April 1971. B\- Ma\- it was prevalent among the rocks on the stream bottom (Fig. 22). The BioLocicAi. Series, Vol. 18, No. 2 Alg.^e of Huntington Canyon, Utai 27 iignnl Fig. 22. Cladophora glomerata attached to a stone at site 2. This photograph was taken in the spring when Cladophora began to be prominent in the flora, and the alga is approximately one half as long as it is at maturity. Photographed April 28, 1972. first quantitative sample in June showed this alga to cover 35% of the stream bottom in riffle areas. The second sample in June showed a peak development of C. glomerata when it covered 43% of the riffle substrate occurring as long deep green streamers from the stones. C. glomerata declined sharply through July and hx the end of the month was represented mostly by stubb)- basal portions of the plant. These fragments have the ability to regenerate (Fritsch, 1906), and many began to do so in September, causing this species to reappear sig- nificantly in the flora. However, the fall growth consisted only of heavily encrusted compact mats which lacked the long luxuriant streamers charactt'ristic of spring growth. Tliis cycle of Cladophora glomerata develop- ment at Lawrence supports the assumption of Blum (1956) that this alga is sensitive to temperatures approaching 25°C and does very poorl\- at higher temperatures. The water tem- perature at this site on June 29, 1971 was 15°C in earl\- morning and approached 25°C by late afternoon. Temperatures through July, August and early September likewise approached 25°C for at least portions of the day. Cladophora glomerata beds at Lawrence provided excellent habitat for development of other organisms. Consequently, they were often full of insects and epiphytic algae. The peak of biological activity of the stream could thus al- most be said to parallel the peak of Cladophora development. Mats of Oedogonium sp. also formed long green streamers intermingled with Cladophora glomerata. This alga could be recognized since the mats were generally formed nearer the water surface and their color was yellow green as op- posed to the deep green of Cladophora. The pattern of development of this genus at Lav^'- rence was similar to that of C. glomerata. Oedo- gonium sp. appeared in April and reached a peak of development in June. By July Oedo- gonium sp. was not evident as a visible alga al- though small filaments were found to colonize glass slides throughout the year and were found in the net plankton until November. Mats of Chara vulgaris began developing in (\arly summer when the water level declined and the water temperature rose. By October C. vulgaris dominated the aquatic vegetation cover- ing 64% of the total substrate. C. vulgaris oc- curred in greatest abundance in slow-flowing water, where it reached 85% cover in October. Riffles averaged only 54% Chara cover at the same time. The water level was extremely low during this period, and C. vulgaris mats literally filled much of the creek channel. By November the plants forming these large mats had begun to die and decompose, and walking through them stirred up a black organic ooze and large amounts of entrapped silt. Visible films of epi- ph\'tic diatoms covered the upper filaments of C. vulgaris. These diatoms consisted mostly of Achnanthes minutissima and Sijnedra ulna. Simi- lar to the Cladophora glomerata mats, Chara vulgaris beds were the site of a great deal of biological activity. In December and January extensive decom- position of C. vulgaris occurred under the ice cover and the stream bed became very murky with silt and decomposition products. The water was significantly influenced by decomposition during this period. Due to high biological oxygen demand, dissolved oxygen levels during Novem- ber, December and January fell to 6, 3 and 8 ppm, respectively, from the usual average of 9-10 ppm. Carbon dioxide levels rose concur- rently from averages of 2-4 ppm to 6, 24, and 16 ppm for the same three months. The higher CO2 levels also lowered the pH slightly through this period. It is interesting that a significant amount of Chara vulgaris remained viable through the winter months, indicating that suf- ficient light penetrated the ice and snow to al- low photosynthesis and also indicating that C. vulgaris is quite resistant to low temperatures. The ice broke in February 1972 due to an early thaw, and the large mats of Chara had 28 Brigham Young Univehsity Science Bulletin entrapped large amounts of silt. The bottom was black and murky, and the water was ex- tremely turbid from silt stirred up from the substrate. With the rise of the spring flood in March, turbidity became so intense that visibility through the water was reduced to zero as higher and faster water began scouring the stream channel and washing silt deposits downstream. During late summer and early fall, a pros- trate, often encrusted alga became quite evi- dent on smaller stones of the stream bottom. This alga was very difficult to identify accu- rately due to its growth form, but was suspected to be Trotoderma viride since this alga was prev- alent on periphyton slides collected in Septem- ber. P. viride appears to prefer wann water, since it first appeared in the summer then dis- appeared as the waters cooled in the fall. The vascular plant, Potomogeton sp. was in- cluded in the sampling at Lawrence since it was an important aquatic plant throughout much of the growing season. Interestingly, few epiphytic diatoms were found growing on living Potomogeton sp. plants as contrasted to Oedo- goniurn sp. and CladopJiora glomerata which supported large popularions of attached diatoms. Hynes (1970) indicated that some species of aquatic plants such as Potomogeton pectinattis support a poorlv developed periphyton assem- blage while living, and apparently this holds true for the Potomogeton at Lawrence. Potomogeton sp. first appeared in early July and bv late July constituted an important part of the total flora. Small amounts remained pres- ent throughout the winter and were still present when the ice broke in February. Most Potomo- geton plants lasting through the winter were re- moved by scouring during spring high water. Net plankton pulses showed a definite cor- relation with the appearance and development of Oedogonium sp. and Cladophora glomerata (Fig. 2.3). C. glomerata fragments were a major component of net plankton samples during late spring and early summer but disappeared in Julv and August. Oedogonium sp. appeared in the net samples in Mav, reached a peak in June when it was also most abundant as a visible benthic form, and fell off shaq^ly in July. Total net plankton occurrence followed much the same curve as Cladopliora glomerata and Oedogo- nium sp., being highest in the spring and ver)' low throughout the summer and fall. Net plank- ton at Lawrence increased significantly in Feb- ruary and March 1972 because of the growth of Vlothrix tenerrima on the substrate during winter months. Periphyton slides retrieved in December and March likewise had populations of U. tenerrima growing on them. Blum (1957) noted a similar winter growth of Ulothrix through tlie late winter months in the Saline River , Michigan. Although the Lawrence site is located low on the creek drainage, few true planktonic al- gae were collected. Clark ( 1958 ) likewise found the lower Logan River, Utah, to be low in true phytoplankton. Kofoid (1903) and Whit- ford and Schumacher (1963) discussed the de- velopment of euplankton in rivers and con- cluded that the water in a stream must be sev- eral weeks old before a true river plankton will develop. Thus, the water in Huntington Creek probably takes much less time than this to pass from its origin into the San Rafael River. Infonnarion on diatom populations in this study came from periphyton and nannoplankton investigarions. A strong vernal increase in peri- phyton was evident in April and early May fol- lowed by a summer low and a general increase from September through December. Winter lows occurred from January to March and fewer total organisms were present during this time than in the summer. This yearly trend was basi- cally fomied by the genera Navicula, Sijnedra, Diatoma, Cymbella and Surirella (Fig 24). Gomphonema likewise followed this general trend except for a significant increase in Sep- tember and October. This September-October Gomphonema pulse was caused by rapid in- crease of G. gracile. G. olivaceum, on the other hand, was more important in the fall and espe- cially in the winter. Nitzscliia (mostly N. palea) was an impor- tant component of the periphyton in early June (30% of the total periphyton). It decreased through the summer until October, when a sig- nificant pulse occurred. It then declined again through the winter months. Whitford and Schu- macher ( 1963 ) classified periphyton into late spring-early fall species and early spring-late fall species. This classification followed their obser- vation that diatoms appearing in late spring usually also showed a high colonization rate in early fall and, likewise, early spring diatoms also were present in large numbers in the late fall. The data on Nitzschia palea from Lawrence indicate that this taxon is a late spring-early fall form. Se\eral diatoms reached theii' peak of de- velopment during summer months. Tliese in- cluded Cocconeis (mostly C. pediculus in June and C. placentula in August), Achnanthcs ininu- tissima, Ct/cloteUa meneghiniana and Pleurosig- ma delicatulum. Cocconeis constituted approxi- mately 22'/( of tlic periphyton from June to Au- gust. Cocconeis placentida was an especially important epiph\'te throughout most of the sum- BiOL<;ciCAi, Series, Vol. 18. No. 2 Alo.-ve of Huntington Canyon, Utah 29 Total Net Plankton: 1 = 50 algae I Selected Genera 1 = 25 algae I Nov. Jan. Mar. Cladophora Oedogonium Oscillatoria Ulothrix Fig. 23. Seasonal distribution of selected net plankton at Lawrence (site 1). 30 BmciiAM Ydi'Mc University Science Bulletin Total Periphyton: 1 = 10 algae m Selected Genera: 1=5 algae ml May June Aug. Oct. Dec. Navlcula Nitzschla Coccone/s Fig. 24. Seasonal distribution of selected periphvtoii at I.jiwrenre (site 1). Biological Series, Vol. 18. No. 2 Alg.ae of Huntington Canyon, Utah 31 mer, and it was not uncommon to collect a fila- mentous green alga covered with hundreds of specimens of this species. Pleurosigma delicatu- lum was most prevalent in July- During the August-October period, Achnan- thes minutissinui comprised about 36% of the periphyton. However, this species was absent from the periphyton in October, indicating that colonization decreased sharply during that period. Cyclotella meneghiniana was the only cen- tric diatom prevalent in Huntington Creek. It showed a peak of development in the summer from July to September with a maximum in August. Nannoplankton in Huntington Creek at Law- rence were high throughout most of the year. The higher nutrient levels in the creek here, and the availability of filamentous green algae as a substrate for diatom growth contributed to the continuously high levels. Some diatom genera, such as Gyrosigma, Cocconeis, Cyclotella, and Achnanthes appeared in high numbers in the nannoplankton beginning in July 1971 when spring and fall genera such as Navicula, SuTirel- la, and Synedra became quite low ( Fig. 25 ) . These latter genera increased again greatly in late fall when most of the dominant summer genera declined in numbers. A low point for the season in total nannoplankton was reached in October. However, a large pulse occurred in November composed mostly of Synedra ulna, which comprised 41? of the total nannoplankton. Synedra also actively colonized glass slides dur- ing this month, and it grew so profusely on d\ing Chara vulgaris mats that a brown film was visible on each Chara plant. From Januarv to March 1972 a scouring of the stream channel occurred as the early run- off waters riled the silt and decomposition prod- ucts built up during the fall and earlv winter season. This scouring process also scoured many of the prevalent winter and spring diatoms from the substrate and from among accumulated plant material, causing extremelv high numbers of these diatoms to occur in the nannoplankton. Thus, nannoplankton in Februars and March exceeded 2 million cells per liter. Important genera during this period included Synedra, Cymhella, Surirella and Navicula. Nannoplank- ton levels were also high in April and May 1971, which was probably caused by renewed coloni- zation following spring scouring. The flora at LawTcnce differed significantly from that of the sites in Huntington Canyon, es- pecially in the growth of Oedogonium sp., Cla- dophora glomerata. and Chara vulgaris, and the absence of Hydrurtis foetidus on the stream bed. The general plankton pattern at this site was similar to that of other sites consisting mostly of diatoms. However, the diatom communities here were much different in structure from those of other sites since Cocconeis ( mostly C. placen- tula), Cyclotella meneghiniana, Pleurosigma deli- catulum, and Gyrosigma spencerii were present in much greater numbers, while Cymbella spp. were greatly reduced. To summarize seasonal community variations at Lawrence, Cladophora glomerata and Oedo- gonium sp. dominated the flora in late spring and early summer, with diatoms such as Navi- cula, Cymbella, Synedra, and Surirella occurring in high numbers on stones and macroscopic al- gae. Chara vulgaris dominated the stream bot- tom from summer through fall and occurred with Protoderma viride, Cocconeis spp., Achruin- thes minutissima, and Cyclotella meneghiniana. Late summer and early fall allowed maximum development of Gomphonema gracile and Nitzs- chia (mostly N. palea), while the late fall en- vironment stimulated another general diatom pulse. Net and nannoplankton assemblages were derived largely from cells and filament fragments released from the substrate, and true planktonic algae were rare in the flora. Highway 10 Bridge (Site 2) Water chemistry and visible attached algal data from this site correlated closely with that from Lawrence and consequently differed from data collected upstream in the canyon. The water at sites 1 and 2 had significantly higher levels of nitrates, phosphates, alkalinity, and es- pecially hardness, silica, and sulfate than the water at site 3, which is the first site located in Huntington Canyon (Table 1). The same table illustrates that the levels of these chemicals in the water at Lawrence are generally higher than at Highway 10. This is because as the creek leaves the canyon it passes through strata and soils which are extremely rich in carbonates. In addition, the creek here drains both fanning and grazing lands which are responsible for the addition of nitrates and phos- phates, and passes near Huntington City which Table 1 . Chemical Data for Huntington Creek, De- cember 17, 1971. Site 1 Site 2 Site 3 Nitrate nig/1 0.6 0.33 0.3 Pbosphatc nig/I 0.16 0.06 0.08 Alkalinity mg/l 410 370 240 Total harHness mg/I 2000 1300 250 ( CaCO, ■Silica mg/l SiO' 16 18 2.7 .Sulfate mg/l 2700 1300 28 Brioiiam Young University Science Bulletin Total Nannoplankton: 1=100 olgoe ml Selected Genero: l:=25 olgae ml Apr. June July Sept. Nov. Jon. Nitzschla 'Occoneis Fip. i'l, Seasoiml distrihutiim of •^^lp(tos per liter on June 8, and 30,250 colonies per liter on June 29). It declined gradually through the summer and then in- creased slightly in October. Tliis trend was un- doubtedly directly txirrelated with the tempera- ture curve in the reservoirs. Clark (pers. comm. ) studied a similar situa- tion in Idaho where Henry's Lake drains into the north fork of the Snake River. Blooms of Asterionella formosa occurred in Henry's Lake in June and October 1971, and this alga was found in the river plankton for 35 miles below this lake during the time of the bloom. A. for- mosa density was 815,200 colonies per liter at the Lake's outlet and decreased to 32,600 colo- nies per liter 35 miles downstream from the lake due to the effects of the river current. A similar reduction in colony number would be expected in Huntington Creek from the reser- voirs on the left fork downstream to the plant site, which represents a distance of approxi- mately 18 miles. Onlv moderate currents are suf- ficient to cause such a reduction (Allen, 1920) and turbulent cunents can often cause extreme reduction in euplankton. For instance, Galstoff ( 1924 ) reported a 40% reduction in plankton during an eight-hour passage of the water of tlie Mississippi River through the Rock Island Rapids. Many of the Asterionelln formosa colonies collected in the plankton at the plant site were fragmented, which Brinley (1950) cited as an evidence that they originated in a lentic environ- ment and were not natural stream inhabitors. Fragilaria crotonensis was another euplank- tonic diatom present in the nannoplankton at site 3. Clark (per. comm.) mentioned that Fra- gilaria crotonensis was abundant in Island Park Reservoir, Idaho, in October 1971. Likewise, Daily (1938) indicated this species as a domi- nant fonn from October to December in Lake Michigan, and Longley (1969) observed the same trend in Flaming Gorge, Utah. Fragilaria crotonensis was prevalent at the plant site from September to November, with a large peak in October when its density reached 80,620 colonies per liter. The source of these algae was likely the reservoirs on the left fork. Other diatoms in the creek were produced largely on the substrate and subsequently re- leased into the current. Thus, understanding trends in periphyton is essential to understand- ing algal trends in the stream as a whole. Peri- phyton data demonstrated a rather smooth seasonal colonization curve of diatom develop- ment on the substrate. A gradual increase in colonization rate occurred through the spring and earl\ summer until July, after which a de- cline occurred until December. Dominant genera included Navicttla, Ct/mbella. Gomphonema, Synedra, Nitzschia, and Achnanthes. As shown by Table 3, the importance of these genera on the substrate correlated rather closely with their importance in the nannoplank- ton. Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 37 Table 3. Percent occurrence of selected genera of periphyton and nannoplankton at plant site (Site 3). 5/13 1971 6/29 1971 7/30 1971 8/20 1971 10/8 1971 11/15 1971 12/17 1971 2/19 1972 Navicula Periphyton Nanno Cymbella Periphyton Nanno Gomphonema Periphyton Nanno Synedra Periphyton Nanno Nitzschia Periphyton Nanno Achnanthes Periph3rton Nanno Hannaea Periphyton Nanno Diatoma Periphyton Nanno Other Diatoms Periphyton Nanno Nondiatoms Periphyton Nanno 26.4 14.7 11.2 17.3 18.0 22.4 26.8 22.7 26.6 14.1 14.0 20.7 15.9 13.3 9.9 13.9 30.5 19.9 44.2 36.1 10.9 26.2 15.9 24.3 13.1 15.4 19.5 18.7 30.4 17.7 26.0 24.6 22.0 32.2 11.7 6.2 3.1 8.7 2.6 10.1 2.7 5.0 7.3 6.7 9.1 3.1 36.2 20.8 14.0 8.9 5.2 3.1 1.5 1.2 3.5 1.9 4.5 8.5 11.8 7.6 8.4 7.7 7.5 8.2 16.5 6.9 14.3 6.2 18.6 32.7 20.3 36.9 26.4 28.7 38.7 20.3 25.3 10.5 16.7 5.0 2.8 11.7 6.2 57.1 12.3 13.7 12.6 6.2 5.8 5.0 2.2 4.1 7.2 3.9 4.4 .6 .5 2.0 4.1 .3 .3 .1 1.1 .3 1.1 1.9 .5 1.1 .4 2.1 1.1 1.7 1.4 2.5 8.0 1.1 5.1 22.1 5.7 9.6 1.1 3.2 4.1 12.0 .8 8.0 1.4 6.3 3.3 22.2 4.5 4.4 .8 3.9 .9 .3 2.7 2.0 2.1 6.0 5.8 A comparison of the total number of algae colonizing periphyton sampling slides with the total nannoplankton at the plant site for the studv period is illuminating (Fig. 27). General- ly speaking, the nannoplankton were dependent upon the periphyton and the peaks and lows for the two corresponded. However, through the summer, especially in July, the production of periphyton was high due to a heavy colonization of Achnanthes (mostly A. minutissima) and Navicula spp. This summer periphyton increase was followed by an early fall nannoplankton in- crease. Tliis nannoplankton pulse was caused by such genera as Navicula, Cymbella, Gompho- nema, Synedra, Nitzschia, and Achnanthes (Fig. 28). Tliese genera had developed on the creek bottom throughout the spring and early summer and apparently were released into the stream in O O o lOOO 750 § 500 i z < a. o z z < z 250 PERIPHYTON NANNOPLANKTON I60 I20 80 40 O O O 5 z z O t— >- I APRIL JUNE JULY SEPT NOV JAN MAR Fig. 27. Density and seasonal distribution of nannoplankton and periphyton at the plant site (site 3). 38 Brigham Young University Science Bulletin Total Nannoplankton: 1 = 100 algae ml Selected Genera: 1 = 50 algae ml Apr. June July Sept. Nov. Jan. Mar. Navicula Cymbella Gomphonema Nitzschia Fig. 28. Seasonal distnbiition of splortpcf niiiiiiopl;iiiktoti at the plant sito (site i). Biological Series, Vol. 18. No. 2 Alg.-\e of Huntington Canyon. Utah 39 the late summer due to certain enviromnental stimuli. This conclusion is supported by de- creased colonization rates during the nanno- plankton pulse. Nitzschia spp. (especially N. palea) were im- portant in the nannoplankton throughout the study period but demonstrated a peak of occur- rence from August to October. The yearly high occurred in August, one month later than the Nitzschia high at Lawrence and one month ear- lier than the Nitzschia peak from localities fur- ther up the canyon. Cocconeis placentula and Achnanthes minu- tissima were predominately summer diatoms at site 3, and Hannaea arcus was a late spring- early summer species. Diatoma vulgare and Gomphonema olivaceum have been reported by Blum ( 1957 ) to be important winter colonizers of bare areas. He found Diatoma vulgare most abundant in early winter in the SaUne River, Michigan, and Gomphonema olivaceum most abundant in late winter and early spring. Peri- phyton data from the plant site show Diatoma vulgare to have been most active in colonization in November 1971. D. vulgare also occurred in high numbers in the plankton during the fall and winter months. Gomphonema olivaceum be- came most important in the periphyton in Janu- ary-March 1972. The cells and mucilaginous stalks on which they grow formed an extensive diatom "ooze" on the entire creek substrate dur- ing these months. Nannoplankton data from the spring of 1971 and the winter of 1972 indicate that Gomphonema spp. were important in the flora throughout the winter and spring. In summary, the algal flora at site 3 was predominately composed of Htjdrurus foetidus in the spring, filamentous blue green algae in the summer and diatoms throughout the entire year. Filamentous algae contributed to the net plankton of the river and diatoms comprised nearly the entire nannoplankton. The plankton at site 3 was also influenced by blooms occur- ring in Miller's Flat and Cleveland Reservoir on the headwaters of the left fork of Huntington Creek. Planktonic algae originating from these reservoirs included Panclorina morum, Asterio- nella jormosa and Dinohrijon cijlindricum in the late spring and summer and Ceratium hirundi- nclla and Fragilaria crotonensis in the fall. Bear-Rilda Campground (Site 4) The campground locality is located three miles upstream from site 3 and exhibited a simi- lar flora. However, certain noteworthy variations between the two floras occurred. These differ- ences are attributed to different ecological con- ditions at site 4 and the effects of construction and pollution from Deer Creek on site 3. The creek at site 4 was high from April to early June 1971 with a definite dechne in water level in late June. Hydrtis foetidus ap- peared here in May on stones in a broad shallow riffle and increased to cover 25% of the sub- strate in early June. By June 29, 1971, this spe- cies had disappeared from the visible benthic algae at site 4, but was still prevalent in the net plankton indicating that it was carried down- stream from higher elevations where it persisted later in the season. A light film of H. foetidus appeared on the substrate in February but dis- appeared in March 1972. High water and prob- able abrasion from ice breakup upstream con- tributed to the disappearance of this alga at sites 3 and 4 during this period. The summer and early fall diatom ooze and blue green algal encrustation noted at the plant site were even more apparent at site 4 where the water was shallower, creating more exten- sive riffles. Algal and sediment buildup began in July and continued through October, when an extensive blue green algal crust was evident under the diatom ooze. In November this crust began flaking off. It is possible that Protoderma viride or an- other encrusting green alga was a member of this community. However, filamentous blue green algae were definitely the predominant constituents since large amounts of blue green algae were found in the net plankton when the crust began to break up (Fig. 29). Also floristic samples from the campground and further up- stream at the junction of the two forks of Hun- tington Creek showed large amounts of Schizo- thrix fragile and other filamentous Cyanophyta. The presence of these algae in Huntington Creek correlates with the findings of Clark ( 1958 ) in the Logan River, Utah, where a blue green encrusting mat was also found on the substrate under the diatom ooze. A new build- up on the substrate was noted in January and February 1972, but it consisted mostly of di- atoms. Filamentous blue green algae were pres- ent at that time but not in sufficient quantities to create an encrusted mat. During spring flood, the high water and abrasion from its increased silt load usually scoured the stones of much of their periphyton. By July, turbulence in the riffle had de- creased significantly and many scattered mats of Oscillatoria cf. tenuis, together with trapped sediments, occurred on the stream bottom. These were small mats covering only 6.4% of the substrate in shallow water although they oc- 40 Brigham Young University Science Bulletin Total Net Plankton: 1=100 algae I Selected Genera: Apr. June July Sept. =50 algae I Nov. Jan. Mar. Ulothrix Fig. 29. Season'ton was noted through the spring of 1971 until Jul\', followed by a decline to November 1971. Periphyton data were compiled from slides placed both in a pool and in riffles in order to compare colonization in the two habitats. Both areas showed a general decrease in most genera collected on slides on June 29, 1971, al- though Achnanthes mimttissima increased great- ly. This species increased from 2,928 cells per cm- on June 8, to 2.3,.532 cells per cm- on June 29, for slides in the riffle, and from 27,298 cells per cm* on June 8, to 12.3,650 cells per cm- on June 29, for slides in the pool (Table 4). From late June to August. Achnanthes (mostly A. minutissima) was the highest contributor to the Table 4. Percent composition of Achnanthes on glass slides at the campground, .lune 8-September 16, 1971. 6/8 6/29 7/30 8/20 9/15 Slides in riffle 3.2 28.1 54.6 43.2 (NS)* Slides in pool 12.8 75.8 75.3 14.9 16.0 *NS — No slide was collected from the riffle in September. benthic diatom flora in terms of number of cells produced. Most other diatoms in the periphyton fol- lowed the general trend of the total for this site discussed above. The most important genera were Navicula, CAjmbella, Gomphonema, Nitzs- chia, and Sijnedra. Stjnedra (mostly S. ulna) dif- fered somewhat by nearly disappearing during the wanner months. Diatoma vulgare showed good growth in November as it did at the plant site, but Gomphonema olivaceum did not show the expected late winter increase. However, nannoplankton data for G. olivaceum showed this species to increase in February and May, which correlated with the conclusion drawn from site 3 that this genus is a late winter and early spring form. Hannaea arcus was definitely a late spring diatom, and Cocconeis placentula a summer di- atom, as indicated by the periphyton and sub- stantiated by nannoplankton data. Certain true plankters were occasionally found on the peri- phyton sampling slides. These algae became entrapped there as they floated downstream and fell out of the water column. A comparison of data from slides placed in the pool and the riffle reveals certain differen- ces in colonization in the two habitats. The total number of periphyton and the number of indi- viduals of most genera were much higher in the pool. The only exception to this was Cocconeis placentula, which showed a comparable colon- ization rate in the riffle to that in the pool. The reason for the high colonization rate in the pool was undoubtedly due to reduced removal of periphyton by the stream current while concur- rently allowing sufficient water flow for ade- quate nutrient and gas exchange for rapid algal metabolism. Periphvton composition percentages for the period May through August 1971 show certain significant differences between the diatoms of the pool and the diatoms of the faster water. The riffle had a higher composition percentage of Gomphonema (mostlv G. olivaceum) , Sijnedra (mostly S. ulna), Ctjinhella spp., Nitzschia (mostly N. palea). Cocconeis (mostly C. pla- centula), Ulothrix sp., and Hijdrurus foetidus than the pool. Converselv, the pool had a higher percentage of Navicula spp., Achnanthes minu- tissima, Diatoma vulgare and Surirella (mostly S. ovata). From comparing periphyton data with nan- noplankton data at site 4 ( Fig. 31 ) , it is evident that high periphyton production in June 1971 caused the high nannoplankton levels of the same period and slightly later. The turbulence of high water during this period probably 42 Bait;ii\M Yoi'Nt: I'Nniusnv Sciknck Bvi.i.ktin Total Nonnoplonkton: 1=100 algae ml Selected Genera: 1=50 algae ml Apr. June July Sept. Nov. Jan. Mar. Fragllaria Cymbella Asterlonella Ceratoneis Fig. ^0. Sccison.il ilistiilnitian itf sclcrtrd niinnopl.iiiklnn ill tho cnnipgrniintl fsito 4). Biological Series, \'ol. 18. No. 2 Alc.-ve of Huntington Canyon, Utah 43 lOOO o o o s Z3 Z z o z < a. o z z < z 750 500 250 PERIPHYTON NANNOPLANKTON APRIL JUNE JULY SEPT NOV Fig. 31. Densitj' of nannoplankton and periphyton at the campground (site 4). 300 O 225 8 5 150 iJ to 5 z 75 X JAN MAR scoured many diatoms from the substrate into the current. Periph\ton production continued to rise in Julv 1971, when nannoplankton levels dropped, probably because fewer diatoms were removed from the substrate by the current dur- ing this period. Tliese periphytic diatoms were subsequently released into the current during earh" fall when plankton levels increased again. The November nannoplankton increase and sub- sequent relativeh' high winter levels were prob- ably due to new colonization, since periphyton levels also rose during this period. The nannoplankton cycle for site 4 basically followed the trend described for site 3. High diatom levels were evident from April to late June, followed by a summer low, and a high pulse in September (Fig. 32). The decline in plankton in October and subsequent rise in No- vember followed a trend similar to that observed at Lawrence, Stuart Station, and Bear Canyon, although the plant site did not exhibit the No- vember increase. The plant site also had much lower plankton levels on June 29, 1971, than the campground. Turbidity in Huntington Creek lOOO 750 O z o z < I a. o z z <. z -J CO 500 250 PLANT SITE CAMPGROUND APRIL JUNE JULY SEPT NOV JAN Fig. 32. Seasonal densities of nannoplankton at the plant site (site 3) and the campground (site 4). MAR 44 BrICHAM IfoUNG UNrvERSITY SCIENCE BULLETIN at the plant site was 40 JTU on June 29 com- pared to 15 JTU at site 4. Likewise, on July 5, 1971 turbidity was 25 JTU for site 3 and 11 JTU for site 4 ( Wingett, per. com. ) . The higher tur- bidity levels were attributed to excavation at the generating station approximately one mile upstream from site 3. Abrasion caused by the extra silt load in the water may have depleted the source of nannoplankton at this site by re- ducing periphyton populations prior to the June 29 collection, thus accounting for the lower nannoplankton levels here during this period. The lower nannoplankton levels in Novem- ber 1971 are attributed to pollution from Deer Creek. This creek flows east from a coal mine across the Utah Power and Light Co. generating station to Huntington Creek. During much of the year its flow was restricted, but during cer- tain periods it flowed freely, carrj'ing an ex- tremely heavy load of coal dust and mining wastes. In October and November the black, soupy water from Deer Creek clouded the clear waters of Huntington Creek and caused heavy coal dust sedimentation on the creek bottom. The effect of this water was probably the main reason for the low November counts here. In summary, the flora at site 4 was similar to the flora at site 3 in containing large numbers of diatoms both on the substrate and in the nanno- plankton. High periphyton production in late spring contributed to corresponding high nanno- plankton levels. Production decreased during late summer and increased again in winter. Nannoplankton levels at site 4 fluctuated greatly and differed somewhat from those of site 3. These differences were apparently caused by ex- cavation above site 3, and pollution from Deer Creek. Encrustations of filamentous Cyanophyta were more abundant at site 4 than site 3 in late summer and visible mats of Oscillatoria sp. oc- curred at the campground. Hydrunts foetidns grew more profusely at the campgroimd in the spring and greatly influenced the net plankton during this period. Both sites were influenced by euplankton from reservoirs on the upper drainage of the left fork. Stuart Fire Station (Site 6) The Stuart Fire Station locality' is located on the right fork of Huntington Creek approxi- mately 8 miles below the proposed site for the dam creating Electric Lake. Tliis site had con- siderably less water volume and lacked the in- fluence of reservoirs and artificial flow regu- lation noted for the left and main Forks of Hun- tington Creek. However, physical and chemical conditions of the water at site 6 were similar to conditions downstream except for slightly higher silica and alkalinity levels. Seasonal fluctuations in the algal flora at Stuart Station differed in many respects from those at other sites. This was probably due in large part to the higher altitude and consequent lower temperature and shorter growing season and to the shading effect from the steep walls in this part of the canyon. Hijdrurus foetidus was much more prevalent at Stuart Station than lower in the canyon. It was abundant here as early as March in 1971, although the creek was mostly frozen over. It remained present throughout the spring and by June it reached a peak of development forming a prevalent dark covering on most of the stones and rocks of the stream bottom. The quadrat method for estimation of cover and frequency showed this alga to cover 30% of the total sub- strate and be present in 100% of the plots on June 8, 1971. Visual estimation on the same date of several sites further up the canyon showed H. foetidus to be even more abundant there than at Stuart Station. By June 29, this species had de- clined significantly and soon after disappeared. H. foetidus reappeared in December 1971 and became abundant in Februar)' 1972 after the ice had melted. This alga usually exhibited more luxuriant growth on larger rocks than on small stones, and it was common to find rich brown filaments trailing in profusion from these rocks. The spring net plankton here was greatly influ- enced bv broken Hi/drums filaments, and the peak in net plankton occurred in early June concurrent to the peak of Hi/drurus production on the substrate (Fig. 33). Filamentous blue green algae formed an im- portant part of the algal communitA' at Stuart Station. They occurred in all floristic samples and net plankton samples from this site, often occurring in abundance. Maximum development of these algae occurred on the substrate from July to October 1971, when filaments of Lyng- hija spp., Pliormidium spp., Oscillatoria spp., and Schizothrix fragile formed extensive en- cnisting mats. These filaments were dense and intertwined, and heavily laden with silt par- ticles, diatom mucilage and frustules, and thick deposits of calcium carbonate, which made the exact characterization of this communit)' diffi- cult. However, Oscillatoria agardfiii was abun- dant in August and Schizothrix fragile and Li/nghi/a acniginco-cocrulea were abundant in October. Fragments of these blue green algae appeared in high numbers in the net plankton from October to November (Fig. 33) similar to sites 3 and 4. Oscillatoria cf. tenuis also ap- peared in October as bright blue green filamen- 1^1(11 cK.KM- Si Mils, \()i . US. \i). 2 Aix;\K oi' Huntincion Canyon, I'taii 45 Total Net Plankton: 1 = 50 algae I Selected Genera: 1=25 algae I Apr. June July Sept. Nov. Jan. Mar. Oscillatoriaceae Mougeotia Splrogyra Hydrurus Fig. 55. Soasiirinl rlistrilnition of sclfcti'ci net plankton at Stuart Station (site 6). 46 BniGHAM Young UwivEnsiTi' Science Bulletin tous entanglements similar to those observed at the campground in July. O. agardhii was also abundant in the flora during the winter months. It was prevalent on periphyton slides in November and February and from floristic data it appeared to be wide- spread on the substrate throughout the Novem- ber-Feb ruar)' period. The high levels of Os- cillatoria spp. in the 1971 spring net plankton were probably the result of a similar coloniza- tion during the winter of 1970-71. Although this blue green algal community at Stuart Station was ver>' important on the sub- strate, it was of little significance on the peri- phyton slides placed in the creek to monitor substrate colonization. Blum ( 1957 ) reported a similar situation in the Saline River, Michigan, where a cnistose Schizothrix-Phormidium com- munity occurred on the river bottom. He found that even after a year's period, sterile rocks placed in the river failed to develop a commu- nits' stnicturt^ comparable to the mature Schizo- thrix-Phormidium crust evident in the river. He concluded that a mature crust required a year or more to develop, and that the Schizothrix- Phormidium communit\' was a permanent mem- ber of the algal flora in tlie Saline River. A simi- lar situation occurs in Huntington Creek. The basic blue green algal community persists at Stuart Station throughout the year and develops extensively during summer and fall months. Cladophora pjomerata likewise chd not ac- tive^lv colonize microscope slides at Stuart Sta- tion, although it occurred abundantly on the sub- strate and significantK' influenced the net plank- ton in the spring and fall. This species covered 6f of the substrate in September and 10.5% of the substrate in October 1971. It occurred more on large rocks than on small stones and was covered with epiphvtic Cocconeis placentula, Gomphonema olivaceum, and other diatoms. It was much reduced in November, exhibiting a stubby growth form, but existed through the winter and became heavilv encrusted with cal- cium carbonate and sediment. In December C. glomerata was intertwined with many filaments of UlotJirix zonata and V. aequalis. lUothrix was otherwise most evident in Mav and Jun(> at this localit\'. Oedogonium sp. was rare at Stuart Station, although it occurred throughout the summer. Stiaeoclonium attenuatum and S. stagnatile oc- cuiTcd here inostK' in the fall months. Mougeo- tia sp.. Spirogijra sp., and Zijgnema sp. were of unique importance in the summer net plankton at Stuart Station and were the algae responsible for the steadv, relatively high net plankton rates through this period as contrasted to the lower summer rates at other sites on Huntington Creek. These species occurred mostly from late June to October, but Spirogtjra sp. was found from early June to Februar\'. Mougeotia sp. showed a signif- icant increase in July when it comprised 62% of the net plank-ton, and was the main contributor to the general increase in net plankton during that month (Fig. 33). The creek upstream from Stuart Station contains many regions with slow water and meandering stream channels, as well as springs, pools, and quiet backwaters. These areas supported luxuriant growths of conjugate algae and were undoubtedly the source of these algae in the net plankton at Stuart Station. Al- gae in these ponds and backwaters probably only entered the creek during runoff from late summer rain storms, but those growing in pools and side waters of the creek itself were con- stantly released into the channel. Diatom colonization of the creek substrate at Stuart Station showed peak development in May and November 1971. with lesser peaks in late June 1971 and Febmar\' 1972. The Novem- ber-March diatom density was much greater at Stuart Station than that of any period at sites 3 and 4 (Fig. 34), suggesting that the aquatic habitat here was more conducive to diatom production than lower in the canyon. The low colonization rate in early June was likely in part a result of the extensive Hydrurus foetidus development during that period. Summer diatom production was low here as it was at sites 3 and 4, although the summer low began in July. Many diatom genera on the substrate con- tributed to the total periphvton trends for the study period (Fig. .3.5). Certain genera such as CijmheUa (mostly C. ventricosa and C. parva), Synedra (mosth' S. uJrtc), and Diatoma (mostly D. vulgare) demonstrated high numbers on the slides collected on June 29, 1971. These genera were responsible in large part for the general periphyton increase of that period. CymheUa spp. were especially abundant in June. Floristic samples taken on June 15, at Stuart Station and select(>d sites downstream demonstrated extreme- Iv high numbers of CymheUa. Diatoma vulgare was also an important colonizer during this period. The fall and winter Diatoma vulgare-Gom- phomnna olivaceum increase was much the same at Stuart Station as at sites 3 and 4 down can- v(m. However, increased D. vulgare colonization began in October rather than in November, and G. olivaceum colonization began increasing in November rather than later in the winter. D. vulgare began forming long prominent zigzag colonies in October which became a dominant part of the periphvton flora in November and Biological Series, Vol. 18, No. 2 400 300 Algae of Huntington Canyon, Utah 47 O o o h o 200 lOO stuart station Campground APRIL JUNE JULY SEPT NOV JAN MAR Fig. 34. Density of periphj-ton at the campground (site 4) and Stuart Station (site 6). continued dominant through the winter until February 1972. G. olivaceum demonstrated a high colonization rate throughout the November- early May period. Nitzschia, as a whole, demonstrated spring and fall highs and a simimer low, thus following the general diatom trend. However, N. acicularis occurred mostly in the summer and early fall, when it was found in both the periphyton and nannoplanlcton from late June to November. Cocconeis placenttila also occurred in greater abundance during the summer and early fall months. It began colonizing in July and reached a peak in August and September, after which it decreased significantly. Butcher (1932) described an Ulvella-Coc- coneis community which was abimdant in En- glish calcareous rivers during summer months. An alga similar to Ulvella, but identified as Protoderma viride (after Prescott, 1962) was found colonizing glass slides at Stuart Station on September 15, 1971. Protoderma is a green alga exhibiting a prostate, often encrusted growth habit. In Huntington Canyon it becomes 400 O O O 300 :^ ^ 200 z o < lOO O z z < z . . . .. PFRIPHYTON NANNOPLANKTON \ \ \/ \ / '- / \ \ \' ^ / \ '/ . \ \ 1 \ / \ ' ^ 1 \ ' \ / \ \ ' \ // 1 \ / \ i * '/ \ / \ * '/ \ \ \ \ \ \ \ \ \ \ \ / \ V \ 400 O 300 O o 200\ s. z lOOg t— >- I APRIL JUNE JULY SEPT NOV JAN MAR Fig. 35. Density of nannoplankton and periph>'ton at Stuart Station (site 6). 48 BiuGHAM Young University Science Bulletin crusted with calcium carbonate and silt parti- cles, making it difficult to identify except when on periphyton slides. This same species was found abundantly on shdes at Lawrence in Sep- tember and October 1971 and was an important alga in the benthic community there. It was likely also an important constituent of the crusts evident at sites 3 and 4 during this same early fall period, although accurate identification was difficult and Protoderma was absent on glass slides at these sites. Four periphyton slides were retrieved from site 6 in September, and Protoderma viride was prevalent in three of the four, covering an esti- mated 10% to 2D% of the surface of each slide. In October P. viride was found on only one of three slides and had decreased in importance on that slide. Tliis alga therefore exhibited a short colonization period here and was probably not as effective in colonizing bare surfaces rapidly as some diatoms, such as Cocconeis and Achnanthes. Visual observation of the stream bottom throughout the summer indicated that Proto- derma viride was more prevalent than our data suggest. Such prostate, often encrusted forms are rare in the plankton (Butcher, 1932), thus eliminating plankton data as a means of moni- toring their production on the stream bed. Hence. Protoderma viride did not appear in nannoplankton counts from Stuart Station. This represents a weakness in subsampling and illus- trates that total numbers of individuals in a flora as determined onlv by one sampling method may not always convey a true picture of the flora as a whole. Protoderma viride mats were few in number on the periphyton slides although each covered a considerable area, making it important in terms of total cover although in- significant in total number of cells when com- pared to diatoms on the same slide. Achnanthes minutissima and Cocconeis pla- centuhi illustrate a similar problem of sampling. Table 5 compares the total number of Achnan- thes minutissima and Cocconeis phirentula cells per cm= and their relative abundance on periphyton slides for the summer and early fall of 1971. Table 5. Density in cells/cm^ and relative abundance of Achnanthes and Cocconeis in the periphyton of Site 6 July-October 1971. GENUS 7/30 8/20 9/15 8/10 Achnanthes Density Composition Cocconeis Density Composition 29,500 61.2% 2,750 5% 37,290 5.3.1% 7,900 11.2% 32,989 61.2% 3,851 7.1% 5,1+8 8.0% 762 1.2% These data show both of these genera to be abundant in the summer flora at Stuart Station, although Achnanthes minutissima appears to be much more important. However, cells of this spe- cies are small and occur on branched mucilagi- nous stalks, often with many cells appressed together. Cocconeis placenttila, on the other hand, is larger and grows adnate to the sub- strate. The microscope slides from this site in September were visually examined prior to clean- ing, and C. placentula appeared as one continu- ous sheet of cells covering tlie substrate. It thus appeared to be more important as a substrate cover than A. minutissima, which was present in higher numbers. Therefore, care must be used in sampling, and, whenever possible, subjective description should accompany numerical charac- terization describing a total flora as it occurs in place. Nannoplankton at Stuart Station were rela- tively constant throughout the year except for lows in Mav, August, and October 1971, and March 1972 (Fig. .36). The high winter and spring nannoplankton levels here were supported by similar high production on the substrate. As periphvton production declined in July and Au- gust, the number of nannoplankton also dropped. In September a large number of Nitzschia spp. and Navicula spp. released from the substrate caused an increase in the number of nanno- plankton. An October low occurred at site 6 as it did at site 4. Generally speaking, nannoplankton levels showed much less fluctuation at Stuart Station than at sites 3 and 4 (Fig. 37), whereas peri- phvton levels fluctuated more (Fig. .34). Nanno- plankton levels were also generalh' lower at site 6 than at sites 3 and 4 (Fig. 37). Tliis was due to the collection of diatoms in the plankton as the current carried them downstream, thus giv- ing higher levels lower in the drainage. How- ever, many fluctuations and occasional lack of correspondence between nannoplankton and peripln ton data suggest that manv factors along the stream affect these levels. For instance, many algae, especially nondiatom species, are de- stroyed as they travel dowoistream. The abun- dance of filamentous conjugales at Stuart Sta- tion and their paucitv at sites 3 and 4 illustrate this fact. Likewise, localized habitat differences are also extremely important in creating differ- ences between floras of different parts of the stream. Ilannaea arcus, for instance, was im- portant at the plant site and campground, but was almost nonexistent at site 6. A noteworthy lack of euplankton was also evident at Stuart Station. Successive collections of nannoplankton from Biological Series, Vol. IS Nd. 2 Aicvk. of HuNTiN't;TON Canyon, Uiam 49 Total Nannoplankton: 1 = 50 algae m Selected Genera: 1 = 25 algae ml Apr. June July Sept. Nov. Jan. Mar. Diatoma Fig. .36. Seasonal dislriliulioii of selertpd iiaiiMiipl.inktoii at Stiiail Station Csite 6). 50 Brigham Young University Science Bulletin 900 6 75 450 225 STUART STATION CAMPGROUND APRIL JUNE JULY SEPT NOV JAN MAR Fig. 37. Density of narmoplankton at the campground (site 4) and Stuart Station (site 6) Stuart Station were made on February 19 and 23, 1971. The results of tliese two samples are summarized in Table 6. Tlie close correlation of these two counts supports the reliability of the sampling techniques used and also indicates rela- tively stable conditions in the creek during this four-day period. In summary, the flora at Stuart Station dem- onstrated many species of diatoms on the sub- strate throughout the year with an Achiianthes- Cocconeis-Protoderma community prevalent in summer and early fall. Filamentous blue green algae were important here throughout the year, Table 6. Nannoplaiiltton totals for February 19 and February 23, 1972, from Stuart Station. February 19, 1972 February- 23, 1972 No. Percent No. Percent Per Compo- Per Compo- Liter sition Liter sition Navicula capitata 14,595 4.5 8,340 2.3 Navicula Iripunclala 13,900 4.3 18,070 5.0 Other Navicula 37,530 11.3 56,990 15.7 Cymbella 115,370 35.2 125,100 34.4 Gomphonema 33,350 10.2 38,225 10.5 Synedra 23,630 7.2 22,935 6.3 Nitzschia 47,955 14.7 47,260 13.0 Achnanthes 24,325 7.1 21,545 6.5 Diatoma yulgare 4,170 1.3 9,730 2.7 Diatoma hiemale 1,390 .4 1,390 .4 Gyrosigma 695 .2 695 .2 Surirella 2,085 .6 4,170 1.1 Cocconeis 4,170 1.3 3,475 1.0 Other diatoms 4,170 1.3 5,500 1.5 especially in the summer-fall period. Hi/drurus foetidus was abundant in spring and CAadoplwra glomerata was quite prevalent in fall. The dom- inant diatoms were Navicula, Cymbella, Gom- phonema, Nitzschia, Achnanthes, Stjnedra, Coc- coneis, Diatoma and Surirella. Bear Canyon (Site 7) Sampling at Bear Canyon was conducted from July to November 1971. The stream gradi- ent at this site was not steep and the stream ran clear, usuallv with lower water flow than at Stuart Station 9 miles downstream. Creen and blue green algae were significant in the flora at Bear Canyon. Ulothrix tenuissima was highest in the net plankton in June, indicating that it was an active stream bottom colonizer during late spring. Oedogonium sp. and Cladophora glomerata were prevalent throughout the sum- mer in the plankton, and Oedogonium sp. was also abundant on tlie substrate. Long streamers of this alga were found on stones and a sub- merged clay shelf in September and October. In September Oedogonium sp. covered 12.3* of the substrate and occurred with 79% frequency, and in October it covered 7.2% of the substrate and occurred in 86% of the plots studied. In Oc- tober Spirogijra sp. filaments were intermingled with the Oedogonium sp. strands. In November the decrease in abundance of Oedogonium sp. was accompanied by the initiation of growth of Hijdrurus foetidus on the substrate. Much of the creek bottom at Bear Canyon and upstream was sandy and provided little habitat for the at- tachment of benthic algae, and consequently. Biological Series, Vol. 18, No. Algae of Huntington Canyon, Utah 51 the total amount of attached algae was low in these areas. The seasonal cycle of Htjdrurtis foetidtis at Bear Canyon probably was much the same as at Stuart Station. It appeared in the late fall and was Ukelv present throughout the winter, since it was prevalent in the early spring when the ice broke. Because of the high altitude and consequent lower temperature of the water here, H. foetidus persisted longer into the summer than at sites lower in the drainage. Thus, this species was abundant in tlie net plankton as late as June 29, and still present in the July 30, 1971, sample. Growth of CladopJiora glomerata was not ex- tensive at Bear Canyon, and when found, it was covered with numerous epiphytic diatoms such as Cocconeis placentula and Gomphonema olivaceum. Filaments of several conjugate algae were retrieved in net samples during the sum- mer and early fall months. These algae largely originated in protected environments upstream from Bear Canyon where luxuriant mats of Spirogi/ra sp. were observed in October. Spiro- gijra sp. was more prevalent in these samples in the fall while Moiigeotia sp. and Ztjgnema sp. occurred mostly during the summer. Closterium spp. (mostly C. moniJiferum) were important in the creek at Bear Canyon. In July their density in the net plankton was 67.5 cells per liter and in August thev were present at 42 cells per liter. CAostcrium production in the creek occurred in the substrate in protected areas, among mats of filamentous algae and in partially submerged streamside vegetation. These same habitats were also the site of production for Trachelomonas robusta, which appeared in the creek in August, September, and November. Nannoplankton samples were taken during the August-November period. Tlie total numbers varied somewhat from the figures obtained at Stuart Station and in general were more stable and quite consistently high (Table 7). One reason for the stability in nannoplank- ton levels at Bear Canyon was a large occur- rence of Nitzschia palea and Gomplwnema oli- vaceum in September, even though most other genera decreased in numbers during this period. A similar Nitzschia sp. pulse contributed to the Stuart Station nannoplankton in September, but the numbers of most other genera increased as Table 7. Nannoplankton totals in cells per liter for Stiiart Station and Bear Canyon for August-No- vember 1971. Aug. Sept. Oct. Nov. Stuart Station Bear Canyon 116,741 215,576 310,271 218,223 66,435 112,295 282,768 265,056 well, thus producing a large pulse. This Sep- tember increase at Stuart Station was followed by a yearly low in October, which also occurred at sites 1, 4, and Bear Canyon. A November nannoplankton pulse was noted at Bear Canyon as well as at other sites, caused by a general in- crease in the numbers of most diatom genera. A second reason for the plankton stability in the upper drainage of Huntington Creek is attributed to the terrestrial environment. The terrain upstream from Bear Canyon consists of large grassy valleys and rolhng mountains. Con- sequently, late summer storms have less effect on the right fork here than in the canyon im- mediately above Stuart Station where the moun- tain sides are steep and easily eroded during storms, thus raising the water level rapidly and increasing the silt load in the creek. This in- creased silt load and high water is Hkely respon- sible for scouring diatoms from the substrate and thereby altering nannoplankton counts. Tie Fork Pond (Site 5) The lentic environment of Tie Fork Pond provided a habitat uniquely different from that of the swift flowing Huntington Creek, and thus the flora here contained many algae which did not occur in the creek. In addition, the cycles of occurrence of some genera common to both environments were very different. Physical and chemical properties of the water in Tie Fork Pond differed in several im- portant aspects from that of the neighboring por- tion of Huntington Creek. Silica fluctuated from levels below to levels above those found in the creek waters. Hardness was usually greater in the pond, with magnesium hardness being much higher and calcium hardness being somewhat lower than in the creek. Total alkalinity in the pond was higher and carbonate alkalinity was usually present along with bicarbonate alkalinity. Turbidity was also higher in the pond because of abundant planktonic algal growth, and water temperature was usually 5-I0°C higher since the small pond was easily and rapidly warmed by the sun. The pond was completely frozen during the winter. On March 11, 1972, it had begun to thaw, but neither visible benthic algae nor plankton were evident. A nannoplankton sample taken from the pond yielded only a few diatom fnistules which appeared to be left from the previous year. In April 1971, the pond was completely thawed, and the remains of the previous year's Chara mat were evident on the bottom. Fila- mentous algae such as Oedogonium sp., Spiro- 52 Bricham Young University Science Bulletin gtjra sp., and Microspora sp. were already float- ing on the surface of the pond, indicating that spring colonization is rapid. The plankton dur- ing this month were predominately diatoms in- cluding Navicula, Cijmhella, Gomphonema, Sijnedra, Nitzschia, Achnanthes and Cocconeis. Filamentous algae developed throughout the summer ( Fig. 38 ) . By June a new growth of Chara vulgaris was evident on the bottom and Spirogyra spp. filaments were abundant through- out the pond. Mougeotia spp. and Zt/gnetna sp. mats were abundant near the south shore of the pond wh(>re a culvert drained under the high- way into the creek. In July Potomogeton sp. was abundant in the pond and the Potomogeton- Cfiara association completely covered the bot- tom. Mougeotia (mostly M. gemiflexa) develop- ment reached a climax during this month and thoroughly saturated the water when it fonned bright green fluffy "clouds" throughout the pond. Tliis summer development of Mougeotia corre- lated closely with its appearance in the net plankton of the creek throughout the canyon, indicating that the same developmental cycle occurred in other habitats supporting Mougeotia growth. Spirogi/ra spp. development occurred mostlv in late summer and early fall in the pond, similar to other locahties. By August the water level in Tie Fork Pond had fallen considerably and very little free water above the Chara-Potomogeton cover was present. Consequently, the filamentous green al- gae declined considerably and generally became restricted to narrow channels near the culvert. Conditions in September were much the same except that a new bloom of Mougeotia (mostly M. gentiflexa) and Spirogt/ra sp. occurred in the limited free water in the pond. The late summer environment of August and September allowed the rapid development of Oscillatoria limosa and O. tenuis and, to a lesser extent, Lynghtja major and L. aerugineo-coerulea. The water level rose again in October and by November, a 1-inch layer of ice covered the pond. Extensive decomposition of the summer acjuatic vegetation began beneath the ice, mak- ing the water black and putrid. Tie Fork Pond supported a large population of diatoms throughout the studv, although sev- eral genera, such as Gomphonema. Si/nedra, Achnanthes, and Cymhella, declined in the sum- mer months. Other genera, such as Nitzschia (including N. palea, N. sigmoiclea, and N. linea- ris), Epithemia (mostly E. gihha), Fragilaria crotonensis, and F. virescens, were ver\' abun- dant in the summer (Fig. 39). Nitzschia spp. fluctuated throughout the study period from .\pril to October. Epithemia (including E. gihha. E. turgida, and E. argus) showed a maximum of 159,750 cells per liter occurring in July. Fragilaria crotonensis and F. virescens oc- curred throughout the summer. F. crotonensis occurred in highest numbers in late June and F. virescens in July. The bloom of F. crotonen- sis was apparently much earlier here than in the reservoirs on the left fork of Huntington Creek, where the bloom occurred in October. Tlie many nondiatom species present in the nannoplankton and the large number of net plankton during the summer in Tie Fork Pond are characteristic of fresh water lentic environ- ments. True plankters in the nannoplankton here included: Trachelomonas robusta, which in- creased in density throughout the summer to a peak in October; Scenedesmus (mostly S. bi- juga), which was most abundant in July ( 113,125 colonies per liter) but persisted in the flora un- til October; N ephrocijtium hinatum, which ap- peared in high numbers in July, declined in August and September, and was essentially gone by October; the desmid Sphaerozosma sp., which composed 25% of the flora in August and Sep- tember, appearing mostly as single cells rather than in its typical colonial form; Cosmarium sp., which occurred throughout the season and pulsed slightly in July and August; and Stauras- trum sp., which occurred from June 29 to Oc- tober 8, being highest in July and August. These last two genera were of minor importance in relation to the entire flora, never comprising more than 37c of the total nannoplankton. True plankters in the net plankton included: Pandorina morum. which increased from July to a maximum densitA' in September of 400 colonies per liter; Euglerui spp., which were prevalent throughout the season, occurring in greatest numbers in August and September when they reached 2,750 cells per liter; Chisterium (mostly C. monilifcntm), which appeared occasionally after May; planktonic Chroococcales (Cyano- phyta) which occurred from July to October; and species in Pyrrhoph\ta (mostly Peridinium cinctum). which appeared in low numbers in July, August, and October. Most of these algae were not significant in numbers. Desmids, for instance, were generally rare in Tie Fork Pond and throughout the drainage since they are more adapted to softwater and acid habitats (Prescott, 1962) than to calcareous waters such as those of Huntington Canyon. Many euplanktonic algae were also found on periphvton slides. Most of these probabU' settled out of the water onto the slides and became a part of the community developing there. For in- stance, Scenedesmus was quite prevalent on the slides throughout the summer. Butcher (1932) Bi(M/^o:r\L Series. \<>i IS. No. 2 Ai.caf, ok Huntinoion C\nv(in, Utah 53 Total Net Plankton 1=2500 algae I Selected Genera 1 = 2000 algae I Apr. June July Sept. Euglena Mougeotia Qscillatoria Splrogyra Fig. 38. Seasonal ilistribulioii of selerteil not plankton at Tic Fork Pond (site 5). 54 BniGiiAM VouNC. Univehsitv Science Bulletin Total Nannoplonkton 1 = 100 olgae ml Selected Genera 1=25 algae ml Apr. June July Sept. E pit he mi a Scenedesmus Fragilaria Fifj. ^t. Sensorial distiibutioii of solciti-d iiiiiiiiopl.nikloii ^it Tii- Fork I'micl I site 5). Biological Series, Vol, 18, No, 2 Alcae of Huntington Canyon, Utah 55 discussed Scenedesmus and other algae such as Pediastrum and Ctjclotella that are cosmopohtan in distribution and usually found on the bottom of ponds, ditches, and slovv-flovving streams where they live and reproduce until they are disturbed and become a part of the plankton. Production of diatoms on glass shdes in Tie Fork Pond was generally less than in Hunting- ton Creek, but since no current continually washed the diatoms downstream, numbers in the plankton of the two habitats were comparable. Trends similar to those observed in Tie Fork Pond occurred in other ponds throughout the Huntington Canyon drainage. One such pond is located adjacent to site 2. This pond maintained an extensive mat of Cham vulgaris throughout the year, with continual production and decom- position adding to the 2 feet of black organic mud on the bottom. A pond located about 2 miles east of the plant site was filled with moss rather than Chara. In May this pond contained Microspora sp. much as Tie Fork Pond and a bloom of Fragil- aria virescens which continued through early June. Microspora sp., Mougeotia sp. and Spiro- gyra sp. were abundant here in the early spring, and Oscillatoria limosa and O. tenuis became abundant in late June. Epithemia gibba was present from May to July and Navicula sp. and Nitzschia sp. were abundant in early summer. Green algae declined generally through the sum- mer, while filamentous blue green algae, es- pecially Oscillatoria tenuis and O. limosa, in- Fig. 40. Shallow pond adjacent to the Right Fork of Huntington Creek, These small ponds represent one source of euplanktonic algae in the flora of Hun- tington Creek, Photographed April 28, 1972, creased greatly. Desmids were more abundant in this pond than in any other habitat sampled in Huntington Canyon. The dominant desmid was Closterium rnoniliferum, common from July to October. A similar mossy pond is located one mile above Stuart Station (Fig. 40). The spring flora of this pond included Vaucheria geminata, Mou- geotia parvula, and Ulothrix tenuissima. In June, Spirogyra dubia occurred and Vaucheria gemiw- ata disappeared. Draparnaldia plumosa was abun- dant in June, as were Chlamydomonas sp., Clos- terium moniliferum, C. erhenbergii, and C. ros- tratum. Tliese desmids, along with Cosmarium sp., were also collected throughout the summer in floristic samples. Mougeotia genuflexa bloomed in July and Spirogyra dubia and Oedo- gonium sp. bloomed in August. Euglena (includ- ing E. acus) was often present in the Spirogyra mats. Epithemia sp. (mostly E. gibba) was pres- ent throughout the season in this pond and was most prevalent in August. Filamentous algae became rare by October except for Oedogonium sp. Spirogyra dubia became prevalent again in November and was accompanied by a bloom of Synedra (mostly S, ulna). The third pond is adjacent to the Bear Can- yon sampling site. Its flora consisted of Spiro- gyra sp., abundant throughout most of the sea- son except for July, Nitzschia sp. and Cymbella sp. in June, and Zygnema sp. in July and Au- gust. Epithemia gibba was also abundant in Au- gust, as were several species that were also found in Tie Fork Pond, including Oscillatoria limosa, O. tenuis, and desmids. Staurastrum eustephanum, especially, was common here in July-September. In September and October Amphipleura pel- lucida appeared abundantly in this pond, and Epithemia gibba continued abundant. Early fall filamentous algae included Spirogyra sp., Zyg- nema sp.. Mougeotia sp., and Vaucheria gemi- nata. Tolypothrix larmta was prevalent in Sep- tember and Oscillatoria tenuis became abundant in October. Chara vulgaris was present in this pond during the summer and fall season but did not form the extensive mats found in Tie Fork Pond. Algal Flora of Huntington Canyon Huntington Creek is a cold, clear, fast-flow- ing, calcareous stream, which supports a diverse algal flora adapted to these conditions. Diatoms are the most abundant algae present, occiuring throughout the year on the substrate and in the plankton. Tlie dominant genera are Navicula, Ci/mbella, Gomphonema, Nitzschia, Synedra, Achnanthes, and Diatoma. Diatoms show maxi- 56 BniGHAM Young University Science Bulletin mum production on the substrate in late spring and early summer and in late fall and early winter. Benthic diatoms are the main contributors to the nannoplankton, and the composition and seasonal fluctuations of the nannoplankton are largely determined by similar fluctuations on the substrate. Water level fluctuations, water temperature changes, and mechanical distur- bances also appear to be factors influencing nannoplankton levels. Pcriphyton colonization is higher in the right fork of Huntington Creek than lower in the can- yon, and nannoplankton amounts increase as the water moves downstream. However, the in- crease is not entirely cumulative since destruc- tion of cells occurs in the turbulent water. True planktonic algae, including Asterionella formosa. Frapilana crotonensis, Dinohnjon cijl- inclricum, Pandorina morum, and Cerathim hir- undinella occur in the plankton of Huntington Creek. These algae are thought to originate in reservoirs on the upper drainage of the left fork of Huntington Creek, and their occurrence in the creek basically correlates with algal cycles in these reservoirs. Filamentous algae are also important con- stituents of the Huntington Creek algal flora. Hydrurus foetidus grows profusely from late winter to early summer, especially in the upper reaches of the canyon, forming thick mucilagi- neous growths on stones and rocks on the stream bed. Blue green algae are present on the creek substrate throughout the year, but show high- est production during summer and fall when encrusted communities form on the stony sub- strate. Other filamentous algae present in the canyon include Ulothrix tenuissima, U. zonata, and Stigeoclonium stagnatile, which occur most- ly in the spring, and Mougeotia spp., Spirogyra spp., Zt/gnerna spp., and Vaucheria geminata, which grow in backwaters, pools, and ponds along the creek through the summer and fall. Fragments from these filamentous algae are an important source of net plankton. Hydrurus foetidus fragments are prevalent in the plankton in the spring, and filaments of blue green algae occur in large quantities during October and November. Most filamentous green algae occur during the summer months, and they are most prevalent in the right fork where protected areas along the stream channel allow for their de- velopment (Fig. 41). Most of these filamentous algae are quickly destroyed as they are carried downstream by the current. Cladophora glomerata and Oedogonium sp. also occur in significant numbers in Huntington Creek. C. glomerata is most abundant in the lower reaches of the right fork during the fall, and Oedogonium sp. is most abundant in the upper right fork during the same period. These genera are likewise prevalent in tlie lower Hun- tington Creek as it flows through Castle Valley, where they form long streamers from the stones during late spring and early summer. Chara vulgaris occurs in lower Huntington Creek from July to December, forming large mats and sometimes filling large sections of the stream channel. Diatoms important in the flora of the lower Huntington Creek include Navicula, Nitzschia, Diatoina, Gomphonema, Synedra, Surirella, Cymhella, Cocconeis, Achnanthes, and Cyclo- tella. Ponds in the drainage support abundant sum- mer algal floras. Filamentous algae, desmids, and such motile genera as Chlamydomoixas, Eu- glena, and Trachelomonas are common constitu- ents of these floras. Fig. 41. A small tributary of Huntington Creek (A) with profuse growths of Microspora willeana and Cladophora glnmrrata. Photograj)henas - - - - - - 1.8 .5%, 78.7 21.7% 1.8 1.1%. 10.5 6.9% - - - - - Pandorina moTum - - - 15.0 5.6% 67.5 28.0% 78.0 8.3% - - - - - Other Volvo- — — — — — 3.8 — — — — — — — caceae — — — — — .4% — — — — — — — Ulothrix — — 96.0 25.3%. 30.0 11.3%. 3.8 1.6% 7.5 .8% — 3.5 2.3% — — 1.5 4.0% 3.8 4.8% 11.0 5.2% StigeocUinium ________ 22.5 — 2.6 _ 1.3 ________ 4.3% _ 7.07o — .6% Oedogonium — — 3.9 .37.5 _ 3.8 54.2 28.0 _ _ 1.0 .6 2.5 _ — 1.0% 14.1% — .4% 15.0%, 18.3% — _ 2.7% .8%, 1.2% Cladophora — — 7.7 44.9 1.5.0 18.0 _ 9.3 7.5 .6 — 1.3 1.3 Rlomerala — — 2.0% 16.9% 6.3% 1.9%, — 6.1% 1.4%, 4.0% _ 1.6% .6% M(mgeotia — — — — 7.5 — — 1.8 — — — — — _ _ _ _ 3.1% — — 1.1% _____ Spirogyra _____ 11.2 7.0 11.0 3.8 3.1 _ .6 2.5 _ — — — — 1.2% 1.9% 7.2% .7% 20.7% — .8%, 1.2% Zygnema _ _ _ _ 15.0 _ _ 3.0 — 1.9 .5 — — — — — — 6.3% _ — 2.0% _ 12.7%, 1.3% _ — Other Filamen- 23.2 15.5 11.6 — — 3.8 7.0 _ — .6 6.1 — — tousChloro- 13.6%, 3.0%, 3.1% _ _ .4% 1.9% _ _ 4.0% 16.4%, _ _ phyta ClosteHum _ _ _ _ 22.5 3.8 1.8 1.8 — — 1.0 .6 1.3 — — — — 9.4%, .4% .5% 1.1% — — 2.7% .8% .6% Cosmarium — — — — 3.8 — — — — — — — — Staurastrum _ _ 7.7 — 22.5 93.7 — 1.8 — — — — — — — 2.0% — 9.4% 9.9% — 1.170 — _ — — — Euglena _____ 3.8 _ 1.8 _ _ _ _ _ — — — — — .4%, _ 1.1%, _____ Ceratium hir- _____ 17.4 127.7 7.0 7.5 — — — — undindla _____ 5.0% 35.3%, 4.6%, 1.4%, _ _ _ _ Other Pyrrho- — _ 3.9 _ _ _ _ 8.7 _ _ _ _ _ phyta _ _ 1.0% _ _ _ _ 5g<5[, _ _ _ Hydmms 78.0 248.0 244.0 135.0 25.5 _ — _ _ _ 11.6 62.0 165.0 foetidus 45.7%, 48.4% 64.0'"^ .50.7% 10.7%, _____ 31.3% 80.1% 77.5% Total Algae 170.7 512.0 378.8 266.2 239.3 939.2 362.2 151.6 528.3 15.0 37.1 78.7 212.2 BiOLOGiCAi, Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 61 Table 12. Number of organisms per liter and relative abundance of nannoplankton at plant site (Site 3) Algae 4/15 5/13 6/8 6/29 7/30 8/20 9/15 10/8 11/15 12/17 1/20 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 1972 Cyclotella 2,780 — 3,127 2,780 — — — 695 _ _ — — — .4% — .9% .5% — — — .8% — — — AsttTionella — — 59,490 30,250 13,344 6,115 3,335 6,096 — — — — — — — 8.7% 9.6% 3.9% 1.0% .4% 1.2% — — — — — Hannaea 1,390 47,260 13,066 1.042 — — 695 — _ 1,668 2,780 3,892 arms — .5% 6.9% 4.1%. .3%- — — .1% — — 1.2%, 1.1%, 1.3% Diatoma — 1,390 2,780 695 — — — — — — — — 973 hifmalf — .5% .4% .2% — — — — — — — — .3% Diatoma — — — — — — _ 18.348 6,960 21,545 8,757 tillUC — — — — — — — — — 20. 27^ 4.9% 8.5%. 2.970 Diatoma 3,475 4,170 2,780 3,475 7.086 10,286 11,120 13,100 1,737 1.668 4,450 2,780 1,946 vul^are .5% 1.4% .4% .9% 2.1% 1.7% 1.2% 2.5% 1.1% 1.8%, 3.2% 1.17c .6% Fra^ilaria 1,390 — 1,390 2,780 80,620 3,474 1.390 1,042 695 973 — — — .5% — .2% .3% 15.4% 2.2%. 1.5% .7% ..3% .3% Mi^ndioti — _ — 695 1,042 1,390 — — — — — — — — — — .2% .3%. .2% — — — — — — — Synedra 90,350 26,130 28,910 9,730 4,170 11,125 25,020 44,480 11,812 6.950 1.5,985 20,850 25,298 14.1% 8.9% 4.27^ 3.1% 1.2% 1.9% 2.8% 8.5% 7.6% 7.77- 11.37- 8.2% 8.3%, Achtuinthes 3,475 8,340 19,460 19,460 42,600 75,500 29,745 30,580 3,474 6,533 6,255 11,120 18,487 .5% 2.8% 2.7% 6.2% 12.3% 12.69fc 3.2% 5.8% 2.2%, 7.2% 4.47c 4.4% 6.1% Cocconeis — 2,780 — — 5,004 14,400 2,780 4,170 1,737 695 1,042 695 1,946 — .9% — — 1.4% 2.4% .3% .8% 1.1% .8% .77c .37c .6%, Amphipleura — — — _ — — 695 2,085 — 347 — — 973 — — — — — — .1%, .4% — .4%, — — .37., Navirula cf. 1,390 1,390 695 — — _ — — _ 4,4,50 1,390 973 capitata — .5%. .5% .2% — — — — — — 3.2% .57c .37c Navicuta cf. — — — 695 4,170 10,286 44,505 15,290 1,737 — — — — rhyncocephala — — — .2% 1.2% 1.7%, 4.9%. 2.9% 1.1% — — — — Navicuta cf. — _ — 18,070 13,344 32,500 43,085 13,900 15,287 — 5.560 13,205 18,487 tripunctata — — — 5.7% 3.9%. 5.4% 4.7% 2.5% 9.8%. — 3.97- 5.2% 6.1% Other 104,250 41,700 115,650 35,305 59,826 93,144 120,930 45,035 15,287 12,093 1.5.568 20,8.50 35,028 .Voficii/a 16.2% 14.2% 15.8% 11.2%. 17.3% 15.6% 13.47o 8.7% 9.8% 1.3.3%, 11.17c 8.27c 11.57c StauToneis — — — — — 348 695 _ — — — — — — — — — — .3% .37c — GomphoniTna 139,000 94,520 116.760 19,460 .30,024 60,500 65,330 26,400 10.425 2,780 15.985 .52,820 75,894 21.6% 32.2% 17.0% 6.2% 8.7% 10.1% 7.2% 5.0% 6.7% 3.1% 11.. 3% 20.8% 24.87c Cymbclta 205.520 58,380 150.120 113,980 90,375 145,500 216,505 80,620 29.187 15,985 25.993 62,5.50 6.5,191 32.0% 19.9% 21.9% 36.1% 26.2% 24.3% 23.8% 15.4% 18.7% 17.7% 18.4% 24.6% 21.3% Nitzschia — — — 695 5,004 2,084 2,362 2,362 — — — — — acicularis — — _ .2% 1.4%. .4%. .3% .4% — — — — — Other 86,175 46,980 129,550 44,420 .59.175 119,416 328,038 136,220 60.462 22,935 34,333 42,395 44,758 Nitzschia 13.4% 16.5% 18.9% 14.1% 17.2%. 19.9% 36.1% 26.0 38.7% 25.3% 24.37c 16.77c 14.67c SurircUa 10.425 4,170 1,.390 695 1,042 2,780 9,7.30 3,335 1.737 347 696 — 1,946 1.6% 1.4% .2% .2% .3% .5% 1.0% .6% 1.1% .4% .57c — .6% Other — 1,390 7,230 3,335 1,042 — 695 — — — 696 695 — Pennales — .9% 1.1% 1.1%> .3% — .1% — — — .5% .6% — Dinnbrynn — — 1,390 1,390 3,127 8,900 695 20,016 — — — — — — — .2% .4% .9% 1.5%, .1% 3.8% — — — — — Total Algae 642,670 292,730 686,940 317,501 344,544 598,096 907,350 52.5,004 1.56.356 90,766 141,031 255,065 305,522 62 BmcHAM Young University Science Bulletin Table 13. Number of organisms per cm^ and relative abundance of periphyton on glass slides at plant site (Site 3) Algae 5/13 6/8 6/29 7/30 8/20 9/15 10/8 11/15 12/17 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 Cyclotetla - - - - 204 .2% - 62 .2%,, — — - - Asterionella ~_ 445 850 202 612 62 — .5% 1.0% .1% .6% — .2%c — — — — Hannaea 154 445 1.740 496 _ _ — 371 — 154 309 arcus .6% .5% 2.0%, .3%, — — — 1.1% — .3% 1.6% Diatoma hitinale - 51 .1% - - 204 .2% - - — — — — Diatoma tiiiue z I 2,625 1,081 — — — — — — — — — 5.1%, 5.7% Diatoma vulgare _ 51 406 598 847 1,544 474 2,.595 407 309 154 — .1% .5% .4%, .9% 3.2% 1.4% 8.0% 5.1% .6%, .8% Fratiilnria — — — — — — 350 247 — _ 154 CTotujicnsis — — — — — — 1.1% .7% — — .8%, Meridian — 51 .1% 2.062 - — — — - - - - - Synedra 3,855 4.530 2,393 3,420 762 1,503 3,830 678 3,861 1.081 14.0% 2.5% 5.2%, 1.5% 3.5%, 1.6%, 4.5% 11.8%, 8.4%, 7.5%, 5.7%, Achnanthcs 1,.390 3.960 10.300 94,100 13,340 15,589 2,060 1,606 325 2.008 618 5.07o 4.8%, 11.7%, 57.1%, 13.7% 32.3%, 6.29t 5.0%. 4.1%, 3.9% 3.3% Cocconeis 103 — — 596 305 1,174 144 — — — — .4% — — .4%, .3%. 2.4% .4%. — — — — Amphipleura — — 64 52 206 864 154 — — — — .1%. .1% .6% 2.7%. — — .8%, Navicula cf. — 1,167 4,530 .5,335 6,997 556 2,471 1.831 407 1,390 463 tripunctata — 2.0% 5.2%, 3.2%. 7.2% 1.2% 7.5% 5.7% 5.1% 2.7%. 2.4%c Other Savicula 7.258 5,255 5,136 24,265 18.973 .3,913 6,322 2.707 868 3,707 772 26.4<7< 6.4%, 5.9%r 14.8%. 19.6%^ 8.1% 19.1% 8..3% 10.8% 7.2% 4.1%,, Gomphonema 6,067 14.415 10,300 5,050 2.501 3,027 885 2.348 732 18.688 7.877 22.0% 17.5%, 11.7% 3.1%. 2.6% 6.3%, 2.7% 7.. 3%, 9.1% 36.2^ 41.5%, Cymbctia 8,408 35,382 38,755 18,000 15.400 8,175 4,324 6.301 2.441 13.437 2.317 30.5%. 43.0%c 44.2% 10.9%t. 15.9% 17.0% 13.1% 19.5%, 30.4%o 26.0% 12.2%o Nitzschia — _ _ 920 406 206 — — acicularis — — — .6% .4% .4% — — — — — Other Nilzschia — 17,649 6,062 9,240 32.094 12,397 12,335 9.267 1.627 5.406 3.861 — 21.4%, 6.9%, 6.2% 32.7%. 25.7% 36.9%. 28.7% 20.3%, 10.5%b 20.3%,, Surirclla 201 303 536 503 204 154 144 371 68 .7% .4% .67o .3% .2%, .3% .4% 1.1% .8% — — Other I'ennales — 294 2.183 _ _ 52 62 — — — — — .3% 2.5% — — .1% .2% — — _ — Dinohryoii — 203 _ — — — 62 — .2% — — — — .2% — — _ _ Osciltatoria — — 2.040 1.056 _ 412 — — 203 154 — — 2.3% .6% — .2% — — 2.5% — .8% Other 93 — _ 1.151 1,877 103 1,853 — 203 Oscillatortaceae .3% — — .7% 1.9% .9% 5.67o — 2.5% — — Anabacna — _ _ 95 64 — — — — .17o .1% — — _ _ _ _ Ulothnx _ _ — 95 103 — — — .1% — .2% — — — — — Stigeoclonium — — — — — _ _ — 68 — — — — — — — — — _ .8%, — _ Oedogonium — — — — — 52 — — _ _ _ — — — — — .1% — — — — — Other Filamentous 738 _ _ 144 _ Chlorophyta — — — .4% — — .4%, _ _ — — Ctostmum — — 85 — 64 _ — — .1%, — .1% EugltTia - 51 1% — - - - - - - - - HydntrlM foetidus 51 247 95 z — .1% .3% .1%C — — — — — — — Total Algae 27.529 82.285 87.700 164.928 97,576 48,271 33,463 32.338 8,027 51..585 18.995 Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 63 Table 14. Number of organisms per liter and relative abundance of net plankton at campground (Site 4) Algae 4/15 5/13 6/8 6/29 7/30 8/20 9/15 10/8 11/15 12/17 1/20 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 1972 Chroococcales — — — — 97.5 22.5 8.7 — — — — — 13.5% 1.2% 10.8% — — — — — Oscillatoria 93.0 123 3.9 7.5 3.8 15.0 30.0 7.7 33.7 4.5 3.1 2.5 7.5 60.0% 21.2% .8% 2.4%, 2.9%, 2.1% 1.6% 9.6% 5.8% 14.6%, 9.5%, 4.4% 14.5% Other Oscilla- 7.7 54.0 _ _ _ 30.0 385.0 5.2 502.5 21.9 10.3 1.9 3.8 toriaceae 5.0% 9.3% — — — 4.1%, 19.9% 6.5% 87.0% 69.9%, 31.4% 3.3% 7.2% Anabaeria — 7.7 1.3% — — — — — — — — - - - Chlamydomonas I 15.0 I I 1.8 I I ~ I I — — — — 11.5%, — — 2.2% — — — — — Pandorina — — — — 11.4 45.0 232.5 3.5 morum — — — — 8.6% 6.2% 11.9% 4.4%, — — — — — Other \'olvo- — — — — — 3.8 — 3.5 — _ _ — _ caceae — — — — — .5% — 4.4%, — — — — — Ulothrix — 46.5 161.0 7.5 7.5 3.8 _ 2.6 3.8 — 1.0 2.5 — — 8.0% 32.0%. 4.0% 5.8% .5% — 3.2% .6% — 3.1% 4.4% — Stigeoctonium — — — — _ — _ _ 22.5 3.9 1.5 — 2.5 — — — — — — — — 3.9% 12.6% 4.6% — 4.8% Oedogonium — 15.5 3.9 11.2 3.8 — 127.5 20.3 — — .5 — — — 2.7% .8% 6.0% 2.9% — 6.5%, 25.3% — — 1.5% — — CtadophoTQ — — 11.6 15.0 15.0 15.0 _ 4.4 _ .6 1.0 .6 _ glomerata — — 2.3% 8.0% 11.5% 2.1% — 5.4% — 1.9% .3.1% 1.1% — Mougeotia — — — — — 7.5 — .9 — — — — — — — — — — 1.0% — 1.1% — — — — — Spirogyra — — 7.7% — — — — 7.7 _ _ — .6 — — — 1.5%> — — — — 9.6%, — — — 1.1% — Zygnema — _ _ — 33.0 3.8 — .9 — 1.0 — — — — 25.3%, .5% — 1.1% — — .3.1% — — Other Filamen- 7.7 — 3.9 _ — — — — — — 2.0 .6 — tous Chlorophyt :a 5.0% — .8% — — — — — — — 6.1% 1.170 — Closterium — 23.0 — — 26.2 3.8 7.5 2.6 3.8 — — .6 .6 — 4.0% — — 20.2% .5% .4% 3.2% .64% — — 1.1% 1.2% Staurastrum — _ — — — 72.0 7.5 — 3.8 — — — — — — 9.9% .4% — .64% — — — — Euglena - — — - - 3.8 .5% 423.0 - .9 1.1% 7.0 - - - - - Ceratium hir- I I I I I 1110.0 7.5 I I undinella — — — — — .58.4% 57.6%, 8.7% 1.3% — — — — Other — 7.5 Pyrrophyta — — — — — — .4% — — — — — — Hydrurus 46.5 310.0 309.0 146.8 15.0 12.4 48.0 37.5 foetidus 30.0% 53.5%, 62.0% 78.. 3% 11.5% — — — — — .37.8% 84.7%, 72.37o Vaucheria - - - - - - - 2.6 3.2% 80.3 - - - - - Total Algae 154.9 579.7 501.0 188.0 130.7 724.0 1930.0 578.2 30.9 32.8 57.3 51.9 64 Bbicham Young University Science Bulletin Table 15. Number of organisms per liter and relative abundance of nannoplankton at campground (Site 4) Algae 4/15 5/13 6/8 6/29 7/30 8/20 9/15 10/8 11/15 12/17 1/20 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 1972 Cyclolella 4,170 — 1,668 — — _ 1,042 — — — _ _ — .5% — .7% — — — .4% — — — Asterionella — — 46,425 88,9,50 13,200 2,357 1,390 2,085 2,085 1,042 — — — — — 9.0% 11.6% 6.1%. 1.0% .2%. .8% .4% .4% — — — llannaea 6,960 16,680 27,105 27,800 2,.362 348 695 — 1,390 3,058 1,390 4,170 3,475 arms 6.1'S 2.1% 5.3% 3.6% 1.1% .2%, .1% — .3% 1.1% 1.1% 1.0% 1.9% Diatoma 2,432 _ 4,170 3,335 _ — — — — — 696 — 1,390 hiifjialf 2.1% — .8% .4%, — — — — — — .5% — .8% Diattrma 1,390 — _ _ _ — — — 348 4,170 5,560 teiiue — _ .3%, — — — — — — — .3% 1.0% 3.1%. Dialoma 5,912 12,510 2,085 8,895 2,780 1,668 15,845 3,335 20,016 4,865 4,450 9,730 4,865 vulnare 3.1% 1.6% .4% 1.2% 1.3% .7% 1.7%, 1.2% 4.3% 1.8% 3. .5% 2.3% 2.7% Frti^lUiria — — 2,780 695 _ 696 695 104,805 10,285 8,340 1,042 1,390 695 — — .5% .1% — .31% .1% 37.7% 2.2% 3.1%. .8% .3% .4% \feridion _ 12,510 6,9.50 2,780 — — — — — 347 — 1,390 — — 1.6% 1.4%. .4% — — — — — .1% — .3% — Synedra 6,602 46.702 11,675 22,795 7,200 5,560 20,8.50 9,730 20,8.50 10,703 17,653 33,360 8,340 5.8% 6.0% 2.3% 3.0% 3.3% 2.. 5% 2..5% 3.5% 4.5% 4.0% 13.7%. 7.8% 4.6%, Achnanthes 1,740 .37,5.30 22,240 61,150 18,725 26,000 49,6.50 9,730 43,090 22,935 6,960 18,070 15,290 1..5% 4.8% 4.3% 8.0% 8.6% 11.5% 5.4%. 3.. 5% 9.2% 8.5% 5.4% 4.2% 8.5% Cocconeis 1,390 — 695 1,390 696 6,255 6,096 _ 2,780 3,0.58 1,668 2,780 695 1.2% — .1% .2% .3% 2.8% .7% — .6% 1.1% 1..3%. .7% .4% Rhoicos- — 1,042 1,390 695 — — — — — — — — — phfTiio — .1% .2% .1% — — — — — — — — — Amphipli-ura — — — — _ — — _ 695 695 — 1,390 — — — — — — — — — .1% .2% — .3% — Cyrosi^ma - - - - - - - 695 .3% - - — 1,390 .3% - Navicula cf. 695 1,042 I 695 I I 695 2,085 8,340 2,085 capitata .6% .1% — .1% — — — .3% — — 1.6% 2.0% 1.2% Navicula cf. — — 2,780 2,085 — 3,052 45,035 1,390 5,560 1,042 — — 4,865 rhyncocephala — — .5% ..3% — 1.4%. 4.9%. .5% 1.2% .4% — — 2.7% Navicula cf. — — — 18,070 10,007 7,225 56,155 7„505 19,460 9,313 ,5,838 18,070 13,205 tripunctata — — — 2,4% 4.6% 3.2%. 6.1%. 2.7% 4.2% 3.4% 4.5% 4.2%. 7.3% Other 11,468 141,760 67,550 94,290 36,585 33,323 107.010 11,120 72,280 59,353 10,842 52,820 15,985 Navicula lo.n 18.2'-, 13.0% 12.4% 16.8% 14.4% 11.5% 4.0%. 15., 5%. 22.0% 8.5% 12.4% 8.9% Pinnularia - 1,042 .1%, - - - - - - - 347 .1% - - - Staurnncis - - - - - - - 695 .1% 53,375 - - 695 .4% 20,155 CiomphnjttTiia 13,553 194,7.37 79,785 69,500 16,675 23,2,59 54,210 10,285 21,545 17,653 76,4.50 11.9% 25.0% 15.5% 9.1% 7.6% 10.. 3%. 5.8%. 3.7% 11.3% 8.0% 13.7% 17.9% 11.2% Cymbclla .38,920 159,.584 11.5,925 230,740 73,250 73,250 215,4.50 33,915 90,350 64,218 31,970 102,860 46,565 34.2% 20.5% 22.5%. 30.2% .33.6% 32.4% 32.2% 12.2% 19.4% 23.7% 24.8% 24.1%, 25.9% Epithcniia - 1,042 .1% - - - - - - - - - - — Nitzschia 6,115 1,390 2,780 3,052 6,096 2,362 2,780 1,390 acicularis — — 1.2%. .2% .7% 1.4% .7% 3.5% .6% — — .3% — Other 20.880 133,440 85,345 102,960 26,2.50 30,250 337,770 43,590 113,980 56,990 23,908 86,180 34,055 Nilzschia 18.4% 17.1% 16.6% 13. .5% 12.6% 13.. 3%. 36.47n 13.0% 24.5% 21.1% 18.5%. 20.2% 18.9% Surirella 348 9,172 2,780 4,170 1,390 348 9,730 1,390 4,170 1,390 2,363 2,780 2,085 .3% 1.2% ..5% .6% .2%. .2%, 1.1% .5% .9% .5% 1.8%. .7%, 1.2% Other 5,210 4,170 5,560 16,000 _ 1,042 — — _ _ _ — — Pennaies 4.6% .6% 1.1%. 2.1% — .5% — — — — — — — Dinobryon — — 15,290 1,390 6,255 6,5.50 — 35,305 2,085 — — — — — — 3.0%, .2% 2.9% 2.9% — 12.7% .4% — — — — Total Algae 116,110 772.963 514,150 763,795 218,145 225,903 926,677 277,937 465,925 270,283 128,866 426,730 180,005 Biol<)(;k:ai. Series, Vol. 18. No. 2 Ai.c.^E of Huntincton C.\nyon, Utah 65 Table 16. Number of organisms per cm- and relative abundance ol periphyton on glas.s slides in a pool at campground (Site 4) Algae 5/13 1971 6/8 1971 6/29 1971 7/.30 1971 8/20 1971 9/15 1971 10/8 1971 11/15 1971 Cyclotella — — — — — 52 .2% 62 .5% — Astcrioncllu — — 85 .1% 1,020 .4% 102 .4% 103 .5% — — Ihmnaeu anus 1,020 2.0* 5,459 2.6% 648 .4% 304 .1% — — 206 .6% Diittomu liUiHulf z 607 .3% 242 .2% — — Di(tti)m(t tcnuc — — — — — — — — Diut(,inia vuli^are 810 1.6? 1,213 .6% 909 .5% 1,522 .6% — 206 1.0% 762 6.4% 1,441 3.9% Frit^ilarid crotunensis — — I — — 62 .5% 3,532 9.5% Mcrkliuii — — — — 102 .4% — — — Si/iicdro 2,677 5.2* 7,919 3.7% 85 .1% .304 .1% — 154 .7% 762 6.4% 1,544 4.2% Achuanthc\ 2,677 5.2% 27,298 12.8% 123,650 76.0% 196,100 75.3% 3,685 14.9% ,3,398 16.0% 412 3.5% 4,602 12.4% Cocconeis 243 .5% — 648 .4% 102 .1% 1,020 4.1% 1,853 8.7% 268 2.3% 31 .1% Navicula cf. ciii)it(itgonii/;N — — — — — 52 — — CAadophora — — 536 — — — — 72 — — .,3% _ _ _ _ .2% Closterium _ _ _ 204 — — — 31 — - — .1% — — — .1% Euglena 51 — — — — — — — Hi/drunis — — 536 — — — — — — — .3% — — — - - Total Algae 51,642 212,667 162,613 260,697 24,719 21,284 11,842 37,128 Table 17. Number of organisms per cm- and relative abundance of periphvton on glass slides in a riffle at campground (Site 4) Algae 5/13 6/8 6/29 7/30 8/20 2/19 3/11 1971 1971 1971 1971 1971 1972 1972 Cyclotetia Astcriimclla Haniuicu arcus Diatonid hii'nuilr Didtinnti triiuc — — — Diittiiimi inlfiiirc 486 708 636 .7% .8% .8* Fnigiliiria croloncnsis — — — Meridion Si/ncdrii Achnantltes Cocconeis Wivictda cf. rhyncocc'phala Navicula cf. tripunctata Other Navicula Gomplwnrmd C.ymbella iVi ( r.SY'/i ia acicu la ris Other \itzschia Surirt'lla 6,075 — 12.7% — 103 154 .2% .9% 3,295 1,287 6.9% 7.9% 204 206 1.54 ,2% .5% .9% — 51 — .3% — 102 — — — 103 — — .1% — — — .2% - 7,113 4,040 1,272 — 204 7,928 1,493 11.0% 4.. 5% 1.6% - .2% 16..5% 9.2% 1,.375 2,928 23,532 20,400 43,200 2,780 1,184 2.1? 3.2% 28.1% 54.6% 43.2% 5.8% 7.3% 81 — — 3,248 1,624 103 — .1% — — 8.7% 1.6% .2% - — — 318 204 1,020 — — — — .4% .5% 1.0% - — — 1,617 6,678 406 3,040 1,.544 — — 1.8% 8.0% 1.1% 3.0% 3.5% - 7,923 5,982 10,.540 2,028 10,276 4,015 1,184 12.1% 6.6% 12.5% 6..5% 10.3% 8.4% 7..3% 15,131 24,015 2,226 2,670 2,670 2,574 1,287 23..3% 26.6% 2.7% 7.1% 2.7% 5.4% 7.9% 24,099 33,963 18,762 3,490 16.510 5,554 5,714 .37.2% .37.6% 22.4% 9..3% 16. .5% 11.1% 35.0% — — — 406 812 — — — — — 1.1% .9% — - 8,080 13,820 12,720 1,886 17,503 8,546 3,088 12.5% 15.3% 1,5.2% 5.0% 17.4% 17.8% 18.9% — 102 — — 204 (Table 17 continued 103 on p. 67 ) Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 67 — .1% — — .2% — .8% Other Pennales 81 .5% 943 1.0% 1,908 2.3% 204 .5% — 2,162 4.5% I Dinobryon — 102 .1% I — — — Chroococcales — — I 612 1.6% — — — Oscillatoria 81 .5% 1,272 1.6% I 406 .4% 103 .2% — Other Oscillatoriaceae z — — — 2,228 2.2% 103 .2% — Ulothrix 81 .5« — — — I 51 .3,% Clostcrium — — — 204 .5% — — — Hy drums — 20.3 .2% 1,272 1.6% — 2,986 6.2% 566 3.5% Total Algae 64,855 90,346 83,680 36,976 99,901 47,980 16,316 68 Bbigham Young University Science Bulletin Table 18. Number of organisms per liter and relative abundance of net plankton at Tie Fork Pond (Site 5) Algae 4/15 1971 5/13 1971 6/8 1971 6/29 1971 7/30 1971 8/20 1971 9/15 1971 10/8 1971 Chroococcales — — 12.4 1.3? I 540.0 4.1% 876.0 8..3? 250.0 .8? 288.0 5.0% Lynghya — — 19.0 2.0% 10.5 .4% 36.0 .3% 195.0 1.8% 300.0 .9% 45.0 .8% Oscillatoria 86.0 15.6* 39.0 9.0? 291.0 30.3? 25.5 .9% 90.0 .7% 2,100.0 20.0% 2,000.0 6..3? 275.0 4.8% Anabaena — .39.0 9.0? 15.5 1.6% 4.5 .2% 45.0 .4% 200.0 .6% Cidothrix — — — — — — 150.0 .5? — Chlamydomona.1 — — — — 330.0 2.5% 186.0 1.7% 2,750.0 8.7% 87.5 1.5% Pandorina — 7.7 1.8% — — 246.0 1.9% 276.0 2.5% 400.0 1.3? 70.0 1.5% Other Volvocaceae — — — — — — — 37.5 .7% Gloeocystis — — — — — — — 38.0 .7% Oedogonium — 85.0 19.6% 127.0 13.2? — 156.0 1.2% 780.0 7.4? 250.0 .8? 137.5 2.4% Cladofihora — — 7.7 .8% 10.5 .4? 81.0 .6? 22.5 .2% 700.0 2.2% 200.0 3.5% Ankistrodesmus I 46.7 10.8% I — — — Mougeotia 93.0 16.9? — 193.0 20.1% 1,335.0 45.3* 11,250.0 86.4? 4,710.0 44.8? 15,555.0 49.0? 4,275.0 73.8% Spirogyra 46.5 8.5? 7.7 1.8? 147.0 15.3% 1,345.5 45.7% 66.0 .5? 255.0 2.4% 6,750.0 21. .3% 100.0 1.7% Zygnema I .39.0 9.0% 43.5 4.5% 120.0 4.1% 30.0 .2% 705.0 6.7% 450.0 1.4% — Other Filamentous Chlorophyta Closterium 185.0 33.6% 69.5 16.0? 7.7 1.8? 61.5 6.4% 23.0 2.4? 100.5 3.4% 120.0 .9% 7.5 .1% 37.5 .3% 50.0 .2% 12.5 .2% Euglena 1.39.5 25.4? 85.0 19.6% 7.7 .8% 4.5 .2? 45.0 .3% 315.0 2.9% 1,850.0 5.8% 187.5 3.2% Pyrrophyta — I I I 30.0 .2% 7.5 .1% I 12.5 .2% Ophiocytium — 7.7 1.8% — I — — I 25.0 .4? Vaucheria — — 12.4 1.3? — — — — — Total Algae 550.0 434.0 960.7 2,946.0 13,020.0 10,518.0 31,655.0 5,791.0 Bi()L()C:k:ai, Sehies, \'oi.. 18. No. 2 .^i.fi.vE of IIuntincton Canyon, Utah 69 Table 19. Number of organisms per liter and relative abundance of nannoplankton at Tie Fork Pond (Site 5) Algae 4/15 5/13 6/8 6/29 7/30 8/20 9/15 10/8 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1972 Cyclotella — — 7,645 3.8% — — — — — — Astcrioiiclla _ _ 2,780 2,088 5,004 — — 1.3% 1.3% .6% — — — — Didtomd — 3,476 9,035 1,042 12,525 348 2,780 348 1,043 — 1.3% 4.3% .7% 1.5% .2% .7% .2% 16.7% Fraiiiluriu — — 7,228 40,310 23,775 4,875 2,780 2,363 — crotoiiciisi.s — — 3.5% 25.5% 2.8% 2.4% .7% 1.5% — Fni'^ihiriti 5,143 — 1,390 4,448 85,950 4,444 9,730 6,533 — viresccus 6.2% — .7% 2.8% 10.5% 2.3% 2.5% 4.1% — Meridicit — 4,170 1.6% — — — — — — — Si/ui'itra 4,448 16,680 26,828 6.255 13,.350 348 5,560 5,8.38 1,043 5.4% 6.4% 12.9% 4.0% 1.6% .2% 1.4% 3.7% 16.7% Achiiantlics 5,143 7,.505 17,.375 2,088 4,170 1,042 4,170 1,390 — 6.2« 2.9% 8.3% 1.3% .5% .5% 1.1% .9% — Cocconcis 13,733 1,589 — — 1,042 4,875 1,.390 348 — 16.6% .6% - — .1% 2.5% .4% .2% — Aniphipli-urti — — 3,475 1,390 — — 2,085 348 — — — 1.7% .8% — — .5% .2% — CyrosijJitui — 696 — 348 — — 1,390 1,043 1,043 — .3% — .2% — — .4% .7% 16.7% Navicula 19,734 34,611 9.175 6,185 19,852 4,170 9,035 12,510 2,085 23.8% 13.0% 4.4% 3.9% 2.4% 2.1% 2.3% 7.9% 33.4% PinnuUirid 2,084 — 695 1,042 2,084 348 695 3,475 — 2.5% — .3% .7% .2% .2% .2% 2.2% — Sttmroiieis 2,084 1,589 — 1,390 3,127 348 695 1,043 — 2.5% .6% — .8% .4% .2% .2% .2% .7% GoinpliDnema 348 69,500 1,042 2.432 7,086 — 1,390 3,085 — .4% 26.1% .5% 1.5% .8% — .4% 2.0% — Ci/inhelti- IK'ntincion C^xnvon. I'taii 81 Table 30. Physical and chemical data fmm Huntington Canyon. Dissolved oxygen (mg/1). Site 6/8 6/29 7/30 8/20 9/15 10/8 U/1.5 12/17 1/20 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 1972 Lawrence 9 5 9 9 10 8 6 .3 8 911 Highway 10 Plant Site Campground Tie Fork Stuart Station Bear Canyon 11* 7* 9* 8* 8 10 7 nd nd nd nd nd = no data available *Data recorded during corresponding time periods by Dr. Robert Wingett, Center for Health and Environmental Studies. Brigham Yoinig University. Table 31. Physical and chemical data from Huntington Canyon. Dissolved carbon dioxide (mg/1). nd nd nd 9 10 8 10 4 6 9 11 10* 9 9* 9* 9 8 9 7 .5 9 11 11 10 9* 10* 9 7 7 9 8 10 11 8 5 nd 10 14 8 nd nd nd nd 5 11 9 9* 9* 8 8 8 7 5 9 9 Site 6/8 6/29 7/30 8/20 9/15 10/8 11/15 12/17 1/20 2/19 3/11 1971 1971 1971 1971 1971 1971 1971 1971 1972 1972 1972 Lawrence Highway 10 Plant Site Campgroimd Tie Fork Stuart Station Bear Canyon 2 4 12.8 12 4 2 6 24 16 18 8 nd nd nd 12 4 0 4 14 20 6 4 0* 1 4.8 8 0 0 2 6 6 2 2 1.4 2 6 12 1 2 2 5 6 2 2 0 0 0 0 0 2 nd nd nd nd 24 2 3 3.6 4 2 2 2 6 4 2 2 nd 0* nd 0 1 2 2 nd nd nd nd nd = no data available *Data recorded during corresponding time periods by Dr. Robert Wingett, Center for Health and Environmental Studies, Brigham Vonng University. Table -32. Physical and chemical data from Huntington Canyon. Phosphate (mg/1) Site 6/8 6/29 8/20 12/17 1/20 2/19 .3/11 1971 1971 1971 1971 1972 1972 1972 Lawrence 1.43 .10 .24 .16 .72 ..30 .15 Highwav 10 nd nd .31 .06 .20 ..32 .15 Plant Site nd .15 .07 .08 .18 .22 .11 Campgrotuid 4.0 ..35 ..57 .07 .04 .13 .05 Tie Fork 7..5 nd nd nd nd nd .15 Stuart Station 1.31 .25 .04 .02 .04 .18 .03 Bear Canyon nd nd .08 nd nd nd nd nd = n- of river algae. Bot. Rev., 22(5):291-341. . 1957. An ecological study of the Saline River. Michigan. Hydrobiologia, 9:361-408. Bbinley, F. J. 1950. Plankton populations of certain lakes and streams in the Rocky Mountain National Park, Colorado. Ohio Jour. Sci., 50:243-250. Butcher, R. W. 1932. Studies in the ecology of rivers: W. The microflora of rivers, with special reference to the algae of the riverbed. Ann. Bot., 46:813-861. Chatvvin, S. L. 1956. The vertical distribution of phytoplankton of Deer Creek Reservoir, Wasatch Col, Utah. M.A. Thesis, Univ. of Utah, Salt Lake City, Utah. Clark, W. J. 1958. 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Salt Lake City. McConnell, William J. and W. F. Sigler. 1959. Chlorophyll and productivity in a mountain river. Limnol, and Ocean.. 4:335-351. Miller. Ga\NT L. 1959. An investigation of pollu- tion in the Price River, Carbon Countv. Utah. M.S. Thesis. Univ. of Utah, Salt Lake City. Newcombe. Curtis L. 1949. Attachment materials in relation to water productivity. Trans. Amer. Microscop. Soc. 64(4) : 355-361. Norrington, Annie. 1925. Phycological study of the Wasatch and Uinta ranges in Utah. Ph.D. Thesis. Univ. of Chicago, Chicago. Odum, H. T. 1957. Trophic structure and productiv- ity of Silver Springs, Florida. Ecol. Monogr., 27: 55-112. Biological Series, Vol. 18, No. 2 Algae of Huntington Canyon, Utah 87 Palmer. Mervin C. 1961. AJgae in rivers of the United States. In Algae and metropolitan wastes. Trans. 1960 Seminar. R.A. Taft San. Eng. Ctr., Cincinnati, Ohio, Tech. Rpt. W61-3:34-38. Palmer, Mervin C. and T. E. Maloney. 1954. A new counting slide for nannoplankton. Amer. Soc. 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Murphy BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 3 JUNE 1973/ISSN 0068-1024 BRIGHAM YOUNG UNIVERSITY SCIENCE BULLETIN BIOLOGICAL SERIES Editor: Stanley L. Welsh, Department of Botany, Brigham Young University, Provo, Utah Acting Editor: Vernon J. Tipton, Zoology Members of the Editorial Board: Ferron L. Andersen, Zoology Joseph R. Murdock, Botany WiLMER W. Tanner, Zoology Ex officio Members: A. Lester Allen, Dean, College of Biological and Agricultural Sciences Ernest L. Olson, Director, Brigham Young University Press The Brigham Young University Science Bulletin, Biological Series, publishes acceptable papers, particularly large manuscripts, on all phases of biology. Separate numbers and back volumes can be purchased from University Press Marketing, Brigham Young University, Provo, Utah 84602. All remittances should be made payable to Brigham Young University. Orders and materials for library exchange should be directed to the Division of Gifts and Exchange, Brigham Young University Library, Provo, Utah 84602. I Brigham Young University Science Bulletin BREEDING ECOLOGY OF RAPTORS IN THE EASTERN GREAT BASIN OF UTAH by Dwight G. Smith and Joseph R. Murphy BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 3 JUNE 1973/ISSN 0068-1024 TABLE (W CONTENTS ABSTRACT 1 INTRODUCTION 1 REVIEW OF LITERATURE 2 STUDY AREA 3 Location and Topography 3 Climate 3 Vegetation 3 Faunal Elements 5 Human Utilization 5 METHODS 6 RESULTS 7 Basic Population Data 7 Population Composition and Density 7 Seasonal Activity Timetables 9 Nest Site Requirements 13 Productivity 23 Territoriality 29 Hunting Activity Patterns and Habitat 43 Predation 45 DISCUSSION AND CONCLUSIONS 54 Populations 54 Nest Site 55 Productivity 58 Territoriality 62 Predation 64 The Ferruginous Hawk 67 The Long-eared Owl 68 Effect of the Investigator 69 SUMMARY 70 ACKNOWLEDGMENTS 71 APPENDIX — WEIGHTS OF PREY SPECIES USED LN THE BIOMASS CALCULATIONS 71 LITERATURE CITED 72 BREEDING ECOLOGY OF RAPTORS IN THE EASTERN GREAT BASIN OF UTAH by Dwight G. Smith' and Joseph R. Murphy- ABSTRACT A comparative study of the breeding ecology of 12 raptor species was conducted in the east- em Great Basin from 1967-1970. The project was designed to deteiTnine the composition and densities, habitat selection, territoriahty and predatory habits of raptorial birds in a semi- arid en\iromnent. All topics were analyzed com- parativeh', relating the requirements and activi- ties of the 12 raptor species. Average vearly population densities of all species approximated 0.5 pairs per square mile, but much of the available habitat was not util- ized. Predominant raptors were the Ferruginous Hawk and Great Horned Owl. Other important raptors included the Golden Eagle, Red-tailed Ha\\'k and Raven. The breeding activities of the collective rap- tor populations occurred over a period of eight months. Great Homed Owls and Golden Eagles \\ere the first raptors to initiate nesting activi- ties, usually in late January and early February. The raptor breeding season tenninated with the fledging of the young Cooper's Hawks and Bur- rowing Owls in late August. The fecundity of the raptor populations varied between years. Specific causes of mortal- ity of eggs and voung included nest desertion and destruction, predation, apparent egg infer- tility, and accidents, most of which could be directly attributed to some fonn of human inter- ference. The observed home ranges of the raptor species were a function of their body size and breeding status. The food of the raptors included at least 55 different prev species, but most relied heavily on only one or two species. A correlation be- tween raptor size and mean prey weight was evident. No examples of raptor predation on game or domestic livestock were found. INTRODUCTION Raptorial birds generally occupy the top levels of their food webs and as such exert considerable influence on local mammal and avian prev populations. Shelford ( 1963) classifies them as major permeant influents and sug- gests that the raptor populations of the Great Basin desert fulfill roles equivalent to such inannnalian predators as the bobcat ( Li/nx Tufiis), coyote (Canis latram). kit fox (Vtilpes uiacrotis), and badger {Taxklca taxtis). Their declining numbers and economic relationships warrant additional interest, and studies of total raptor populations are needed as a means by wliich we ma\' elucidate their responses to changing pressures and environmental condi- tions. Although their large size and predatory habits render them conspicuous, their extensive territorial recjuirements present difficulties to raptor ecologists desiring to obtain data on rep- resentative populations. Hence, there have been few previous attempts to study collective rap- tor populations in detail. The objective of this study is tc; provide quantitative data on the breeding ecology of central Utah raptors. Aspects of the study which are emphasized include raptor populations and their distribution, yearly productivit)', territo- riality, and predation. All topics are treated comparatively, relating the requirements and ac- tivities of the 12 raptor species. The species studied include four buteonids, the Golden Eagle (Aqtiila chrysaetos), Red-tailed Hawk (Buteo jnmaicensis) , Fernaginous Hawk (Buteo recalls), and Swainson's Hawk (Buteo swain- 'I)ep.trtnipnt nt Biology. Sonlliciii Coniiciticiil Slalo ('oIIckc New Iliivon. < oiinot lu ill Oft'jl') -DepiTrtlilcnl of Zoology. lirit'.Ii.im Voiiii^ t,^iivci\ily. I'rovii. lll.ili 84()0i HiuciiAM VouNc University Sf:iENCE Bulletin sonii); two falcons, tlic Prairit> Falcon (Falco incxicantis) , and Sparrow Hawk (Falco spar- vcrius); three owls, the Great Horned Owl (Bubo virginkiniis). Short-eared Owl (Asia fltiiniiicus), and Burrowing Owl [Speotyto cuni- ciihiria); the Marsh Hawk (Cirnis cijaneus), Cooper's Hawk {Accipiter coopcrii), and Raven (Corviis corax). REVIEW OF LITERATURE netaili'd studies on eiilleeti\e raptor popula- tions in North America have been conducted ill Michigan and W\i»ming (Craighead and Craighead, 1956), the' Alaskan tundra ( Pitelka, Toni'ich and Treichel, 1955a, 19551)), and the Tule Lake region of northern California (Dixon and Bond, 1937; Bond, 1939). In other popula- tion studies Mathisen and Mathisen (1968) ex- plored tin- species and seasonal abundance of raptors in Nebraska, and Baunigartner and Bauingartner (1944) examined the food habits and population fluctuations of hawks and owls in Oklahoma. Recenth' Hicke\' ( 1969) has sum- marized much information on the general status and broad trends of cuiTcnt raptor populations, but his work centers around the Peregrine Fal- c(.n (Fiiico peregrinufi) . Other comparative studies have dealt with the ecology of Great I'orned Owls and Rcd-tailcd Hawks. The more informative of these have been conducted in Wisconsin (Orians and Kuhlman, 1956), New York (Hagar, 1957), and Minni'sota (LeDuc, 1970). Brown (1966, 1970) has provided much inlormation on African raptor populations, par- tieularlv with respect to their niclu' allocation. Other associative studies have focused on a ]-)articular aspect of raptor ecology, most coni- niDiih predation. Specific comparative food habits studies on hawks and owls have been con- ducted bv Fisher (1895), Errington (1932c, 1933), Mendall (1944), and Craighead and Craighead (1956); on hawks by McAtce (1935), Errington and Breckinridge (1938), Hamerstrom ;iii(l Ilamcistroin ( 1951), and Storer (1966); and on owls bv Cahn and Kemp (1930), Wilson (1938), Fitch (1947). Kirkpatrick and Conway (1947), Pear.son and Pearson (1947), Marti (1969a), and Earhait and Johnson (1970). Life history studies of most of the raptors have been conducted in a varietN' of habitats, and many of them have been summarized in the works of Rent (1937, 19.38) and Brown and Amadon (1968). The following arc among the more noteworthv of a large amount of published literature on various phases of the nesting ecol- ogy of the raptors studied in this report, to- gether with the rcjgions in which they were studied: Golden Eagle. C-'ameron (1905), McGahan (1967, 1968), Montana; Finley (1906), Dixon (19.37), Carnie (1954), California; Arnold (1954), North America; Wellein and Ray (1964), Boeker and Ray (1971), Rocky Moun- tains; Sandeman (1957), Watson (1957), Brown and Watson (1964), Lockic (1964), Brown (1969), Scotland. Great Homed Old. Dixon (1914), Fitch (1940), California; Errington (19.32b, 1938), Iowa; Swenk (1937), Missouri Vallev; Baum- gartner (1938, 1939), Iowa and New York; Er- rington, Hamerstrom and Hamerstrom ( 1940), north central United States; Houston (1971), Saskatchewan. Ferruginous Hank. Cameron (1914), Mon- tana; Bowles and Decker (1931), Angell (1968), Washington; Salt (19.39), Canada. Red-tailed Hawk. English (1934), Michigan; Fitch, Swenson and Tillotson (1946). California; Austing (1964), North America; Luttich, et al., (1970), Luttich, Keith and Stephenson (1971), Canada; Scidensticker (1970), Montana. Swainson's Hawk. Cameron (1908, 1913), Montana; Bowles and Decker (1934), Wash- ington. Prairie Falcon. Decker and Bowles (19.30), Washington; Fowler (1931), California; Bailey and Niedraeh (1933). Webster (1944), Ender- son (1964), Colorado; Edwards (1968), Alberta. Marsh Hawk. Breckinridge (1935), Minne- sota; Errington and Breckinridge (1936), north- central United States; Hammond and Henry (1949), North D;ikota; Hamerstrom (1969), Wisconsin. i Cooper'.s Hawk. McDowell (1941), Schrivcr (1969), Pennsylvania; Meng (1959), New York and Pennsylvania. S})arrow Hawk. Sherman (1913), Iowa; i Rocst (1957), Oregon; Endcrs(m (1960), II- ' linois; Heintzelman (1964), Heintzelman and Nagv (1968), Pennsylvania; Wilkmghbv and Cade (1964), New York. Short-eared Owl. Kitchin (1919), Washing- ton; Sinder and Hope (19.38), Toronto; Lockic BiOLor.iCAi, Sf.hies, \'ol. 18, No. 3 BuEEniNC. Ecology of Utah Raptohs (1955), Scotland; Johnson (1956), California; BorrtTO (1962), Colombia; Short and Drcw- (1962), Michigan; Munyer (1966), Illinois. BurroiL'ing Old. Rhoades (1892), Florida; Errington and Bennett (1935), Scott (1940), Iowa; Grant (1965), Minnesota; Coulombc (1971). Thomsen (1971), California. Raven. Oberholser (1918), North America; Harlow (1922), Pennsylvania; Bowles and Decker (1930), Washington; Nelson (1934), Oregon; Cushing (1941), California; Parslow (1967), Holyoak and Ratcliffe (1968), Great Britain and Ireland; Ratcliffe (1962), England. Literature pertaining to raptors of the Great Basin includes egg-collecting notes (Wolf, 1928); population studies of wintering eagles (Edwards, 1969); nesting studies of the Golden Eagle, Great Horned Owl, and Ferruginous Hawk (Murphy, et al., 1969); raptor population trends ( White, 1969a ) ; and notes on interactions between Red-tailed Hawks and Great Homed Owls (Smith, 1970). STUDY AREA Location and Topography This study was conducted in an 80-square- niile section of the eastern edge of the Great Basin Desert in north central Utah. It included parts of Utah and Tooele Counties, in Town- ships 7 and 8 South, Range 3 West, Salt Lake base and Meridian (Fig. 1). The area chosen is a representative portion of the habitat of this part of the Great Basin. Its coverage is thought to be sufficient to enable the compila- tion of an accurate record of the raptor species populations. The topography is characterized bv broad, flat, alkaline valle\s separated b\- high ridges and hills. Its major ph\siographic featines, from east to west, include Cedar Valley, the Thorpe and Topliff Hills of the Tintic Range, and Rush Valley. Valley elevations range from 4800 ft in Cedar Valley to 5300 ft in Rush Valle\ . Maxi- mum elevations were 6190 ft in the Thorpe Hills and 6453 ft in the Topliff Hills. A major feature of the hills was tht- numer- ous sandstone and limestone cliffs and rock outcroppings resulting from the erosion of a series of Paleozoic strata ranging in age from the Lower Cambrian to Upper Pennsylvanian (Bullock, 1959; Bissell, et al., 1959) (Fig. 2). A second striking feature of the hills is the pres- ence of several large quarries, originally mined for clay, calcite, or limestone, but long since abandoned. These cjuarries are characterized by steep, sheer walls occasionalK' reaching over 200 feet in height. Climate The general climatic conditions of this por- tion of the Great Basin have been characterizi'd by Fautin (1946) and Shelford (1963). The mean annual precipitation is 16 inches at the extreme northern edge of the study area and 12 inches over the majority of the rest of the area. Slight local variations occur, with the high- er elevations receiving larger amounts ( Feltis, 1967). Although the area receives some snow- fall, most of the moisture falls from March through May and July through August. Ex- posure particularly alters the pattern with re- spect to snowfall accumulation and persistence, and north facing slopes may have from 3 to 12 inches of snow for over a month after southern exposures are bare. Approximate annual temperatures range from -30°C to 65°C. Wide seasonal and daily varia- tions occur, amounting to as much as 30°C or more during the summer months. July is the hottest month of the year, averaging 23°C. Sub- zero temperatures can be expected for short periods from December through mid-March. High winds are a common feature of the early spring months and rnay result in locally heavy dust stonns. These become less severe but may persist throughout all months of the year. Water flow is ephemeral and no permanent streams, seeps, ponds, or impoundments are present within the study area. Vegetation Two distinct vegetational associations occur, the northern desert shrub and the dwarf conifer communit\-. The desert shrub community is present over lower elevations of most of the valley floors and consists of various shrubs and grasses (Fig. 3). Several of these, becoming lo- cally dominant and fonning large, continuous stands, include, in order of their importance, l)ig sagebrush (Artemisia tridentata ), rabbit- i)rush (Cliri/sothamnu.s nau.scosu.s) , shadscale (Alriplex confeitifolia). i^reast'wood {Sarcoha- ttis vermiculatus) , winterfat (Eurotia hiiuita), HiuciiAM Voi'SG Univeivsity Science Bulletin Fig. 1. Location, topograpliv .iiul wgetation of flic shulv area. Hi(n.(H;K:\i. Skhiks. Vol. 18, No. 3 Bueedinc Kcologv ok Utah IIaptoivs ;l#^- Fig. 2. \i(\\ of a portion of the Thorpe Hills, showing tho> nnmeroiis anil the seattered nature of the Pinyon-Juniper community. limestone and sandstone cliff lines Russian thistle (Salsola kali) ami hoisobriisli {Tctnuhjmia ghibnita). Both Indian liccgiass (On/zopsis hijmenoides) and cheat gias.s {Bro- mus tectorum) arc present throughout most of the shrub stages, with the latter apparently in- creasing its coverage ( Christensen and Hutchin- son. 1965). The better drained slopes and hills support the pigm^' conifer forest or woodland biome (Kendeigh, 1961 j. Tiiis is characterized by the uniform physiognomy of its principal species, the two most important being Utah juniper {Juni- pertis osteospcrma) and pinyon pine (Pimi.i mdnoplu/Ua). The trees average approximately 10-1.3 ft in height and occur in stands varying in densit\- from 10 to 100 trees per acre ( Smith, 1968). Important shrubs of the underston' in- clude matchweed (Gutierrczia sarothrac) and Ephedra {Ephedra sp. ). Other components pres- ent in lesser amounts include cliffrose (Cowania mcxicana) and mountain mahogany (Cercocar- ptts ledif alius). Faunal Elements Fautin (1946) listed a total of i286 animals known to occur in the northern desert shrub communit\', including 28 mammals, 45 birds (exchisi\'e of the raptors and aquatic species), 10 reptiles and 203 insects. Most of these also occur within the pinvon-juniper community which to dat(^ has recei\ed no in-depth study in this area. Hardy ( 1945 ) did record 79 bird species of the pigmy conifers and noted that 14 species were summer residents. The major mammalian herbivores include the mule deer (Odocoilciis hemiomts), black-tailed jackrabbit (Lepus califoruicus), Townsend's ground squiiTcl {Spermo])hilus townsendi), an- telope ground squirrel [Ammospermophilus leucunis), desert cottontail {Sylvilagus audu- houi), and desert wood rat {Dipodomys sp. ), pocket mouse (Perognathus sp.), and several miuids and cricetids. Carnivores other than rap- tors include the mountain lion (Felts concolor), coyote (Canis latrans), kit fox (Vulpes macro- tis), bobcat {Lynx mfiis), and badger {Taxidea taxus). Two of the more common summer bird species include the Honied Lark {Eremophila al- f)cstris) and Mourning Dove {Zenaidura ma- croura). Common reptile species include the gopher snake {Pituophis melanoleucus), striped racer {Coluber taeniatus), collared lizard (Crotaphytus collaris), and Uinta lizard {Uta stamburiana) . Human Utilization Two small settlements are present immedi- ately northeast of the study area and portions of the adjacent land are dry-fanned, but the most important human activities include livestock raising and hunting. Most of the valleys and lower elevations are seasonally utilized for sheep HiuciiAM VouNG Univeksity Science Bulletin range and are heavily overgrazed. In addition, the direct infkicncc of Hvestock interests has resulted in the initiation of predator control programs and govennnent trappers periodically remove coyotes, bobcats, and kit foxes. Recreational hunting activities assume major proportions. Almost all parts of the area are accessible by graded dirt roads, and large num- bers of deer hunters in season and rabbit hunters throughout the year utiUze the area for sport. ii'-?«'»gT;s.'«.: Fig. .3. Sagebrush ami IniiR-hgrass comiiiuiiit\ iif Cedar X'allev. METHODS The stud\' was conducted from December 1966 until August 1970. Most of the field work took placi' duiing the four breeding seasons but observations were recorded during every month of the year. Intensive field work began in De- cember of each \ ear and continued through August. During this time at least weekK' or bi- weekly \isits were made, but often the observa- tion periods were more frequent. Throughout the four breeding seasons the longest interval of time between successive visits was 13 days in April 1970, Field data cards were designed and printed, and copies of that portion of the study area mapped by the U,S. Geological .Survey were Xeroxed. All observations on raptor nests, ac- tivities, and locations were recorded on them and supplemt^nted by tape recorded notes. The major task of the observer during each breeding season involved the location of all raptor nests. These were found by systematically searching all potential nest sites; that is, all cliff lines, rock outcioppings, and wooded areas were methodicalh' examined. Discovered nests were plotted on an area survey map, then gaps in the distribution wen- intensively reexamined lor missed nests or signs of raptor activit\' sev- eral times dmintr the breedini: season. Addi- tional techniques were employed to discover nests; these included observations of behavioral patterns (particularK displays and tiTritorial postures), the mapping of old nests, and the utilization of a fixed wing monoplane for aerial surve\s. The latter proved to be of limited use, due prinuuilv to its miniminn speed and altitude re(|nirenu'nts, but was useful in checking the oc- cupane\' of nests of the previous years. Instances in which apparently nonnesting pairs or individuals were occupying an area necessitated numerous additional and time-con- Biological Stints, \ol. 18, \i BiittDJNc; Ecology of Utah Haitous suming checks to ensure the accuracy of their status. Apparent transients required similar ef- forts. Certain raptor species required proportion- all\' greater efforts than others in locating their nests. This proved to be particularly true of the Great Homed Owl and Short-cared Owl. Their secluded nest sites and nocturnal habits re- quired several earlv morning and late evening visits in an effort to locate hooting males. Baum- gartner (1939) and Errington (1932b) employed this method successfully in other habitats, but the extreme ruggedness of most of the study area terrain allowed only partial success. How- ever, both owl species were observed occasion- ally during these two time periods, particularly on overcast davs or on rainy or snowv days. In contrast, Burrouing Owls were easily located because of their great diurnal activit\', more ac- cessible nesting sites, and the habit of one or both of the adults of roosting atop or alongside the burrow. Onl\ t\\'o of the diurnal raptors, the Marsh Hawk and Sparrow Hawk, presented problems with respect to the location of their nests. Both species are conspicuous during their daily acti\'ities but verv secretive relative to the actual location of their nests. These were most easily found by continuous observation of the adult pairs, one of which would eventually re- turn to the nest site. Three of the Marsh Hawk nests were found only after the increased de- velopment of the \oung had rendered their loca- tion conspicuous. The tendencN' of raptors to reoccupy their nest sites and territories (to be discussed in detail later) greatly facilitated the task of lo- cating nests during the last three years of study. Data used to compute the raptor activity timetables is based primariK' on the more readily accessible nests. In addition, the necessary time period between field observation days promotes a possible time error of two days. Tlie presence of the investigators may have accelerated some events in the nesting cycle, with the fledging period being particularly vulnerable to change. Raptor territories and food habits were de- termined during the nesting seasons of 1969 and 1970. Territories were plotted by observations of pair activities from blinds and by plotting sight locations. The points of maximum distance from the nest site were then connected and the encompassed area determined with a compen- sating polar planimeter. The determined terri- tory has been described as maximum territory (Odum and Kunezler, 1955) or home range (Craighead and Craighead, 1956). Food habits of all raptors were determined by weekly tabu- lations of prey items and analyses of pellets gathered from the nest site. Again the more ac- cessible nests were checked most frequently. After the prey had been identified and counted it was removed from the nest. An exception was to leave fresh prey for the young, after marking it for identification. Pellet contents were identi- fied by comparison with specimens of the Brig- ham Young University Life Sciences Museum collection, following techniques described by Errington (1930, 1932a), Glading, Tillotson and Sellech (1943), and Moon (1949). Dr. V. A. Nelson, entomologist. Southern Connecticut State College, New Haven, Connecticut, assisted in the identification of some insect remains. All statistical analyses followed programs for the Epic Model .3000 computer except regres- sion, which was determined using Fortran pro- grams. Numerical data within the text is normal- ly presented as mean data, followed by the stan- dard error, sample number, and range. The "t" test, anah'sis of variance and chi-square tests were used to compare data, and linear regression analysis was used to test the significance of correlated variables. The level of significance is 0.05 unless otherwise noted. All analytical meth- ods are discussed by Goldstein ( 1964 ) and Simpson, Roe, and Lewontin ( 1960 ) . RESULTS Basic Population Data The study area supported a total of .354 in- dividuals of 12 raptor species during the four years of study. This included 141 nesting pairs, 20 nonnesting pairs and 32 individuals. The species breakdown was as follows: Golden Eagle, 17 pairs; Great Homed Owl, 31; Fer- ruginous Hawk, 40; Red-tailed Hawk, 26; Swain- son's Hawk, 5; Prairie Falcon, 3; Marsh Hawk, 5; Cooper's Hawk, I; Sparrow Hawk, 10; Short- eared Owl, 1; Burrowing Owl, 6; Raven, 16. Population Composition and Density Annual species populations are presented in Tables \-4. Both the total nesting population and the number of nesting species varied from year to year. The collective raptor population consisted of 8 species in 1967 and 1968, 9 in 8 Biuf:ii,\M VouNC I'nivehs nv S(:ii-.N( K Bulletin Table 1 . Summarv of raptor nesting populations. 1967. No. No. of No. No. No. re- No. successful No. of nests No. sq. Species of nesting single nesting nesting nesting incomplete miles per pairs pairs birds failures attempts attempts histories pair Golden Eagle 4 3 1 1 0 _ 0 20 Great Horned Owl 5 4 1 0 - - 0 16 Ferniijinous Hawk 8 8 2 3 0 - 0 10 Red-tailed Hawk 5 4 0 0 0 - 0 16 Swainson's Hawk 1 1 0 0 - - 0 80 Prairie Kalcon 0 - 1 - - - - - Marsh Hawk 0 _ 1 _ _ _ _ _ Cooper's Hawk 1 1 0 ? ? - 1 80 Sparrow Hawk 4 3 1 1 0 _ 1 20 S lort-eared Owl 0 _ 2 _ _ _ _ _ Burrowing Owl 0 - 1 - - - - _ Raven 4 4 0 0 - - 0 20 Totals 32 28 10 5 0 - 2 - Table 2. Summary of raptor nesting populati ons, 1968. No. No. of No. No. No. re- No. successful No. of nests No. sq. Species of nesting single nesting nesting lencsting incomplete miles per pairs pairs birds failures attempts .lUeiupts histories pair Golden Eagle 4 4 2 0 0 0 20 Great Horned Owl 10 9 5 0 0 2 8 Ferruginous Hawk 10 9 2 0 0 0 8 Red-tailed Hawk i 7 3 2 1 1 11 Swainson's Hawk 1 1 0 - 0 0 80 Prairie Falcon 1 1 1 0 0 0 80 Marsh Hawk 0 - - - _ - - Cooper's Hawk 0 - - - - - - Sparrow Hawk 3 3 1 0 0 0 27 S lort-earcd Owl 0 - - - 0 - - Burrowing Owl 0 - - - - - - Raven 4 4 0 0 - - 0 20 Totals 40 38 6 14 2 1 3 - Table 3. Summary of raptor nesting populations, 1969. Species No. of pairs No. of nesting pairs No. single birds No. nesting failures No. re- No. successful No. of nests No. sq. nesting nesting incomplete miles per attempts attempts histories pair Golden Eagle .54121 Great Horned Owl S 8 1 2 0 Ferruginous Hawk 13 12 1 2 0 Bed-tailed Hawk 7 6 12 1 Swainson's Hawk 2 2 12 0 Piairic I'aleon 0 - 1 — - Marsh Hawk 2 2 0 10 (.'ooper's Hawk 0 - 0 - - Sparrow Hawk 2 2 2 10 Short-eared Owl 0 - 1 - - Burrowing Owl 3 3 0 10 Raven 4 4 110 Totals 46 43 10 14 2 0 16 10 6 11 40 40 40 27 20 1969, and 11 in 1970. Only 7 of the 12 species nested in all four study \ears. Of the more sporadic nesters, 3, the Prairie Falcon, Marsh Hawk and Burrowing Owl, nested during two of the four years (not necessarily consecutively ) and 2, the Short-eared Owl and Cooper's Hawk, nested in only one of the four \(\irs. .Ml, how- ever, were represented bv either nonnesting pairs or individuals during one or more of their nonbreeding \ears, and are therefore considered to be a minor but nonnal element of the raptor breeding population of this area. The minimum and maximum sizes of the total raptor population varied from 74 to 102 iiidi\icluals and from 32 to 46 pairs. Individuals coiniiioiiK comprised from 9 to 13 percent of Bioi.or.icAi, SiiiiiEs, Vol. IS, No. .3 Hui i dino Ecology ok I'nii H.^i'tou.s Table 4. Summary of raptor nesting populations, 1970. No. No. of No, No. No. re- No. successful No. of nests No. sq. Specie.s of nesting single nesting nesting nesting incomplete miles per pairs pairs birds failures attempts attempts histories pair Golden Eagle 4 3 0 0 _ _ 0 20 Crt-at Horned Owl 8 6 19 3 1 1 0 10 Kemiginous Hawk 9 y 2 2 0 - 0 9 Ked-lailed Hawk ( 4 0 1 0 (1 0 11 SwainsDiis Hawk 1 1 1 0 - - 0 80 Prairiu Falcon 2 2 0 1 0 - 0 40 Marsh Hawk 3 2 1 1 1 0 1 27 Cooper's Hawk 0 - 1 - - - - - Sparrow Hawk 1 1 1 0 - - - 80 Short-eared Owl 1 1 0 1 0 - 0 80 Burrowing Owl .3 3 0 1 0 _ 0 27 Raven 4 ■-) 0 0 - - 0 20 Totals 43 32 24 10 2 1 1 - the total population. Raptor populations in- creased from 1967 (32 pairs, 10 individuals) to 1969 (46 pairs, 10 individuals) and then de- clined slightly in 1970 (43 pairs, 6 individuals). The peak number of nesting raptor species did not coincide with the peak raptor populations but rather occurred one year later. The yearly variation in populations was due in part to some shifting of raptor nesting sites onto the study area from previous nesting sites and territories immediatelv adjacent to the study area. Other possible reasons will be discussed later. Five species, the Golden Eagle, Great Horned Owl, Ferruginous Hawk, Red-tailed Hawk and Raven comprised over 81 percent of the average vearlv raptor populations. Of these, the Fernigi- nous Hawk was consistently the numerically dominant raptor, averaging approximatel\' 25 percent of the annual breeding population. The next most numerous species were, in order of their abundance, the Great Homed Owl (which approximated over 19 percent). Red-tailed Hawk, Golden Eagle, and Raven. Of the re- maining raptors. Sparrow Hawks were almost twice as abundant as Swainson's Hawks, Marsh Hawks, and Burrowing Owls, while the Cooper's Hawk and Short-eared Owl were relatively rare breeding elements. Although a conspicuous pemianent resident, the Prairie Falcon rarely achieved breeding status and comprised less than t\\'0 percent of the average yearly breed- ing population. The relative percent composition of the large raptors varied only slightly and each species maintained its proportional abun- dance during the four study years. Thus the population increase from 1967 to 1969 reflected a similar increase in the number of pairs of each, with the notable exception of the Raven population, whicli remained stal)le. The limited populations of the smaller raptors prevent clear- cut evaluations. Both the Marsh Hawk and Bur- rowing Owl populations became established dur- ing the last two study years, but the Sparrow Hawk population declined. Yearly population densities averaged 0.5 pairs per square mile (range 0.4-0.58), based on the 80-square-mile study area. However, approxi- mately one-half of the area was apparently not utilized for any purposes by the nesting rap- tors. This was particularly true of the lower \'alley elevations which were situated far from potential nesting sites. If this area were elimi- nated from the determinations, then the raptor nesting densities would be increased to 1.0 pairs per square mile (range 0.8-1.16). Seasonal Activity Timetables Winter Populations. Central Utah supports a large and varied winter raptor population. Im- portant permanent year-round residents winter- ing in the area include Golden Eagles, Ravens, Great Homed Owls, and Prairie Falcons. Gold- en Eagles and Ravens occur singly or in small groups of two to five individuals. Some Golden Eagles may form hunting contacts and share communal roosts with Bald Eagles {Haliaetus leucocephahis). Estimated average yearly win- ter populations of each were 13 Golden Eagles and 9 Ravens. In contrast. Great Horned Owls and Prairie Falcons were less common. A few Great Homed Owls were flushed in the vicinity of their nesting site of the previous year and a single Prairie Falcon was obsei-ved every year, occupying a large winter territory in Cedar Val- ley. It was occasionally obser\'ed hunting among flocks of Homed Larks and Dickcissels (Spiza americana). Large influxes of Bald Eagles and Rough- legged Hawks {Buteo lagopus) began arriving in the valleys in late November and December. These conspicuous winter residents rosted com- 10 Biur.iiAM YouNC Uni\ i-.nsirv Scmknc:!-. Bi'i.i.etin munallv in canyons and lightlv wooded areas near settlements. Dnriiig the daylight hours the\' ranged widely to hunt in the \allevs, returning to a communal roost shortly before dark ( Ed- wards, 1969). Estimated populations of each in the study area were 30 Bald Eagles and 18 Rough-legged Hawks. Winter live trapping studies revealed 5 Long- eared Owls ( Asio ottis ) , and a number of Short- eared Owls. The latter were frequently observed (up to 8 individuals per group) ranging out- ward from their diurnal communal roosting sites during the late evening hours. An average of 25 Marsh Hawks, 2 Shai^p- shinned Hawks (Acripitcr striatus), 3 Red-tailed Hawks, 1 Ferruginous Hawk, and 1 Screech Owl (Ottis asio) were present in the \'alleys during the winter months. The Marsh Hawk popula- tions indicated a major influx of this species into the area during the winter, but the status of the wintering Red-tailed Hawks and Ferruginous Hawks was uncertain. Two of tlie Red-tailed Hawks wintered in the yieinit\' of a previously used Red-tailed I lawk nesting site and ma\ have been permanent residents. The populations of these winter residents fluctuated and appeared to be related to climatic changes, particularly temperature. Their num- bers declined sharply in late JanuaiT and earl\' February, and they left the area by mid-March, a transition coinciding with the arrival and rapid buildup of the breeding populations. Transients. Known transients, including Red- tailed, Swainson's, and Cooper's Hawks were ob- served from late Februan" to carK' Maw Large numbers of transient Sparrow Hawks were ob- served between early April and mid-Ma\-, simul- taneously with the arri\al of tlie breetliiiu population of Sparrow Hawks. A single Osprev {Pdiuliiin liali(ictus) was observed roosting in a dead cottonwood in Cedar Valley on 29 April in the late e\-ening and presumabh' roosted overnight. The niajorit\' of the transients re- mained onK one or two da\s in the area, par- ticularh' those observed later in the breeding season. Activitij timetables. The \cdv\v aeti\'it\- tiTne- tables of the raptor populations are presented in Tables .5-8. The breeding activities of the populations occurred over a period of eight months and avi'raged 202.7 da\s a year (range 163-22S da\s). Ho\\e\er. the in(li\idual species activities occupied only a portion of this period. .\lthough slight yearly variations in the timing and duration of the events of the nesting c\cle were evident, the chronological sequene(> of each raptor species reniaincxl essentialh un- changed with respect to the total raptor popu- lations. Golden Eagles and Great Horned Owls were the first raptors to initiate their nesting activity. Golden Eagles were observed occupying their territories as early as 20 Januars', and courtship displa\s were observed from this time onward. Their nests were constnicted or rebuilt in Febru- ary and early March and decorated with green- ery. A Great Horned Owl was recorded on its nest site of the previous year on 2 December and pair fonnation had occurred as early as 10 January in some years. Average egg deposition dates for both species ranged from mid-February to earl\' March, with Golden Eagles generally preceding Great Honied Owls b\- one or two weeks. Red-tailed and Fenaiginous Hawks were the first of the migrator\- raptors to arri\'e in the study area each year. The first Red-tailed Hawks were observed in the vicinit\' of previous nesting sites during the first week in Febniar)' and were paired within one or two weeks, .^t this time pairs would react aggressively when the nest site was approached, screaming and soaring in increasingly higher circles overhead. Onl\' three pairs were observed constructing nests, but the process was a mutual activit\', with both mem- bers of a pair transporting juniper branches to the nest site. Eggs were usually deposited in late March and earlv April. Tlu' first Ferrugi- nous Hawks were obsened from two to five weeks later, usually during the first week in March but as earl\ as 25 February. Eggs were usualK deposited in mid-.\pril. As with Red- tailed Hawks, nests were constructed rapidly In- both members of a pair until finished, usual- K within one to three da\s. Both species were higliK secretive during nest eonstniction and if intirrupted would fre(iuentl\' stop building activities and begin another nest at a new site. FiMruginous Hawks exhibited a greater tenden- e\ to abandon newly constructed nests ( 12 oc- eurrenc(\s) than Red-tailed Hawks (5 occur- rences ) . Swainson's Hawks were the last of the Buteos to nest, appearing in the- \alle\s in earlx and inid-.\pril and beginning their nesting between two and three weeks later. Of the medium and small sized raptors, the Ra\-ens were the first to begin nesting, usually from late Februarv- to mid-Mareh. Fairs of Prai- rie Falcons and Marsh Hawks were observed in late March and early April. The Prairie Fal- cons were \er\ aggressive at this time both toward humans and other raptors, particularly (ireat Horned (a\]s. which if flusliefi were at- Biological Stiuii.s, \'ol. KS, \i Biu:i;i)iNo Kcoi.oGV ok Utah IlAnoiw 11 SJ= 'S £.5 o .§2 I ft o « > 00 ^ in ^ •^ CO •— I CO t^ 05 lO CO CO 1— I 00 00 05 t^ Tj< ^H CO O O-l --H Oa >>>!-; t^ t^ t^ CO -H CM (M ^> >> (M CO lO r— I CD >— I >— I >> >> l> 00 M >-l fN I— I l> > > > > t^ > > > > in ■^ _ -H i-H fM O: •— I c-i >> > > > Tf O t> — ( 1— I 1— I t^ 1— I ►^> > > > Z-I AI OI/AI ST/AI OI/AI 8T/III oj c ^ CD pi CO C-l r^ ■£"?,« ~ --. - "^ ^ . in CO CD CD CM O t^ t^ 00 > i-H CD t-H > , >> I I I I c^J 05 CM 1—1 ^-^ t-H > in I— I > CO > o > in T-H > CM t -^^ >> CM in — 1 ^H JO >> ' > CD CM CO'^^^—iOO-HCOOC-^ o '>.■¥ ■^ -¥■ -X ^ O S ^ _ b£ ?: v; W c 2 ^ 'c r- ^ .^y: -r S K a: -^ t^ c ii S t. X M :3 ^ - Cj O > 3 CL, 0/ O CO H lis. o £ 4). 3 aj g 1^1 2 w_S ta N 4! i^ fo -0 > 5"^ 3 <- ^^^ -C ca S £ n c. > CD O ■^ O CM CM CM O] x; CM -H > > t^ in t^ CM in 00 rH > > ^ CO CM t~- in I-H CM >-H m CM CO I-H H-1 1 — 1 1-H I-H I-H > ' > CM > CO CO CM ^ CM T^ CM CM CO ^ in > K > > tt' in CM 00 CO r-H CO >^ I-H ^ 0 •-H Tfi 00 ^ CO t^ fM HH HH "^ : > 05 05 O r-H t-H CO KK >a> ^ in o -* t-H CO CM in CM CO 05 > CM o CM t-H O O CO o O '^ ■y T3 "m Oj c« c 3 « w I-l rr 0 0 0 c X '3) j « ■^ 2 ^ i4 0 u p Ui OOfc. -:/( C 5 5 ^^ f ffiffi §^ ^ ^0 -o -=" -^^KW^ f^ffi.-= > !3 0^ fe S « <^ S :s ^ e- 1: t; 12 Bhic.iiam Vouno Univehsity Science Bulletin lis s i £.5 a. I- u <= to b£ re c 2 S^Si iS-^" O O -^ CO 05 in lo ■— I TTi 00 00 O -< »o o CD O i-l ^H CO ^ O CM CO .—I CO rH CM 05 1— I > > > > ^ in cr> oi a > K>>> 00 05 (N Tf 00 '-< l^ •— I i— I 1—1 in 00 o 00 1^ CO o (M in O ' CO ^ in > > O r-H Tf I-H ,-H "^^ ^ I ^ I-H HH HH > IT- > CM i-H in o > 00 t- o 01 CM t^ o CO in CO t^ (M in rt o (M 00 CO 00 05 r-H t^> 00 OS s 1— I ^ CD .-H I— i" I— i" I— (~ 00 o C t~- CO 00 M CO <* ■— li— ICCt^OO (M ■* ol^ (M fM C-] --I CM ,-H r-( 00 cq 00 O (N r-H 05 t^ 00 r-HCqinCMr-H CO r-H .-H(M ■^ 00 C^I O (M O o "^ c. o ""' r r > r-^ r ^ CO t^ CD CM t^ t-; r > !r' f t- CO -* in CM C-l r-K CO CO *>. HH I — I HH HH "^ "> !r^ C^ > Ti— l(Mi-H(Mr-HCM(M -HCNin'-l >>>>t-'>> tr'!r'r> I Tt< 00 CO CO CO ' -H > > > ■ •--," I— l" I-H I in CM t- I I-H (M p- CO CD 00 I-H CM r-H r-H CO I-H CO O t^ CO Ol CM f^ rH Ol I-H I-H HH HH r^ >^ <*! .r^ t^ t^ CO o ^ CD 05 I— I ^^ '-^ ] -"^ CO t"' t"' !r' I> 00 00 o t> hh (M CO <^ 00 00 o o r-H (M in CO 00 00 O 05 r-H (N CO r-i ►^ HH CM -H CD CM ^ >= cj c tu T* or - b .5 ' -'" "^ u c^^ =5 -^ -ii : fc. CS c;; £. " Biological Sf.hiks. Vol. IS, No. 3 Bkeedino Ecology oi' Ut.mi Uai'toiis 13 tacked, although no actual contacts were ob- served. The 1969 egg deposition dates of the Marsh Hawk were computed, using the results from the 1970 data for this species. Individual Short-eared Owls were observed in the vicinity of their nesting territon' in the first week in March, and activit)' dates computed from the data of Bent (1938) and Craighead and Craig- head ( 1956 ) indicate that egg deposition oc- curred within three weeks. Sparrow Hawks were observed as early as 10 April, perched on conspicuous locations in the vicinity of their future nesting sites. Pair bonding had occurred by 27 April and egg deposition from two to three weeks later. By late April Burrowing Owls were seen roosting beside the entrance to their nest holes and protested vigorously when in- vestigated. Their activity' timetables were com- puted from the date of fledging on the basis of data given by Bent (1938). Only egg dates are available for the Cooper's Hawk, but backdating 31 days (average from Craighead and Craighead, 1956) suggests that in this area their territories are selected by mid- April. The breeding raptor populations were well established by April and Mav, which were the months of ma.\inium activity. By late May and early June nests of the Great Horned Owl were terminated with the fledging of the voung. By the end of June and the first week of July, Red-tailed Hawks, Ferruginous Hawks, Golden Eagles, Ravens, Prairie Falcons, and Marsh Hawks had all completed their nesring activities, and Swainson's Hawks, Burrowdng Owls, and Sparrow Hawks had finished their nesting ef- forts bv late July and earlv August. The newly fledged young of most species remained within the nesting tcnitor\- for a period after fledging and were frequently seen in fam- ily hunting groups. Defense of the young by adults was particularly strong during this time period but gradually lessened. Within three to five weeks the young had drifted out of the nesting area and into other parts of the valley. The migratory species began moving out of the area in late August and early September. Their replacement by the first elements of the wintering population was not as sudden as the spring transition, and the interim raptor popu- lations consisted only of pemianent residents which were consequently comparatively low in number. Nest Site Requirements Spatial Disirihution. Figures 4-7 show the \early distribution of raptor nests (all species) on the study area and clearly indicate that the nests were unevenly distributed. The majority of sites were present at middle and higher ele- vations and consistently distributed along the periphery of the central mountains or within the woodland. Only Burrowing Owl, Marsh Hawk, and Fenuginous Hawk (one nest) nest sites were present in the valleys, below the fringes of the Pinyon-Juniper woodland. Nest Site. The nest site selections of the 12 raptor species are summarized in Table 9. The raptors nesting on the study area utilized a wide variety of sites, but some species exhibited a narrower range of selection than others. Actual sites chosen by one or more species included cliffs, quarries, abandoned mining structures, trees, burrows, or the ground. Almost 35 percent of the nesting sites se- lected were located in cliffs. The choice of cliff sites by five of the raptor species appears to be related to several factors, including the physiog- raphy of the cliff, its vertical height, aspect, position, altitude, and height above the valley floor. Excluding the rock walls of quarries, which are actually artificial structures, the maximum height of cliffs within the study area did not exceed 150 feet, and the great majority averaged less than 50 feet. Two distinct types, sandstone and limestone, are present. Limestone cliffs, because of their distinctive weathering patterns which result in numerous crevices and ledges, provided greater numbers of suitable nesting sites and were heavilv utilized bv the raptors. The position of the cliff refers to its remoteness. Cliff sites which overlooked the valleys were preferred over similar cliffs located in the in- terior of the hills. Sites were frequently chosen in the first large cliff (over 20 feet high) above the valley floor. This was particularly evident in locations where several cliff lines were available at increasingly higher elevations in stairstep fashion. Several abandoned quarries within the study area were utilized for nesting sites by at least six of the raptor species. The amount of use was related to the size and ruggedness of the quarr\- walls and was apparently independent of the amount of human disturbance. The larg- est quarries were utilized simultaneously by two or three raptor species ever\' year. Trees were also a common nesting site (34.6 percent) on the study area. The; majorit)' were located in junipers, the predominant tiees in the area, but a few were constmcted in pinyon, cliffrose, and cottonwood. Nests in jimipers and cliffrose were most frequently constructed in the tops of the trees, approximately 11 feet 14 BiuGiiAM Young University ScitNCE Bulletin 1 2 3 4 5 6 7 8 9 10 11 12 \_J nesting pairs I I non-nesting pairs /\ individuals Golden Eagle Great Horned Owl Ferruginous Hawk Red-tailed Hawk Swainson's Hawk Prairie Falcon Marsh Hawk Cooper's Hawk Sparrow Hawk Short-eared Owl Burrowing Owl Raven Fig. 4. Distribution of the raptor breeding population in 1967. Biological Series, \'ni, 18. No. 3 Bueeding Ecology of Ut..\h H.m'iohs 15 1 Golden Eagle 2 Great Horned Owl 3 Ferruginous Hawk 4 Red-tailed Hawk 5 Swainson's Hawk 6 Prairie Falcon 7 Marsh Hawk 8 Cooper's Hawk 9 Sparrow Hawk 10 Short-eared Owl 11 Burrowing Owl 12 Raven \_) nesting pairs I I non-nesting pairs /\ individuals Fig. 5. Distrihution of the raptor breeding populatinn in 1968. 16 Bnir.HAM Young Univfksity Science Bulletin ® 1 Golden Eagle 2 Great Horned Owl 3 Ferruginous Hawk 4 Red-tailed Hawk 5 Swainson's Hawk 6 Prairie Falcon 7 Marsh Hawk 8 Cooper's Hawk 9 Sparrow Hawk 10 Short-eared Owl 11 Burrowing Owl 12 Raven \^ nesting pairs I I non-nesting pairs /\ individuals Fig. 6. Dislritiiitimi of the raptor breeding population in 1969. Biological Sehils, \'ol. 18, No. Bueedinc Ecology of Utah Uaptoiis 17 r. 1 Golden Eagle 2 Great Horned Owl 3 Ferruginous Hawk 4 Red-tailed Hawk 5 Swainson's Hawk 6 Prairie Falcon 7 Marsh Hawk 8 Cooper's Hawk 9 Sparrow Hawk 10 Short-eared Owl 11 Burrowing Owl 12 Raven \_J nesting pairs I I non-nesting pairs /\ Individuals Fig. 7. Distrihufion of the niptor breeding population in 1970. 18 BiuciiAM YnvNc Un'ivkhsity .St:iEVf:E Bulletin Table 9. Summary of nesting site selections of raptors on the study area, 1967-1970. Quarrv Site' Structure Site Tree Site Pinyon Juniper Cliffrose Cottonwood Species No. % No. % No. •I \n. % No. % No. % Colden Eagle 4 2.8 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 Great Horned Owl 7 5.0 0 0.0 0 0,0 4 2.8 0 0.0 0 0.0 Ferruginous Hawk 0 0.0 0 0.0 0 0.0 24 17.0 1 0.7 0 0.0 Ked-tailed I lawk •2, 1.4 0 0.(1 .! 2.1 7 .5.0 1 0.0 1 0.7 Swainson's Hawk (1 0.0 0 0 0 0 0.0 5 3.5 0 0.0 0 0.0 Prairie Falcon 1 0.7 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 Marsh Hawk 0 0.0 0 0.0 0 0,0 0 0.0 0 0.0 0 0.0 Cooper's Hawk 0 0.0 0 0.0 0 0,0 1 0.7 0 0.0 0 0.0 Sparrow Hawk 5 3.5 2 1.4 0 0.0 O 1.4 0 0.0 0 0.0 Short-eared Owl 0 0.0 0 0.0 0 (1,0 0 0.0 0 0.0 0 0.0 Burrowing Owl 0 0.0 (1 0.0 (1 (1,0 (1 0.0 0 0.0 0 00 Haven 1 0.7 0 DO 0 0,(1 0 0.0 0 0.0 0 0.0 Totals 20 14.1 2 1.4 3 2.1 43 30.4 0 0.7 1 0.7 Ciround Site chlf Site Sagebi ■ush Shadscale Greasewood 5-25 25-75 75-150 Species No % No. % No. % No. % No. 3 No. % Colden Eagle 0 0.0 0 0.0 0 0.0 0 0.0 9 6.4 1 0.7 Great Horned Owl 0 0.0 0 0.0 0 0.0 3 2.1 13 9.2 0 0.0 Ferruginous Hawk s 5.7 3 2.1 0 0.(1 0 0.0 0 0.0 0 0.0 Red-tailed Hawk 0 0.0 0 0.(1 0 0.0 -T 1.4 5 3.5 i 0.7 Swaiiisoo's Hawk 0 0.0 0 0,(1 0 0.(1 0 0.0 0 0.0 0 0.0 Prairie Falcon 0 0.0 0 0.(i 0 0,(1 (1 0.0 0 1.4 0 0.0 Marsh Hawk 2 1.4 2 1.4 0 0.0 0 0.0 0 0.0 0 0.0 Cooper's H;iwk 0 0.0 0 0,0 0 0.0 0 0.0 0 0.0 0 0.0 Sparrow Hawk 0 0.0 (1 0,0 0 0.0 0 0.0 0 0.0 0 0.0 Short-cared Owl 1 0.7 0 0.0 0 (1,(1 0 0.0 0 0.0 0 0.0 Burrowing Owl 0 0.0 1 0.7 5 3.5 0 0.0 0 0.0 0 0.0 Haven 0 0.0 0 0.0 0 0.0 3 2.1 7 5.0 3 2.1 Totals 11 7.8 6 4.2 5 3.5 8 5.6 36 25.5 5 3.5 above ground, which is the average height of the pigmy woodland trees of this area. The majority of the nests had western ex- posures ( 33 percent ) , but 27 percent faced south and 25 percent east, while only 15 percent faced north. Tree nest exposure, determined b}' the inclination of the slope, is included in the above (sec Table 10). With reference to alti- tude, 25 percent of the nests were situated be- tween 48(X)-5200 feet, 63 percent between 5200- .5800 feel and II percent l)et\\een 5800-6400 feet. The data of Table 11 indicate that several of the raptor species exhibited a vertical strati- fication of nesting sites. Nests of the Golden Eagle were built on cliffs, rock outcroppings, and in (|uarries. None were constructed in trees, but ground nests and artificial structures were utilized in areas im- mediatelv adjacent to the stud\' area. Occupied e\ries averaged 5690 ±: 62.0 feet (range 5380- 6170 feet). No apparent exposure preference was exhibited. All pairs maintained from one to I'.ililr 1(1. .Suiniii.irv of exposures of occupiod nests, I9'iT- 1^)7(1. North West South East Species No. % No. % No. % No. % Golden Eagle C»reat Horned Owl Ferruginous Hawk Red-tailed Hawk Swainson's Hawk Prairie Falcon Marsh Hawk Gooper's Hawk Sparrow Ihiwk Short-eared Owl Burrowing Owl Raven Totals 4 1 3 4 0 1 0 0 4 0 0 4 21 2.8 0.7 2.1 2.8 0.0 0.7 0.0 0.0 2.8 0.0 0.0 2.8 14.7 4 15 10 6 0 2 0 1 1 0 0 8 47 2.8 106 7.1 4.3 0.0 1.1 0.0 0.7 0.7 0.0 0.0 5.7 33.3 3 8 15 6 1 0 0 0 3 0 0 2 38 2.1 .5.7 10.6 4.3 0.7 0.0 0.0 0.0 2.1 0.0 0.0 1.4 26.9 3 2.1 3 2.1 8 5.7 5 3.5 4 2.8 0 0.0 4 2.8 0 0.0 1 0.7 1 0.7 6 4.3 0 0.0 35 24.7 Bioi.or.K At. Sfkiks, \ 'OL. 18. No, . :^ BMiiiiniNc 1' ^COl.OG^ ;■ (IF Ut..\h Raftohs 19 Table 11. Summary of ; iiltitudinal distribution of raptor nests, 1967-1970. 4800 5000 5200 5400 5600 5800 6000 6200 5000 5200 5400 5600 5800 6000 6200 6400 Species No. . % No. % No. % No. % No. % No. % No. % No. % Golden Eagle 0 0.0 0 0.0 1 0.7 4 2.8 6 4.3 0 0.0 3 2.1 0 0.0 Great Homed Owl 0 0.0 0 0.0 5 4.0 9 6.4 10 7.0 1 0.7 0 0.0 2 0.1 Ferruginous Hawk 1 0.7 8 5.7 17 12.1 16 11.3 0 0.0 0 0.0 0 0.0 0 0.0 Red-tailed Hawk 1 0.7 2 0.1 10 7.0 5 4.0 0 0.0 3 2.1 0 0.0 0 o.n Swainson's Hawk 0 0.0 4 2.8 1 0.7 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 Prairie Falcon 0 0.0 0 0.0 1 0.7 0 0.0 2 0.1 0 0.0 0 0.0 0 0.0 Marsh Hawk 4 2.8 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 Cooper's Hawk 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 0.7 0 0.0 0 0.0 Sparrow Hawk 0 0.0 0 0.0 6 4.3 0 0.0 3 2.1 0 0.0 0 0.0 0 0.0 Short-eared Owl 1 0.7 0 0.0 0 0.0 0 0.0 0 0.0 0 0.(1 0 0,0 0 0.0 Burrowing Oul 6 4.3 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 Raven 0 0.0 0 0.0 0 0.0 3 2.1 1 0.7 1 0.7 7 5.0 2 0.1 Totals 13 9.2 14 8.6 41 29.5 37 26.6 22 14.2 6 4.2 10 7.1 4 0.2 five alternate nests, and one or more of tliese would also be decorated at the onset of the breeding season. Great Horned Owls selected chffs, trees, and quarries for breeding sites. Quarries were a fre- quently utilized site (almost 26 percent of all Great Homed Owl nests were in quarries), and each year at least one pair nested in the niches, ledges, or cracks of an abandoned quarry. None of the pairs showed any attempt at nest con- struction but instead occupied old nests of Ravens, Red-tailed Hawks, Ferruginous Hawks, or deposited the eggs directly on the dirt or rock floor of a crevice or ledge. Tree nests were found only in junipers within the study area, but the owls did use old Rod-tailed Hawk nests situated in tall cottonwoods in canyons located outside and to the north of the study area. Nests aver- aged 5640 ± 5.3.7 feet (range 5340-6320 feet) in altitude. Over 55 percent of the nests faced west and almost 30 percent had southern ex- posures, while less than 1 percent faced north. Nests were selected in cliffs wliich ranged from 21 to 65 feet in height, but sheer size of cliff appeared to be less important than seclusion, and crevices were more frequently occupied than ledges. Ferruginous Hawks were selective in their choice of nesting sites. Nests were constructed in junipers, cliffrose, on low ledges ( less than five feet high) or directlv on the groimd (Fig. 8). The most common nesting site was in a low tree or shrub, either on the peripher\- of the wood- land or in ver\' lightK' wooded areas of the foot- hills. The average altitude of all Ferruginous Hawk nests was 5290 ± 2.5 feet (range 4990- 5500 feet). Low foothills and knolls appeared to offer the best sit(>s and were heavily utilized. In contrast, no nests were located in steep-sided canyons, cliffs, or heavily wooded areas, al- though such sites were equally available in these same localities. Red-tailed Hawks exhibited a wide choice of nesting sites somewhat paralleling that of the Great Horned Owl. Their most common nest sites were in junipers, but other localities in- cluded cliffs, quarries, pinyons, and cottonwoods (Fig. 9). Nests averaged 5380 ± 52.4 feet, but had a wide altitudinal amplitude (range 4880- 5880 feet). Unlike Ferruginous Hawks, Red- tailed Hawks constructed their nests in a variety of habitats. Tree nests were most commonh' built on the periphery of the woodland or in lightly wooded areas but a few were also con- structed in the center of dense woodlands and in steep-wallcd canyons. Cliff sites were usually in large rugged cliff lines but again some varia- tion occurred and some nests were consti-ucted on cliffs only 10-15 feet high. Red-tailed Hawks were frequently usurped from their nesting sites by the earlier nesting Great Horned Owls; they then chose secondary, more exposed nesting sites a short distance away. The choice of nesting sites by the Swainson's Hawks showed considerable overlap with Fer- ruginous Hawks. Their nests were without ex- ception constructed in low junipers and averaged 5130 ± 30.4 feet in elevation (range 5080- 5240 feet). As with Ferruginous Hawks, their most common nesting site was on a low foothill or knoll or at the edge of a juniper woodland. Nesting sites of the Prairie Falcon averaged 5.590 ±: 88.3 feet (range .5.380-5760 feet). Of the three nests on the study area, two were located in (luarries and one in a limestone cliff crevice. One quarry site was also located in a crevice but the second was located in an unused Gold- en Eagle nest. Heights of the nests above the cliff base ranged from 13-78 feet. In 1970 a pair 20 Bricham Young University Science Bulletin Fig. 8. Ferruginous Hawk ground nest in central Cedar Valley- hatched egg. May, 1968. Till' nest contains two chicks and one un- Fig. 9. Hed-tailed H:nvk nest in juniper tree, Skull Vallev. Tooele Co.. I'tah. Two vouiig visible al top of tiest. May 1972. of Prairie Falcons prevented a pair of Great Homed Owls from successfully completing their nesting attempt and then took over the aban- doned nest site ( Fig. 10 ) . The four Marsh Hawk nests were situated in Cedar Valley and averaged 4930 ± 27.6 feet in elevation (range 4870-4990 feet). All nests were located in thick sag(>bmsh and rabbitbrush. Although all were ground nests, their location within the extensive sagebrush growth rendered them relatively inaccessible. Tlic only nesting of the Cooper's Hawk on the study area was in a juniper at an elevation of 6020 feet. The site was located deep within a dense juniper stand atop a ridge between two adjacent peaks, and overlooked Rush Valley. The nest was small and hidden within the mid- dle branches of the tree. Sparrow Hawks nested in junipers, quarries and abandoned mining structures. Nests aver- aged 5460 • 49.7 feet in elevation (range 5.350- 5670 fe(!t). Quarr)' sites were actually small crevices in the \-ertical walls which ranged from re sitiiatetl in small crevices within the tree tmnks. Both types of nesting sites were also used BioLcx;icAL Seiues, \'()l. 18, No. 3 Bheeuing Ecology of Utah IUptoks 21 Fig. 10. Cliff nesting site of Prairir Falcons and Great Homed Oivls in the western Thorpe Hills. l)V Starlings (Stunii.s vulgaris) nesting in the same localities. The onh' Short-eared Owl nest on the study area was located at an elevation of 4S90 feet. The nest site was placed at the base of a large clump of sagebmsh and was partially sheltered and hidden b\' its branches. A few twigs had been arranged on the nest floor and down was placed among them; otherwise, no nest con- struction was attempted. Nests of the Burrowing Owl averaged 4920 ± 1.6 feet in elevation (range 4920-49.30 feet). The three nests of the 1969 season and two of the 1970 season were grouped together, fomiing small colonies which were located in a stand of grea.sewood, in dry sand and soil ( Fisj. 11). The remaining nest was located in the bank of a dr)' reservoir. All were within unused burrows of kit foxes, badgers, or Townsend's ground squirrels. With feu' exceptions Raven nests were lo- cated in the most remote, inaccessible regions of the study area. Their average elevation was 5950 *- 65.5 feet (range 5590-6;32() feet). All were well constructed, compact, and set far back into a protective crevice. All had an over- hanging ledge or rockshelf which prevented direct exposure of the nest (Fig. 12). Reoccupation of Nests and Nesting Localities. Most of the regularly nesting raptor species showed a strong tendency to reoccupv their ter- ritories and often their exact nesting sites of the previous year. This was particularly true of crevice-nesting raptors, and it is probable that these partially protected sites are used for an indefinite number of breeding seasons. Table 12 summarizes the reoccupation data. Unfortunately it was not possible to mark individuals, hence it is impossible to detemiine if the same pairs were present each vear. However, many pairs and individuals of pairs exhibited distinctive color or plumage patterns and behavioral char- acteristics and could be identified on this basis. Most of the large raptors selected different nest sites within the same territory each vear. This was particularly true of the Fermginous Hawk which selected a different nest site 75 percent of the time, but also remained within the same locality for suc-eessive years 77 percent of the time. Similarly, pairs of Golden Eagles, Great Homed Owls, Red-tailed Hawks, and Svvainson's Hawks showed strong attachments to 22 Hkigiiam Young Univeksity Sciknce Bulletin , , «««C*»/. '» ^%^. ■4i » ■-*' '»•„♦ Fig. 11. Burrowing Ov moiincl. nesting site in northeastern Cedar Valley, July 1970. Both adults are on the a particular area and were often found there even during years in which tliey did not nest. Long term consecutive occupation of a nest site was more rare. One pair each of Great Homed Owls (nesting in a cliff site) and Ferruginous Hawks (nesting in a tree site) occupied their same respective nest sites for all four vears of this study. Another Great Horned Old pair liad oc- cupied their nest site for the fourth consecutive year but were displaced by a Prairie Falcon pair. Several pairs of Golden Eagles, Great Homed Owls, Fcrrusinous Hawks, and Red-tailed Hawks reoccupied the same nesting site for three con- secutive years, and every large raptor occupied at least one nesting site for two consecutive years. Most commonh-, those species which nested in a different site selected a new site veiy near that of the previous Near. For example, a pair of Golden Eagles selected three sites in the same (juarr\- for three a>nsecutive vears, each but 3() feet from the previous years site. The same phiMiomenon was observed in Fer- ruginous, Ri'd-tailed, and Swainson's Hawks. The amount of shifting appeared to be related to the dei^ri'c of disturbance as well as the success of the pre\'ious year's nest, but pairs would often tolerate considerable disturbance and ri'main within the same nesting localitv. Of the medimn and small raptors, thi' Raven showed the greatest population stabilitv'. The Fig. 12. Raven nest located in \v<'ll-[>rotected crevice. Biological Sehies, \'ol. 18, No. 3 BiiEiiiiiNC Ecology of Utah IIaptohs 23 Tablf 12. Siimman,' of reoccupation of nesting sites and territories. No. years occupation of a L nest site No. years territorial occupatior [• I 2 3 4 1 2 3 4 Total no. Species No. % No. % No. % No. % No. % No. % No. % No. % of sites Golden Eagle 5 55.6 .7 22.3 2 22.2 0 0.0 0 0.0 0 0.0 2 40.0 3 60.0 9 Great Horned Owl 6 40.0 7 46.7 1 6.7 1 6.7 0 0.0 4 400 3 30.0 3 30.0 15 Ferruginons Hawk 18 75.0 2 8.3 3 12.5 1 4.2 1 1 . 1 0 1,5.4 4 30.S 6 46.2 24 Red-tailed H.iuk 8 57.1 5 35.7 1 7.1 0 0.0 0 0.0 1 14.3 1 14.3 5 71.4 14 Swainson'-. Hawk 1 .33..3 ■T 68.7 0 0.0 0 0.0 1 50.0 0 0.0 0 0.0 1 .50.0 3 Prairie Falcon 3 1(10.0 0 0.0 (1 0.0 0 0.(1 1 .33.0 2 67.0 0 0.0 0 0.0 3 Marsh Hawk 5 1 00.0 (1 0.0 0 0.0 0 oo 1 1 00.0 2 67.0 0 0.0 0 0.0 5 Cooper's Hawk 1 100.0 0 0.0 0 0.0 n 0,0 1 lOOO 0 0(1 0 0.0 0 0.0 1 Sparrow Hawk 4 66.7 1 16.7 1 16.7 0 0,0 0 0.0 1 25 0 3 75.0 0 0.0 6 Short-cared Owl I 100.0 0 0.0 0 0.0 0 0 (1 1 100.0 0 0.0 0 0-0 0 0.0 1 Burrowing Owl 6 UHi.O (1 0,0 0 0.0 0 0,(1 2 50.0 2 .50.0 0 0.0 (1 0,0 6 Raven 0 33.3 1 16.7 2 33.3 1 16,7 0 0.0 0 0.0 0 0.0 4 100.0 6 Totals 60 71.75 20 17.9 10 8.2 3 2.3 8 36.7 14 23.2 13 15.8 22 29.7 93 'Tulais iniluilo nc:>tiTig and nonnesting pans four pairs of Ravens on the stuch' area occupied their respecti\e territories for four consecutive years and selected but six different nesting sites. Sparrow Hawks also tended to reoccupv the same territories, but their fluctuating popula- tions altered their reoccupation frequencies. None of the Burrowing Owl or Marsh Hawk pairs reoccupied their exact nesting sites of the pre\ious \ ear, but all returned and nested with- in the same locality. The Prairie Falcons chose three different sites in three different nesting at- tempts, two of which were located within the same torriton'. Productivitv Clutch Size. The summan' of clutch size fre- quencies from 1967-1970 is presented in Table 13. Golden Eagle clutches on the study area averaged 2.07 ± 0.07 eggs ( 14 clutches, range 2-3). Differences between the mean clutch size of each of tlie four study years was not signifi- cant. Total fecundit)- averaged 6.75 ± 0.96 eggs a year. Great Homed Owl clutches averaged 2.82 ± 0.15 eggs (22 clutches, range 1-4). Clutches of 1968 and 1969 were significantly larger than clutches of 1967 and 1970 (t--= 2.53; 2.63, re- spectively) but not significantly different from one another (t= 1.26). In addition, clutches of 1967-1970 were also not significantly different (t= 1.15). Total vearh' fecundit)- averaged 15.5 ± 3.3 eggs. Clutches of the Fenuginous Hawks aver- aged 3.23 ±: 0.12 eggs (34 clutches, range 2-4). Clutches of 1968 and 1969 were significantly larger than clutches of 1967 and 1970 (t= 2.56; 2.75, respectively) but not significantly different from one another (t= 0.05). Again, clutches of 1967 and 1970 were not significantly different (t= 1.35). Total yearly fecundity- averaged 28.3 ± 5.6 eggs. Red-tailed Hawk clutches averaged 2.89 ± 0.13 eggs ( 19 clutches, range 2-4). Although clutch size showed an increasing trend through- out the tour study \ears, none of the possible differences betwen yearh' clutch sizes was sig- nificant. Total yearly productivity averaged 13.8 ± 1.43 eggs a year. Table 1.3. Summar)' of frequency distribution of raptor tlutch sizes from 1967-1970. No. eggs in clutch Species 1 3 3 4 5 6 7 Golden Eagle 0 13 1 0 0 0 0 Great Horned Owl 1 5 13 3 0 0 0 Ferruginous Hawk 0 5 13 16 0 0 0 Red-tailed Hauk 0 4 13 2 0 0 0 Swainson's Hawk 0 -1 1 0 0 0 0 Prairie Falcon 0 0 0 0 1 0 0 Marsh Hauk () 0 1 0 0 0 1 Cooper's Hawk 0 0 1 0 0 0 0 Sparrow Hawk 0 0 0 3 3 1 2 Short-eared Owl 0 0 0 0 0 0 1 Burrowing Owl ? ? ? ? ? p p Raven 0 0 1 3 4 2 4 Totals 1 31 44 27 8 3 9 24 BiiK.iivM YouNC Univihshv Sciknck Buli.ktin Clutches of the Svvainson's Hawk averaged 2.2 ± 0.17 eggs (.5 clutches, range 2-3). There were no significant variations in clutch size be- tween any of the foin- study years. Total yearly fecundity averaged 2.7.5 ± 0.6 eggs, rating low- est of the large raptors on the study area. (Comparisons of the average clutch sizes of the large raptors indicate that the mean clutch size of Ferruginous Hawks was significantly larger than the Golden Eagle (t= 8.23), Great Horned Owl (t= 2.11), and Swainson's Hawk (t= 4.76) average clutches but did not differ significantly from average Red-tailed Hawk clutch size (t= 1.01). Red-tailed Hawk clutches averaged significantly larger tlum those of Gold- en Eagle (t— .5.72) and Swainson's Hawk (t= 3.2) but did not differ significantly from Ferniginous Hawk or Great Homed Owl (t = 4.47 for both) and Swainson's Hawk clutches (t=2.63). Golden Eagle and Swainson's Hawk clutches did not differ significantly from one another (t= 0.678). Of the smaller raptors, onlv Sparrow Hawks, Marsh Hawks, and Ravens had sufficient clutch size data for analysis. Sparrow Hawk clutches averaged 5.22 ± 0.38 eggs ( 9 clutches, range 4-7 ) . No significant differ<>nces between \earl\' clutch sizes were found. Total yearly productivity averaged 10.0 ± 2.18 eggs. Clutches of the Marsh Hawk averaged 5.0 ±1.4 eggs (2 clutches, range 3-7). No compari- sons were possible. Raven clutches on the study area averaged 5.35 ± 0.,34 eggs ( 14 clutches, range 3-7). There were no significant differences between yearly clutch size. Total productivity averaged 18.8 ± 1.9 eggs. No significant differences were found be- tween th(> average clutch sizes of the Marsh Hawk, Sparrow Hawk, and Raven but all were significantly larger than the clutches of the large raptors on th(> study area. Ilatchahilitij. In 1967 the ov(>rall hatching success of the efforts of all nesting raptors on the study area was 82.5 ± 7.6 percent, the high- (>st of the foiu- study years. In 1968 the overall hatching success was 77.4 ± 5.7 percent, but in contrast the lowest hatching success occurred during the 1969 season (75.6 ± 9.2 percent). In 1970 the overall hatching success was slightly higher at 82.0 ' 4.7 percent. There were no significant variations in yearly overall hatching success between any of the four study years. The overall hatching success of the five large raptor species when calculated separately showed no significant differences between years. with the hatching percentages being as follows: 1967, 84.7 ± 8.7 percent; 1968, 75.9 ± 7.6 percent; 1969, 76.7 ± 10.24 percent; 1970, 84.2 ± 7.1 percent. From 1967-1970 Golden Eagle nesting ef- forts hatched 70.8 it 14.9 percent of all eggs for an average of 1.2 young per nest per year. How- ever, the breeding seasons of 1967 and 1970 were highly successful, hatching 100 percent of all eggs produced for an average of 2.0 young per nest; whereas the combined results of 1968 and 1969 revealed a two-year hatching success of less than 42 percent and an average of but 0.88 young per nest. The average hatching success of Great Horned Owls from 1967-1970 was 89.4 ± 3.6 percent for an average of 2.5 young per nest per year. Great Horned Owl hatching efforts were most successful in 1967 ( 100 percent hatched, average of 2.0 young per nest) and least successful in 1969 (80 percent hatched) al- though the efforts of 1969 actualh- resulted in a greater number of young (2.5) produced per nesting effort. The average hatching success of Fermginous Hawks on the study area from 1967-1970 was 65.2 ± 5.2 percent for an average of 2.3 young produced per nest per \'car. Ferruginous Hawk nesting success was lowest in 1967 (5.3.3 percent hatched, 1.3 young per nest) but highest in 1969 (81.8 percent hatched, 3.0 \()ung per nest). The hatching success was comparati\el\- low during all four breeding seasons, and a total of .35 eggs produced no young. Red-tailed Hawk nesting efforts successfully hatched 76.7 :^-: .3.9 percent of all eggs produced from 1967-1970 for an average of 2.3 \'oung per nest per year. As with Ferruginous Hawks, Red-tailed Hawk hatching success was highest in 1969 (88.9 percent hatched, 2.5 young per nest) but lowest in 1970 (69.2 percent hatched, 2.2 )'oung per nest). Swainson's Hawks had the highest hatching success of an\- raptor on the study area, success- fully hatching all eggs produced each year. Swainson's Hawks averaged 2.2 yoimg per nest per year but hatched 2.5 young per nest in 1969, their most jiroductive \-ear. The Prairie Falcon nest for which the initial clutch size was known hatched all five eggs. Hatching success is unknown for the Cooper's Hawks and liunowing Owls (the latter because of the inaecessibilitN' ot the nests). The only Short-eared Owl nest on the study area hatched six young from a clutch of seven eggs (85.7 percent). The two Marsh Hawk nests for which clutch size data are available hatchcxl 70 percent Biological .Seiuiss, \'ol. 18, No. 3 Bheedinc Ect)Loc;v oi- Utah HArrons 25 of the eggs for an average of 3.5 young per nest, but the figures are misleading inasmuch as one nest successfulh' liatchcd all seven eggs of the clutch whereas the other nest failed to produce any young. Sparrow Hawk hatchabilits' is known for 1968-1970. During this time their hatching suc- cess averaged 94.1 ± 4.9 percent for an average of 4.7 young per nest. Their hatching success was greatest in 1969 and 1970 ( 100 percent hatched in both \ears). From 1967-1970, Ravens successfully hatched 70.5 ± 7.6 percent of all eggs produced for an average of 3.64 young per nest. Raven hatching success was highest in 1970 (85 percent hatched, 5.0 \oung per nest) but lowest in 1969, when less than 46 percent of the total eggs produced hatched young for an average of 2.2 young per nest. Comparisons of hatching success between the different raptor species reveals that Swainson's Hawks had a significantly greater degree of overall success than Ferruginous Hawks (t^ 6.70) and Red-tailed Hawks" (t:= 5.85) but did not differ significanth' from the other large rap- tors. Great Horned Owls had the second highest overall hatching success, significantly higher than Feniiginous Hawks (t=r: 3.S3) but did not var\' significanth- from that of the other larger raptors. Fledoung fledged 6 7 10 6 2 1 5 4 0 12 5 58 Percent young fledged 100.0 70.0 47.6 46.2 100.0 20.0 50.0 80.0 0.0 ? 41.7 clutches) uere subsequenth' abandoned as was the Great Horned Owl nest of 1968 (Smith. 1970). Their most commonly chosen siti's, i.e., quarries, are in highh vulnerable situations which inxite human presence and interference. Twice in 1968 Red-tailed Hawks built nests in quarr\' sites which were almost daily subject to human disturbances. In both cases the nests were subsequentl)' abandoned before eggs were deposited. In 1970 a Great Horned Owl occu- pied its quarr\' nest of the former three seasons. Later interaction with a Prairie Falcon appar- enth' caused it to abandon this crevice site be- fore egg deposition took place. This Great Horned Owl pair successfully renested only 42 feet from their original site which was then occupied ( unsuccessfulh' ) 1)V the Prairie Falcon pair. Nest desertion frequently led to renesting attempts by Red-tailed Hawks, particularK if nests had been deserted before egg deposition occurred. None, however, were successful dur- ing the four-year study. Golden Eagles also frequently deserted their nests, with 25.9 percent of all nesting attempts temiinated b\ desertion. As with Great Homed Owls and Red-tailed Hawks, the most frequent cause of nest desertion was some form of human interference. Two pairs each deserted their nests in two of the three years in which they at- tempted to nest. Egg collecting and photogra- pliv activities were observed around these nests before their desertion. A renesting attempt oc- curred in 1969 but was unsuccessful. Ferruginous Hawks deserted nests 22.2 per- cent of the time. Several of the pairs would tolerate no activity around the nest, particularly during the time period immediately after egg deposition had been completed; these birds de- DiiiciiANt Young Universitv Science Bulletin Tabic 18. Summar)' of causes of mortality, 1967-1970. Total no. Successful nests" Unsuccessful nests \cst (iestniction Nest destruction '•KR'' t-gg losses [uvenile losses Egg not Eggs E^s™. faff Species prodviced Infertile Other All causes laid laid Young Young Golden Eagle.s 27 2( 2) K 1) i( 1) 1 3( 7) 0 0 0 1( 2) Great Horned Owl 62 2( 2) 2( 3) 4( 4) 5 K 3) K 3) 1 0 1( 3) Fermftinou.s Ilauk 11.3 8( 9) 5( 6) 5( 6) 2 6(18) 0 0 1( 2) K 4) Red-tailed Hawk .55 0 5( 7) 4( 4) 4 2( 5) 1( 3) 0 0 K 3) Swainson's Hawk 11 0 K 1) 0 0 0 1( 3) 0 0 0 Prairie Falcon 5 K 1) K 1) K 1) 2 0 0 0 0 0 Mar.sh Hawk ■p ■? p 1( 2) 0 1( 3) 0 0 0 0 Cooper's Hawk .3 ■? ? v ? ? ■p p ■p p Sparrow Hawk 40 0 0 3( 5) 1 1( 3) 0 0 0 1( 5) Short-eared Owl 7 1( 1) 0 0 0 0 1( 6) 0 0 0 Burrowing Owl ? ? ? 'J 2 p p a p ■> Haven 75 4( 5) 7(18) 11(16) 0 0 0 0 0 0 Totals 398 18(: 20) 22(37) .30(39) 17 14(39) 4(15) 1 1( 2) 5( 17) •Numbers in uiliimns i efpr l^ nuiiil>ri of iicsts. nmntwrs in parpiilli icMs following refer til mini tier of eggs or young. serted their sites immediately after the nesting tree had been chmbed or ground site ehc-eked. However, none of tht; nests were abandoned after the adults had hatched young. In 1969 one Swainson's Hawk nest with three young aged 1.5 weeks was deserted. Only one of the pair was seen in the nest vicinity. Three days later several pieces of the remains of a Swainson's Hawk were found beneath the roost of a pair of Golden Eagles which main- tained a territorv in the same area. Evidently this predation caused the termination of the Swainson's Hawk's nesting aetixitics. Prairie Falcons abandoned two ot three nesting sites because of human activities. In ad- dition, Marsh Hawks, Sparrow Hawks, Short- eared Owls, and Burrowing Owls also deserted one or more of their nests because of human presence or interference. Marsh Hawks deserted a nest containing three eggs which, when checked, were infertile. Prairie I'aleons aban- doned one nest due to aggress on eonhicts willi Great Horned Owls (pre\ionsl\ disci:ssed) and deserted anotlier nest located in a <|uarry whicli was frequently visited b\ hunters and campers. Sparrow Hawks abandoned two nests because of similar activities. Apparentlv our investiga- tions were the cause of th<> nest desertion b\' Burrowing Owls and the Short-(uued Owl. Nest destruction occurred in 4.9 percent ot the 141 initiated nests. Causes of nest destruc- tion included human interference and accidents. Human interference in this case refers to the destruction of the young and/or adults. An ex- posed quarr\' site was occupied in 196S by a pair of Great Horned Owls. lDespil<' distur- bances they persisted in their attention to the nest and succeeded in hatching three young, but both the ni'st and \()ung were su])se(iiientlv destroyed. In 1969 the same site was occupied by a Red-tailed Hawk pair which also succeeded in hatching thre(> voung. Again the nest was destroyed before the young fledged. Another Great Horned Owl nest occupied in 1969 was destroyed before egg deposition. The body of one of the adults was found beneath the nesting tree, minus its feet and several tail feathers. Two Ferruginous Hawk nests were similarly destroyed. One containing two eggs was located alongside a well-traveled road. The female was later found shot, the eggs broken and the nest destroyed (Weston and Ellis, 1968). The second nest was located in a favorite rabbit hunting locale and produced four \()ung. Shortly before the young would have fledged, the nest was found destroyed, with three shotgun shells King beneath the nesting tree. One Sparrow Hawk nest was also destroNcd. This nest was located among the ruins of an abandoned mining structure and had been deliberatcK- exposed. An accident destroyed a Golden Eagle nest in 1967, the onl\' observed instance of the nat- ural destruction of a raptor nest. The nest had been positioned in a loose shale quarry wall which collapsed, killing both voung ( Murph\- et al., 1969). Based on tlie successful nests (i.e., those wliich fledged at least one young) 6.5 percent ot ail eggs produc(Hl by all raptors species were apparenth' infertile and another 11.4 per- cent were lost before hatching. Eggs which did not hatch after a suitable time period were judged infertile; how^ever, additional eggs may have been infertile but were destroyed prior to our cheeking them. Ferruginous Hawks had the highest apparent percentage of infertile eggs (10.1 percent) of an\' raptor species. Seven Ferruginous Hawk nests contained one infertile egg each and one contained bvo. Most com- monly, one of a clutch of three or four eggs Biological Seuies, X'ol. IS, Ni Bheedinc Ecolocv ■ >!■• Utah Kaitohs 29 was infertile. Both Golden Eagles and Great Horned Owls also produced infertile eggs. In 1968 a Golden Eagle pair produced a clutch of two eggs. One egg disappeared early during the incubation period, but the adult continued to incubate the remaining egg. After 49 days the egg had not hatched and was subsequenth' abandoned. Raven nests also appeared to pro- duce a high number of infertile eggs on the studv area, with 6.7 percent of their total eggs judged to be infertile. Reasons for other egg losses are mostly un- known, but the eggs usually disappeared during incn])ation. Howe\er, one case is interesting. In 196S a Red-tailed Hawk pair produced a clutch of two eggs. During the incubation period one member of the pair was found destroyed (pre- sumabh' shot). One egg disappeared but the remaining adult rcmated with a new individual and successfully incubated and then fledged a )'Oung from the remaining egg. Losses of young are also combined because of lack of knowledge of specific causes. Juvenile mortalit\' occurred most commonly in Raven nests, but Golden Eagle, Great Horned Owl, Ferruginous Hawk, and Red-tailed Hawk juve- niles also occasionalb' disappeared. Little infomiation was obtained on post- fledging mortality, although this is the period during which the majority of deaths among first-year birds occurs (Hickey, 1949; Lack, 1954; Sprunt, 1963). In previous studies on raptor mortalit\' in this area, Ellis, Smith, and Murphy (1969) recorded a high percentage of juveniles among birds which had been illegally shot b\- hunters and suggested that juveniles are particularly \'ulernable to tliis fonn of destnic- tion. Territoriality The definition and concept of a territory has been much discussed in the literature (Noble, 1939; Nice, 1941, 194.3; Odum and Kuenzlcr, 1955). Within the study area, however, the minimal amount of intraspecific home range overlap coupled with the ver\- few instances of observed territorial defense suggests that the most applicable concept is the "maximum home range" category- as described by Odum and Kuenzler (1955). Using this method, the ex- treme positions and movements (jf raptors arc plotted and connected and the area contained within is the derived liome rantje. The home ranges plotted in 1969 and 1970 were deter- mined from a minimum of 25 obser\ations per pair. Home Range Estahlislitnetit ami Defense. Home range establishment dates of all raptor species from 1967-1970 have been previously pre- sented in Tables 5-8. At the beginning of the raptor breeding season, the permanent residents selected their future nesting sites and confined their activities within a restricted area. During this period Golden Eagles were often observed in such conspicuous activities as soaring, court- ship display, and occupying a prominent perch. Great Horned Owls were frequently active in the early evening hours making short flights from one perch to another. Both individuals and pairs were observed hooting from the cover of one perch, then making a short flight to a new perch and hooting again. No intra- specific or interspecific actions were observed during this period, although on a few occasions a Golden Eagle of one nesting pair flew within sight of the nesting locale of a neighboring pair, maintaining a good distance from the actual nest site. Indeed, the pairs at times seemed to be keeping watch on their neighbor's nest while establishing their own territorial rights, much in the manner described by Di.xon (1937). No Golden Eagle and Great Homed Owl interac- tions occurred, although pairs nested in close proximity in 1968, 1969", and 1970. There is little or no overlap in their respective activity pat- terns and they do not usually come in contact with one another. Unlike other large raptors. Golden Eagles did not attack flushed Great Homed Owls e\'en when owls were flushed within 50 feet of active Golden Eagle nests. Returning migratory pairs rapidly occupied their territories and assumed territorial estab- lishment acti\'ities. Ferruginous, Red-tailed, and Swainson's Hawks were highly aggressive at this time. In several locales Ferruginous Hawk pairs nested in close proximity. Their morning and evening soaring flights frequently provoked interaction, and at times members of three pairs would be observed soaring but short distances from one another. Usually the act of soaring kept the pairs distant, but occasionally one would apparently venture too close and provoke a response. One or both members of a pair would posture and chase one or both members of another pair simultaneously, although no actual contact was ever observed. In one ex- ample of interspecific contact, a Ferruginous Hawk pair attacked a Great Horned Owl \\'hich had landed some 30 feet from its cliff nest. The Hawks dov(> at it in turn several times, each time coining to within 3-9 feet of its head but a\oiding contact. The owl in turn met each at- tack by raising its wings in defense posture and vigorously clapping its beak. The hawks persisted until the owl flew into a nearby cliff crevice, whereupon the hawks resumed their 30 Bbioiiam Young Univehsity Science Bulletin soaring. In this case the Ferruginous Hawks had arrived in the area and occupied their terri- tory of the previous year in the moniing and were activel)- defending it in the late afternoon of the same day. Hed-tailed Hawk pairs defended their terri- tories against Great Horned Owls, Ferruginous Hawks, and Golden Eagles but no intraspecific conflicts were observed. Red-tailed Hawks al- ways attacked flushed Great Horned Owls and on at least three occasions struck from above with open talons, although never visibly injuring them. The owls made no attempt to defend themselves during such attacks but instead flew to the nearest cover. On one occasion a Red- tailed Hawk pair attacked and drove a Golden Eagle out of their territory. Tlie eagle was per- sistently attacked from above when approxi- mately 1 1/5 miles from the Red-tailed Hawk nesting site and rapidh' flew out of the area, followed for a distance by the red-tails. Red- tailed Hawks also threatened Ravens, but onlv if close to the nest site. The Ravens maintained a cautious distance from soaring Red-tailed Hawks and usuallv onlv a swoop in their direc- tion sufficed to chase them away. Encounters between Swainson's Hawks and FerRiginous Hawks often occurred and are dis- cussed by Murphy, et. al., (1969). Prairie Falcons quickly and aggressively re- acted to the presence of anv raptors within their nesting vicinitv during this period. How- ever, Ravens were tolerated surprisingly close to the nesting vicinity, and in 1970 a pair of Ravens nested within 75 feet of an active Prairie Falcon e\rie. Both sites, however, were out of sight of one another and hidden within recesses in cliffs. Ver\' little information was obtained on ag- gression and territorial reactions of the medium- and small-sized raptors during this period. Gen- erally their nests were widely spaced and showed no overlap, with the exception of the Burrowing Owls. A Sparrow Hawk pair was observed at- tacking a Red-tailed Hawk flying about 50 feet above its nest site, but reacted passively to the presence of Ravens and Golden Eagles. Burrowing Owls vigorously protested distur- bances from investigators but allowed Marsh Hawks to fly within their home ranges. Marsh Hawks were similarly tolerant of the Burrowing Owls and on two occasions nested within the home range of Short-eared Owls. As the breeding season progressed, the raptors generally became less aggressixe toward one another and fewer aggression contacts were observed. At times much tolerance was shown toward other raptor species flying over the nest site, while on other occasions they would be attacked and driven away. Definite vertical ter- ritoiy limits appear to be present and were easily observed during the reactions of a pair to the presence of investigators. On several oc- casions a second and sometimes a third pair were observed soaring above a nesting pair which were themselves attacking the investi- gators. At these times the intruding pairs re- mained unchallenged as long as they maintained their higher altitudes. However, in one such instance a Ferruginous Hawk pair from a near- by nest flew over a Red-tailed Hawk nest at low altitude; the intruders were immediately attacked b\' the nesting pair, which suceessfulh' drove them awav after one grappled with one of the Ferruginous Hawks. Home Range Coverage. The home ranges de- termined during the breeding seasons of 1969 and 1970 are plotted in Fig. 13-21. Generally the specific size and shape of the raptor home ranges appeared to be a function of their size and breeding status ( i.e., nesting pair, nonnest- ing pair, or individual), the topography of the surrounding locale, and apparently the breeding population densities. Home ranges of nesting raptor pairs were usually larger than home ranges of nonnesting pairs and both maintained larger home ranges than individuals of the same species. Almost all of the raptors nesting in the foothills had home ranges extending far into the desert but only short distances into the interior of the hills. Their nests, therefore, were usuall)' located at the edge of the home range. Average home ranges of all raptors except Swainson's Hawks, Sparrow Hawks, and Bur- rowing Owls were larger in 1970, correlating with the overall decreased raptor population densities. None, however, were significantly larger than the average home ranges of 1969. Additional home range information of the raptor species is presented as follows (only home ranges which were entirely within the study area limits are included in the following data). The iiome ranges of nesting Golden Eagle pairs averaged 9.05 ± 1.1 sq miles in 1969 (3 pairs, range 6.6 — 11.8 sq miles) and 8.98 ± 0.6 s(i miles in 1970 (3 pairs, range 7.91 - 10.3 sq miles). Maximum diameters of the home rani^es a\ c-ra,y;ed 4.09 -± 0.4 miles in 1969 (range 3.08 - 4.99 miles) and 3.85 ± 0.4 miles in 1970 (range 3.25 — 4.8 miles). Golden Eagles possessed the largest home ranges of any raptor nesting within the stud\' area and appeared to be little aifeeted 1)\ topograpliic barriers. They also appear to eoiisistenti\ utili/.e a sizeable Biological Stuiiis, \'ol. 18, No. 3 Bueeding Ecology ok I'taii Haptous 31 Kig. 13. Home ranges ot Cioldfn Eagles (1) and .Swainson's Hawks (5) in 1969. 32 Bil. ly, Xo. 3 Biu;t;i)iNG Ecology of Utah Hai'tohs 35 Fig. 17. Home ranges of Prairie Falcons (6), Marsh Hawks (7), Sparrow Hawks (9), Short-eared Owls (10), Burrowing Owls (11) and Ravens (12) in 1969. 36 BnioHAM Young Univkhsity Science Bulletin Fig. 18. Home ranges of Golden Kagle.s (1), Red-t.nled Hawks (4) and Swainson's Hawks (5) in 1970. Bk)looic;al Suuts, \'oi.. 18, \ii. 3 Bukkding Ec:olo(::y of Uiaii IUptohs 37 Fig. 19. Home raiip's of Great Iliirncd Owls (2) in 1970. 38 Bnir.nA%r Young University Scienck Bulletin Kij;. 20 lloiiu' rallies 1)1 Kcrniniiioiis Hauks (3) in l!)7(l. BiOLOciCAi, Skmies, \'oi.. 1,S, No. ,5 Bhkkding I'a:olo(;y ok Utah liAPioi 39 Fig. 21. Home ranges of Prairie Falcons (6), Marsli Ilauks (7). .Sparrow Hawks (<)), .Short-eared Owls (10). Burrowing Owls (11) ami Ravens (12) in I970. 40 Bricham Young University Science Bulletin portion of their home range, in contrast to many of the smaller raptor species on the study area. In 1969 an individual Golden Eagle occupying a home range in the southeast por- tion of tlie stiul\' area maintained a home range of 2.48 s(i miles with a maximum diameter of 2.33 miles, although it was far removed from the home ranges of the nesting Golden Eagle pairs. Home ranges of Great Horned Owl pairs averaged 1.88 ± 0.1 sq miles in 1969 and 2.16 =t 0.2 sq miles in 1970 (7 pairs in 1969 and 1970 each, range 1.62 — 2.22 sq miles and 1.36 — 2.7 sq miles, respectively). Maximum diame- ters of home ranges in 1969 averaged 1.87 ± 0.1 miles (range 1.3 — 2.53 miles) and 2.1 ± 0.3 miles in 1970 (range 1.89 — 2.8 miles). Great Horned Owls ranged widely into the des- erts from their nesting sites in the foothills and maintained large home ranges. Their home ranges appeared to he restricted by the topogra- phy of the nesting locale, and pairs from two nests only 0.46 miles apart but on opposite sides of the Thorpe Hills showed no home range ox'crlap although both nesting sites were active during all four breeding seasons. Instead, the pairs hunted in opposite valleys and were never observed near the tops of the intervening ridges. In other areas, however, slight overlaps in ad- jacent home ranges were observed between three pairs in 1969 and two pairs in 1970. In 1970 two nonnesting Great Horned Owl pairs maintained home ranges of 1.64 d= 0.2 sq miles, significantly smaller than the average home ranges of the five nesting pairs (t = 3.2). The observed home range of an individual on the study area in 1969 was about 1.04 sq miles with the maximum diameter of 1.72 miles, relatively smaller than the home ranges main- tained by either nesting pairs or nonnesting pairs. The home ranges of Ferruginous Hawk pairs averaged 2.04 ± 0.2 s(j miles in 1969 (9 pairs, range 1.36 — 3.02 sq miles) and 2.52 ± 0.2 sq miles in 1970 (5 pairs, range 1.76 — 3.10 sq miles). Maximum diameters a\eraged 2.0S6 ± 0.1 miles (range 1.51 — 2.61 miles) in 1969 and 2.02 ± 0.1 miles in 1970 (range 1.75 - 2.6 miles). As with Great Horn(>d Owls their shapes and boundaries were in large part de- termined by topography, and all observed home ranges extended widely into th(< valleys but only short distances into the hills in which the nesting site was located. Five adjacent home ranges overlapped in 1969 and three in 1970, although in no case was the degree of overlap extensive. In 1970 a nonnesting pair possessed a home range of 1.76 sq miles, the smallest home range of any Ferruginous Hawk pair of that year and significantly smaller than the average home ranges of the 1970 nesting pairs (t = 3.0.3, at the 0.001 level of probability). Home ranges of individuals tm the study area in 1969 and" 1970 averaged 1.51 ± 0.07 sq miles (3 indi- viduals, range 1.36 — 1.66 sq miles) and were significantly smaller (t = 3.7) than the home ranges of 1969 and 1970 pairs. In 1969 the home ranges of four Red-tailed Hawk pairs averaged 2.19 ± 0.2 sq miles (range 1.48 — 2.78) and had average maximum diameters of 2.21 ± 0.13 miles (range 1.79 — 2.48 miles). In 1970 the home ranges of four Red-tailed Hawk pairs averaged 2.805 ± 0.3 sq miles (range 2.16 — 3.74 sq miles) and had average maximum diameters of 2.25 ± 0.09 miles (range 2.07 — 2.52 miles). Home ranges of Red-tailed Hawks were larger than the home ranges of other Butco and Great Horned Owl pairs but smaller than Golden Eagle home ranges. In 1969 home range overlaps occurred between four adjacent Red-tailed Hawk pairs and in 1970 between two adjacent pairs. As with other large raptors, the home ranges of Red-tailed Hawks ranged widely into the des- erts but very little into the hills. The average home ranges of two nonnesting pairs in 1970 were 2.59 :h 0.3 sc] miles, significantly less than the average home ranges of nesting pairs (t = 3.95). The home range of an individual present on the stud\ area in 1969 was 0.92 sq miles, also significantly smaller (t — 5.4) than the average home ranges of the 1969 Red-tailed Hawk pairs. Swainson's Hawk pairs possessed the small- est home ranges of any of the large raptors on the study area and averaged 1.83 ± 0.23 sq miles in 1969 (2 pairs, range 1.6 — 2.06 sq miles) and 1.18 s(j miles in 1970 (1 pair). The average maxinmm diameter of the 1969 home ranges was 2.09 miles ±0.1 miles (range 1.94 - 2.23 miles) and that of the 1970 home ranges 1.51 miles. As Swainson's Hawks were few and widely spaced, no overlap of home ranges oc- curred. Indi\iduals (one each year) were pres- ent in both 1969 and 1970 and maintained aver- age home ranges of but 0.87 ± 0.03 sq miles, significantly smaller (t = 3.51) than the aver- age home ranges of the pairs. The home ranges of two Prairie Falcon pairs in 1970 aviTaged 2.35 ± 0.12 sq miles (range 2.18 — 2..52 sc} miles) with average maximum diameters of 2.09 ± 0.05 miles (range 2.01 — 2.17 miles). Prairie Falcons maintained the largest home range of any of the medium- Biological Sehies, \()L. 18, No. 3 Bueedinc Ecology ok Utah IUftohs 41 and small-sized raptors but they were also larger than the average lionie ranges of the Swain- son's Hawks nesting in 1970. Craighead and Craighead (1956) found similar large Prairie Falcon home ranges ni-ar Moose, Wyoming. Possible reasons for the maintenance of such large territories b\ a medium-sized raptor are presented by Schoener (1968). In 1969 an in- dividual Prairie Falcon maintained a narrow home range of 1.64 sq miles with a maximum diameter of 2.59 miles. The home ranges of two Marsh Hawk pairs in 1969 averaged 1.62 ± 0.3 sq miles (range 1..58 ~ 1.66 s(| miles) and had average maxi- mum diameters of 1.83 ± 0.09 miles (range 1.7 — 1.95 miles). In 1970 the home ranges of three pairs a\eraged 1.74 ± 0.15 sq miles (range 1.38 — 2.02 sq miles) and had maxi- mum home range diameters averaging 1.97 ± 0.13 miles (range 1.58 — 2.62 miles). Marsh Hawk home ranges were entirely within the Cedar \'allev area east of the Thorpe and Top- liff Hills. Sparrow Hawk home ranges averaged 0.31 ± 0.08 sq miles in 1969 (4 pairs, range 0.18 — 0.56 sq miles) and 0.26 sq miles in 1970. Maximum diameters of the ranges averaged 0.743 ± 0.003 miles ( range 0.63 ~ 0.81 miles ) in 1969 and 0.62 miles in 1970. None of the wideh' spaced Sparrow Hawk nests overlapped. In 1970 an individual maintained a home range of 0.16 sq miles with a maximum diameter of 0.58 miles. In 1969 the a\erage home ranges of three Burrowing Owl pairs was 0.36 ± 0.11 sq miles (range 0.16 — 0.62 sq miles). In 1970 the aver- age home range of three Burrowing Owl pairs was 0.28 ± 0.04 sq miles ( range 0.20 — 0.36 sq miles). The avera,u;e maximum diameters of the 1969 home ranges was 0.71 ± 0.09 miles (range 0.53 — 0.91 miles) and of the 1970 home ranges was 0.593 zt 0.05 miles ( range 0.51-0.72 miles). All Burrowing Owl home ranges were located east of the Thorpe and Topliff Hills and confined to the valley floor, primaril)- within the greasewood communities. The home ranges of the three adjacent pairs of 1969 and two ad- jacent pairs of 1970 overlapped considerably. The only Short-eared Owl pair on the study area occupied in 1970 a home range of 1.48 sq miles, with a maximum diameter of 1.76 miles. In 1969 an individual Short-eared Owl had oc- cupied the same territory but had maintained a home range of only 0.66 s(j miles with a maxi- mum diameter of 1.21 miles. In both cases the home range extended o\cr the vallev floor and did not enter the foothills or hills. In 1969 two Raven pairs possessed home ranges averaging 2.31 ±: 0.32 sq miles (range 1.86 — 2.76 sq miles ) with average maximum diame- ters of 2.22 ± 0.15 miles (range 2.07 — 2.53 miles). In 1970 two Raven pairs maintained home ranges of 2.74 =t 0.17 sq miles (range 2.5 — 2.98 sq miles) with average maximum di- ameters of 2.12 ± 0.26 miles (range 1.76 — 2.48 miles). Raven pairs maintained larger home ranges than all of the other raptor species ex- cept Red-tailed Hawks and Golden Eagles. They also appeared to be little influenced by topography and possessed widely ranging terri- tories. Intraspecific and Interspecific Associatioi^. Nesting and home range associations between raptor species are examined as follows through ( 1 ) an analysis of observed hostile interactions between species, (2) the degree of overlap of intra- and interspecific home ranges, and (.3) measurements of distances to nearest neighbors of all raptor species. A catalog of obsei'ved hostile interactions is presented in Table 19. All forms of interactions, including stooping, pursuits, fights, and displays are combined. Most of the observed interac- tions concerned territorial disputes or nest de- fense or displacement activities caused by the presence of the investigator; this has been pre- vioush' discussed in other sections of this paper. The two most aggressive species appear to be the Ferruginous and Red-tailed Hawk, and one is tempted to suggest that their aggressiveness directly results in their high nesting populations and positions of dominance. Undoubtedlv their high populations and competition for similar nest- ing sites produce some conflicts both within the species populations and between these and other raptor species with similar habitat requirements, such as Swainson's Hawks. The similar habitat requirements of Red-tailed Hawks and Great Horned Owls almost certainl\- produces the same' degrees of hostile interactions. Unfor- tunately, many of the observed interactions were prompted by disturbance caused by the investi- gators. This is particularly true of the previ- ously discussed attacks on Great Horned Owls by Red-tailed Hawks, Ferruginous Hawks, and Prairie Falcons, and it is probable that this noc- turnal species has little or no contact with these hawks in its normal activity patterns, although both Cameron (1914) and Weigand (1967) observed Ferruginous Hawks attacking Great Horned Owls. Few interactions of any kind were observed ix'tween an\ of the medium- and small-sized raptors. Their small populations and wide dis- 42 BiucnAM VouNo University Science Bulletin Table 19. Catalog of interspecific and intraspecific interactions observed on the study area from 1967-1970. 1 3 o n3 Ul "s be Species Attacking 13 es p £S OX ■l1 O .2 c U O l| UK ll o ll 1 > Golden Eagle 0 0 1 3 0 1 0 0 0 0 0 0 Great Horned Owl 0 0 4 12 0 4 0 0 0 0 0 2 FernigiiioMS Hawk 0 0 5 6 4 0 0 0 0 0 0 0 Red-tailed Hawk 0 0 6 2 0 0 0 0 2 0 0 0 Swainson'.s Hawk 2 0 12 0 0 0 0 0 0 0 0 0 Prairie Falcon 0 0 0 0 0 0 0 0 0 0 0 0 Marsh Hawk 0 0 0 0 0 1 0 0 0 0 0 0 Cooper's Hawk 0 0 0 0 0 0 0 0 0 0 0 0 Sparrow Hawk 2 0 0 0 0 0 0 0 0 0 0 0 Short-cared Owl 1 0 0 0 0 0 0 0 0 0 0 0 Burrowing Owl 0 0 0 0 0 0 0 0 0 0 0 0 Raven 3 0 0 3 0 1 0 0 1 0 0 2 Totals 8 0 28 26 4 7 0 0 3 0 0 4 persal account for at least part of this lack (par- ticularly intraspecific contacts), but their dif- fering habitat requirements also prevent much interspecific contact with the large raptor species. However, this is not true of the Prairie Falcon, which ranks third in aggressiveness on the basis of observed aggression contacts. In this case, however, Prairie Falcons are a raptor with habitat requirements similar to those of the larger species. Information on intraspecific and interspecific overlap of home ranges is useful in estimating the degree of association of the various raptor species and is detemiined from the pooled data of the home range determinations of 1969 and 1970. The large Golden Eagle home ranges overlapped to some extent with ever)- nesting raptor species. Golden Eagle home ranges over- lapped with almost one-half of the nesting Great Horned Owl pairs in amounts ranging from 6-100 percent overlap; with 45 percent of the Ferruginous Hawk home ranges in amounts varving from 6-100 percent; with one-third of the Red-tailed Hawk home ranges in amounts varying from 5-90 percent; with 2.5 percent of the Swainson's Hawks in amounts varying from lS-65 percent and with most of the small- and medium-si'/ed raptors in amounts varying from slight (as with the Burrowing Owls) to consid- erable, (ireat Horned Owl home ranges showed very similar overlaps with the majority of the raptors but did not overlap with home ranges of tlie Short-eared Owl and Bunowing Owl, supporting Errington's supposition (1938) that they will tolerate no other owls within their home range. Overlap between adjacent Great Homed Owl pairs was present in 32 percent of the popula- tion but in \er\ slight (2-5 percent) amounts. Ferruginous Hawk home ranges also over- lapped with the majority of the raptor species in amounts varying from appro.ximatcly 2-100 percent. In 1969 and again in 1970, three close nesting Ferruginous Hawk pairs in the extreme southeast portion of the study area overlapped approximately 5-10 percent of their adjacent boundaries, but in vers' slight amounts. The majoritx' of the medium- and small-sized raptors had home ranges overlapped by the large rap- tors as discussed previously. No intraspecific overlap between adjacent ranges of Sparrow Hawks, Marsli Hawks or Ravens occurred, but most were widely spaced. Marsh Hawk home ranges did o\'erlap with Short-eared Owl home ranges (approximately 24 percent), Burrowing Owl home ranges (6-85 percent), and Raven home ranges (35 percent), but did not overlap with Sparrow Hawk or Prairie Falcon home ranges. With one exception all Burrowing Owl home ranges overlapped, both with adjacent pairs and extensively within all members of the small colony. The distances to nearest neighbors should in- dicate to some extent the degree of tolerance disphui'd bi'tween adjacent pairs of the same species and that existing between different rap- tor species. In the following, results from all four stud\' years are pooled. Golden Eagle nests were spaced an avi-rage of 2.18 :+: 0.23 miles apart ( 14 nests, range 1.28 — 3.6 miles). The nearest nests were separated by the high ridges of the intervening Thorpe Hills and the pairs tended to hunt in opposite valleys. Dis- tances between (Golden I'agle and Great Homed Biolocic:al StiuES, \'i)l. 18, No. 3 Bkei-dinc 1''.(:()i.()gv ■ii" Utah Raptohs 43 Owl nests avfiagod only 0.695 ± O.IS miles (range 0.05 — 1.52 miles), but distances be- tween Golden Eagles and the large Butco hawks on the study area averaged 1.54 ± 0.22 miles to Ferruginous Hawk nests (range 0.55 - 2.51 miles); 1.52 ± 0.13 miles to Red-tailed Hawk nest sites ( range 0.83 — 2.65 miles ) ; and 2.32 ± 0.994 miles ( range 0.73 — 3.91 miles ) to Swainson's Hawk nesting sites. Despite their ver\ similar nesting requirements, distances be- tween Golden Eagle and Ra\en nests averaged 1.37 ± 0.21 miles (range 0.06 — 3.0 miles). Distances between adjacent Great Horned Owl pairs averaged 1.19 ± 0.21 miles (range 0.64 — 3.5 miles). The maximum distances were ob- served between nests across areas which lacked suitable nesting cliffs and had verv little cover. Great Horned Owl nests were often in relatively close proximit\' to nests of most of the diurnal Buteos, averaging 0.766 ± 0.16 miles to Ferru- ginous Hawk nest sites (range 0.21 — 1.7 miles); 0.8S6 ± 0.17 miles to Red-tailed Hawk nests (range 0.004 — 1.4S miles); and 0.677 ± 0.09 miles to Raven nests. As with the Gold- en Eagle nests. Great Horned Owls nested far from Swainson's Hawk nesting sites, averaging 2.2 - 0.16 miles distant (range 1.85 — 2.69 miles ) . Distances between adjacent Ferruginous Hawk nests averaged 1.55 ±0.1 miles (range 0.81 — 3.39 miles). Ferruginous Hawks aver- aged 0.826 ± 0.13 miles (range 0.39-2.06 miles) from Red-tailed Hawk nest sites and 0.788 ± 0.13 miles (range 0.29—1.06 miles) from Swain- son's Hawk nests. In contrast, distances to nests of the Riuen averaged 1.3 ± 0.22 miles ( range 0.46 — 2.44 miles). Distances between adjacent Red-tailed Hawk nests averaged 2.05 ± 0.18 miles (range 1.27 — 4.2 miles) and were the most widely spaced of the large raptors except for those of the Swainson's Hawk and Raven nesting sites, averaging 1.17 ± 0.07 miles to the former (range 0.95 — 1.35 miles) and 1.08 *: 0.12 miles to the latter (range 0.55 — 1.84 miles). Me;isurements of distances between the medium- and small-sized raptors proved to be unre;ilistie because of their small populations and wide range of habitat reejuirements. The majority were ver\ distant from any of the larg(> raptor nesting sites, but exceptions were noted. Frairie Falcon pairs nested within 0.013 miles (within the same eliffiine) of an active Great Horned Owl nest, and Ravens in 1968 nested but 0.28 miles from a (iolden Eagle nest, witli ,ill nests successluli\ ficdging at le;ist one \i)ung. Adjacent Marsh Hawk nests averaged 2.39 ± 0.57 miles apart (range 1.12 — 3.65 miles). Most of the Marsh Hawk, Burrowing Owl, and Short-eared Owl nesting sites were in close proximiti} (i.e., less than one-half mile apart); this is undoubtedly a result of their similar habi- tat requirements. Nests of the Burrowing Owl colony averaged but 0.042 ±: 0.01 miles apart (range 0.015 — 0.08 miles) and were the most closely spaced of anv intr;ispecific nests on the study area. In summary, intraspecific nests maintained minimum average distances apart, with the noted exception of the Burrowing Owl; but in- terspecific nesting site distances varied greatly, primarily because of apparent tolerance differ- ences among species and the influence of ac- tivity patterns which will be discussed later, all of which combined to reveal the habitat as a mosaic of distinct home ranges centering around the nesting sites. Hunting Activity Patterns and Habitat The hunting activity periods of the raptors are presented in Fig. 22 and 23. These were derixed from observations of birds from blinds and from notes on the specific activity of rap- tors when sighted. The area contained within the lines represents the relative degree of ac- tivity, and the thin lines which may or may not be presi'ut represent additional but limited activ- ity. Although it is a well-known fact that raptors will hunt at any time if hungry or when in need of prey for their young, they do exhibit definite hunting periods. The activity patterns of all of the diurnal raptors fall into a pattern of separate morning and afternoon or early eve- ning hunting periods, and all showed a lull or midafternoon period of inactivity. Among the large raptors, Ferruginous Hawks were the first to initiiite hunting activities in the day, and their most intensive hunting periods oc- curred from first litijlit, 0545 lirs to sunrise (ap- proximately 0600 hrs) and between 1745 hrs and 2045 !ns in the late afternoon and evening until shortly after sunset. Ferruginous Hawks typic;illy hunted over mixed sagebrush-grass- land areas but were also observed hunting in th(> sagebrush-Tt'fra(/(y;/i/« areas near the nests. Both Red-tailed Hawks and CJolden Eagles initiated their hunting activities in the mid- mornimr at approximately 0830 hrs and both sp(>cies terminated their morning hunt near 1200 hrs. Golden Eagles ranged over a wide area and have bc^'u observed hunting in a variety of habitats, liut Red-tailed Hawks most frecjuently hunted in sagebrush stands. Although 44 BmaiiAM Young University Science Bulletin golden eagle great horned owl swainson's hawk - RED-TAILED HAWK - FERRUGINOUS HAWK " 6 LIGHT 9 12 3 NOON Fig. 22. Hunting activity patterns of the large raptors on the study area. 9 DARK PRAIRIE FALCON MARSH HAWK COOPER'S HAWK SPARROW HAWK- burrowing owl- Fig. 23. Iluiiliiig activity ])al(crns of medium- and s[uall-si/cd raptors. lU'cl-tailc'c! Hawks also ranged widely, one pair lumted over a small sagebrnsh stand less than 0.0.3 miles from their nestiijg site. Both species had similar intensive hunting periods, from approximately 1445 to 1830 hrs, but Red- tailed Hawks tended to hunt throughout a greater portion of the dav than any other large raptor species. The morning hunting periods of the Swainson's Hawk began well after that of the Ferruginous Hawk had terminated, and their afternoon hunting periods were completed before Ferniginous Hawks began to hunt. .Swainson's Hawks also tended to hunt in the im- mediate n(\sting \ieinitv in habitats similar to tliose in whieli Ferruginous Hawks predomi- nantly hunted. .\il of the small raptors nesting (ju the study arc. initiated tlieir hunting periods very early in tlie morning and generally before sunrise. Marsli Hawks were partieularh active at this time hut continued until well into the morning hours. .Sparrow Hawks were the last of the small raptors to b(\gin lumting, initiating their morning limit at approximately 0745 hrs. Spar- Biological Seiues, \'ol. 18, No. BlUCKIMNG KCOLOGV OF UlAIl l{ArTOH,>, 45 row Hawks probably hunted during more hours of the dav than anv other raptors on the stud\- area, although still exhibiting peak late morning (1045-1200 hrs) and late afternoon periods. Thev hunted o\'er a wide variety of habitats in- cluding pinvon-juniper, winterfat, and mixed grassland areas. Prairie Falcons exhibited simi- lar hunting habitat preferences. On the other hand, both Marsh Ha\yks and Ravens appar- ently preferred to hunt o\er sagebnish or mixed grassland-rabbitbrush stands. All of the nocturnal raptors on the study area showed some tendency to hunt during da\liglit hours. Great Horned Owls and Short- eared Owls began hunting periods in the late e\'ening liours after sunset but before darkness. Both showed essentially two periods of in- tensive hunting, one beginning at approximateh- 2030-2045 hrs and continuing until 2400 hrs, and the other beginning in the earh' morning hours from 0430 to shortly after first light. On two occasions Great Horned Owls were ob- served in the late afternoon from appro.ximately 1645 hrs until darkness. In both instances the day was overcast and snowy. Similar observa- tions of diurnal hunting by Great Horned Owls have been noted jjy Fitch (1940) and \'aughn ( 1954 ) . Burrowing Owls arc \er>- alert and ac- tive during the daylight hours, and their peak aeti\it\' p(>riods are from approximately 0430 to 0645 hrs and from 1740 to 2330 hrs. They were also observed hunting, although infrequently, as late as 0850 hrs in the morning, and may occasionally hunt at any time of the day. Predation The prey of 9 species of raptors was ex- amined in 1969, and of 11 in 1970. A total of 2111 prey individuals of 55 prey species were identified and tabulated (Tables 20-39). The prey of the collective raptor population in- cluded 75.2 percent mammals ( 1588 prey indi- viduals of 17 mammal species), 8.5 percent rep- tiles (27 individuals of 7 species) and 15 per- cent invertebrates (316 individuals of 8 families). Minor but not significant variations in prey species and frecjuencv occurred l^etween the two \ears. Golden Eagles utilized a total of only ten prey species, including five mammal and five avian species. Mammals were much more fre- quently preyed upon (96.5 percent of the total prey) and comprised the bulk of the prey bio- mass (99.4 percent), whereas birds comprised 0.6 percent of the prey biomass and averaged only 3.3 percent of the individuals taken. Lago- Tahle 20. Food habits of Golden Eagles in 1969. No. % Approx. % Species Indv. Indv. Biomass Biomass Lepus californicus 155 74.5 356,500 88.6 St/hilafius sp. 43 20.8 43,000 10.7 Ainin()S))crmophihis leucurus 3 1.4 435 0.1 Peroi()S))erniophiltis leucurus 9 7.6 1,305 0.7 Mustclii frenala 2 1.7 356 0.2 Zeiiaidura macroura 1 0.8 153 0.1 Otocoris alpestris 3 2.5 56 Tr." Buteo sicainsoni 1 0.8 988 0.5 Totals 119 99.9 194,258 100.0 'Present in trace amounts only. 46 BiiiciiAM VouNf. University Science Bulletin 'HiWe 22. Food habits of Croat Ilonu.l Owls in 1969. No. % Species Indv. Indv. Leptis californicus 165 58.9 Siilvil(iii,us auduboni 32 11.4 Neotoma Icpidii 6 2.1 Per()L:,milIius parvus 2 0,7 Dipadditii/s ruirrops 8 2.9 Dipodoniiia urdii 11 3.9 Microtiis sp. 5 1.8 Pertinuisciis numictduftis 7 2.5 CijanocvpJudus ciiinwrcpludus 3 1.1 Zcnaidum macroura 5 1.8 Phalaenopfdtis mttUdUi 1 0.4 Scorpionida 35 12.5 Totals 280 100.0 .Xppro.v. % Biomass Biomass 379,500 91.4 32,000 7.7 1,.302 0.3 .30 Tr." 520 0.1 748 0.2 190 Tr. 119 Tr. 50 Tr. 765 0.2 62 Tr. 30 Tr. 415,316 100.0 'Present iti time niiKninls only. Table 23. Food habits of Great Homed Owls in 1970. No. % Approx. % Species Indv. Indv. Biomass Biomass Lepus californicus 83 49.1 190,900 89.6 Si/hnhiiius sp . 19 11.2 19,900 8.9 Neotoma lipida 1 0,6 217 0.1 Dipodoniifs ordii 24 14.2 1,632 0.8 Dipitdoitnjs microps 3 1,8 195 0,1 Pcntmiiscus iiianirtddlus 12 7.1 204 0.1 Microdipodops mchis tacniatus 3 1.6 507 0.2 Totals 190 99.9 275,961 99.6 'l*ir>«pnt in irare amounts only. 48 HniniiAM Young IInivkhsity Science Bulletin total l)i()mas.s of Great Horned Owl prey, at least one species of scorpion was taken quite frecjuently during all four study years (see Murphw et al., 1969). Although scoqiions were not taken by all Great Horned Owl pairs, they showed up consistently and almost exclusively in tlie n(-st site pellets of a pair nesting in the west Thorpe Hills area, serving to indicate the possibilities of error when analyzing food habits of raptor pairs. Interestingly, the female of this pair had an irregular left eye and it is tempting to speculate that there was a possible connection. Errington, Hamerstrom, and Hamer- strom ( 1940 ) suggested that predation on ar- thropods is most characteristic of recently fledged owls, but as previouslv noted, the scorpions were found every year that this fe- male was present. One Black-billed Magpie was taken by a pair of Great Homed Owls nesting in pinyon-juniper. Magpies were com- mon around the towns and cultivated areas of the northeast portion of Cedar Valley and fre- quenth' nested in cottonwoods and elms in those areas. They did not nest within the study area, probabK' I)ecause of a combination of un- suitable habitat and possible predation. Ferruginous Hawks within the study area utilized a total of 17 prey species, including 9 mammal, 6 avian, and 2 reptile species. Mam- mals comprised S9.5 percent of the prey indi- viduals and 99.4 percent of the total prey biomass. In contrast, birds comprised only 8.7 percent of the total prey items and 0.2 percent of the total prey biomass, while reptiles in- eluded 1.7 percent of the total prey individuals and 0..3 percent of the total prey biomass. Lago- Table 27. Food habit.s of Red-tailed Hawk.s in 1970. No. % Appro.x. % Species Indv. Indv. Biomass Biomass" Leptis californicus. 71 50.7 163,300 90.0 Sijlviliii:,us- sp. 15 10.7 15,000 8.2 Spennopltihis townsencU 1 0.7 191 0.1 Amiiiospcrmophihis leucums 9 6.4 1,304 0.7 Peromi/scus mdnicultifiis 26 1S.6 442 0.2 Mir rot Its sp. 1 0.7 38 Tr. Thomomi/s holtac 2 1.6 340 0.2 Otecoris alpcstris 3 2.1 84 Tr. Tt/ranniis verticalis 1 0.7 36 Tr. Stiirnis vuli^aiis 9 6.4 756 0.4 PHitophis nichinoleiicits 1 0.7 372 0.2 Crot(ip]ii/lus coUaris 1 0.7 30 Tr. Totals 140 100.0 181,893 100.0 'I'rt-'i.i'nl in Iraie iinnninls onlv- Table 28. Food habits of Swainson's Hawks in 1969, No. % Approx. % Species Indv. Indv. Biomass Biomass" Lepiis californicus 42 51.2 96,600 95.0 St/lvihif^us sp. 4 4.9 4,000 3.9 Perotni/sctis nianiculatus 7 8.5 119 0.1 Mirrotits .v/). 3 3.7 114 0.1 Spcrniophiltis lounsendi 1 1.2 191 0.2 Calamospiza melanoconjs 3 3.7 99 0.1 Lanius ludoviciamis 1 1.2 52 0.1 Orcoscoptes iiwntanus 1 1.2 45 Tr. Sai/ortiis sat/o 2 2.4 56 0.1 Zonotrichia leucophnjs 1 1.2 30 Tr. Pituophis mehinoleucHS 1 1.2 372 0.4 Locustidae 15 18.3 95 Tr. Carabidae 1 1.2 0.23 Tr. Totals 82 99.9 101,688 100.0 •Prc-icril irt irate nnioiints unlv. Bioloc;ic:al Skiues, Vol. 18, No. 3 Ukkicdinc; E(X)i,<)f:v oi- Vt.\u Hai-tohs 49 Table 29. Food habits of Swainson's Hawks in 1970. No. % Species Indv. Indv. Leptis californicus 15 19.0 St/IvihiiS.tis audohoni 9 11.4 Pcronujscits maniculatus 2 2.5 Micwtus sp. 1 1.3 Otocoris (dpestiis 11 13.9 Unident. Pa.s.serincs 8 10.1 Lociistidac 17 21.5 Carabidac 5 6.3 Tcncbrionidac 2 2.5 Grvllidat- 9 11.4 Totals 79 99.9 Appro.x. % Biomass Biomass* 34,500 78.2 9,000 20.4 34 0.1 38 0.1 308 0.7 240 0.5 11 Tr. 1 Tr. 1 Tr. 4 Tr. 44,137 100.0 'Piesent III tiace aniounts only. Table .30. Food habits of Prairie Falcons in 1970. Species No. Indv. Amiuospermiipliilus leuciirtis 5 Peromijscus maniculatus Lepus californicus (juv. ) Otocoris alpcstris Oberholscria chlorura Pooecetcs L:,rami)icus 1 2 7 1 1 Sturnis vuli^aris Sturnella neglecta Locustidao 3 1 5 Totals 26 Indv. 19.2 3.8 7.7 26.9 3.8 3.8 11.5 3.8 19.2 99.7 Appro.\. Biomass 725.0 17.0 2,300.0 196.0 30.0 27.0 84.0 145.0 3.2 3,527.2 Biomass* 20.6 0.5 65.2 5.6 0.9 0.7 2.4 4.1 Tr. 100.0 aiiioiiiits tmly. Table .31. Food habits of Marsh Hawks in 1969. No. % Appro.x. % Species Indv. Indv. Biomass Biomass* Lepus californicus (juv.) 12 31.6 1,200.0 50.1 Spennophilus tounsendi 5 13.2 755.0 31.5 Pcroini/scus maniculatus 7 18.4 119.0 5.0 Reifhrodontomi/s Megalotis 2 5.3 24.0 1.0 Otocoris alpcstris 4 10.5 112.0 4.7 Zenaidura macroura 1 2.6 153.0 6.4 Pooecetes gramineus 1 2.6 30.0 1.0 Carabidae 6 15.8 1.4 1.3 Totals 38 100.0 2,394.4 101.0 * Present in Ii.lie ^iindiints imlv. iiioiphs attain were the mo.st frequent prev item, averas^ing 62.5 percent of the total prey and contributing 97.4 percent of tlie prey bio- mass in each of the two years. Tlie next most frequently taken pre\- items were, in order of their aNcrage vearh' freqiiencv; Ords kangaroo rat, C(;nstituting 11.8 percent of the total prey but only 0.5 percent of the prey biomass; the antelope ground sfjuirrel. which averaged 7.3 percent of the total prev individuals and 0.25 percent of the prey biomass; and the Homed Lark, which averaged 6.5 percent of the total prey and 0.15 percent of the prey biomass. The two kangaroo rat species and pocket mouse reflect cssentiallv crepuscular hunting activity patterns of the Ferruginous Hawk as discussed earlier. Ferruginous Hawks also infrequently pre\'ed on gopher snakes. 50 BniGiiAM '^'ouNG University Science Bulletin Mammals wen- also the major prey of Red- tailed Hawks, coinprisinu; S9.1 pcreent of the prey individuals and 99.4 percent of the total prey biomass, while birds constituted 9.1 per- cent and 0.2 percent, and reptiles accounted for 1.8 percent and 0.3 percent of the total prey items and total pr('\- biomass, respectively. The major items of importance were again the lago- morphs, which accounted for 64.4 percent of the prev items and 98.5 percent of the total prey ijiomass. In addition. Red-tailed Hawks preyed on 6 other mammal species, 5 avian, and 3 reptile species. Other mammal species of im- portance included tlu' deer mouse, which com- prised 12.7 percent of its total diet; meadow mice, comprising 6.2 percent; and the antelope ground sciuirrel, which constituted 3.2 percent. Starlings and Finvon Javs were the most fre- ((ueiitlv taken avian pre\ species. Starlings were first recorded in Utah in 1949 in and around url)an areas (Behle, 1954). Since that time they ha\e spread widely throughout the state and Table 32. Food habits of Marsh Hawks in 1970. No. % Approx. % Species Indv. Indv. Biomass Bioma.ss° Lepus californicus 5 13.5 5,000.0 86.9 Peroiui/scus maniculatus 15 40.5 255.0 4.4 SpeimopJiiliis tounscncU 1 2.7 191.0 3.3 Otocoiis (iIjK'stris 7 18.9 196.0 3.4 Pooecetcs ^raminetis 3 8.1 81.0 1.4 Demiestidae 5 13.5 1.2 Tr. CrofopJuilus collaris 1 2.7 30.0 0.5 Totals 37 99.9 5,754.2 99.9 tit in hiifo anioiiiii'i Table .33. i'ood liabits of Sparrow Hauks in 1969. No. % Approx. % Species Indv. Indv. Biomass Biomass* Microtus sp. 5 6.5 190.0 17.6 Peromiisciis nuiniciilatiis 18 23.4 306.0 28.3 Otocoris alpestris 6 7.8 168.0 15.6 Sialia currucoide.s 2 2.6 90.0 8.3 Passer domcsticus 2 2.6 50.0 4.6 Sftirnis viiliiuris 3 3.9 252.0 23.3 Uta st(insl)uriami 1 1.3 4.0 0.4 Aranae 2 2.6 0.8 Tr. Locustidae 29 37.6 18.3 1.7 Curculionidae 7 9.1 0.7 Tr. Uniden. Colcoptcra 2 2.6 0.6 Tr. Totals 77 100.0 1,080.4 99.8 'Pirst-nt in li.irc nnioimts imly. Tal)le 34. Food habits of Sparrow Hawks in 1970. Species No. Indv. % Indv. Approx. Biomass % Biomass* Peronu/sciis maniculatus 7 21.2 119.0 30.4 Passer clomesticus 3 9.1 75.0 19.2 ^Itirnis vulgaris 2 6.1 168.0 42.9 Uta stansl>uriana 3 9.1 12.0 3.1 Pltrynosonia plat i/ rhinos 1 3.0 9.0 2.3 Locustidae 13 39.4 8.2 2.1 Curculionidae 4 12.1 0.4 Tr. Totals 33 100.0 391.6 100.0 'Present in trace amounts onlv. Biological Sehies. \'ol. 18, No. .3 Bkeedinc Ecology ok Ut.\h K.-vptobs 51 Table 35. Food habits of Short-eared Owls in 1970. No. % Appro.x. % Species Indv. Indv. Biomass Biomass Dipodomifs ordii 7 20.0 476 37.4 Reithrodoiitomys tnei:.(ilotis 2 5.7 24 1.9 Peromt/sciis maniadatus 19 54.3 323 25.9 Pcroi:.nathu.s parvus .3 8.6 45 3.5 Unidentifk'cl pa.s.scrine 1 2.9 30 2.4 Sturnis vulgaris 1 2.9 84 6.6 StttrncIIa ncjjccta 2 5.7 290 22.6 Totals 35 100.1 1,272 100.3 Table 36. Food habits of Burrowing Owls in 1969. No. % Approx. % Species Indv. Indv. Biomass Biomass" Dipodomtjs ordii 11 12.4 748.0 73.1 Peroi:.nathtis formosits 1 1.1 19.0 1.9 Microtus sp. 2 2.2 76.0 7.4 Phalaenoptilus mittali 1 1.1 62.0 6.0 Otocoris alpcsfris 3 3.3 84.0 8.2 Vta staushuriana 1 1.1 4.0 0.3 Locustidae 29 32.6 18.3 1.9 Scarabidae 19 21.3 5.7 0.6 Silphidac 11 12.4 3.3 0.3 Carabidae 7 7.9 1.6 0.2 Teiu'brionidae 2 2.2 1.1 0.1 .■\iaiiae 2 2.2 0.8 Tr. Totals 89 99.8 1,023.8 100.0 * Pi (-sent in liiice .immmts only. Table 37. Food habits of Burrowing Owls in 1970. No. % Approx. % Species Indv. Indv. Biomass Biomass D'.jxidoiiu/s ordii 4 5.5 272.0 61.9 Pcromt/sctis iiuinicu hit us 2 2.7 34.0 7.7 Reithrodontomys megalotis 1 1.4 12.0 2.7 Otocoris alpestris 2 2.7 56.0 12.7 Passer doniesticus 1 1.4 25.0 5.7 I'td staml)tiriarm 3 4.2 12.0 2.7 Locu.stidac 34 46.6 21.4 4.9 Silphidac 13 17.8 3,9 0.9 Caial)idae 8 11.0 1.8 0.4 Scarabidae 5 6.8 1.5 0.3 Totals 73 100.1 439.6 99.9 are perhaps the iiKJSt eoinnion nestini^ species on the stiuK' area in such areas as quarries and abandoned niiiiiiiL!; structures, where they are oceasionalK' prcNctl on 1)\' raptors. Red-tailed Hawks also infrecjuently preved on snakes, the two species recorded from this stndv being tlu' gopher snake and striped racer. Swainson's Hawks on the stndy area utilized a total of 1.5 pre\' species ineluding 5 ruamiiial. 5 a\ian, 1 reptile, and 4 invertebrate species. The relati\e composition of the Swainson's Hawk diet is as follows: mammals, 51.9 percent of the total pre\' individuals and 99.1 percent of the total pre\' biomass; birds, 16.9 and 0.8 percent; reptiles, 0.6 and 0,2 percent; invertebrates, .30.6 and less tlian 0.1 percent. Swainson's Hawks were the only large raptors studied in which the average frecjuencv of lagomorjih prev was less 52 BmoiiAM VouNG University Science Bulletin than lialf of tlic total diet. Lagomorphs thus constituted 56.1 pcrct'ot of the diet in 1969 hut onlv 30.4 percent in 1970. However, in both years the higonioiphs, hv \irtne of tlieir large body size, comprised almost 99 percent of the total prey biomas.s. The second most numerous prey items were Locustid insects which com- prised an average 19.9 percent of the yearly diet, although contributing comparatively small amounts of the total biomass. Other insects taken included carabids, tenebrionids, and gryllids. Deer mice were taken iiifrequentlv, as were meadow mice. Horned Larks were the most frequently taken avian species and consti- tuted almost 7 percent of the total prev taken. Information on the food habits of the Prairie Falcon was obtained only during the 1970 breeding season. Prairie Falcon prey consisted of nine species, including three mammal, five avian and one insect species. Birds were the most frequently taken prey and comprised 49.8 percent of the prey individuals Ijut only 4.1 percent of the total prey biomass. Mammals comprised 30.7 percent of the prey individuals and contributed a prev biomass of 86.3 percent, while invertebrates accounted for 19.2 percent of the prev individuals but for little or no bio- mass. The two most freeiuentlv taken prey species were the Honied Lark (26.9 percent of the total prey individuals) and antelope ground squirrel (19.2 percent), but juvenile black- tailed jackrabbits comprised over 65 percent of the prey biomass, even though taken only one- sixth as often. Tile food of Marsh Hawks included 10 prey species, of which there were 4 mammals, 3 birds, 1 reptile, and 2 invertebrate species. Marsh Hawks preyed most fretjuently on mam- mals (62.5 percent of the prey items) which also contributed the bulk of the prey biomass (91.9 percent). Of the other major prey groups, birds were taken 21.4 percent of the time and comprised 8.5 percent of the prev biomass, rep- tiles 14.7 and 0.7 percent and invertebrates 1.4 and 0.3 percent, respectively. The most im- portant prev of the Marsh Hawks included black-tailed jaekral)liits and the deer mouse. The majorit) of rabbits taken were immatures, Table 38. Food habits of Ravens in 1969. No. % ."Vpprox. % Species Indv. Indv. Bioma.ss Biomass" Leptis calif orniciis ( juv ) 19 3L1 19,000.0 95.6 Peromijscus manicidatus 12 19.7 204.0 1.0 Microtus sp. 3 4.9 114.0 0.6 Neotonia Icpida 1 1.6 217.0 1.1 Spizella passcrina 1 1.6 38.0 0.2 Passer domesticus 3 4.9 75.0 0.4 Oreoscoptes monfunus 1 1.6 45.0 0.2 Masticoph is taeniattis 1 1.6 169.0 0.9 Dermestidae 9 14.8 0.9 Tr. Silphidae 6 9.8 1.8 Tr. Curculionidae 2 3.3 0.2 Tr. Unident. Coleoptera 3 4.9 0.9 Tr. Totals 61 99.8 19,864.8 100.0 'Pi<"ioiit in ttiiro nninunts milv. Table 39. Food iiabits of Ravens in 1970. No. % Approx. % Species Indv. Indv. Biomass Biomass" Si/Ivihii:,us sp. 6 16.7 6,000.0 90.7 Pcroniijsctis iimniculatiis 13 .36.1 221.0 3.3 Otocoris alpestris 4 11.1 112.0 1.7 Sttirnis vul'j,(iris 1 2.8 84.0 1.3 Maslirophis lacnialus 1 2.8 169.0 2.6 Sccl()}>or()us grasciosus 2 5.6 26.0 0.4 Unident. Coleoptera 9 25.0 2.7 Tr. Totals 36 100.1 6,614.7 100.0 •I*resent in Irace amounLs only. Biol()gic:al Sehiks. N'ol. 18, No. 3 Bhkkding Ecology of IItah Haptohs 53 juveniles, or carrion but they comprised 22.6 percent of the total prey biomass. Deer mice were taken more frecjuently, yet, by contrast, Townsends ground scjuirrels comprised only 8 percent of the prey items but 17.4 percent of the total prey biomass. Horned Larks and Mourning Doves were also taken occasionally. Sparrow Hawks on the study area utilized a total of 12 species, which included 2 mammal, 4 birds, 2 reptiles, and 4 invertebrates. The relatixe composition of the prey frequency and biomass of the major prey groups of the Spar- row Hawk is as follows: maiumals, 25.6 percent and .3S.2 percent; birds, 16.1 and 57.0 percent; reptiles, 6.7 and 2.9 percent; and invertebrates, 51.7 and 1.9 percent. Locustids were the most important ia\ertebrate prey species, averaging 38.5 percent of the yearly diet. The more im- portant vertebrate prey species included the deer mouse, which comprised 22. .3 percent of the total pre\' items and 29.5 percent of the total prey biomass, and Starlings, which con- tributed the bulk of the prey biomass (.33.3 percent), although taken infrequently. Of the a\ian prey species, English Sparrows, Starlings, and Western Bluebirds reflect the habitat se- lection of Sparrow Hawks, being the most com- mon nesting birds in and around the abandoned mines, (juarries, and mining structures. The oc- currence of Western Bluebirds as prey is inter- esting, because the disappearance of a bluebird and the subsecjuent failure of its nesting efforts coincided with the appearance of this species in tlie prey of a Sparrow Hawk pair. The blue- birds had selected a nesting site within the wooden walls of a luining cabin only 80 feet from tlie Sparrow Hawk nest and were incu- l)ating a clutch of five eggs when checked the day before the disappearance. Two days later the remains of a bluebird were found among the pre\- items in the Sparrow Hawk pair's lust. Powers (1966) cites possible examples of Sparrow Hawk predation on bluebirds in Montana, and Drinkwater (1953) recorded a ease of Sparrow Hawks capturing young blue- birds by nest robbing. Information on Short-eared Owl food habits was obtained only in 1970 and is derived from the analysis of 19 pellets gathered from the un- successful nest site. Pellet anahsis \ielded a total of 7 prey species and 35 individuals, but onl\' mammals and birds were present. Mam- mals contributed SS.6 percent of the prey indi- viduals and 68.2 percent of the prev biomass, while birds comprised 11.5 percent and 31.8 percent, respecti\'ely. The two most important prey species were Orel's kangaroo rat and the deer mouse. D(>er iTiiee were taken almost three times as often as any other prey species and contributed 26.4 percent of the total prey bio- mass. Ord's kangaroo rat was the ne.xt most fre(|uently taken prey and comprised 37.4 per- c(>nt of the prey biomass. Western Meadowlarks contributed 22.8 percent of the total prey bio- mass. Burrowing Owl prev included a total of 15 species of which there were 5 mammal, 3 avian, 1 reptile, and 6 invertebrate species. Burrowing Owls preyed most frequently on invertebrates, which comprised 80.4 percent of the prey indi- \iduals but only 4.8 percent of the total prey biomass, the lowest of all the major animal groups except the reptiles. Mammals contributed 80.4 percent of the total prey biomass and almost 13 percent of the prey individuals taken, while birds comprised 4.3 percent of the prey items and 16.3 percent of the prey biomass. Locustids were taken more frequently than any other species, averaging 39.6 percent of the prey indi- viduals but only 3.4 percent of the total prey l)iomass. In contrast, Ord's kangaroo rat com- prised only 9 percent of the yearly prey items but contributed 67.5 percent of the total prey biomass. Burrowing Owls lined the entrance of their burrows with chewed up prey remains and manure, a fact also recorded bv Stoner (1932, 1933), Bent (1938), and Scott (1940). Ha\'ens on the study area utilized a total of 16 prey species which included 5 mammal, 5 avian, 2 reptile, and 4 invertebrate species. The majority of their food habits were determined from castings and prev remains at the nest, and there is the possibility that some of the prey brought to the nestlings may have been carrion. Mammals comprised 55.1 percent of the prey individuals and 96.2 percent of the total prey biomass. Birds comprised 11 percent of the prey individuals but only 1.9 percent of the total prey biomass, as did reptiles. Inverte- brates, entirely insects in this case, accounted for 28.9 percent of the prey individuals but con- tributed only minor amounts to the total prey biomass. Lagomorphs constituted the princi- pal prey and averaged 23.9 percent of the yearly prey individuals and 93.2 percent of the total prey biomass. Although birds were taken infrefjuentlv. Homed Larks and English Spar- rows were the most common avian prey species. Dermestids and unidentified beetles were the most frefiu(>ntly taken invertebrates. In 1970 the deer mouse was the most commonly recorded prey species, but no black-tailed jackrabbits were found— in contrast to 1969. Almost two- tiiirds of the jackrabbits were immatures or juveniles, and there is the possibility that some were taken as carrion. 54 BniGHAM Young University Science Bulletin DISCUSSION AND CONCLUSIONS Populations The average yearly raptor population sup- ported by this area of the Great Basin is ap- parently low. Craighead and Craighead (1956) recorded yearly populations of 140 raptors (9 species, 64 pairs, 12 individuals) during a two- year study of a 36-square-mile Michigan wood- lot habitat, and a population of 91 raptors ( 10 species, 45 pairs, 1 individual) in a 12-s([uare- mile study area near Moose, Wyoming, r(>pre- senting average densities of 1.8 and 3.8 raptor pairs per square mile in Michigan and Wyo- ming, respectively. These are almost four and ten times the avi-rage densities of raptor pairs recorded from this study. Additional compari- sons are available from studies of particular species. Golden Eagles nesting on the study area average 20 square miles per pair. Compara- tively, Dixon (1937) recorded densities of ap- proxiinateh' 36 square miles per pair in Southern California, and Arnold ( 1954 ) found similar pair densities in Colorado. In other studies Lockie (1964) found Golden Eagle densities of one pair per 27.1 square miles in the Scottish Iliglilands and McGahan (196S) reported one pair per 66.3 sejuare miles in Montana. Watson (1957) found relatively high breeding densities of one pair per 9 square miles in another Scot- tish study, but in a later study covering a wider portion of the same area Brown and Watson ( 1964 ) found Golden Eagle pair densities rang- ing from approximately 20 to 34 square miles per pair. Great Horned Owl densities averaged one pair per 10 square miles in central Utah. Studies in other habitats have reported much higher densities. I5aunigartner (19.39) estimated pop- ulations of one pair per 0.5 scjuare miles of riparian habitat near Lawrence, Kansas, and one pair to 3 or 4 sciuare miles near Ithaca, New York. Fitch (1947) estimated a very high popu- lation density of one pair per 0.25 square miles in California chaparral. In other studies Erring- ton, Hamerstrom, and Hamerstrom (1940) found one pair per 2 scjuare miles near Prairie du Sac, Wisconsin; Orians and Kuhlman (1956) recorded average densities of one pair per 5 square miles, also in Wisconsin; and Ilagar (1957) reported Great Horned Owl densities of one pair per 4.4 scjuare miles in central New York. Cniighead and Craighead (1956) found average densities of one pair per 5.8 square miles in Michigan and one pair per 3 square miles of stud\ area in northern \\'voming. Densities of Ferruginous Hawks on the study area averaged one pair per 8 stjuare miles. Data on population studies from other areas are lack- ing. Red-tailed Hawks averaged approximately one pair per 13 scjuare miles on the study area. Comparisons with other areas indicates these densities to be exceptionally low. Fitch, Swen- son, and Tillotson (1946) reported densities of one pair per 0.5 square miles in Madera Coun- ty, California, and Orians and Kuhlman (1956) found densities of one pair per 2.2 and 2.8 square miles in Wisconsin. In other studies Hager (1957) reported densities of one pair per 2.2 s(juare miles in central New York; Le- Duc (1970) found one pair per 1.62 square miles in southeast Minnesota; and Luttich, Keith, and Stephenson ( 1971 ) reported one pair per 2.7 sfjuare miles near Rochester, Alberta. Craighead and Craighead (1956), however, re- corded a similar low densit>' of one pair per 12.9 square miles in Michigan but found high densities of one pair per 1 square mile in Wy- oming. Comparable infonuation on the population densities of the majority of the rest of the raptors nesting on the study area is lacking, but Craighead and Craighead (1956) found greater densities of Swainson's Hawks, Prairie Falcons, Marsh Hawks, Short-eared Owls, and Ravens than were present in the central Utah area. The relativelv low raptor population densi- ties encountered in this study may be due to a number of factors. As previously noted, ap- proximately (me-half of the area ( i.e., much of the inter\ening vallev floors) is not used by any of the breeding raptors for any purpose. If these areas are eliminated, then the relative rap- tor population densities become more efjuitable witli tliose of other geographic areas. In addi- tion, tiie raptor population studies presented in tlie literature are often representative only of a specific or confined area, which was chosen be- cause of its high concentration of raptors (see Craighi'ad and Craighead 1956, p. 5; Orians and Kuhlman 1956, p. .382), thus artificially eliminating the bare or dead areas. Hence, the raptor dat;i ma\- or may not be representative of the entire area to which they are referred. Tile Utah area regularly supports from 9 to 11 raptor species, fully as many as was found by Craiglu'ad and Craighead (1956) in both Micliigan and Wyoming. In addition, a broad overlap of raptor species occurred between these ;ire;is, with fiv(^ of the ITtah stud\- area species BiOLOCicAi, Seiues, \'ol. 18, No. 3 Bkkkding Ecology of Utah Hai'tohs 55 also present in Micliit!;an and seven in Wyoming. The majority of the raptors on the stndy area show a wide geographic range and exhibit con- siderable adaptability to various habitats. That this is not a major cause of the observed den- sity \'ariations is also shown bv the much higher densities of the same species in man\' areas of their range as already noted, with the single exception of the Golden Eagle. However, lack of suitable cover and habitat has apparently limited the populations of the smaller raptors, particularly the Sparrow Hawk and Cooper's Hawk. The latter species, although known to nest occasionally in the pinyon-juniper com- munity (Wolf, 1928; Bee and Hutchings, 1942), is probabh outside of its optimum habitat. It would appear however, that the relatively low populations of most of the raptors in the study area cannot be attributed to habitat factors alone. The lower producti\'ity of this Great Basin Desert biome should limit the raptor popula- tions to some extent, even though mammalian predator control programs havt' resulted in higher populations of lagomorphs and rodents, the chief food source of the raptors. Additional evidence supporting this possibility is derived from the observed fluctuations of raptor popu- lations in response to lagomoqih population fluctuations, a subject which will ])e discussed in detail later. Two important raptor species on the stud\' area, the Golden Eagle and Ferni- ginous Hawk, were not part of the raptor popu- lation composition of the areas studied by Craighead and Craighead (1956). Their size, liome range requirements, and apparent intoler- ance of other raptor species almost certainly influenced the density of small raptors, par- ticularly in view of the previously noted Golden Eagle predation on Short-eared Owls and Swainson's Hawks. Ferruginous Hawks appar- ently have restricted habitat requirements and did not nest in the riparian cottonuood com- munities in canyons to the north and east of the study area. Here nesting Red-tailed Hawks maintained densities on the order of one pair per 0.5 - 2.0 sq miles, approximately similar to those densities reported from other parts of their range, and furtlier indicative of the possible ef- fects of the large and aggressive Golden Eagles and Ferruginous Hawks. Population Fhictuations. Variations in yearly raptor populations were evident during the four-year stud\'. Raptor populations were high- est in 1969, averaging 37.8 percent above the 1967 raptor populaticm levels, while 196S and 1970 populations were intermediate. In addi- tion, a high proportion of pairs of the 1969 pop- ulation attempted to nest (93.4 percent), com- pared to 87.5 percent of the 1967 population, 95.0 percent of the 1968 population, and 74.4 percent of the 1970 raptor population. These population variations were due primarily to yearly fluctuations of several of the large raptor species, specifically the Great Horned Owl, Red-tailed Hawk, Ferruginous Hawk, and Swainson's Hawk and were apparently inde- pendent of the relatively stable populations of the medium- and small-sized raptors. The tendency of pairs to reoccupy nesting sites and territories has the effect of stabilizing the raptor population. This tendency is ap- parently prevalent in almost all raptor species. Craighead and Craighead (1956) reported that almost 75 percent of the raptor pairs in the Michigan and Wyoming study areas reoccupied their same nesting vicinity. Elsewhere, Luttich, Keith, and Stephenson ( 1971 ) reported that only 12.4 percent of their Red-tailed Hawk pairs built a new nest during the four-year study near Rochester, Alberta, and both Hagar (1957) and Orians and Kuhlman (1956) ob- served numerous instances of Great Horned Owls and Red-tailed Hawks reoccupying their nesting sites or territories of the previous year. Cade ( 1960), and more recently. White (1969b) have expressed the opinion that a traditional or "genetic" linkage may be responsible for the almost continuous occupanev of certain cliffs or locales by Peregrine Falcons ( Falco pere- grintis) in Alaska, and Herbert and Herbert ( 1965 ) have suggested the same of falcons in the New York City region. Conceivably, such a tradition may apply to other raptor species equally as well, and nesting locales may be re- used continuously for long periods of time. Nest decay and disintegration in this area of the Great Basin is remarkably slow, and nesting sites which were photographed in 1941-1944 by Robert G. Bee (Unpubl. notes, BYU Life Sci- vnccs Museum) were still present and in some cases in use by the same species in 1967-1970, suggesting a similar trend towards long tenn oc- cupancy of a particular site. Nest Site Coiiijxirisoius with Other Geographic Areas. The 12 raptor species nesting on the study area show a wide variation in nesting selection throughout their geographic range. In this por- tion of the Great Basin the majority of Golden l]agle iK-sts are located in cliffs ( 100 percent in the study area) but Murphy, et al., (1969) recorded a few built on artificial structures or 56 UnicHAM VouNG University Science Bulletin dirccth' on the groiiiul, and Bcc and Uutchings (1942) reported Golden Eagles nesting in juni- pers and Douglas fir. In southern California, Dixon (1937) found Golden Eagles nesting al- most exclusively in cliffs, oaks, or eucal)ptus trees. Carnie (1954) also found Golden Eagles nesting in both cliffs and trees in the coastal ranges of California. Elsewhere, Wellein and Ray (1964) reported that in Colorado, New Mexico, and Wyoming 87 percent of their Gold- en Eagle nests were in cliffs, 11 percent in trees, and 1.3 percent wi-re on the ground. In Sas- katchewan, Whitfield et al. (1969) noted that all Golden Eagle uests were constructed in cliffs. In Scotland, Watson (1957) found 70 percent of the Golden Eagles nesting in cliffs and 30 percent in trees, but Gordon ( 1955) indi- cates that the majority of nests in the central Highlands are in trees, and in cliffs in the Hebrides. In this area 59.3 percent of the Great Horned Owl nests were in cliffs, 25.9 percent in quarries, and 14.8 percent in junipers, but in the eastern portion of their range most nest in trees. Orians and Kuhlman (1956), LeDuc (1970), and others have recorded all (heat Horned Owls nesting in trees. In studies from the western portion of the range, Dixon (1914) found Great Horned Owls in California utilizing cliff sites and Fitch (1947) reported a ground site in Madera Coun- ty, California. In Utah, Sugden ( 1929) reported a Great Horned Owl nesting in the ruins of Indian cliff dwellings, and Bee and Ilutchiugs (1942) found nests in junipers, ccjttonwoods, quarries, and directly on the ground. On the studv area. Ferruginous Hawks nested in trees, primarily jimipers, (69.4 percent) and on the ground. Cameron (1914) in Montana and Bowles (1931) in Washington have de- scribed ground nests of the Ferruginous Hawk and Jacot (19.34) found a bulky nest in a 34- foot c-edar. Bent (19.37) reported Ferruginous Hawks nesting in swamp oaks in North Da- kota. In Canada, Godfrey ( 1966 ) describes nesting sites in trees, ledges, river cutbanks, and on hillsides. Augell ( U)68) observed a Fer- ruginous Hawk nest built on a slight cliff ledge in Franklin County, Washington. In central Utah, Bee and Hutchiugs (1942) found Ferni- ginoiLS Hawks nesting predominatelv in junipers but noted that they also nest in tall trees and cliff ledges. The nesting site selections of Hed-tailed Hawks show wide variations throughout their range. On the study area 54.5 percent of their nests were constructed in tr<'es, 36.4 percent in cliffs, and 9.1 percent in (|uarries. In other parts of the state. Wolf (1928) reported them nesting in trees and cliffs and Hardy (1939) describes a Red-tailed Hawk nest constructed on a pinna- cle ill the Book Cliffs of central Utah. Else- where tlu-oughout most of their range, they most commonly nest in trees. In California, Fitch, Swenson, and Tillotson (1946) recorded all 18 pairs oi their Red-tailed Hawks nesting in trees, as did Orians and Kuhlman (1956) in Wiscon- sin; Hagar (1957) in central New York; Free- meyer (1966) in Lyon County, Kansas; Tyler and Saetveit (1969) in South Dakota and Iowa; and LeDuc (1970) in southeast Minnesota. However, they will evidently nest in any avail- able site, and Dixon and Bond (1937) found eight pairs nesting in the Petroglyph Cliff area in northeastern California. All Swainsons Hawk nests on the study area were constructed in low junipers in the foothills. Wolf (1928) and Bee and Hutchings ( 1942) also found this to be the same site preference for their Swainsons Hawk nests. In Montana, Cameron (1913) found Swainson's Hawks nesting in a variety of low trees, but primarilv in ash and cottonwoods. Two of the three Prairie Falcon nests on tlie study area were located in quarries and the third was located in a limestone cliff crevice. Cliff nesting appears to be the rule for this species throughout its range, and no exceptions seem to have been recorded. Burrowing Owls similarly show few deviations from the typical burrow nest site. Both Marsh Hauks and Short- cared Owls are more commonly found nesting around water. Bent (19.37) describes a number of nests located in marshes and swamps in Massachusetts, North Dakota, and New Jersey. Bent also notes that J. W. Sugden wrote him of a Marsh Hawk nest site in a dry wheat field at least four miles from water in Salt Lake County, Utah. All of the Sparrow Hawks on the study area nested in holes and crevices of structures, quar- ries, or junipers. Hole nesting is apparentlv mandatory for this .species and the majorit\' of sites reported in the literature are of this type, although the cavity may take the fonii of a nesting box ( Heintzelman, 1964). Ra\-ens on the stud\- area nested in high re- mote cliffs, but Bee and Hutchings (1942) also found their nests in mining structures and tri'es. Elscnvherc. Ra\'eiis hav(> shown e(|ual if not greater adaptai)ilit\-. In Washington, Bowles and l^ceker (19.30) found Ravens nesting in clilf potlioles, aband(;ned houses, on telephone poles and oil derricks, and among the beams of a railroad trestle. Rent (1946) recorded 13 Biological Skuii:.s, \'t)L. 18, No. BiitEDiNG Hi:()Loi;v of Utah Rai'tors 57 of 17 nests in cliffs or ledges, and the remain- ing 4 in conifers var\ing from 45-85 feet. In the north they nest in cliffs or ledges, often in close proximity to Peregrine Falcons and Rough-leggetl Hawks (Fay and Cade, 1959; Cade, 1960). In England they commonly nest in high cliffs or in both deciduous and conifer trees "^(Holyoak and Ratcliffe, 196S). Differentiation amonp, Species' Nest Sites. The revieu' of the literature presented above suggests that these raptor species show a wide range of nesting site selection throughout the \arious portions of their geographic range. Yet in areas where they nest together, such as here in central Utah, both similarities and subtle differences may be present. The similarities observed are, of course, to some degree a func- tion of the uniformity of the habitat. For the larger raptor species, and many of the smaller raptors also, the foothills and hills lying between large expanses of surrounding desert provide the most attractive of the potential nesting sites, offering at once a combination of remoteness, inaccessibility, and surveillance of possible ap- proaches. All of the raptors except the Marsh Hawks and Burrowing Owls nested most often in junipers or cliffs, which simph represent the predominant form of available nesting sites. .Some species, however, selected a narrower range of nesting sites than did others. Both Ferruginous Hawks and Swainson's Hawks apparenth required a restricted form of nesting habitat. Both nested exclusively on the low foothills surrounding the perimeters of the \'allevs and in low junipers which were either isolated or situated on the fringes of the pinyon- juniper woodland. Ferruginous Hawks particu- larly seemed to prefer isolated knolls and tended to nest at higher elevations than Swainsons Hawks. Three such knolls present in the south- eastern corner of the studv area were each con- tinuously occupied by a bre("ding pair of Fer- ruginous Hawks during the four study years. Observations of nesting sites in adjacent locales reinforce this conclusion. In contrast, Creat Homed Owls and Red- tailed Hawks showed a much wider selection of nesting sites. Both commonly nested in cliffs, quarries, or trees but these sites tended to be more remote than those of the Swainson's Hawk and Ferruginous Hawk. Both appeared to pre- fer nesting sites in long cliff lines or within canyons over the more exposed tree sites, in contrast to the Ferruginous Hawks and Swain- son's Hawks, neither of which nested in can- vons or on high cliffs. However, tree sites were occasionalK used, and Great Homed Owls sometimes nested in abandoned Ft^rruginous Hawk juniper nests, such exposed sites utilized only if they were removed from active Ferru- ginous Hawk nests and territories. Although Great Horned Owls did on occasion nest in rela- tively close proximity to active Ferruginous Hawk nests (average distance of 0.766 ± 0.16 miles, minimum of 0.21 miles), these close nests were always within cliff crevices and relatively unexposed. Neither Great Homed Owls nor Red-tailed Hawks nested in thick pinyon-juniper woodlands, preferring instead to nest in semi- isolated junipers or within 50-70 feet of the edge of the woodland. On the other hand, some differences between the two species were ap- parent. Great Homed Owls tended to nest at slightly higher elevations than Red-tailed Hawks and preferred to nest within crevices or caves, whereas Red-tailed Hawks usually nested on cliff ledges. Golden Eagle nesting sites overlapped con- sideiablv with those of Prairie Falcons and Rav- ens and, to a lesser extent, with Great Horned Owls. Both Golden Eagles and Prairie Falcons always chose cliff or quarry nesting sites, which may reflect their need for high cliffs; a pair of Falcons nesting in 1970 utilized a Golden Eagle quarr\' nest \\'hich had been constructed the previous vear. Of the remaining raptors, the Cooper's Hawk showed virtually no overlap in its choice of nest- ing sites. No other raptor nested within thick pinvon-juniper woodlands and at such high ele- \-ations. In contrast. Short-cared Owls and Marsh Hawks both exhibited similar choices in nesting sites with both nesting in rabbitbrush- sagebrush stands on the desert floor. Burrowing Owls similarly nested on the valley floor, but achieved a measure of isolation owing to their utilization of buiTOws for nests. Sparrow Hawk nesting sites overlapped with none of the medium- and small-sized raptor species on the study area. Sparrow Hawks most commonly nested in and around human struc- tures. They did not nest directly on the valley floors except at higher elevations and in juniper cover. Statistical comparisons of the average nest- ing elevations of the raptor species reinforce the above statements. Analysis of variance tests indicate that the average nesting elevations of the five large raptor species differed significantly (p<0.01, "F" = 19.1). Paired "t" tests reveal that all possible differences are significant ex- cept between the CJreat Horned Owls and Golden Eagles. However, although these two species show much overlap in nest site elcva- 58 Biiir.iiAM YdUNG University Science Bulletin tion, it has already been sliown that they prefer different sites. Siniihir analysis of variance tests of the five medium- and small-sized raptor species for which sufficient comparative data is available also show significant differences in their average nesting elevations but only at p<0.05 levels ("F" = 12.2). Most of the lesser variation is attributable to die essentially similar nesting site elevations of Marsh Hawks, Short-eared Owls, and Burrowing Owls as discussed pre- viously; and paired "t" tests between those species most likely to be competitive revealed signifi- cant differences in nesting elevations between all medium- and small-sized raptors, with the three exceptions noted. The other three species, i.e., Prairie Falcon, Cooper's Hawk and Raven, nested in sites similar to those of the large rap- tor species (cliffs and/or at high altitudes). Comparisons lietween these and the cliff-nesting Red-tailed Hawks, Great Horned Owls, and Golden Eagles reveal that there was no signifi- cant difference in average nesting elevation be- tween Prairie Falcons and Golden Eagles, but Ravens and Cooper's Hawks nested at signifi- canth- iiigher eknation than Golden Eagles, Great Horned Owls, and Ri^d-tailed Hawks. Populations and Breeding Habitat Require- ments. Although Ferruginous Hawks were the predominant raptor species on the study area, their abundance was confined to certain locali- ties which can be readil\- described topographi- cally and, to an extent, by the physiognomy of the surrounding vegetation. In areas where the optimum conditions were absent, their numbers dwindled rapitlly and tliey were replaced by the Red-tailed Hawk. Red-tailed Hawks in turn were apparently incapable of displacing Ferru- ginous Hawks from the foothill rdgions, although thev were present in immediately adjacent lo- cales if a suitably different nest site (i.e., a cliff or steep-sided canyon) was available. This situation is strikingh- evident in areas where the two species nest in close proximity (<1.0 miles apart). Woodbury and Cottam (1962) liave de- scribed the various ecological habitats of Utah, and it miglit Ik' useful to examine the presence and relative populations of the raptor species within those habitats occurring in the study area and surrounding localities. The applicable habi- tat tvpes of Woodbury and Cottam include tiie following: pigmy conifers, present o\er all of the high<-r, better drained portions of tlie study area and adjacent locales; desert scrul), present over the lower elevations of Cedar and Rush valleys; canvonlieads, present in tlic liiglier mountain ranges immediately north and south of the study area; and cultivated valleys, not one of Woodbury and Cottam's original habitat tvpes, but nevertheless present over a large por- tion of Cedar N'allev northeast of the study area. Six of the raptor species nested within the pinyon-juniper habitat, but all spent some if not most of their limiting activity periods in the adjacent desert areas. Of these tlie Cooper's Hawk appears to belong most exclusively within the woodland, nesting in relatively dense stands and hunting primarily in the lightly wooded areas or o\er small hill-top meadows. In con- trast, lioth the Swainson's Hawk and Ferru- ginous Hawk are the least exclusive members, nesting on its fringes, or as in the case of the Ferruginous Hawk, in the transitional area be- tween pigmy conifers and desert scrub. Ferru- ginous Hawks constructed almost one-third of their nests within the desert scrub commimity, well beyond the limits of the woodland, and thev achieve their maximum populations in such localities. Raptors associated with the desert scrub community in tiie study area include Marsh Hawks, Short-eared Owls, and Burrowing Owls. These species all nested on the valley floors at essentially the same altitude and appeared to be restricted to tiiis community. However, all other raptors except the Cooper's Hawk hunted within tiiis community. The predominant raptors nesting in canyons included Great Horned Owls and Red-tailed Hawks (Fig. 24). Canyons apparently pre- cluded Ferruginous Hawks and Swainson's Hawks in some way, as neither attempted to nest within this habitat type, either on the study area or in adjacent locales. Large can- yons to the northeast supported dense popula- tions of nesting Red-tailed Hawks, with nesting pairs a\eraging 0.5 linear miles apart in years of maximum populations. The cultivated land northeast of the study area also differed in raptor spi'cies composition and relative populations. Here Sparrow Hawks and Magpies were the most common raptorial forms, with both utilizing the windrows of eot- tonwoods for nesting sites. Red-tailed Hawks and Great Honu'd Owls infre(]uentl\' nested here also; such nests were usualh' disrupted or destro\('d by humans before completion of the e\ele. Productivity C.lulcli Size Comparisons. Comparisons with other populations indicate slight variations in a\-eiage eluteh size of most of the study area Biological iliauEs, \'ol. IS, No. 3 Bul'.edinc; Ecology oi' Utah ll,-\rTons 59 P 1 Fig. 24. Great Horned Owl nest in West Canvon, March 1969. The nest was constructed the previous year bv Red-tailed Hawks. raptors, but the majority are in.significant. Con- sequentlv, a few comparisons should suffice. Yearly Golden Eagle clutches on the study area averaged 2.07 ± 0.07 eggs. In a series of studies in Cahfornia Dixon ( 1937 ) reported av- erage clutches of 2.0 eggs, Hanna (19.30) found an average clutch size of 1.7 eggs, and Slevin (1929) found an average clutch size of 1.95 eggs for 21 clutches. In Scotland Gordon (1927) reported an average clutch size of 1.91 eggs per clutch for 82 clutches. Jollie (1943) found 1.8 eggs per clutch for five clutches in Colorado, and more recently McGahan ( 1968 ) recorded an average clutch size of 2.1 eggs for 20 nests in Montana. Great Homed Owl clutches on the study area averaged 2.82 ± 0.15 eggs. Surprisingly, only a few studies are available for comparison. Craighead and Craighead (1956) reported aver- age clutch sizes of 1.9 eggs in Michigan and 2.2 eggs in Wyoming. Wolhuter ( 1969 ) reported an average clutch size of 1.9 eggs for nine nests near Lawrence, Kansas, and Tyler and Saetveit ( 1969 ) reported average clutches of 2.0 eggs for three nests in South Dakota and Iowa. In- terestingly, all are significantly lower than the av- erage Great Horned Gwl clutches of this area(t = 5.43 for the Kansas comparison, t := 5.54 for the South Dakota and Iowa comparison, and t = 4.49 for the Wyoming area comparison). Insufficient comparative data is available on the average clutch size for Ferruginous Hawks. Red-tailed Hawk clutches on the study area averaged 2.89 ± 0.13 eggs. In Michigan, Craig- head and Craighead (1956) recorded average clutches of 2.0 eggs, but in Wyoming an average of 2.3 eggs per clutch was found. Elsewhere, Freemeyer (1966) found an average clutch size of 1.9 eggs for 21 nests in Kansas; LeDuc ( 1970) foimd an average of 2.3 eggs per clutch for three nests in Minnesota; and Luttich, Keith, and Stephenson ( 1971 ) reported an overall av- erage of 2.0 ± 0.1 eggs per clutch in Saskatche- wan. Paired "t" tests indicate that the average clutch sizes recorded from this study are signifi- cantly larger than the overall average clutches of each of the other areas noted above. Swainson's Hawk clutches on the study area averaged 2.2 ± 0.17 eggs. In the only other 60 Bricham Young University Science Bulletin informative study available Cameron (1913) found an average cluteh size of 2.6 ± 0.67 eggs in Montana, significantly higher than those from this area. The single Prairie Falcon clutch contained 5.0 eggs. Craighead and Craighead (1956) re- ported average Prairie Falcon clutches of 5.0 eggs in Wyoming, but Enderson (1964) found an average clutch size of 4.5 eggs for 55 nests from the intemiountain area. Marsh Hawk clutches on the study area average 5.0 ^t 1.4 eggs. Elsewhere, Hammond and Henry (1949) in a three-year study in North Dakota found a range of 4.87 ± 0.806 to 5.25 ± 0.774 eggs per clutch for 60 clutches, while Craighead and Craighead (1956) found average clutches of 4.35 eggs per clutch in Michigan, and Sealey (1967) reported an aver- age clutch size of 4.18 eggs for 21 nests in Al- berta and Saskatcliewan. The single Short-cared Owl clutch contained 7 eggs. In other areas Goelitz (1918) reported an average clutch size of 7.3 eggs for four nests in Saskatchewan, but Kitchin (1919) found an average clutch size of only 3.5 eggs for seven nests in western Washington. At the northern edge of the range, Pitelka, Tomich, and Treichel (1955a, 1955b) reported an average clutch size of 6.8 eggs for 22 clutches. Sparrow Hawk clutches in tlie study area averaged 5.22 ± 0.38 eggs. In Michigan and Wyoming their average clutch sizes were 4.4 eggs (Craighead and Craighead, 1956). Rocst (1957) indicates an average clutch size of 5.1 eggs irt Oregon, and Heintzelman and Nagy (1968) found an average clutch size of 4.23 eggs for 13 nests in Pennsylvania. In experi- mental propagation studies, Willoughby and Cade ( 1964 ) reported an average clutch size of 3.66 eggs for 12 clutches. Raven clutches on the study ari-a averaged 5.36 ± 0.34 eggs. Comparatively, Craighead and Craighead ( 1956 ) found mean clutch sizes of three nesting pairs in Wyoming to average 5.7 eggs. In England, Hatcliffe (1962) reported an average clutch size of 4.6 eggs for 139 nests. Hatchinst in Michigan and 2.1 young hatclied per nest in Wyoming. Hagar ( 1957 ) reported an average brood size of 1.9 young per nest in New York and Luttich, Keith and Stephenson ( 1971 ) found an overall hatching rate of 1.9 young per nest of 75 nests in ,'\lberta. Swainson's Hawks on the study area averaged 2.2 young hatched per nest per year. Compara- tively, Craigliead and Craighead (1956) reported an a\'eragc of 1.25 young hatched from four clutches in Wyoming. The Prairie Falcon nest on the study area hatched 3 of 5 eggs. Elsewhere, Craigliead and Craighead ( 19.56 ) ft)und all five eggs of a nest in Wyoming hatched, but more recently Ender- son (1964) found onlv 1.9 voung hatched per nest studied. The two Marsh Hawk nests hatched an av- erage 3.5 young per nest. Coniparati\'e!v, Ham- mond and Henry (1949) reported an axeragc iiatching rate of 4.07 young piT nest for 60 nests in North Dakota, Craighead and Craig- head (1956) found a very low hatching rate of 1.4 young per nest for 13 nests in Michigan, and Sealey (1967) found an average of 1.55 young hatched per nest for II nests in Alberta and Saskatchewan. From 1968-1970 Sparrow Hawks on tlie study arc;i hatclii'd an a\'erage of 4.7 young per nest. Biological Sehies, \'ol. 18, No. 3 BiiELniNc: Ecology of Utah ri.\PTORs 61 In other areas, Craighead and Craighead (1956) found an average of 2.5 young hatched per nest in Mieliigan and 4.3 young hatched in Wyo- ming. In another study, Ileiiitzehnan and Nagy (196S) reported 3.29 young hatched per nest for 13 nests in central Penns)'lvania. Ravens produced an average of 3.64 young per nest on the study area. In their study, Craighead and Craighead (1956) reported an average of 5.0 young hatched per nest for three nests in Wyoming. Fledging Rates. During the four-year study. Golden Eagle nests fledged an average of 1.0 young per nest. Elsewhere, ^Vellein and Ray ( 1964 ) recorded an a%'erage of 1.32 birds fledged per nest from 23 nests in the southern Rockies, and McGahan (1968) found an average of 1.37 young fledged per nest from 45 successful nest- ings in Montana. In a series of studies in Scot- land, Watson (1957) found an average of 0.8 yoimg fledged per nest over a twelve-^ear study period, Sandeman (1957) recorded 1.4 young fledged from 19 successful nests, and Brown and Watson (1964) reported 1.3 young per nest from 19 successful nests. Recently, Dunstan (in Adolphson and Jonkel, 1969) found an average of 1.67 Noung fledged per nest from 21 nests in South Dakota. From 1967-1970 Great Horned Owl nests fledged an average of 2.0 young per nest for 27 nesting efforts. Comparatively, Craighead and Craighead (1956) found an average of 0.55 young fledged per nest in Michigan and 2.0 fledged per nest in \\'yoming; Orians and Kuhlman (1956) reported an average of 1.87 voung fledged per nest in Wisconsin; and Hagar ( 1957) recorded an average of 1.7 young fledged in New York. Recently, Wolhuter ( 1969 ) found an average of 1.5 young fledged per nest in Kansas. Ferruginous Hawks fledging rates averaged 2.0 voung per nest. In comparison, Dunstan (in Adolphson and Jonkel, 1969) reported an average of 2.66 \<)ung fledged per nest for three nests in South Dakota. Red-tailed Hawks fledged an average of 1.74 voung per nest on the study area. Compara- tively, tliis is higher than Craighead and Craig- head (1956); Fitch, Swenson, and Tillotson (1946); LeDuc (1970); and Luttich, Keith and Stephenson ( 1971 ) ; but this is lower than the overall average of 1.9 xoung fledged per nest reported by Orians and Kuhlman (1956) and Hagar (1957). Ellis in Florida and Dunstan in South Dakota (in Adolphson and Jonkel, 1969) found an average of 1.2 young and 2.5 young fledged per nest, respectively, for each of the two areas, with the latter data obtained from 20 nests. Jonkel (in Adolphson and Jonkel, 1969 ) reported an average of 0.52 young fledged per nest for 31 nests, also in South Dakota. Swainson's Hawks on the study area fledged an average of 1.4 young per nest. Craighead and Craighead (1956) found only 0.4 young fledged per nest for five nests in Wyoming. Recently, Adolphson (1969) found an average of 2.0 young fledged per nest in South Dakota. The Prairie Falcon nest fledged only one of three young. In Colorado, Enderson (1964) re- corded an average of 1.2 \oung fledged per pair and Sealey (1967) reported an average of 2.5 young fledged per nest in southern Al- berta. The four Marsh Hawk nests of 1969-1970 fledged an a\'erage of 2.5 young per nest. Else- where, Hammond and Henr)' (1949) reported an average of 2.1 young per nest fledged in North Dakota, and Craighead and Craighead (1956) found a very low fledging rate of 0.17 young per nest in Michigan for 13 nests. From 1968-1970 Sparrow Hawks on the study area fledged an average of 2.83 young per nest. Comparatively, Craighead and Craighead ( 1956 ) found an average fledged rate of 3.4 young per nest in Michigan and 3.8 young per nest in W\'oming. The six nests of the Burrowing Owl on the study area fledged an average of 3.33 young per nest. In comparison, Grant (1965) esti- mated a rate of 3.83 voung fledged per nest in Minnesota. Ravens fledged onl\' 2.57 voung per nest on the study area. Craighead and Craighead ( 1956 ) found an average of 3.3 voung fledged per nest in Wyoming. Si/nopsis of Mortoliti/ and Populiifion Trends. As is evident from the comparison of the rela- tive hatching success and mortality data with other studies, no significant differences exist and most of the variations existing are within the ranges reported from this study. The same holds true also for the majority of the causes of mor- tality, with nest desertion, egg infertility, and human interference being the principal causes of the obser\'ed mortality of eggs and voung. There was no evidence of any mortality of voung or eggs attributable to mammalian predation, even though ground nests of Ferruginous Hawks, Red-tailed Hawks, and Golden Eagles (the lat- ter outside the study area l)ut within the same habitat type) were directly accessible, and sev- eral carnivores, including coyotes, bobcats, kit foxes and mountain lions were present in the study area. Angell (196S) reported a Ferru- R2 limtMiAM VouNG Univehsity .S(:ienc;k Bulletin ginous Hawk pair successfully defending their brood against an intruding coyote, which sug- gests that these raptors are little troui)led l)\ such mammals. A\ian predation could be an important factor, but it was actualh' only ob- ser\-ed in the two cases of Golden Eagle preda- tion on otlier raptors, as previously mentioned. Territoriality Co))i])iirisoii.s iiith Other Areas. Compara- tive information on home range size is available from a tew published sources. Golden Kagles on the study area maintained average home ranges of 9.02 sq miles. This is almost equivalent to the 9.0 sq miles of territory reported by Watson (1957) for five pairs in Scotland; however. Brown and Watson (1964) found average Golden Eagle home ranges \ary- ing from 20 to 34 sq miles. Great Horned Owls on the study area main- tained a\-erage home ranges of 2.02 sq miles. Comparaliveiy, Miller (1930) observed that Great Horned Owls maintained an irregular shaped territory, with the largest diameter of no more than one-half mile, while Baumgartner (1938) found Great Horned Owl territories to haw a diameter of 0.5 miles. Craighead and Craighead (1956) found h)ur pairs near Moose, Wyoming, to ha\e an average home range of 0.82 ± 0.15 s(| miles, or roughly half that of the owls in central Utah. Red-tailed Hawk home ranges on the study are, I a\eraged 2.5 s([ miles. Fitch, Swenson, and Tillotson (1946) reported that 6 Red-tai'ed Hawk territories in Ga!ih)rnia chaparral ranged from onh 0.125 — 0.313 sq miles, but it is possible tliat peripheral areas were not included in their d-ti'rminations. Craighead and Craig- head ( 1956 ) reported somewhat larger home ranges of six pairs in Michigan, which averaged 1.45 ± 0.21 s(| miles. In Wvoming, they found eight pairs ha\ing average home ranges of 0.731 -+: O.ll S(( miles. There is no apparent comparative data for the home ranges of Ferruginous Hawks and Short-eared Owls. Swainson's Hawk home ranges on the stud\ area axcrageil 1.51 s(i miles per pair. (Craighead and Craighead (19.56) reported an a\(Mage of 0.95 ± 0.55 for five pairs. Prairie Falcons on the stud\ area a\eraged 2.35 s study area were in a sense territorial, it is questionable as to wliether territoriality limited or regulated their populations. Brown (1969) has suggested types of territorial behavior which acting as a functiem of population densities would not be limiting at low densities (i.e., all raptors would be able to breed), but they would tend to be limiting at high population levels because some pairs would be excluded from Ijreeding. Un- forttmately, none of his categories exactly fits the territorial behavior of the raptor population within the present study area which, as we have already shown, depends primarily on tiie relative food supply as a breeding stimulus. Territoriality certainly regulated the indi- \id\ial species popidations and probablv also the combined Butco species populations in regions of tlie studs' area with di-nse raptor populations, but of course it would not be operative in the re- gions of low population density. In addition, evidence of old nests was present in many re- gions of the study area which remained unused by the raptors during this study. This tends to preclude the possibilitv that territory was a major limiting factor in regulating breeding populations, except locally, and suggests instead that the raptor population of this area may be undergoing a long-tenn overall decline caused l)v an as vet unidentified factor or factors. Predation Comparison.'i iiith Other Areas. Raptors are considerably opportunistic in their predatory hal)its and take a variety of prey throughout different parts of their range. For this reason, and because literature on food habits of the various species of raptors is plentiful, compari- sons will be limited only to the major food items. All of the large raptors in this area relied heavily, indeed almost completely, on tlu' lago- moiphs for their chief food source. Although the frequency of lagomorphs to total prey items in the diet varied somewhat between the five large raptor species, their relative contribu- tion to tlic total prey l)iomass was consistently above 90 percent for each species, with the re- maining prey species contributing only minor amounts to the total prey biomass and common- ly to the total prey frequency . Elsewhere, the studies of Gloyd (1925), Mc- Atee (1935), Woodgerd (1952), Arnold (1954), Carnie (1954), McGahan (1968), Whitfield et al. (1969), and Packard et a). (1969) have shown a similar predominance of lagomorphs (Lepus and Sijh:Hiii!,us sp. ) ranging from 28 to 96 perc(Mit in Colden Eagle diets. Other impor- tant prey items from these studies included ground si|iiirrels (principally Sj)crmophihis), wliicli constituted over 26 percent of tlic prey taken by California Golden Eagles in Carnie's (1954) study, and a variety of avian species wliieh gcMicrally constituted less than 15 percent of the total prey items. Murie (1944) reported an Alaskan population which fed prim;u-ily on ground squirrels (CiteUus unduhitus). A number of European studies ha\-e reported high(M- avian prev bcqueneiis ( Hagaii, 1952; Lockie and Stephen. 19.39; Uttendorfer, 19.39); Watson, 1957; iJrown and Watson, 1964), and the latter re- ported that Red Grouse and Ptarmigan ( Lago- pus s\). ) comprised 60 percent ol the total mim- BiOLOciCAi, Seiuks, Vol. IS, No. 3 Bheedinc Et:oi.or.Y of Utah Rm-fobs 65 bt-r of prey iti-ins of a Scottish Golden Eagle population. Errington (1932c), Ellington, Hanierstrom and Hamerstrom (1940), Alcorn (1942), Baum- gartner and Baumgartner (1944), Fitch (1947), brians and Kuhlman (1956), Crawford (1968), Seidensticker (1968), and Marti (1969a) also found lagomorphs to be the principal volumetric contribution to the Great Horned Owl diets within their respective study areas, but found most other prey species more important in temis of frequency. Thus, Fitch (1940) found wood- rats (Neotoma fuscipes) and Jerusalem Crickets (Stenapclmatus) being taken most commonlv; Brodic and Maser (1967), Crawford (1968), Seidensticker (1970). and Marti (1969a) found murids taken most frequently; and Baumgart- ner and Baumgartner (1944) reported cotton rats (Sigmodon hispidus) as the most frequently taken prev item on their study area. In other areas lagt)morphs were absent or negligible con- stituents of Great Horned Owl diets. Burns (1952) reported a Florida Great Horned Owl family preying primarily on American coots (Fulica americana), and Bond (1940) found harvest mice (Reithrodontomt/s mcg.aIotis) to be the principal constituent of the diet of a Ne- vada population. Red-tailed Hawk diets similarlv show wide variations throughout their range, and lago- morphs are often unimportant constituents. Fisher (1895) and McAtee (1935) found murids to be the principal food item of their food habits studies, and Errington (1932c) and Errington and Breckinridge (193S) reportctl almost e([ual numbers of mice and ground squirrels. Later stud- ies ha\e also revealed the importance of ground squiiTels, which comprised the majority of prey items of studies in Wyoming ( Craighead and Craighead, 1956), California (Fitch. Swenson, and Tillotson, 1946), and Canada ( Meslow and Keith, 1966). Recently, Luttich et al. (1970) have shown the Richardson's ground s<{uirrt'l (Spermophilits ricJiardsonii) to be- the most im- portant constituent of the total prey biomass of Alberta Red-tailed Hawk populations. In con- trast to the heavy utilization of inamiiials noted from the above studies, Orians and Kuhlman ( 1956) foimd their Wisconsin population preying consistentl)' upon birds, of which pheasants (Phdiiauits colchinus) were tlie most iiiipoitant item. However. Hardv (1939) found the most important pre\ of a Red-tailed Hawk nest in central Utah to consist of lagoin(n[)]is and blow- snakes. In Montana, Cameron (1914) found Fer- ruginous Hawks to !)(■ feeding primarilv on prairie dogs ( Ct/nomt/s sp. ) and meadow mice, but Fisher (1895) and Angell (1968) reported that lagomorphs comprised the greater propor- tion of prey items from their studies, followed by ground squirrels. Both Cameron (1914) and Angell (1968) noted that birds were taken most fretjuently during the first weeks after the young had hatched, an observation in agree- ment with the present study. Food habits of Swainson's Hawks apparently vary greatly. Cameron (1913), Munro (1929), Fisher (1S95), and White (1966) have all re- ported large numbers of insects taken by this species, but their principal volumetric prey items are apparenth' ground squirrels (Craighead and Craighead, 1956). In Utah, Stanford (1929) reported a pair feeding on field mice and crick- ets. Prairie Falcons on the Utah study area preyed most fre(]uently upon Horned Larks and ground squirrels, but juvenile lagomorphs con- tributed much of their total prey biomass. Else- where, the studies of Fowler (1931), McAtee (1935), Bond (1939), Enderson (1964), and Edwards ( 1968 ) reported similar prey prefer- ence's, with the exception of the lagomorphs. In other studies, T\ler (1923) reported the virtu- ally complete utilization of birds by a Cali- fornia population, while Craighead and Craig- head (1956) found both meadow mice and ground scjnirrels to be taken twice as often as avian prey. Marsh Hawks on the study area preyed pri- marily upon deer mice, although birds were also taken and juvenile lagomorphs were im- portant constituents of the total prey biomass. McAtee (1935) found birds, particularly Song Sparrows (Melo.spiza sp.), to be the most fre- (|uent species in the stomachs he examined, fol- lowed by meadow mice and lagomorphs. Breck- inridge (1935) and Errington and Breckinridge (1936) also reported a predominance of avian prey but found that gnnmd squirrels and cotton- tails comprised the larger portion of the total prey biomass. In contrast, Craighead and Craig- head ( 1956 ) reported meadow mice occurring most frequently in Michigan, followed by birds, \\itii rabbits and ground s((uirrels each com- prising relatively nnnor amoxnits of the total prey biomass. Short-eared Owls on the study area utilized prim:uily white-footed deer mice, followed by kangaroo rats. Elsewhere, Short-eared Owls seem to exhibit a distinct preference for small mannnais, paiticularK deer mice and meadow nnce, and Errington (1932e), Snyder and Hope (1938), Fischer (1947), Kirkpatrick and Con- 66 IJmciiAM Young Univehsitv Sciknck Bulletin way (1947), Johnston (1956), Short and Drew (1962), and Munyer (1966) all recorded high incidences of these two prey species. In addi- tion, all of the above studies also recorded large numbers of birds taken as prey. Sparrow Hawks on the study area took a wide variety of prey, but invertebrates were their main dietary item, particularly grasshop- pers; deer mice were next in importance. Heint- zelman (1964) has summarized much of tlie in- formation on North American Sparrow Hawk predation and indicates that murid rodents and grasshoppers are the most common components of the Sparrow Hawk diet. Invertebrates, particularly grasshoppers, com- prised the majority of the prey taken by Bur- rowing Owls on the study area. Scott (1940) reported Burrowing Owl populations in Iowa to be preying primarily on locustids and scara- bids and noted that vertebrates were rarely taken, in agreement with the findings of Bourdo and Hesterberg (1950) in Michigan. Grant (1965) and Marti (1969a), however, while not- ing a similar heavy utilization of invertebrates, also found that murids formed a conspicuous portion of the total prey biomass. Suqjrisingly, lagomoiphs were an important element of the Raven diet in central Utah, but an unknown percentage was undoubtedly car- rion. Deer mice were next in importance and were the most fre limits of the study area which allow a maximization of their productiv- ity. Undoubtedh', their status as the largest of the North American Buteos is also contributory. The Long-eared Owl The status of the Long-eared Owl in this area of the Great Basin is uncertain. Although Hen- shaw (1875) and Bee and Hutchings (1942) re- corded this species nesting in pinyon-juniper, only one nest was fomid in this habitat type during the present study. It was located in an old Ferruginous Hawk nest constructed in the top of a juniper and within a dense pinyon- juniper stand in southwestern Rush \'alley ( Fig. 27). The nest was approximately 2.5 ft x 3.0 ft and almost flat. On 3 Ma)' it contained three newly hatched young and three eggs and on 26 May fi\e nearly full grown young were present and sul)se(|ui'ntly banded. Fifteen p(>ll(ts and several prey remains were removed from tlie nest and analyzed. The re- sults are presented in Table 40. Mammals com- prised 90.4 percent of tlie total prey taken and 93.3 percent of the total prey bioniass. The two principal species \\ere, in order of their im- portance, Old's kangaroo rat and the dei'r mouse. The mean prey weight taken by this species was 40.S gms, or only 4.5 gms higher than the in(\ui prey weight taken by the closely related species, the Short-eared Owl. This is, however, three and four times larger than the mean prey weight taken by Sparrow Hawks and Burrowing Owls on the study area, although a wide over- lap within the variety of prey taken by these four raptors is evident. The absence of Long-eared Owl nests on the study area invites comment, as does their ap- parent scarcity in the pinyon-juniper community. .'\s pre\i()usly discussed. Long-eared Owls com- prised a sizeable portion of the wintering owl populations and were trapped almost three times as often as Great Horned Owls. Yet they were virtually absent from the same area during the breeding season. Although both Long-eared Owls and Great Horned Owls prey on some similar species, their prey selection differential is great; hence, their rare breeding status can- not be attributed to severe competition with the larger owl. However, the combination of breed- ing habitat recjuirements and potential preda- tion offers another possibility. Long-eared Owls do not construct their own nests but rather utilize abandoned nests of a wide variety of avian and mammal species, and in other parts of their range, sciuirrel nests and Cooper's Hawk nests are frequently utilized ( Bent, 1938; Arm- strong, 1958; Re)nolds, 1970). In addition, these nests are nonnallv placed in dense conifer stands ( Randle and Austing, 1952). In the pinyon-juniper habitat, however, the only nests a\ailable are those of the Ferruginous Hawk, Red-tailed Hawk, and Swainson's Hawk. All of these are constructed in the tops of junipers and are direeth exposed to potential predators from aljove. I'^irthermore, probably all ot the large raptors wliieli nest in this area are capable of killing Long-eared Owls, and in other areas Golden Fagles ( McGahan, 196S), Great Horned Owls ( l'",rringt()n, Hamerstroiii, and Hamer- Table 40. Food liahils of Long-eared Owls 1970. No. % Approx. % Species Indv. Indv. Biomass Biuma.ss Dipo(lonu/s ordii 10 45.5 680 75.7 Pcronu/scus inanictihitus 7 31.8 119 13.3 Microlus sp. 2 9.1 24 2.7 Perowls recjuire well-concealed nesting sites in dense cover or thickets, all of which are lack- ing in the pinxon-juniper commimity. Hence, their breetling suec(\ss is rendered uncertain be- cause of the high le\e]s of exposinc of the only available nesting sites. Effect of the Investigator The effect of the investigations and the pres- ence of the investigators are difficult to evaluate except where such presence clearly led directly to the destruction of the raptor's nests, eggs or young, or resulted in adult mortality. The effect of the investigators on raptor nesting activities was often deleterioiLS. Despite the fact that nest visits were kept short, particularly in cold weath- er, adverse effects occurred. Most commonly these effects took the fonn of nest abandonment, with loss of eggs and yoiuig occurring less fre- (juently. There is some indication, however, that the birds adjusted somewhat to the investi- gators after the first breeding season, and several of the pairs which had abandoned their nests in 1967 tolerated similar nest visits during the subscciuent breeding seasons and nested success- fully. However, some— particularly two Golden Eagle pairs— never became tolerant of human presence and activities. The aggressiveness of the adults toward the investigatois varied greatly, both among species and among pairs of a species and even within the members of a pair. Generally Golden Eagles and Swainson's Hawks rapidly departed and did not reappear during nest visits, but Ferru- ginous Hawks and Red-tailed Hawks always pressed attacks if young were in the nest, al- though terminating them before actual contact was made. Great Horned Owls were probably BiiioiiAM Young University Science Bulletin the most dangerous raptors in the study area. Several females made det(>rmhied attaeks, and three made actual eontact, two knocking one of the authors out of the nesting tree, and the tiiird lacerating the scalp and forehead of a colleague ( Bruce Arnell, personal communica- tion). Of the medium-sized and small-sized rap- tors, Prairie Falcons were the most aggressive and Ravens and Sparrow Hawks the most vocal. None, however, made serious threats or dc- tennined attacks against the investigators. In summary, the activities of the investiga- tion did apparentlv provoke the nesting raptor species to some extent and apparently resulted in mortality in e.xtre'me cases. The effect of this mortality on the total population and popula- tion trends is tmknown, but it is certainly not as drastic as the sum total of untoward human actix'ities directed against the nesting raptors, which must contribute to the overall low raptor densit\' of this area. Only additional evidence will permit definite conclusions, however. SUMMARY A studv of the breeding ecologv of raptorial birds was conducted in central Utah from 1967 to 1970. The objectives of the study were to provide four years of (juantitative data on the breeding raptor populations and their distribu- tion, their habitat utilization, vearlv productivity and success, territorialits , and predation. The study area supported a total of 354 indi- viduals of 12 raptor species during the four study years. The vearlv raptor population varied from 8 to 11 raptor species and from 32 to 46 pairs. Individuals commonly comprised from 9 to 13 percent of the yearly raptor population, and a varying percentage of pairs did not at- tempt to nest. Ferruginous Hawks were the predominant raptor species and comprised some 19 percent of the total yearly raptor popu- lation. Other important raptors included the CJolden Fagle, Red-tailed Hawk, and Raven. Yearly population densities averaged 0.5 pairs per square mile, much lower than raptor populations found in Michigan and Wyoming ((Iraigliead and Craigliiad, 1956). However, much of the area was not utilized, and if such areas were eliminated from the calculations, the raptor population densities would be increased. The breeding activities of the collective rap- tor population occurred ovi'r a period of eight months. Raptor species exhibited a definite breeding sequence relative to one another, and each species initiates! its nesting activities at slightly different time periods, although some overlap occurred between early and late nesters of different species. Cireat Horned Owls and Colden Eagles were the first raptors to initiate nesting activities, usuall\- in late January or earh February. Red-tailed Hawks were the first of tlie migratory raptors to return and begin nest- ing and were closely followed by Ferruginous Hawks. Swainson's Hawks were the last of the large raptors to begin nesting, usuailv in lati' May or June, and at approximately the same time Cooper's Hawks and Burrowing Owls ini- tiated tluMr nesting activities. The raptors exhibited a wide range of nest site selection within the limits imposed by the study area ]ial)itat. The large raptors nested primarily in cliffs (including ([uarries) or juni- pers; but many of the medium- and small-sized raptor species, such as the Marsh Hawk, Short- eared Owl, and Burrowing Owl were ground nesters. Obserxations indicated that several of the raptor species exhibited a vertical stratifi- cation of nesting sites. Territories and, less com- monly, nesting sites were usually reoccupied by a pair of the sanie species. The fecundity of the collective raptor popu- lation varied between years. Specific causes of mortality of eggs and young included nest de- sertion and destruction, predation, apparent egg infertilit\-, and accidents. Human interference was the probable cause of most of the observed nest desertion and destruction. Approximately 6.5 percent of all eggs produced were apparent- ly infertile, of which the majority were from Ferruginous Hawk nests. The observed home ranges of the raptor species were a function of their relative size and breeding status. Thus, nesting pairs main- tained larger home ranges than nonnesting pairs, wliieh in turn held larger home ranges than in- dividuals Tlie sizes and shapes of the liome ranges confonned generally to the topography of the nesting Idcale and usualK' ranged widely into the surrounding desert. Distanci'S bi'tween nearest neighbors of closely related species of similar weight were greater than between rela- ti\(l\ unrelated species. An exception occurs bi'twcen species witli iliffering acti\itv pat- terns, such as tlu' nocturnal owls and the diurnal hawks. ( )verlapping of home ranges was seldom substantial between pairs of the same species, but it was somewhat more frecjuent between pairs of diftereiit species. Biological Seiues. \'oi,. IS, \o. 3 Bukkdinc Ecology of Utah Raptobs 71 Kach of the raptor species maintained defi- nite luinting activity periods. The ob\ious dif- ferential occurred between the diumal hawks, eagles and ravens, and the nocturnal owls; but at least one species, the Ferruginous Hawk, ex- hibited a crepuscular hunting activity timetable. The food of the raptors on the study area included at least 55 different prey species, but most relied hea\'ily on only 1 or 2 species. The principal prey of the majority of the large rap- tors was the black-tailed jackrabbit, which also figured prominently in the diets of some of the medium-sized raptors. Other prey species of im- portance to one or more raptor species included the antelope ground scjuirrel, two kangaroo rat species, the white-footed deer mouse, and the Horned Lark. Tlie smaller raptors also took large numbers of invertebrates, principally or- thopterans. Gencrallv the raptors preyed heavily upon the most aliundant potential prey species, and a correlation of predator-prey size was found, indicating that the various raptor species preyed most heavily upon the largest prey species which they could most efficiently cap- ture and kill. No examples of raptor predation on game or domestic livestock were found dur- ing the study period. ACKNOWLEDGMENTS We wish to express our sincere appreciation to Dr. C. Lynn Hayward, Dr. Herbert H. Frost, and Dr. Glen Moore for reading and criticizing an earlier version of this manuscript. Grateful acknowledgment is also expressed to many others who contributed to the successful com- pletion of this work, including Dr. Clyde C. Ed- wards for his assistance in the field from 1967- 1970; David H. Ellis, Franz J. Camenzind, and J. Bradford Weston for field assistance from 1967-1968; W. Bruce Arnell for field assistance from 1969-1970; and Charles R. Wilson for field assistance from 1969-1970. Miss Nancv Lee Balan typed and edited the final manuscript. We express gratitude to the Southern Con- necticut State College Computer Center for its services and to the Brigham Young University Department of Zoology for furnishing equip- ment and transportation. Tliis stud\ was supported in part by a Na- tion;il Defense Education Act Fellowship and in part bv a research grant from the National Audubon Societv. APPENDIX-WEIGHTS OF PREY SPECIES USED IN THE BIOMASS CALCULATIONS. Species MAMMALS Lepus californicus Si/Ivilagus sp. Spermopliilus tDunsendi Ammospermophihis leuctirus Eutcnnius minimus TfioDuimyv hotlac Perognathus parvus Peroiinuthtis formosus Dipodomtjs microps Dipodomi/s ordii Microdipodops meii.acephalus Ontjchomijs leucogaster Reithrodentomi/s mcii.(dofis Peromiiscus mitniculalus Neotoma lepida Micruttts sp. Mustehi frenata BIRDS Btiteo sitditisoui Appro.v. wt. in gms. Source 2300 Haskell and Reynolds (1947) 1000 Seidenstickcr (196S) 191 Cornish and Mrosovsky (1965) 145 This study 78 This study 170 This study 15 This study 19 This study 65 This study 68 Desha (1967) 24 This study 38 Marti (Unpubl IBP data) 12 Marti (Unpubl IBP data) 17 Bee (1947) 217 Marti (Unpubl IBP data) 38 Bee (1947) 178 Marti (Unpubl IBP data) 988 Craighead and Craighead (1956) 72 Brigham ^■ouNc University Science Bulletin Zetiaklura macroura Ask) flammeus Chordeiles minor Phdlacnoptilus nuttallii TijTdnnns verticelis Sai/ornis saija Olocoris cdpestris Pica pk;a Ctjanocephalus ct/anocephalus Oreoscoptes montamis Sialki curnicokles Larius hidovickimis Passer domesticus Oherholseria chlorura Calanwspiza mchnocorijs Poecetes graminetts SpizcUa hreiceri Zo not rich ia leiicoph n/s Stiirnis vulgaris Sturnella neglecta REPTILES Crotaphytus collaris Ufa sfanshuriana Sceloporus graciostis Phrynosoma platyrhinos Cncmidophorus tigris Masticof)his tacniatus Pituophis melanoleucus INVERTEBRATES Curahidae Scarabidae Sdphidae Curcidionidae Tcnchrionidae Locustidae Aranae Scorpionidae 153 Hiitt and Hall (19.38) 340 Craiglicad and Craifjhead ( 75 Thi.s .study 62 Thi.s studs' 36 This stud) 28 This study 28 Bohlc (1943) 173 SeidcnstickcT (1968) 108 Foole (1938) 45 This study 45 Marti (Unpubl IBP data) 52 Esten (1931) 25 Poole (1938) 30 This study 33 Marti (Unpubl IBP data) 27 Poolc (1938) 30 This study 30 Baldwin and Kendeigh ( 1938 84 Poole (1938) 145 Poole (1938) 30 This study 4 This study 13 This study 9 This study 24 This study 169 This study 372 This study 0.23 Marti (Unpubl IBP data) 0.3 Marti (UnpuhllBPdata) 0.3 Marti (Unpubl IBP data) 0.1 Marti (Unpubl IBP data) 0.55 Marti (Unpubl IBP data) 0.6.3 This study 0.4 Marti (Unpubl IBP data) 1.45 This study 1956) LITERATURE CITED Adoi.phson, D. and C |onkel. 1969. 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Wilson Bull. 62:214. Bowles, J. H. and F. R. Decker. 1930. The Ravens of the state of Washington. Condor 32:192-201. Bowles, J. H. and F. R. Decker. 1931. The Fer- ruginous Rough-leg in Washington. The Murrelet 12:65-70. Bowles, J. H. and F. R. Decker. 19.34. Swainson's Hawk in Washington state. Auk 51:446-4.50. Brecklnhidge, W. J. 1935. An ecological study of some Minnesota Marsh Hawks. Condor 37:268-276. Brodie, E. D. and C. Maser. 1967. Analysis of Great Homed Owl pellets from Deschutes County, Ore- gon. The Murrelet 48:11-12. liROWN, J. L. 1969. Territorial behavior and popu- lation regulation in birds. Wilson Bull. 81:293- .329. Brown, L. H. 1966. Observations on some Kenya eagles. Ibis 108:. 53 1-571. Brown, L. H. 1969. Status and breeding success of Clolden Eagles in north-west Sutherland in 1967. Brit. Birds 62:34.5-363. Brown, L. H. 1970. African birds of prey. Collins London. Brown, L. H. and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw Hill, New York. 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Historical observations on the ecology of Rush and Tooele Valleys, Utah. Proc. Utah Acad. Sci., Arts and Letters. 42:90-105. Collins, C. T. 1962. Red-tailed Hawk attacks Long- eared Owl. Wilson Bull. 74:89. Cornish, E. and N. Mrososty. 1965. Activity during food deprivation and satiation of si.\ species of rodents. Animal Behavior 13:242-248. Cdulombe, H. N. 1971. Behavior and population ecology of the Burrowing Owl in the Imperial Valley of Califomia. Condor 73:162-176. Craighead, F. C. and J. J. Craighead, Jr. 19.56. Hawks, owls, and wildlife. Stackpole Co. Harris- burg. Crawford, R. D. 1968. Some food habits of the Great Horned Owl in north-central Missouri. Iowa Bird Life 38:119-121. Gushing, J. E. 1941. Winter behavior of Ravens at Tomales Bay, Califomia. Condor 43:103-107. Decker, R. R. and J. H. Bowles. 1930. The Prairie Falcon in the state of Washington. Condor 47:25- 31. ^ Desha, P. G. 1967. Variation in a population of Kangaroo Rats Dipodomijs orii media (Rodentia: Heteromyidae) from the high plains of Te.xas. Southwestem Natur. 12:275-290. Di.xon, J. B. 1914. History of a pair of Pacific Homed Owls. Condor 16:47-54. Dixon, J. B. 1937. The Golden Eagle in San Diego County, Califomia. Condor .39:49-56. Di.xon, J. B. and R. M. Bond. 1937. Raptorial birds in the cliff areas of Lava Beds National Monument. Califomia. Condor 39:97-102. Drinkwater, J. 19.53. Yomig bluebird taken from nest-box bv Sparrow Hawk Fiiico sparverius. Auk 70:215. Earhart, C. M. and N. K. John.son. 1970. Size dimorphism and food habits of North American owls. Condor 72:251-264. Edwards, B. F. 1968. A study of tlie Prairie Falcon in southern Alberta. The Blue Jay 26:32-36. Edwards, C. C. 1969. Winter behavior and popu- lation dynamics of American Eagles in western Utah. Unpublished Ph.D. dis.sertation. Department of Zoology, Brigham Young University, Provo, Utah. Ellis, D. H., D. G. Smith and J. R. 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Hafner Pub. Co. New York. C)'. ' r^Acifo Brigham Young University Science Bulletin MUS. COM^. ZOOL. LtfiNARY -J!lo1r-Bo'feat HOV 51973 HARVARD EFFECTS OF A NUCLEAR uNiv^ONATION ON ARTHROPODS AT THE NEVADA TEST SITE by Dorald M. Allred BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 4 JULY 1973/ISSN 0068-1024 BRIGHAM YOUNG UNIVERSITY SCIENCE BULLETIN BIOLOGICAL SERIES Editor: Stanley L. Welsh, Department of Botany, Brigham Young University, Provo, Utah Acting Editor: Vernon J. Tipton, Zoology Members of the Editorial Board: Ferron L. Andersen, Zoology Joseph R. Murdock, Botany WiLMER W. Tanner, Zoology Ex officio Members: A. Lester Allen, Dean, College of Biological and Agricultural Sciences Ernest L. Olson, Director, Brigham Young University Press The Brigham Young University Science Bulletin, Biological Series, publishes acceptable papers, particularly large manuscripts, on all phases of biology. Separate numbers and back volumes can be purchased from University Press Marketing, Brigham Young University, Provo, Utah 84602. All remittances should be made payable to Brigham Young University. Orders and materials for library exchange should be directed to the Division of Gifts and Exchange, Brigham Young University Library, Provo, Utah 84602. Brigham Young University Science Bulletin EFFECTS OF A NUCLEAR DETONATION ON ARTHROPODS AT THE NEVADA TEST SITE by Dorald M. Allred BIOLOGICAL SERIES — VOLUME XVIII, NUMBER 4 JULY 1973/ISSN 0068-1024 TABLE OF CONTENTS INTRODUCTION 1 METHODS 1 RESULTS 7 BEETLES 7 Araeoschizus sulcicoHis 7 Centrioptera muricata 7 Conibiosoma elongatum 8 Edrotes orhiis 8 Eleodcs armata 8 E. grandicollis 8 E. hispilabris 9 E. longipilosa 9 E. nigrina 9 Eupsophylus castaneus 9 Euschides htctatus 9 Eusatttis agnatus 9 Metoponium convexicoUe 9 Pelecijphorus pantex 9 P. semilaevis 9 Triorophus laevis 9 Trogloderus castatus 10 Changes within Sectors 10 Grid vs. Transect Extrapolation 11 Crater Occupants 12 ANTS 12 Aphaenogaster megommattis 12 Crematogaster coarctata 12 Iridomijrmex pniinosum 12 Mijrmecocijstus mexicanus 12 M. mimicus 12 Pheidole bicarinata 13 Pogonormjrmex calif ornicus 13 P. nigosus 13 Veromessor lariversi 14 V. smithi 14 Changes within Sectors 14 Grid vs. Transect E.xtrapolation 15 ORTHOPTERANS 15 Arenivaga erratica 15 Cetithophilus fossor 15 C. kimellipes 15 Litaneutria minor 15 Stenopelmatus fuscus 15 Changes within Sectors 15 SCORPIONS 16 Hadrurus spadix 16 Vaejovi^ becki 16 V. boreius 16 V. confusus 16 Changes within Sectors 16 Crater Occupants 16 Grid vs. Transect Extrapolation 16 SOLPUGIDS 16 Bronchia potens 16 Eremobates scopulatus IV Eremorhax pulcher 17 Hemerotrecha calif ornica 17 H. proxima 17 H. scrrata 17 Changes within Sectors 17 Crater Occupants 17 Grid vs. Transect Extrapolation 17 SPIDERS 17 Calilena restricta 17 Gtuijilwsa hirsutipes 17 Iliipliidrassu.s- cuiiii 17 Ilirptjllus hcspcwlus 17 Loxosceles unicolor 18 Megamijrmecion naturalisticum 18 Ncuuntigraphis chamherlini 18 Orthonops gcrtschi 18 Physocijclus tanneri 18 Pailochorus utahensbi 18 St/.spira cclectica 18 Changes within Sectors 18 Grid vs. Transect E.xtrapolation 19 SUMMARY 19 LITERATURE CITED 20 EFFECTS OF A NUCLEAR DETONATION ON ARTHROPODS AT THE NEVADA TEST SITE' by Dorald M. Allred^ INTRODUCTION Allred, Beck, and Jorgensen (1963b, 1964) and Jorgensen, Allred, and Beck (1963) dis- cussed the effects of the nuclear detonation "Sedan" on vegetation and rodents at the Ne- vada Test Site. My report discusses the effects of that same detonation on arthropods. Project Sedan, a phase of the Plowshare pro- gram for peaceful uses of nuclear energy, was detonated underground at a depth of 194m on July 6, 1962. The thermonuclear device of 100 short kilotons created a crater 98m deep and .390m in diameter (Fig. 1). Intense radioactive fallout was generally confined within an area of 6.5km by 9.7km. Ecological studies, which utilized the techniques described by Allred, Beck, and Jorgensen ( 1963 ) for trapping ground- dwelling arthropods, were made before and af- ter the detonation. METHODS Can pit-traps were placed at intervals be- tween 305m (1000 ft) and 2743m (9000 ft) from ground zero (GZ = the center of the nuclear detonation) as shown by the circles on Fig. 2. One year after the detonation, pit cans were also arranged in three grids as shown on Fig. 2. Each grid consisted of four transects 3m apart, each transect with five cans 6m apart. Cans along the main transect, which was 2438m long, were open for the capture of ani- mals from June 17 through July 5, 1962 (pre- test). Arthropods were removed from the cans at two-day intervals prior to the detonation. Be- ginning on August 25 after the detonation, which was as soon as safety conditions allowed entry into the area, the cans were opened and left until September 2.3, 1962 (posttest). During this latter time, collections were also made at two-day intervals, except for three periods when strong winds created sufficient movement of radioactive dust to create a safety hazard. Dur- ing this period, entry into the area was not al- lowed, and collection intervals of five to seven days were used. A year later, from 20 to 30 June, and 15 to 25 August 1963, cans were opened and visited at two-day intervals. Pit cans on the three grids which were es- tablished in 1963 were also open from 20 to 30 June and 15 to 25 August 1963, and visited every second day. Jorgensen, Allred, and Beck (1963:51) des- ignated two pretest and three posttest zones (Fig. 2). On the basis of their analysis of vegetation before the detonation and subse- quent effects of the blast (Ibid: 54), I desig- nated nine sectors for analysis of the arthropod populations (Fig. 2). The major vegetative types according to sectors are shown in Table 1. For purposes of comparative populations be- tween the 2438m transect and the grids, I grouped those sectors of similar vegetative types and damage with the specific area of the grid. The grid closest to GZ (lOt) is compared to the section of the transect within sectors 1 to 3, the second grid (lOu) with sectors 4 to 6, and the grid farthest from GZ (lOw) with sectors 7 to 9. In order to extrapolate population indices from other areas of similar vegetative types of the test site to those expected in the nine sec- tors of the Sedan experiment, relative popula- tion factors were determined for four major types which correspond to the zones and vege- tative analysis as designated by Jorgensen, All- red, and Beck (1963:51, 54), and the nine sec- tors as used in my report (Table 2). These are ■BYUAEC Report C00-78(i fin denier for Health and Environmental Studies, Brigham Youni; Univ,, Provo, Utah 84h02. Bhioham Young Univkhsitv Scienck Bulletin *-1 k •■■i^~ ■■-■.- H| -■^ ^^. -"^■-•^ ** 1 -'■"'■ -s. « \ 1 ^'_ A • ■- y Biological Slhies, \'ol. IS, No. 4 Effects of Nuclear Detonation on Arthhopods ft) c o N +> ft) c ft) «/) c ft) i- o LJ z O N m q: to Z O M CD CC Ixl I LJ z o CM u z o N Ld Z O M . or uu /o w /OU ss PP 00- NN- MM- 0- N • M- LL- KK- JJ- L- K- ■ J' II' HH- GQ. h'.' G- FF- EE- DD- F • E • D' CC BB • AA C . 7'A o o .0. •o • e • . ® . • 0- •o- . ® . . 0. o • .0 . • 0- •o- ■ . 0- . 0. ' o .0 . 9000 8500 8000 7750 7500 7000 6500 6000 5500 5250 5000 4750 4 500 4250 4000 3 750 3500 3250 3000 2750 2500 2250 2000 1500 1000 GZ KEY • RODENT TRAP O CAN ® RODENT TRAP AND CAN SCALE 500 O) 00 r^ (D lO en O \- u u CO 00 CM GRID (A c < ft) i- I o N II a C E- P Brigham Young Uniyehsity Science Bulletin TABLE 1. Principal vegetative types and conditions in nine sectors before and after the detonation of Sedan. Sector Feet from GZ Pretest Posttest 1 2 3 4 5 6 7 8 9 0-1500 1500-2500 2500-3500 3500-4500 4500-5500 5500-6500 6500-7500 7500-8500 8500-9500 Salsola-Grass Sahola-Grass-Hymenoclea Hijmenoclca-Grmjia-Grass Coleogtjnc-Grm/ia-GjTass Coleog,ijiic-Gr(itii(i Coleogijnc-Graijia Coleogyne-Grayia Coleogtjne-Grayia-Lycium Coleogyne-Grayia Covered with soil Covered with soil ditto Vegetation destroyed; partly covered with soil Vegetation damaged; layer of dust No change; layer of dust No change; layer of dust No change; layer of dust No change; layer of dust TABLE 2. Relative abundance factors" 1959-1963. of arthropods in four vegetative types at the Nevada Test Site, Plant Commvmity""' Group and species Gr Ly Co Gr Ly Co Gr Ly Sa (dis) (dis) (undis) Tenebrionid Beetles Araeoshiztis sulcicoUis 1 48 56 46 Centrioptera imiricata 1 39 25 5 Conibiosoma cloi}gatum 1 39 25 7 Edrotes orbus 3 8 5 1 Eleodes aniiata 1 7 6 5 E. grandicoUis 1.4 8 4 1 E. his p Hal iris 12 34 17 1 E. longipilosa 0 0 0 1 E. nigrina 0 0 0 0 Eupso])hyhis castaneus 0 2 1 4 Euschides btctatufi 0 1.3 1.3 1 Eusattus agnattts 1 2.6 0 0 Metoponium eonvexicoltc 1 2.5 1.3 2 Pelecyphonis pantex 1 3 1.6 3 P. semilaevin 0 1.5 1 2 Triorophus laevis 1 32 18 5 Trogloderus costatus 4 18 9 1 Ants Aphaenogaster megommatus 0 2 1 2 Crematogaster eoarctata 1 1 1 1 Iridomynnex pruinosum 1 2 7 9 Mynnecoeystus mexicanus 1 9 8 12 M. mimints 1 2 2 2 Pheidole bicarinata 1 2 1 1 Pogonoimjrmex californiciis 1 1.5 1 1 P. rugosus 1 121 86 129 Veromessor lariversi 7 4 3 1 V. smithi 0 0 1 2 (Jrthopterans Arenivaga erratica 0 1 2 3 Ceuthophibis fossor 1 1.5 1 1 C. lamcUipes 1 1 1 2 Litaneiitria vunor 1 1.5 4 6 Stenopelmatus fuscus 1 5 4 5 Biological Series, Vol. 18, No. 4 Effects of Nuclear Detonation on Arthropods Table 2 (Continued) Scorpions Hadriirus spadix Vaejovis hecki V. horeus V. conftisus Solpugids Bronchia potens Eremohates scopulatus Eremorhax pulcher Hemerotrecha californica H. proximo H. serrata Spiders Calilcna rcsfricta Gnaphosa hirsiitipes Haplodrassus eunis Herpt/Uus hesperolus Loxoscclcs itnicoJor Megoimjnnecion naturolis- ticitm Neoonagrophis chamberlini Orthonops gertschi Physoctjchis tanneri Psilochoriis utahensis Syspiro eclectica *.Mi numbers are i-elated to the factor of "1" which represents the least abundant, "0" indicates not found Factors are not compar- able between species. ••Sa = Salsola; Gr Ly (dis) = Grayia-Lycium disturbed, Co Gr Ly (dis) = Coleogyne-Grayia-Lycium disturbed; Co Gr Ly (undis) = Coleogyne-Grayia-Lycium undisturbed. 1 3 3 4 1 2 2 2 0 .5 .3 .5 1 3 2 3 0 .5 2 3 1 1.5 1 1.5 1 1 .5 .5 0 3 3 5 0 2 1 2 1 1 1 1 0 3 2 3 1 4 6 9 1 5 9 14 1 3 5 7 0 0 0 0 0 0 1 2 1 1.5 2 2.5 0 1 1 1.5 0 0 0 0 1 1 1 1 0 .5 1 1 (1) Salsola. (2) disturbed Grayia-Lycium, (3) disturbed Coleogyne-Grayia-Lycium, and (4) undisturbed Coleogyne-Grayia-Lycium (Table 2). Similar factors were determined for the seasonal occurrence and abundance of each species of arthropod in other areas of the test site not affected by the Sedan experiment so as to determine the expected species and their populations during the different sampling peri- ods in the environs of project Sedan (Table 3). Factors of adjustment were used to standardize sectors and grids, as well as other areas and seasonal collecting at the test site, to the number of stations and collections. Five equations were used as follows. For pretest and posttest populations of each sector and vegetative type, FN, = N,: X Ts where PNa = number of animals collected adjusted to the number of collecting attempts, Nc = actual number of specimens collected, and Ts = adjustment factor of the number of traps in a given sector or vegetative type, as determined by the greatest number of traps used in any of the vegetative areas or sectors, divided by the number of traps in the specific sector or vegetative type considered. Seasonal adjustment factors were determined by Sp = Ph Pi. where Sf = the seasonal adjustment factor, Ph = the greatest population collected in one of the four months, June through Septem- ber, over the whole test site, and P,, = the lowest population as above. The base factor for determining the expected population of a given species for a specific vegetative type and month was calculated as Bp =^ PNa SJuf + SJyp where Bp =r the base factor, PNa = as explained above, SJup = the seasonal adjustment factor for June, and SJyp = the seasonal adjustment factor for July. 6 Brigham Young Univebsiti- Science Bulletin The posttest expected population was de- period considered, fomiined by If the period considered was more than one Fx = Bf X Sf month, then tlie etjuation should read: where Px = Bk x (Sif + Sjf) Px = the expected population for a given where period, Sik = the first seasonal adjustment factor, Bf ^ the base factor as explained above, and and Slf = the second seasonal adjustment factor, Sf ^= the seasonal adjustment factor for the and so on. TABLE 3. Relative abundance factors" of arthropods related to above-ground activity during four months at the Nevada Test Site, 1959-1963. Month Group and species June July Aug. Sept. Tenebrionid Beetles Araeoshiziis sulcicollis 1.6 1 2.2 3 Centrioptera nniricata 37 22 4 1 Conibiosoma elonp^atiim 1 2 1 1 Echofes orbtts 1 2 10 9 Eleodes armata 1 1.2 3.2 8.8 E. grandicoUis 1 2 7 8.5 E. hispiUiljris 3 1 1.4 1.4 E. loriiiipilosa 0 1 1 0 E. nigrina 0 0 3 0 Eupsopliyhis ca.staneus 18 1 0 0 Euschides luctatus 0 0 0 3 Eusattus agnatus 0 0 2 0 Metoponitim convexicolle 1.5 1 1 1.5 Pelectjphorus pantex 0 1 ' 76 30 P. semilaevls 0 1 20 10 Triorophus laevis 17 7 . 2.4 1 Trogloderus costatus 1.4 1 3.6 1.2 Ants Aphaenogaster megommatus 1 122 133 0 Crematogaster coarctata 8 , 17 21 1 Iridomtjrmex pruinusum 27 14 3 1 Mtjrmecociistus niexicanus 1 1 2 2 M. mimicus 1 2 2 1 Pheidole bicarinata 6 7 3 1 Pogonomtjrmex califoniicus .3 5 3 1 P. rugosus 1.5 1 2 1.5 Veromessor lariversi 6 10 1 0 V. smithi 1 0 0 0 Orthopterans Arenivaga erratica 15 1 3 0 Ceuthophilus fossor 79 34 1 2 C. lamellipes 0 1 5 6 Litaneutria minor 3 4 3 Slenopehnatus fu.scus 4 7 5 Scorpions Hadrurus spadix 1 2 1 Vaejovis becki 2 2 2 V. horeus 1 2 2 V. confusus 3 2 2 SolpuRids Bronchia potens 7 11 0 Biological Serifs, Vol. 18, No. 4 Effects of Nuclear Detonation on Arthropods Table .3 ( Continued ) Eremohates scopulafus 2 1 0 0 Eremorhax pulcher 1 1 0 0 Hemerotrecha californica 65 20 2 1 H. proxima 0 0 0 0 H. serrata 1 5 6 2 Spiders Calilemi restricta 3 4 1 1 Gnaphosa hirsittipes 14 11 1 7 Haplodrassus ctmis 1 0 1 2 HerpijUus Iiesperohis 2 1 0 4 Loxosceles unicolor 5 9 7 1 Megamiirmecion naturalistictim 3 3 2 1 Neoancti^raphis chamherlini 1 1 1 2 Orthonops p,ertschi 7 6 0 1 Pht/soctjchis tanneri 0 0 1 0 Psihchonis titahensis 5 5 4 1 Syspira eclectica 5 6 4 1 'All numbers are related to the factor of "1" which represen ,ts the least abundant. " 0" indicates not found. Factors are not com- parable between si)ecies. RESULTS Beetles Araeoschizus sulcicoUis. Beetles of this spe- cies were present in all sectors except number 8 before the detonation, and most densely con- centrated in sectors 5, 6, 7, and 2, respectively (Table 4). One and two months after the deto- nation, populations were 86 percent below the e.vpected normal, and somewhat evenly dis- tributed between all sectors except number 8, where none were found. In June 1963, popula- tions were 62 percent below the expected nor- mal and occurred in only four sectors, including number 8, but none were closer to GZ than 1067m. In August 1963, populations were 93 percent below the expected normal and were found only in sector 8. Ecologically, significant differences in popu- lation occurred from the expected normal in all sectors except numbers 1 and 2. The pretest population in sector 2 was considerably higher than the nomi, whereas the posttest population was not significantly different. In sectors 3 to 9, pretest and posttest populations were signifi- cantly lower than the expected norm. Centrioptera muricata. Beetles of this species were present in only four sectors before the det- onation and were most densely concentrated in sectors 7 and 8 ( Table 5 ) . One and two months TABLE 4. Effects of a nuclear detonation on populations of beetles of the species Araeoschizus sulcicoUis. No. specimens Pre- test Posttest Aug.-Sept. 1962 J' ine 1963 Aug. 1963 Sector Actual Expected Actual Expected Actual Expected 1 3 o 0 0 2 0 3 2 11 o • 0 7 0 9 3 4 1 8 0 2 0 3 4 1 4 2 5 1 0 1 5 28 5 56 6 17 0 24 6 18 4 36 0 11 0 15 7 14 4 28 7 8 0 12 8 0 0 0 2 0 5 0 9 7 2 14 0 4 0 6 . Total 86 20 144 20 52 5 73 "Colleclion attempts not made. 8 Bricham Young Univehsiti- Science Bulletin TABLE 5. Effects of a nuclear detonation on populations of beetles of the species Centrioptera muricata. No. specimens Pre- test Posttest Aug.-Sept. 1962 June 1963 Aug. 1963 Sector Actual Expected Actual Expected Actual Expected 3 6 7 8 1 4 9 9 0 0 2 0 0 0 1 1 0 0 0 0 1 3 6 6 0 0 0 0 0 0 1 1 Total 23 2 2 0 16 0 2 after the detonation, populations were not re- duced from the e.xpected. None were found in sectors 3 and 6 immediately after the detona- tion, and in 1963 none were found in any sector. Ecologically, pretest populations were not significantly different from the e.xpected nonn in any sector except numbers 3 and 4, where they were lower. Similarly, posttest populations were also significantly lower than the norm in these two sectors, whereas in other sectors pop- ulations were as expected. Conibiosoma elon<^(itum. One specimen was taken in sector 9 before the detonation; none were taken after. Elsewhere on the test site beetles of this species were relatively abundant in Coleogtjne and Grciyia-Lijcitim, but not in Salsola. Seasonally they were common from June to September. Edrotes orhtis. Animals of this species were present only in sector 6 before the detonation. One and two months after the detonation they were densely concentrated in sectors 3, 4, and 5, whereas none were foimd in sector 6. Post- test populations occuned in six of the sectors. One and two montiis after the detonation, the population actually increased over the expected by 64 percent. In June 1963 the population showed an increase of 300 percent, whereas in August 1963 a decrease of 100 percent from the expected occurred. Ecologically, pretest populations were not significantly different from the expected nonn, except in sector 3 where they were lower. Post- test populations were significantly higher than expected in sectors 3, 4, and 5. Eleodes armata. Beetles of this species were present in all sectors except numbers 1 and 8 prior to the detonation (Table 6). Greatest concentrations were in sectors 7, 6, and 5, re- spectively. One and two months after the det- onation they were not found in sectors 2, 3, and 6, but were still most densely concentrated in st'ctors 5, 6, and 7. Populations immediately after the di'tonation were dimiiiislied by 74 per- cent. In June 1963, beetles were found only in tiiree sectors, and their populations were 66 percent iiiglier than expected. In August 1963, the population iiad diminished from the ex- pected norm by SO percent. Ecologically, these beetles were significantly more abundant in sectors 5, 6, and 7 before the detonation tlian was expected. Eleodes grandicoUis. Beetles were found only in sectors 1 and 4 before tlie detonation. One and two montlis after the detonation l)eetles were present in sectors 3, 4, 5, and 7, l)ut not TABLE 6. Effects of a nuclear detonation on populalioiis of hcitlt's ol the species Eleodes armata. No. specimens Pre- test Posttest Aug.-Sept . 1962 June 1963 Aug. 1963 Sector Actual Expected Actual Ex pected Actual Expected 2 4 D e 1 0 0 1 3 4 0 2 0 0 0 1 4 2 1 1 2 0 0 0 5 12 4 7 0 1 0 2 6 14 0 8 0 1 0 2 7 19 2 10 2 1 2 3 9 7 2 4 0 0 0 1 Total 62 9 32 5 3 2 10 'Collertion allcmpts not made. Biological Series, Vol. 18, No. 4 Effects of Nuclear Detonation on Arthropods in sector 1 as previously found. A decrease of 30 percent from the expected population oc- curred. In June 1963, no beetles were found, and in August 1963, tlie population was 75 percent lower than the expected norm. Ecologically, pretest populations were not significantly different from the expected in any sector, except number 3. Likewise, the post- test population in sector 3 was the only one that differed significantly from the expected norm. Eleodes hispilabris. Beetles of this species were found only in sectors 1 to 5 before the detonation, and only in sectors 1, 2, 3, 6, and 7 after detonation. In no sector were they densely concentrated. One and two months af- ter the detonation the population had diminished from the expected norm bv 34 percent. In June 1963, the population was the same as expected, and in August 1963, it had increased over the norm by 50 percent. Ecologically, pretest populations in sectors 1 to 4 were significantlv higher than expected, and posttest populations in sectors 2, 3, 4, and 6 were significantlv lower than the norm. Eleodes longipilosa. One specimen was taken in sector 3 after the detonation in June 1963. In other areas of the test site, these beetles were taken in similar vegetative types in May, July, and August, but only in small numbers. Eleodes nigrina. Two specimens were taken in sectors 3 and 4 in August and September 1962, immediatel) after the detonation, but none at any other time. In other areas of the test site these beetles were taken only in the Pinvon-Juniper conimunitv, mainly in .August. Their occurrence in the disturbed Grat/io-Li/citim and Coleogyne near the Sedan crater was unex- pected. Eitpsophijlus castoneus. Eight beetles of this species were taken in sectors 3, 4, and 5 after the detonation in June 1963. None were taken at other times. In other areas of the test site these beetles were most common in vege- tati\e types other than those near the Sedan crater and, seasonally, were most abundant in Mav and June. Euschides Itictcitus. Two specimens were taken in sector 4 immediately after the detona- tion in .August and September 1962. None were found at other times. In other areas of the test site these beetles were relatively common in vegetative types similar to those which surround the Sedan crater, but the\' were essentially ab- sent between May and September. Eusattus agnattis. Thirteen beetles of this species were taken in sectors 1 to 4 in August 1963; none were taken at other times. In other areas of the test site these beetles were most abundant in the same vegetative types that surround the Sedan crater, but they were ab- sent from June to September. Metoponium convexicoUe. Four specimens were found in sectors 3, 5, 6, and 9 after the detonation in June 1963. None were found at other times. In other areas of the test site these beetles were most abundant in the same vegetative types as in the Sedan environs, but their populations were at a minimum in August, with an increase in September. Pelecyphoms pantex. None were found prior to the detonation or in June 1963. Im- mediatclv after the detonation in August and September 1962, 46 specimens were found in sectors 3 to 7. In August 1963, 1.30 beetles were found in all sectors except number 1. In other areas of the test site these beetles were relatively abundant in the same vegetative types as occur around the Sedan crater. Seasonally in other areas, thcv were most abundant in August and September and essentially absent at other times. This explains their absence in June and July before the detonation, as well as in June 1963. Felecijphorus semUaevis. Beetles of this species were not found in the Sedan area prior to the detonation. After the detonation in Au- gust and September 1962, three specimens were found in sectors 4, 5, and 7. None were found in June 1963, but in August 1963, 16 beetles were found in sectors 1 to 7 and in 9. In other areas of the test site these beetles were common in the same vegetative types that surround the Sedan crater. Seasonally, however, they oc- curred almost exclusixelv in August and Sep- temlier. This explains their absence in June and Jul\' in the Sedan area. Triorophus laevis. Before the detonation these beetles were present in everv sector ex- cept numbers 7 and 8 (Table 7). They were most densely concentrated in sector 6. One and two months after the detonation tliey were found only in sectors 3, 4, 5, and 7, and most denseiv concentrated in sectors 3 and 4. At tliat time the population was 1000 percent greater than the expected norm. In June 1963, these beetles were found onlv in sectors 5 to S, and their population was 29 percent less than the expected norm. In August 1963, beetles were not found in any sector. Ecologically, pretest populations were signif- 10 BlUGHAM VoUNG UNIVERSITY SCIENCE BULLETIN TABLE 7. I Effects of a nil clear detonation oil popiil;i itioiis of bee ties of the species ' iriorophus I aevis. No. specimens Pre- test Posttest Aug.-SepI :. 1962 J' jne 1963 Aug. 1963 Sector Actual Expected Actual Expected Actual Expected 1 1 o o 0 1 0 0 2 4 « 0 0 3 0 0 3 1 20 0 0 1 0 0 4 2 15 0 0 1 0 0 5 1 5 0 5 1 0 0 6 11 0 2 4 8 0 1 7 0 4 0 4 0 0 0 8 0 0 0 2 0 0 0 9 9 0 1 0 6 0 1 Total 29 44 3 15 21 0 2 •Collection attempts not made. icantlv lower in sectors 3 and 4 and higher in sector 6 than was expected. After the deto- nation, the only significant difference was a de- crease in the population below that expected in sector 3. Trogloderus costatus. Beetles of this species were present only in sectors 1 and 2 before tiic detonation. {)ne and two months after the detonation they were found only in sectors 3, 4, and 5. In that period their populations were only 23 percent less than the e.xpected norm. In June 1963, the populations were 100 percent above the norm and, in August 1963, 307 per- cent above the expected. lilcologicallv, these beetles had a lower pre- test population in sectors 3 and 4 than expected, but after the detonation their populations in sectors 1 to 4 were significantly iiigher. Changes trithin Sectors. Some significant differences occurred between the population trends in different sectors during the posttest recover)' time. Populations generally and con- sistently were less than tlie expected normal but for few exceptions. In August 1963, the popu- lation in sector 2 was 13 percent above the expected, whereas in sector 8 it was 400 per- cent higher. At other posttest times in tiiese two sectors the populations were considerabh' less than the expected normal. However, sectors 3 and 4 had posttest population increases dur- ing eaeli sampling date except one, June 1963. when the population was only 7 percent less than e.xpected. At other times the population was from 125 percent to 291 percent above the ex- pected nonnal. As indicated by analysis of the vegetation, sector 3 was in tlie fringe area where tiie plants were desl roved and or cov- ered bv a shallow layer of soil throw-out. Si-ctor 4 was typified by a removal of most of the vegetation by flying debris, with a small amount of throw-out deposition. Pretest populations in sectors 1 and 2 were moderate and in sectors 5 and 9 generally were high. Except for sec- tor 8, pretest populations of sectors 3 and 4 were lowest of all sectors. The hypothesis is presented that the unexpected increase in post- test populations in sectors 3 and 4 may have been due to piiysical transport by the force of the detonation of beetles from sectors 1 and 2 to sectors 3 and 4. Furthermore, as a result of reverse air movement immediately after the detonation, some beetles may have been car- ried back towards sectors 3 and 4 from the more outh ing sectors where populations were higiiest. Because of the tough protective exo- skeleton and nature of these beetles, one may assume that thev were able to withstand the shock and buffeting. This hypothesis is sup- ported by a change of species distribution in tile sectors. In sector 3 in August and Sep- tember 1963, four species were present that were not taken in this sector before the deto- nation. Two of tiiese were present before the test in sectors 1 and 2, one was present in sector 4, and tiie other was not found prior to tlie test. In sector 4, six species were found posttest tliat were apparently not there pre- test. Two of these were present in adjacent sectors hi^fore tiie detonation, l)ut tiie other four were not found prior to tiie detonation. Complete or ncariv complete elimination of tile population occurred in five of tiic sectors at some period after detonation. A reduction of 100 percent occurred in August and Septem- i)er 1962 in sectors 2 and 8, and June and .Au- gust 1963 in sector 9. Ninet\-foiir percent re- diution was noti'd in sector 6 in August Biological Series, Vol. 18, No. 4 Effects of Nucle.^r Detonation on Arthropods 11 and Soptcmber 1962, and 96 percent in sector 5 in August 1963. Total populations of all species of tenebrio- nid beetles were 5S percent lower than the e.K- pected normal in August and September 1962, 61 percent lower in June 1963, and 58 percent lower in August 1963. Beetles of eight species were found both before and after the detonation. Six other species were found after the test that apparently were not present before (Table 8). Seasonally and ecologically, four of these should have been present before the detonation, whereas the other two were not expected. However, five of the species were expected to be present after the test, but one species found after was unexpected. Heretofore Eleodes nigrina was found only in the Pinyon-Juniper community, and its occur- rence in the Grmjia-Lijchim and Coleogyne com- munities was unforseen. Species stabilization in the sectors was great- ly upset during the postshot periods of August and September 1962 and June 1963 (Table''9). By August 1963, the numbers of kinds of spe- cies had become somewhat stabilized, but in lower numbers than during the predetonation time. Conibiosoma elongatum was taken before the detonation in sector 9 but not after in any sector. This species was taken from June to September in similar \egetative types in other areas of the test site; so its disappearance was unexpected. Grid vs. Transect Extrapolation. Results be- tween the main transect stations and the grids could not be correlated relative to the numbers of beetles captured. On the basis of adjustment to the number of can traps used in each grid and the respective sectors of the main transect, considerable differences were noted. In June 1963, the transect cans caught 190 percent and 55 percent more beetles, respectively, than did the grid cans in regions 1 and 3. At the same time in region 2, the transect cans caught 9 percent less than did the grid cans. In August 1963, the grid cans consistently caught more beetles than did the transect cans— 20 percent, 57 percent, and 37 percent more in regions 1, 2, and 3, respectively. In Julv and August 1963, when the grids and transect were utilized simultaneously, beetles of 19 species were collected. Six of these were found only in those cans arranged as a grid, whereas 13 were captured in cans on the TABLE 8. Species of tenebrionid beetles found after but not prior to a nuclear detonation. Species Eleodes nigrina Eup.mphyhis castaneus Euschides luctatus Metoponium convcxicoUe Pelcciiphoriis pantex Pelecijphorus semilaevis Sector where Presence found Date Expected 4 Aug.-Sept. 1962 no 3,4,5 June 1963 yes 4 Aug.-Sept. 1962 yes 3,5,6,9 June 1963 yes 2 to 9 Aug.-Sept. 1962 Aug. 1963 yes 1 to 7,9 Aug.-Sept. 1962 Aug. 1963 yes TABLE 9. Number of speci ies of tenebrionid beetles found in speci ific sectors pretest and posttest Sedan. Sector Posttest Pretest Aug.-Sept. 1962 June 1963 Aug. 1963 1 2 3 4 5 6 7 8 9 5 5 5 5 4 5 3 1 3 6 10 7 2 8 0 3 3 2 4 5 6 3 3 2 1 3 4 3 3 3 3 3 2 2 'Collettion attempts not made. 12 Bmgham Young Uniyersity Science Bulletin main transect and on tlie grid. None were taken on the transect that were not also taken on the grids. Crater Occupants. Minimal populations of beetles of five species were found in the bottom of the Sedan crater in July and August 1963, one year after the detonation. These were Centrioptera muricata, Chilometopon abnorme, Coelocnemus sulcata. Eleodes armata, and Eleodes hispilahris. Three of these were previ- ously taken in the environs of the Sedan crater. Coelocnemus sulcata was not reported from the test site heretofore, whereas C. abnorme was re- ported previously from other areas of the site. Centrioptera muricata was taken before the test on transect F in sector 2, approximately 488m from the lip of the resulting crater. Eleodes armata was taken before the detonation within 488m of the crater and E. hispilabris within 183m of the crater. Ants Aphaenogaster meg,ommatiis. Ants of this species were not found prior to or immediately after the test, but a single specimen was taken in June 1963 in sector 7. The usual habitat of this species is not the vegetative types that oc- cur in the environs of the Sedan crater but is commonly the Larrea-Frameria commimity. Seasonally these ants were most active above ground in July and August, and only one speci- men was taken elsewhere on the test site in June. Crematogaster coarctata. Two ants of this species were taken in sectors 3 and 9 prior to the test, and only one was taken on the grid in sector 2 in August 1963. This species was not commonly found elsewhere at the test site in the vegetative types peculiar to the Sedan crater environs, although seasonally it was abundant from June to August in other areas. Iridomyrmex pruinosum. Animals of this species were present in small numbers in sectors 1, 2, 5, 8, and 9 prior to the test. After the test in June 1963, three specimens were found in sector 7. Elsewhere on the test site this species was common in the same vegetative types as those which surround the Sedan crater. Sea- sonalh' it was most common in Jime and July, but rapidly diminished in above-ground activity in August. Myrmecocystus mexicanus. Ants of this species were present in sectors 4 to 9 prior to the detonation (Table 10). One and two months after the detonation none were found in any sector except 4 and 9. In June 1963, ants were found in sectors 5 to 7. In sector 6, 175 percent more ants were found than expected. In Au- gust 1963, ants were found in sectors 3, 7, and 8; none were expected in sector 3. In other sec- tors, except 7, fewer animals were found than expected. An increase of 175 percent occurred in sector 7. Considering all sectors at the period of one and two months after the detonation, populations were 94 percent less than expected; in June 1963, 42 percent more; and in .\ugust 1933, 55 percent less. Ecolo'jjieallv, pretest and posttest popula- tions were significantly lower than expected in all sectors except numbers 1 and 2. Mt/rmecocystus mimicus. Ants were present in sectors 2, 5, 7, 8, and 9 before the detonation (Table 11). One and two months after the test, specimens were found only in sector 9. In Juni- 1963, ants were present in sectors 5, 7, and 8, and in sectors 5 and 7 in August 1963. In sector S in June 1963 twice as many ants were present as expected, and in August 1963 in sector 5, A'A times more ants were present than expected. One and two months after the detonation, populations in all sectors had di- minished from the expected by 84 percent. In TABLE 10. Effects of a nuclear detonation on popui.itions oi ants ot the species Mijrmrcpcij.stua tiwxicauus. No. specimens Pre- test Posttest Aug.-Sept. 1962 June 1963 Aug. 1963 Sector Actual Expected Actual E.X pected Actual Expected 3 0 0 0 0 0 1 0 4 2 1 4 0 2 0 2 5 9 0 17 4 5 0 9 6 7 0 12 11 4 0 7 7 5 0 8 2 3 11 4 8 2 0 2 0 1 2 2 9 7 2 12 0 4 0 7 Total 32 55 17 19 14 31 Biological Series, Vol. 18. No. 4 Effects of Nuclear Detonation on Arthropods 13 TABLE 11. Effects of a nuclear detonation on populations of ants of the species Myrmecocystus mimicus. No. specimens Pre- test Posttest Aug.-Sept. 1962 June 1963 Aug. 1963 Sector Actual Expected Actual E.xpected Actual Expected 2 1 o • 0 3 0 1 5 4 0 4 1 1 9 2 7 18 0 16 2 5 4 11 S 5 0 5 2 1 0 3 9 7 5 6 0 2 0 4 Total 35 5 31 5 12 13 21 '('ollection attempts not niade. June 1963 the population wa.s 58 percent lower, and in August 1963, 38 percent lower than ex- pected. Ecologically, pretest and posttest popula- tions were not significantly different from the expected nonn, except in sector 7, where the population before the test was higher than e.x- pected. Pheidole hicarinata. Before the detonation, ants were found in all sectors except number 9 (Table 12). None were found one and two months later. In June 1963, ants were found only in sectors 4 and 5 and none were found in any sector in August 1963. A 100 percent reduction from the e.xpected occurred one and two months after the detonation, whereas the populations in June 1963 were 75 percent lower, and in August, 100 percent lower than expected. Ecologically, the only significant deviation from the expected norm was in sector 2 before the detonation, when populations were higher than expected. Pogonomyrmex californicus. Ants of this spe- cies were found in everv sector except number 9 before the detonation (Table 13). One and two months after the detonation they were found in sectors 4, 5, 6, and 9. In June 1963, they were foimd in all sectors except numbers 7 and 8, but in August 1963, only in sectors 1 to 5. One and two months after the detona- tion the population was only 23 percent less than expected, in June 1963 it was 46 percent less, and in August 1963 it had diminished by 76 percent. Ecologicall}', populations in most sectors be- fore the test were significantly different from the e.xpected norm. In sectors 1, 2, and 9 they were lower than expected, whereas in sec- tors 3 and 5 they were higher. After the det- onation, populations in all sectors except 5 and 6 were lower than the expected norm, whereas in sector 5 the population was higher. No sig- nificant change from the expected occurred in sector 6. Pogonoinijrmex rtigosus. Only one specimen of tiiis species was found before the detonation in sector 9. One and two months after the deto- nation, two specimens were found in sector 9. None were found in June and August 1963. In other areas of the test site ants of this species T.^BLE 12. Effects of a nuclear detonation on populations of ants of the species Pheidole hicarinata. No. specimens Pre- test Posttest Aug.-Sept . 1962 J' ane 1963 Aug. 1963 Sector Actual Expected Actual Expected Actual Ex pected 1 1 o o 0 1 0 0 2 7 o e 0 3 0 1 3 2 0 1 0 1 0 0 4 1 0 0 1 1 0 0 5 5 0 1 2 2 0 1 6 4 0 1 0 2 0 1 7 2 0 1 0 1 0 0 8 2 0 1 0 1 0 0 Total 24 0 5 3 12 0 3 "Collection attempts not made. 14 Bricham Young University Science Bulletin TABLE 13. Effects of a nuclear detonation on populations of ants of the species Pogononnjrmex californicus. No. specimens Pre- test Posttest Aug.-Sept. 1962 J> uie 1963 Aug. 1963 Sector Actual Expected Actual Expected Actual Expected 1 4 0 e 1 3 3 3 2 3 e s 3 1 1 1 3 40 0 22 5 13 3 17 4 14 6 9 1 5 1 7 5 28 25 18 6 10 4 14 6 7 14 4 4 3 0 3 7 5 0 4 0 3 0 3 8 5 0 4 0 3 0 3 9 0 2 0 2 0 0 0 Total 106 47 61 22 41 12 51 •Collection attempts not made. were most abundant in the Coleogijne and Grayia-Lijchim communities, where seasonally their above-ground activity was greatest from June to September. Veromessor lariversi. Seven ants of this spe- cies were found in sector 5 before the detona- tion. None were found after the tests e.xccpt on the grid in sector 2, where two specimens were taken in June 1963. In other areas of the test site, ants of this species were inhabitants principally of Piinon-Junipcr areas and were most active in June and July. Veromessor smithi. Five ants of this species were found onlv in June 1963 after the deto- nation in sectors 5 and 6, and on the grid of sector 8. In other sections of the test site these ants were taken infrequentlv in few numbers only in the Coleogyne community in June. Changes within Sectors. In August and Sep- tember, 1962, populations in all sectors were consistently less than the expected nomial, ex- cept in sector 6 where they were the same as expected. In June 1963, all populations were less than the expected normal, except in sector 6 where they were 200 percent higher. All pop- ulations in August 196.3 were less than the ex- pected nonn. Pretest populations were lowest in sectors 1 and 2 and higliest in sectors 3 and 5. No significant changes in species composi- tion occurred in the sectors by August and September immediately after the test. How- ever, in sector 9 one species was found after the detonation that was not taken prior to the test. Most changes were noted in June 1963, when three species were found in sectors 5, 6, and 7 that had not been found there previously. Similarly, two species were found in August 1963, in sectors 2 and 3. Eight species were found before the detonation, only four in Au- gust and September immediately after the det- onation, seven in June 1963, and only four in August 1963 (Table 14). One species, Vero- messor lariversi, taken in sector 5 before the detonation, was never taken subsequently, and TABLE 14. Number of species of ants found in specific sectt>rs pretest and posttest Sedan. Sector Pretest Posttest Aug.-Sept. 1962 June 1963 Aug. 1963 1 2 3 4 5 6 7 8 9 3 4 3 3 6 3 4 5 5 0 2 1 1 0 0 4 1 1 1 2 5 2 4 1 1 1 2 2 1 2 0 2 1 0 *Colle«"ti<)n attempts not ni.idc. Biological Sekies, Vol. 18, No. 4 Effects of Nuclear Detonation on Ahthropods 15 two species, Aphaenogaster megommatus and Veromessor sniithi in sectors 5 and 7, taken in June 1963, were not found at any other time. Complete or nearly complete elimination of the population occurred in eight of the sectors at some period after the detonation. A reduc- tion of 100 percent occurred in August and September 1962 in sectors 1, 2, 3, 7, and 8, and in August 1963 in sectors 6 and 9. Ninety percent reduction was noted in sector 4 in Au- gust 1963. In June 1963, populations in general were not reduced as drastically as at other times. In fact, in sector 6 in June 1963, a 200 percent increase in population occurred when compared to the expected norm. Similarly, the popula- tion in sector 6 in August and September 1962 was the same as anticipated. Total populations of all species of ants were 64 percent lower in August and September 1962 than the expected normal, only 30 percent lower in June 1963, but 69 percent lower in August 1963. Grid vs. Transect Extrapolation. One speci- men of Mynnecoct/stus mexicanus was taken on the grid in sector 8 in June 1963 and one on the grid in sector 4 in August 1963, although beetles of this species were not taken on the main transect in that sector. Similarly, other species taken on the grids but not on the corresponding transect in 1963 are Crematogastcr coarctata and M. mimicus in sector 2 in August, Pheidolc hicarinata in sector 2 in June, and Veromessor smithi in sector 8 in June. None were found on the transect that were not also taken on the corresponding grid. Orthopterans The few specimens of this group collected in June and August 1963 have not as yet been identified to species. Consequently, effects of the detonation on these insects are discussed only for the immediate posttcst period of Au- gust and September 1962. Arenivaga erratica. Roaches of this species were found in all sectors except 5, 8, and 9 be- fore the detonation. After the test, the specimens which were found onlv in sectors 3, 4, 5, and 9 represented a 450 percent increase above the number expected. In other areas of the test site roaches of this species were abundant in the same vegetative tvpes as those which occur in the environs of the Sedan crater. Seasonally, however, populations of these roaches were at low levels during August and September. Ceuthophihis jossor. Crickets of this species were found in sectors 1 to 7 (except 6) before the detonation. After the test they were found only in sector 9 in small numbers. In other areas of the test site these insects were most common in the same vegetative types that occur around the Sedan crater. Seasonally they were most abundant from March through July, and in few numbers in August and September. This sea- sonal variation likely accounts for the few numbers found immediately after the detona- tion in the Sedan area. Ceuthophihis lameUipes. These crickets were found in all sectors except numbers 2 and 7 before the detonation. Afterward, they were found in all sectors except number 6. Their numbers after the test were diminished by 97 percent from the expected normal. In other areas of the test site these crickets were most abundant in the same vegetative types that oc- cur in the environs of the Sedan crater. Season- ally they were most abundant from August to November. Consequently, such few numbers after the detonation seem significant. Litaneutria minor. Three praying mantids were found only in sectors 1, 5, and 6 before the detonation; none were found after. In other parts of the test site these insects were most abundant in Coleogyne, which also occurs in the area of the Sedan crater. Seasonally they were relatively abundant during August and Septem- ber. Their apparent absence after the test likely was due to normal low populations in this par- ticular area. Stenopelmatus fuscus. Before the detona- tion, Jerusalem crickets were found only in sec- tors 1 to 5. After the test they were taken in sectors 3 to 9, except 7 and 8. In all sectors except 3 and 5 the numbers found were greater than expected. Considering all sectors, popula- tions increased by 36 percent over the expected. In other areas of the test site these crickets were most abundant in Graijia-Lijcium and Pinyon-Juniper areas. Tlieir populations were low in other vegetative types. Seasonally they were most abundant from May to August and in October. Consequently, their high popu- lations in the environs of the Sedan crater in August and September were expected. Changes within Sectors. In August and September 1962, populations in all sectors ex- cept number 7 were considerably less than the expected normal. In sector 7 an increase in numbers occurred. Considering all species and all sectors, a 93 percent reduction in popula- tion occurred after the detonation. Before the detonation, species distribution was about equal between all sectors except num- 16 Bricham Young Univehsity Science Bulletin bers 8 and 9, which had only one species present. After the detonation, numbers of spe- cies were concentrated in sectors 3, 4, 5, and 9. Three of the four species in sector 9 after the test were found no closer than sectors 5 and 7 prior to the test. Scorpions Hadriiius spadix. Scorpions of this species were found in few numbers and only in sectors 1, 4, and 5 before the detonation. In August and September 1962 (after the test) they were found in greater nimibcrs than ex- pected and only in sectors 3 and 5. In June and August 1963, they were found in few num- bers in sector 7. In no sector did the numbers deviate significantly from the expected, either before or after the detonation. In other areas of the test site these scorpions were most abun- dant in the Artemisia and Mixed plant associ- ations, types which were not common in the environs of the Sedan crater. Seasonally over the test site these animals were active from April to October, predominantly in July. Vaejovis becki. Before the detonation these scorpions were found in sectors 3 to 9, except 4. After the test in August and September 1962, the scorpions were found only in sectors 3, 4, 5, and 7. In June 1963, they were found only in sector 7, and in August 1963, only in sector 8. In no sector did the numbers found deviate significantly from the expected, either before or after the detonation. In other areas of the test site these scorpions were abundant in the same vegetative types that occur in the environs of the Sedan crater. Seasonally they were collected from March to September, pre- dominantly from June to August. Vaejovis boreus. Scorpions of this species were not found in the Sedan area prior to the detonation. In August and September 1962 they were found in sectors 3, 4, and 5, but none were found in June or August 1963. The numbers present in the sectors did not deviate signifi- cantly from the expected, either before or after the detonation. In other areas of the test site these scorpions were not abundant in the Grat/ia- Ltjcium community and were not found at all in the Coleoi^ijne and Salsola communities. Sea- sonallv tliey were taken from June to Septem- ber, and predominantly from JuK- to September. Vaejovis confusus. Before the detonation these scoipions were found in all sectors except numbers 6 and 8. In August and September 1962 they were found in sectors 3, 4, 5, and 7. In that latter period, populations had in- creased bv 438 percent above the expected. In June 1963, scorpions were found in sectors 2 to 7 (except number 6), and in August 1963 only in sectors 1, 2, 5, and 9. Significant differences from the expected occurred in sectors 1 and 2 before the detonation and in sectors 3, 4, 5, and 7 after the detonation, when more scorpions were found than expected. In other areas of the test site, scorpions of this species were moder- ately abundant in the similar vegetative types that occur in the environs of the Sedan crater. Seasonally, specimens were taken from March to November, predominantly from June to Au- gust. Changes iiithin Sectors. Significant differ- ences occurred in populations in sectors 6, 8, and 9 in August and September 1962, when numbers were reduced by 100 percent. Simi- lar reductions occurred in sectors 1, 6, 8, and 9 in June 1963 and in sectors 3, 4, 6, and 7 in August 1963. Significant changes occurred in sectors 3, 4, 5, and 7 in August and September 1962, with increases of 575 percent, 950 per- cent, 350 percent, and 125 percent, respectively. Only one significant increase occurred in June 1963— sector 7 with 166 percent. No increases were noted in August 1963. Considering all sec- tors, populations in August and September 1962 increased 160 percent but decreased liy 50 per- cent and 72 percent in June and August 1963, respectivelv, from the expected nomial. Species composition in the sectors before the test vaiied from one to three. In August and September 1962, sectors 3 and 5 contained all four species, but in June and August 1963, no sector contained more than one species, except sector 7, which had three in June. Crater Occupants. One specimen of Had- ruriis spadix was found in the bottom of the crater in July 1963. Grid vs. Transect Extrapolation. Scorpions of lladrunts spadix were found on the grids in sector 2 in August, sector 4 in June and August, and sector 8 in June, but not on the correspond- ing parts of the main transect. Those belonging to Vaejovis becki were found on the grids in sectors 2 and 4 in August, but not on the tran- sect. Scorpions of V. confusus were taken on the grids in sector S in Jime and sectors 4 and 8 in August, but not on the corresponding transect. Solpugids Ihunchia potens. These solpugids were found in few numbers and only in sector 8 be- fore the detonation. None were found after. BiOLOCiCAL Series, Vol. 18, No. 4 Effects of Nucxear Detonation on AnTHROPODS 17 In otlier areas of the test site, these organisms were found in the Coleogijne and Graijia-Lijc'mm communities in relative abundance from June to September, predominantly in June and July. Their seasonal limitations likely explain their absence in August and September, but not their absence in June 1963. Eremohates scopulatus. These specimens were found only in sector 1 before the test; none were foimd after. In other areas of the test site these animals were present in the similar vege- tative types that occur in the area of the Sedan crater, found predominantly in May, but also present in June and July. This seasonal limita- tion likelv explains their absence in June and August after the test. Eremorhax piilcher. This solpugid was found only in sector 4 prior to the detonation; none were found after except on the grid in sector 2. In other areas of the test site this new spe- cies, described bv Muma in 1963, was taken in few numbers in the Grayia-Lycium and Sahola communities in June and July. Hemerotrecha californica. Solpugids of this species were foimd before the detonation in sec- tors 2, 3, 5, 6, and 7. None were found after the test. In other parts of the test site these animals were most abundant in the Coleogyne and Grayia-Lycium communities, but none were found in Sahola. Seasonally they were taken from April to September, predominantly in June. Their absence in the sectors in June 1963 was unexpected. Hemerotrecha proximo. This species de- scribed as new by Muma (1963) was repre- sented by specimens found in sector 8 after the test, but only in August and September, 1962. In other areas of the test site the few speci- mens of this species that were taken were pre- dominantly in the Grayia-Lycium community in October. Their occurrence in sector 8 was expected, but not so early in the season. Hemerotrecha scrrata. A single specimen was found in sector 2 before the test, but none after. In other areas of the test site these sol- pugids were commonly found in the same vege- tative t\pes that occur in the environs of the Sedan crater. Seasonally they were found from June to September, predominantly in July and August. Changes within Sectors. The almost com- plete absence of solpugids in any of the sectors after the detonation is indicative of the tre- mendous influence of the detonation on sol- pugids, although seasonal differences must be considered as somewhat influential also on their occurrence. Crater Occupants. Specimens of two spe- cies taken from the crater in August 1963 were not found on the main transect, but one of the species was taken on the grids in sectors 2 and 4. One specimen each of Eremohates zinni and Therobates cameronensis was found in the crater in August 1963. In other areas of the test site E. zinni was the most abundant in the Grayia-Lycium community and was also found in Sahola; none was taken in Coleogyne. Sea- sonally this species was found only in July and August. Therobates cameronensis was found in moderate abundance in Coleogyne and Grayia-Lycium but not in Sahola. It occurred from May to July. Grid vs. Transect Extrapolation. Only one species of solpugids was taken on the grids but not on the main transect— Eremohates zinni, taken in sectors 2 and 4 in August 1963. A specimen of Eremorhax piilcher was taken from the grid in sector 2 in August 1963, but not on the cor- responding parts of the transect. Spiders Calilena restricta. A single specimen was taken in sector 6 before the test. None were taken after. In other areas of the test site these spiders were only moderately abundant in the Grayia-Lycium community. They were active from February to December, predominantly from June to November. Gnaphosa hirsutipes. Only three spiders of this species were taken before the test, all in sector 7. None were taken after. In other areas of the test site these spiders were relatively abundant in the same vegetative types that oc- cur in the environs of the Sedan crater. They were active from Febraary to November, pre- dominantly in June and July. Haplodrassus eunis. Three specimens of this spider were taken in sectors 2 and 3 before the detonation. None were found after. In other areas of the test site these spiders were com- mon in undisturbed vegetation of the types that occur in the environs of the Sedan crater. Tiiey were active all months of the year, but in predominant numbers only in the nonsum- mer months of October to April. Herpyllus hesperolus. A single spider of this species was taken in sector 8 before the test, and one specimen was taken after the detonation in sector 7 and in August 1963. One specimen was taken on the grid in sector 2 18 BuicuAM Young University Science Bulletin in June 1963. In other areas of the test site these spiders were rehitively abundant in un- disturbed vegetation of the types which occur in the area of the Sedan crater. Seasonally they were active the year around, but predominantly in April. Few were taken from June to August. Loxosceles ttnicolor. Spiders of this species were not found prior to the detonation. After the test, a single specimen was found in sector 8 in June, and two in sectors 2 and 7 in August 1963. These spiders were not found in other areas of the test site in the same vegetative types that occur near the Sedan crater. Thev were found predominantly in the Mixed type of vegetation from April to September, predomi- nantly in July and August. Me