Volume 34 Number 3 September 2000 Published by The Raptor Research Foundation, Inc THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966) OFFICERS PRESIDENT: Michael N. Kochert SECRETARY: Patricia A. Hall VICE-PRESIDENT: Keith L. Bildstein TREASURER: Jim Fitzpatrick BOARD NORTH AMERICAN DIRECTOR #1: Phiup Detrich NORTH AMERICAN DIRECTOR #2: Petra Bohall Wood NORTH AMERICAN DIRECTOR #3: Robert Lehman INTERNATIONAL DIRECTOR #1: Eduardo Inigo-Elias INTERNATIONAL DIRECTOR #2: Reuven Yosee OF DIRECTORS INTERNATIONAL DIRECTOR #3: Beatriz Arroyo DIRECTOR AT LARGE #1: Jemima ParryJones DIRECTOR AT LARGE #2: Robert Kenward DIRECTOR AT LARGE #3: Michael W. Collofy DIRECTOR AT LARGE #4: Miguel Ferrer DIRECTOR AT LARGE #5: John A, Smallwood DIRECTOR AT LARGE #6: Brian A. Milsap EDITORIAL STAFF EDITOR: MarcJ. Bechard, Department of Biology, Boise State University, Boise, ID 83725 U.S.A. ASSOCIATE EDITORS Alien M. Fish Fabian Jaksic Juan Jose Negro Daniel E. Varland Charles J. Henny Cole Crocker-Bedford Ian G. Warkentin James C. Bednarz Marco Restani BOOK REVIEW EDITOR: Jeffrey S. Marks, Montana Cooperative Research Unit, University of Montana, Missoula, MT 59812 U.S.A. SPANISH EDITOR: Cesar Marquez Reyes, Instituto Humboldt, Colombia, AA. 094766, Bogota 8, Colombia EDITORIAL ASSISTANTS: JOAN Clark, Keleigh Hague-Bechard, Euse Vernon Schmidt The Journal of Raptor Research is distributed quarterly to all current members. Original manuscripts dealing with the biology and conservation of diurnal and nocturnal birds of prey are welcomed from throughout the world, but must be written in English. Submissions can be in the form of research articles, letters to the editor, thesis abstracts and book reviews. Contributors should submit a typewritten original and three copies to the Editor. All submissions must be typewritten and double-spaced on one side of 216 X 278 mm (814 X 11 in.) or standard international, white, bond paper, with 25 mm (1 in.) margins. The cover page should contain a tide, the author’s full name(s) and address (es). Name and address should be centered on the cover page. If the current address is different, indicate this via a footnote. A short version of the title, not exceeding 35 characters, should be provided for a running head. An abstract of about 250 words should accompany all research articles on a separate page. Tables, one to a page, should be double-spaced throughout and be assigned consecutive Arabic numer- als. Collect all figure legends on a separate page. Each illustration should be centered on a single page and be no smaller than final size and no larger than twice final size. The name of the author(s) and figure number, assigned consecutively using Arabic numerals, should be pencilled on the back of each figure. Names for birds should follow the A.O.U. Checklist of North American Birds (7th ed., 1998) or another authoritative source for other regions. Subspecific identification should be cited only when pertinent to the material presented. Metric units should be used for all measurements. Use the 24-hour clock (e.g., 0830 H and 2030 H) and “continental” dating (e.g., 1 January 1990). Refer to a recent issue of the journal for details in format. Explicit instructions and publication policy are outlined in “Information for contributors,”/. Raptor Res., Vol. 33(4), and are available from the editor. COVER: Adult female Barred Forest-Falcon (Micrastur Ruficollis) with female Dot-winged Antwren {Microrhopias Quixensis). Painting by N. John Schmitt. Contents Differential Winter Distribution of Rough-Legged Hawks {Buteo lagopus) by Sex in Western North America, chad v. oison and David P. Arsenault 157 Availability and Ingestion of Lead Shotshell Pellets by Migrant Bald Eagles in Saskatchewan. MichaelJ.R. Miller, Mark E.Wayland, Elston H Dzus, and Gary R.Bortolotti .... 167 Stand Structures Used by Northern Spotted Owls in Managed Forests. Larry l. Irwin, Dennis F. Rock, and Gregory P. Miller 175 Population Fluctuations of the Harris’ Hawk {Paeabuteo unicinctus) and its Reappearance in California. Michael A. Patten and Richard A. Erickson 187 The Food Habits of Sympatric Forest-Falcons During the Breeding Season in Northeastern Guatemala. Russell Thorstrom 196 A Comparison of Raptor Densities and Habitat Use in Kansas Cropland and Rangeland Ecosystems. Chilsopher K Williams, Roger D. Applegate, R. Scott Lutz, and Donald H. Rusch 203 A Review and Checklist of the Parasitic Mites (Acarina) of the Falconiformes and STRIGIFORMES. James R. Philips 210 Short Communications Diurnal Vocal Activity of Young Eagle Owls and its Implications in Detecting Occupied Nests. Vincenzo Penteriani, Max Gallardo, and Helene Cazassus 232 Food Habits of the Striped Owl {Asio clamator) in Buenos Aires Province, Argentina. Juan P. Isacch, Maria S. B6, and Mariano M. Martinez 235 Diet of Breeding Cinereous Harriers {Circus cinereus) in Southeastern Buenos Aires Province, Argentina. Maria S. B6, Sandra M. Cicchino, and Mariano M. Martinez 237 Abundance of the Ogasawara Buzzard on Chichijima, The Pacific Ocean. Tadashi Suzuki and Yuka Kato 241 Letters 244 Book Review. Edited by Jeffrey S. Marks 247 The Raptor Research Foundation, Inc. gratefully acknowledges a grant and logistical support provided by Boise State University to assist in the publication of the journal. THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. VoL. 34 September 2000 No. 3 J Raptor Res. 34(3); 157-1 66 © 2000 The Raptor Research Foundation, Inc. DIFFERENTIAL WINTER DISTRIBUTION OF ROUGH-LEGGED HAWKS {BUTEO LAGOPUS) BY SEX IN WESTERN NORTH AMERICA Chad V. Olson Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT 59812 US. A. David P. Arsenault Department of Environmental and Resource Sciences, University of Nevada, Reno, NV 89557 US. A. Abstract. — ^We conducted roadside surveys of Rough-legged Hawks {Buteo lagopus) in Montana, Cali- fornia, and Nevada for four consecutive winters from 1995-96 through 1998-99. The proportion of adult males to adult females and of adults to juveniles in the samples did not change significantly throughout the winter at any location. Adult females outnumbered adult males on all but one survey in Montana, and adult males outnumbered adult females on every survey in California and Nevada. The mean ratio of males to females was significantly lower in Montana than in the southerly locations, suggesting that on average, females wintered farther north than males. Furthermore, the annual mean percentage of adult females at all locations was correlated with average temperature and snowfall. The ratio of adults to Juveniles did not differ significantly between locations within a year, suggesting there was no differential winter distribution by age. However, the proportion of juveniles in each location varied significantly among years. The sex ratio of juvenile Rough-legged Hawks trapped in Montana was nearly identical to ratios observed for adults on road surveys. Sex ratios of 63 museum specimens provided further evidence that, on average, female adult and juvenile Rough-legged Hawks winter far- ther north than do males. We reviewed three hypotheses for latitudinal segregation of the sexes and suggest that thermal regulation is an important factor influencing differential winter distribution in Rough-legged Hawks. Key Words: Buteo lagopus; Rough-legged Hawk; roadside raptor surveys; winter distribution; latitudinal seg- regation; differential migration. Distribucion diferencial por sexo de Buteo lagopus al pasar el invierno en el oeste de Norteamerica Resumen. — Llevamos a cabo conteos de carretera de Buteo lagopus en Montana, California, y Nevada por cuatro inviernos consecutivos desde 1995-96 hasta 1998-99. La proporcion de machos adultos en relacion a hembras adultas y de adultos a juveniles en la muestra no vario significativamente a traves del invierno en ninguna localidad. Las hembras adultas sobrepasaron a los machos adultos en todas las localidades exceptuando a Montana y los machos adultos sobrepasaron a las hembras adultas en cada monitoreo en California y Nevada. La proporcion media de machos a hembras fue significativamente mas baja en Montana que en las localidades del sur, lo que sugiere que en promedio, las hembras pasaron el invierno mas al norte que los machos. Aun mas, el porcentaje de la media anual de hembras adultas en todas las localidades fue correlacionado con la temperatura promedio y la precipitacion de la nieve. La proporcion de adultos y juveniles no difirio significativamente entre localidades entre anos, lo cual sugiere que no existio una diferencia por edades de la distribucion de individuos que pasan el invierno en este sitio. Sin embargo, la proporcion de juveniles en cada localidad vario significativamente entre anos. La proporcion de sexos de 63 especimenes de museo provee evidencias de que en promedio las hembras adultas y los juveniles de Buteo lagopus pasan el invierno mas al norte que los machos. Resumimos tres hipotesis para la segregacion latitudinal por sexos y sugerimos que la regulacion termica es un factor importante que influye en la distribucion diferenciada de Buteo lagopus. [Traduccion de Cesar Marquez] 157 158 Olson and Arsenault VoL. 34, No. 5 Rough-legged Hawks {Buteo lagopus) are Holarc- tic raptors that, in the western United States and Canada, winter from southern British Columbia and Alberta, south through California and New Mexico (American Ornithologists’ Union 1998). As do all North American buteos, they exhibit re- versed sexual size dimorphism, with females being larger than males. Several studies have provided evidence of differential winter distribution (Russell 1981, l^ellen 1994). I^ellen (1994) studied mi- grant and wintering Rough-legged Hawks in Swe- den and found significantly more adult females and juveniles among wintering birds than among southbound migrants in autumn, although this was not consistent for every year of the study. Russell (1981) examined Rough-legged Hawk specimens collected from mid-December-mid-February in the eastern United States and found that females predominated in the north and males were more numerous in the southern portion of the range. However, he did not determine the age of speci- mens. Contrary to Ejellen (1994), Mindell in Palm- er (1988) reported that juvenile Rough-legged Hawks tend to migrate farther south than adults in North America. Several hypotheses have been proposed to ex- plain differences in winter distribution between sex and age classes in birds. The arrival-time hy- pothesis suggests that the sex which establishes the territory (usually males) should winter closest to the breeding grounds (King et al. 1965, Myers 1981, Wallin et al. 1985, Kjellen 1994). The social- dominance hypothesis proposes that subordinates which cannot compete successfully for resources with dominant birds migrate farther south or use suboptimal habitats (Gauthreaux 1985, Kerlinger and Lein 1986). The body-size hypothesis asserts that because of thermal advantages, larger individ- uals winter farther north than smaller individuals (Ketterson and Nolan 1976, Searcy 1980). The purpose of our study was to determine the age and sex ratios of Rough-legged Hawks winter- ing in western North America within, between, and among winters to better understand their winter distribution. Furthermore, we wanted to explore the possible causal effects of the observed sex and age distributions. Study Areas and Methods This study was conducted in the Mission Valley, Mon- tana (47°50'N, 114°25'W), Sierra Valley, California (39°60'N, 120°25'W), and Lovelock Valley, Nevada (40°25'N, 118°50'W) (Fig. 1). Study sites were chosen be- 50° jv 104“ W 0 500 Figure 1. Mission Valley, Montana (A), Sierra Valley, California (B), and the Lovelock Valley, Nevada (C) study sites in the western United States. Also shown is Watson’s (1984) study site in Idaho (open triangle) and approxi- mate northern and southern extent of Rough-legged Hawk wintering range (shown by dashed line; Palmer 1988). cause of their abundance of wintering raptors. The Mis- sion Valley is in the northern portion of the winter range of the Rough-legged Hawk. Land use in these areas is predominately agriculture and livestock grazing. The Si- erra and Lovelock valleys are 1130 km and 960 km far- ther southwest, respectively, in the mid to southern por- tion of the Rough-legged Hawk’s winter range (see Palmer 1988). Each of these valleys has an extensive sys- tem of secondary roads with limited vehicular traffic and numerous utility poles and fence posts that are used by perching hawks. The Mission Valley (40 X 20 km) is in west-central Montana approximately 65 km north of Missoula at an elevation of about 800 m. The Sierra Valley (30 X 15 km) is in the Sierra Nevada Mountains, California, approxi- mately 40 km northwest of Reno, Nevada, at an elevation of about 1500 m. The Lovelock Valley (30 X 20 km) is 145 km northeast of Reno, Nevada, at an elevation of approximately 1200 m. We conducted 27 roadside surveys from November through April during four consecutive winters from 1995-99, hereafter referred to as winters one through September 2000 Rough-legged Hawk Winter Distribution 159 four. Of these, 21 were conducted in Montana (i.e., northern location) , and 6 in California and Nevada (i.e., southern locations) . One transect was surveyed monthly in the Mission Valley during each winter except the first, during which two transects were surveyed simultaneously (by two groups of observers). The survey day varied among winters one through four; surveys were conduct- ed near the beginning of the month during winters one and two, and on day 20 of each month during winters three and four. The two transects in the Mission Valley were 63 and 60 km long, respectively. The 60-km transect was abandoned after the first winter, and the longer tran- sect was reduced to the last 43.5 km after the first survey of the second winter because of time restrictions. There- after, the 43.5-km transect was surveyed consistently. One 73-km transect was surveyed monthly in the Sierra Valley the second winter, and opportunistically the third and fourth winters. Finally, one 48-km transect was surveyed m the Lovelock Valley, Nevada, during the first and sec- ond winters (both in January). Surveys began between 0830-1030 H, depending on the time of year, to allow enough time for hawks to dis- perse from roost sites to foraging areas. Each transect was surveyed by two observers in one vehicle traveling at a continuous speed of 25-35 kph and took 2. 5-4. 5 hr to complete depending on the number of birds sighted. Ob- servers stopped the car to determine the age and sex of each bird sighted. All birds were initially detected without the use of optics, after which binoculars and 15-45X spotting scopes were used for species identification and determination of age and sex. The sex, age, activity, dis- tance from observer, location, and time were recorded for every Rough-legged Hawk sighted. Multiple features were used for determining sex and age based on Cade (1955), Clark and Wheeler (1987) and Wheeler and Clark (1995). Juvenile Rough-legged Hawks cannot be sexed by plumage, so sex determination was confined to adults. Any uncertainty in the identification of sex or age was recorded as “unknown.” In addition to doing road surveys, we also obtained the sex ratios of Rough-legged Hawks collected throughout the western U.S. (west of 104‘TV) from various museums (see acknowledgments for list of museums). We limited the analysis to specimens collected between 1 December- 28 February to minimize the number of migrating birds in the sample. To examine whether a latitudinal gradient existed, we divided the specimens into three latitudinal ranges: 31°-40°, 41°-46° and 47°-49°N. For assessing the sex ratio of juvenile Rough-legged Hawks, we inspected trapping data from Montana. As part of a separate study, Rough-legged Hawks were trapped, banded, and radiotagged each winter in Mon- tana since 1995. The age and sex of each hawk was de- termined using plumage characteristics, iris color, and body measurements. Also, for investigating social inter- actions, we conducted extensive behavioral observations on radio-tagged birds in Montana, recording all intraspe- cific and interspecific interactions. All interactions in- volving noninstrumented birds were also recorded. A bird was described as “winning” an interaction if it: (1) successfully displaced another bird from a perch or from the immediate “air space” (Bildstein 1987) or (2) suc- cessfully defended a perch or “air space” when chal- lenged by another bird. Thus, the frequency of “win- ning” interactions considered both the instigator and the recipient. We used a chi-square test to evaluate differences be- tween sex and age ratios throughout each winter at a location. Because survey data were analyzed as propor- tions, they were arcsine transformed (Wilkinson et al. 1996). Differences in sex and age ratios between and among years and among locations were tested with AN- OVA and Tukey’s pairwise comparisons using SYSTAT 7.0 (Wilkinson et al. 1996). The survey conducted the first winter was not included in the statistical analysis because it was the only survey done in a southern location that year. Additionally, because survey results from California and Nevada were nearly identical, they were combined and are heretofore referred to as southern surveys. Five surveys were excluded from the analysis because fewer than seven hawks were detected. Two other surveys at- tempted in California were abandoned because of poor visibility, and two surveys were not included in the anal- ysis of age ratio because they were diagnosed as outliers. Climatological data for the Mission Valley were ob- tained from the Western Regional Climate Center. We tested for correlations between sex ratio and climatic dif- ferences between and among years using the Pearson correlation. We did not compare climatological data with the southern locations because of the lower number of surveys and inconsistency of survey dates. A one-sided Mann-Whitney U procedure was used for testing whether female specimens were recovered farther north than males for the museum specimens. Finally, data were checked for skewness, normality, outliers, homogeneity of variances, and auto-correlation (Wilkinson etal. 1996). Results We detected more adult males than females on all surveys in the southern locations, and more adult females than males on all surveys in the northern location, except for one in February of the third winter (Table 1). The proportion of adult males to adult females did not vary significantly throughout a winter in any location (Chi-square test; P > 0.05); however, the sex ratio was signifi- cantly different between the northern and south- ern locations within and among winters (Table 2). The proportion of females detected on surveys in the northern location was significantly lower in the third winter compared with the first but did not differ significantly between any consecutive winters (Table 2). However, the mean percentage of adult females was significantly inversely correlated with average temperature (r = —0.982, df = 3, P = 0.018) and less strongly correlated with average snowfall (r = 0.901, df = 3, P = 0.099) among winters in Montana. The proportion of adults to juveniles did not vary significantly within any winter in any location (Chi-square test; P> 0.05) (Table 3); however, the 160 Olson and Arsenault VoL. 34, No. 3 Table 1. Percentage of adult female Rough-legged Hawks (number of adults in parentheses) detected on surveys in northern (N = Montana) and southern (S = Nevada and California) locations during four consecutive winters (1-4) from 1995-96 through 1998-99. Climatic data shown at the bottom of the table include the average deviation from monthly normal, averaged for each winter. Month Montana California N1 N2 N3 N4 SI S2 S3 S4 Nov. 69 62 57 70 20 33 33 (13) (29) (14) (46) (5) (9) (3)- Dec. 80 65 60 29 (10) (26) (42) (7) Jan. 79 77 61 55 11 20 0 (19) (13) (31) (56) (9)t (5) (1)- Feb. 77 49 63 33 (22) (35) (35) (12) Mar. 73 75 67 74 0 29 (11) (12) (33) (39) (2)" (7) Apr. 71 73 100 67 100 (V) (22) (1)- (6) (1)- Mean % ± SD 75 ± 4 72 ± 7 60 ± 7 65 ± 5 11 ± 0 27 ± 7 31 ± 3 Ave. temp -0.86° -0.51° +2.8° + 3.1° (C°)" Snowfall (cm)*^ +3.6 +9.4 -14.3 -6.3 ® Survey not included in analysis because fewer than 7 hawks were detected. Survey not included in analysis because it was the only one done in a southerly location the first year. Average monthly deviation from 90-year climate averages, Nov.-Feb., recorded at St. Ignatius, Montana by the Western Regional Climate Center. age ratio differed significantly between and among most winters in each location (Table 4) . Still, the age ratio was not significantly different between northern and southern locations within a winter (Table 4). Additionally, the average percentage of adults among winters in Montana was not correlat- ed with differences in average temperature {P = Table 2. Pair-wise mean comparison (ANOVA, Tukey’s method) of sex ratio between northern (N) and south- ern (S) locations in winters 1-4 (1995-99). Sex ratios of male and female Rough-legged Hawks differed signifi- cantly between northern and southern locations both within and among winters. N1 N2 N3 N4 S2 S3 N1 1.00 N2 0.97 1.00 N3 0.01* 0.10 1.00 N4 0.11 0.55 0.79 1.00 S2 0.00** 0.00** 0.00** 0.00** 1.0 S3 0.00** 0.00** 0.00** 0.00** 0.9 1.0 * Significant at 0.05 alpha level. ** Significant at 0.001 alpha level. 0,89) or snowfall {P = 0.53). Finally, the number of Rough-legged Hawks (birds/km) differed great- ly between the first winter and all remaining win- ters in Montana, but numbers fluctuated consid- erably less among years in California (Table 3). The proportion of hawks per survey where the age, sex, or both, were unknown averaged 12% ± 1 (±1 SE, range = 0-35%). We had a lower num- ber of unknown hawks on surveys that recorded the greatest number of individuals, as well as on sunny days when hawks tended to soar in thermals. Of the 65 museum specimens examined, we found that females were recovered significantly far- ther north on average than males (one-sided Mann-Whitney U, P = 0.019, ages not distin- guished, Table 5). Furthermore, the sex ratios were similar to those recorded on road surveys at equiv- alent latitudes. The three lowest latitude specimens were males (min —31°; a juvenile male collected near El Paso, Texas), and the four specimens col- lected from the highest latitude (^48°) were all females. Additionally, the mean latitude for male and female specimens was 43° N ± 4.2 and 45° N ± 2.8, respectively. September 2000 Rough-legged Hawk Winter Distribution 161 Table 3. Percentage of adult Rough-legged Hawks (number of hawks in parentheses) detected on surveys in north- ern (N = Montana), and southern (S = Nevada and California) locations during four consecutive winters (1-4) from 1995-96 through 1998-99. Also, average number of Rough-legged Hawks/km (i.e., hawk density) on survey route for November-February surveys each winter. Month Montana California NP N2 N3 N4 SI S2 S3 S4 Nov. 100 62 74 87 63 82 50 (13) (47) (19) (53) (8) (11) (6)^ Dec. 100 81 78 58 (10) (32) (54) (12) Jan. 86 45 79 78 75 71 100 (22) (29) (39) (72) (12)^ (7) (1)" Feb. 92 83 70 60 (24) (42) (50) (20) Mar. 65 50 89 80 67 88 (I7)d (24) (37) (54) (3)b (8) Apr. 87 69 33 40 100 (8) (32) (3)>^ (15)d (I)*’ Mean % ± SD 88 ± 13 56 ± 11 81 ± 6 72 ± 16 75 63 ± 6 85 ± 4 75 RLHAs/km 0.33 1.1 0.86 1.4 0.25 0.16 0.15 0.05 “ Sum of two transects. Survey not included in analysis because of the low number of hawks detected. Survey not included in analysis because it was the only one done in a southerly location the first year. Survey not included in analysis because it was diagnosed as an outlier. We trapped 55 Rough-legged Hawks in Montana from 1995-99 (20 adults and 35 juveniles). Overall, 55% of adults and 77% of juveniles were female, based on measurements (Table 6) . The number of juvenile females trapped outnumbered juvenile males every year; however, adult females only out- numbered adult males in the third and fourth win- ters (Table 6) . For juveniles, the average propor- Table 4. Pair-wise mean comparisons (ANOVA, Tukey’s method) of age ratio between northern (N) and south- ern (S) locations in winters 1-4 (1995-99). Age ratio dif- fered significantly between northern and southern loca- tions between and among most winters, but were not significantly different within a winter (shown in bold). N1 N2 N3 N4 S2 S3 N1 1.00 N2 0.00*=^ 1.00 N3 0.08 0.01* 1.00 N4 0.03* 0.01* 0.99 1.00 S2 0.00** 0.95 0.03* 0.08 1.00 S3 0.34 0.02* 1.00 0.99 0.10 1.00 * Significant at 0.05 alpha level. ** Significant at 0.001 alpha level. tion that was female was 76.6% and ranged among winters from 83.3% (1995-96) to 66.7% (1998- 99). We recorded 171 intraspecific and 85 interspe- cific interactions while tracking and observing 17 (7 adults, 10 juveniles) instrumented hawks during the winters of 1997—98 and 1998—99. Thirteen per- cent of 123 intraspecific interactions between known-age birds involved adult females displacing adult males, compared with <1% where adult males displaced adult females (Table 7) . However, interactions between and within other age and sex Table 5. Sex composition of Rough-legged Hawk spec- imens collected from different latitudes between 1 De- cember-28 February, and west of 104°W longitude in the western United States (see Acknowledgments for list of museums) . Latitude (°N) N % Females 47°-49° 25 68 (17) 4U-46° 24 62 (15) 31°-40° 16 31 (5) 162 Olson and Arsenault VoL. 34, No. 3 Table 6. Age and sex composition of Rough-legged Hawks trapped in the Mission Valley, Montana (Olson unpubl. data). Sex Ratio (M ; F) War Adult Juvenile 1995-96 4:1 1:5 1996-97 2:1 3:11 1997-98 2:4 2:7 1998-99 1:5 2:4 Total: M 9 (45%) 8 (23%) F 11 (55%) 27 (77%) classes occurred more frequently. Juveniles failed when attempting to displace adult females and adult males 45% and 25% of the time, respectively, whereas adults rarely failed when attempting to dis- place juveniles (Table 7) . When comparing the ra- tio of aggressive encounters won versus the total number of aggressive encounters for each age and sex class, we found adult females won 85% (N = 108) of interactions, compared with 42% for adult males {N= 33), 72% for juvenile females (N = 46) and 33% for juvenile males (N = 15). The mean occurrence-rate of aggressive intraspecific interac- tions was 0.387/hr {N =17) over 384 total hours of observation. Discussion Our observations indicated that adult female Rough-legged Hawks tend to winter farther north than adult males, but that differential migration does not occur between adults and juveniles. Wat- son (1984) reported that 81% of all Rough-legged Hawks were adults and 69% of adults were males in his study site in southern Idaho (43°45'N, 112°45'W), which lies midway in latitude between our northern and southern study sites (Fig. 1). Watson’s ratio of adult males to adult females was larger than that in Montana and smaller than that in California and Nevada, suggesting a latitudinal gradient in the distribution of the sexes. Addition- ally, Russell (1981) examined 42 male and 64 fe- male specimens (adults and juveniles) collected between 10 December-14 February in the eastern United States (east of 104°W) and found that fe- males wintered, on average, 3° farther north than males. Furthermore, Russell showed a clear gradi- ent in sex ratio from north to south. When we combined this evidence with the sex ratios record- Table 7. Frequency of intraspecific perch displacement between and among different age and sex classes of Rough-legged Hawks wintering in the Mission Valley, Montana, 1997—99. Failed displacement attempts are shown in parentheses. Interactions involving one or both birds of unknown age and sex are excluded. Displacer-Displaced Frequen- cy Rela- tive Fre- % QUENCY Failed Adult female-Juv (unk sex) 39(1) 32% 3% Juv (unk sex)-Juv (unk sex) 25 (5) 20% 17% Adult female-Adult female 23 (1) 19% 4% Adult female-Adult male 16 13% 0% Adult male-Juv (unk sex) 6 5% 0% Juv (unk sex)-Adult female 6(5) 5% 46% Adult male-Adult male 4(1) 3% 20% Juv (unk sex) -Adult male 3(1) 2% 25% Adult male-Adult female 1 1% — Total 123 (14) — — ed for museum specimens in the western United States, a gradient from north to south, with pre- dominantly females in the north and males in the south, appeared to be consistent (Table 5). Al- though certain biases can be introduced by using museum collections, the sex ratios were similar to those observed on road surveys at the same lati- tudes. Because Russell (1981) did not distinguish adults from juveniles, it has remained largely unknown whether juveniles also exhibit differential migra- tion between the sexes. Seventy-seven percent of juveniles trapped in the Mission Valley, Montana, during the winters of 1995-99 were females based on measurements. Moreover, the highest propor- tion of juvenile females occurred the same year that we observed the highest proportion of adult females on road surveys and the lowest densities of hawks. Differential trapability between sexes could bias the sex ratio of trapped birds; indeed, adult females tended to be more difficult to trap than adult males. However, if this pattern were true for juveniles, then the trapping ratios would underes- timate rather than overestimate the proportion of juvenile females. Furthermore, juveniles are much more easily trapped than adults, and the likelihood of juvenile males being so consistently underrep- resented seems small. Therefore, we concluded that the trapping data indicated that sex differenc- September 2000 Rough-legged Hawk Winter Distribution 163 es in winter distributions are similar for adults and juveniles. Intraspecific interactions and territoriality in Rough-legged Hawks during winter are highly complex and poorly understood (Watson 1984, Bildstein 1987, Palmer 1988). Aggression and ter- ritoriality may change daily depending on weather (Temeles and Wellicome 1992), food availability, and a variety of other unknown factors (Watson 1984). Watson recorded the frequency of aggres- sive intraspecific interactions between known-sex Rough-legged Hawks wintering in Idaho and found that 70% of all interactions {N = 76) involved fe- males displacing males. Watson (1984) did not dis- tinguish between juveniles and adults, however. When separating the different age and sex classes, we found that adult females displaced adult males much more frequendy. Additionally, adult females displaced other adult females more often than adult females displaced adult males, which differed greatly from Watson’s (1984) findings in Idaho. When considering the success rate of displacement attempts and the overall success rate for each age and sex class, it appeared that adult females are the most dominant class and juvenile males are the least dominant. Interactions between adult males and juvenile females were more complicated and remain poorly understood. Two major differences between Watson’s (1984) study site and the Mon- tana study area, were that Rough-legged Hawks in Idaho frequently fed on road-killed carrion, where- as hawks in the Mission Valley rarely fed on carrion and foraged almost exclusively on small mammals (C. Olson unpubl. data) and the densities of Rough-legged Hawks were much higher in three of four years in the Mission Valley (x — 1.14 birds/ km) than in Idaho (x = 0.18 birds/km; Watson 1984). It is unknown, however, how these factors influence the social interactions of Rough-legged Hawks during winter. The ratio of juveniles to adults on the road sur- veys did not differ significantly within a season; however, the proportion of juveniles did vary among winters. Furthermore, the overall density of Rough-legged Hawks in Montana was considerably lower in the first winter than in the following three winters. The low numbers observed in the first win- ter followed a major decline in voles (Microtus spp.) in the area. Rough-legged Hawk numbers are known to fluctuate considerably (Baker and Brooks 1981, Mindell and White 1987, Palmer 1988, Virkkala 1992, Swem 1996, Potapov 1997), and fluctuations in the number of wintering juve- niles are often attributed to changes in reproduc- tive success prior to the subsequent winter (Bent 1937, Brown and Amadon 1968). However, a vari- ety of local and regional factors such as prey avail- ability, weather, and/ or the presence of conspecif- ics, also may influence the distribution and density of wintering juveniles. Review of Hypotheses Based on the arrival-time hypothesis, we would expect the sex that establishes the breeding terri- tory to winter farthest north. Several lines of evi- dence suggest that the arrival-time hypothesis does not apply to Rough-legged Hawks. First, males usu- ally establish territories in most North American raptor species (Newton 1979, Johnsgard 1990), and hence we would expect to find a preponder- ance of adult males wintering farther north. Sec- ond, although not well-documented. Rough-legged Hawks are thought to arrive on the breeding grounds already paired (Bent 1937, Mindell in Palmer 1988). If pairs do arrive simultaneously, such behavior would be inconsistent with the arriv- al-time hypothesis. Finally, the arrival-time hypoth- esis would act predominately on breeding birds (Myers 1981), and because juvenile Rough-legged Hawks are not likely to breed in their first season, we would not expect similar latitudinal segregation among juveniles (I^ellen 1994). The social-dominance hypothesis proposes that subordinate individuals are forced to winter farther south to avoid competition with dominant conspe- cifics (Gauthreaux 1985). Hence, the dominant sex would be expected to display aggressive behav- ior toward individuals of the opposite sex and/ or subordinate age classes, especially in more north- ern wintering areas. In Rough-legged Hawks, the larger females should be dominant within each age class. Thus, according to the social-dominance hy- pothesis, adult females should winter farthest north, juvenile males farthest south, and adult males and juvenile females overlapping in the mid- dle, depending on which class is most dominant (Kerlinger and Lein 1986). Although it appears that adult female Rough-leg- ged Hawks are dominant over the other classes, and juvenile males tend to be subordinate, it re- mains unclear whether juvenile females dominate adult males, or vice versa. Roughly 70% of behav- ioral interactions did not involve adult males. Con- versely, 64% of interactions involved juveniles, sug- 164 Olson and Arsenault VoL. 34, No. 3 gesting that frequency of antagonistic interactions, alone, does not explain why Rough-legged Hawks exhibit differential migration by sex and not age. Although habitat segregation by sex has been at- tributed to social dominance in other species (Koplin 1973, Mills 1976), studies supporting the social-dominance hypothesis have failed to show that intraspecific competition, and not various en- vironmental factors, results in the latitudinal seg- regation of the sexes. If our data accurately reflect the sex ratios of juvenile hawks wintering in the Mission Valley, then they indicate that similar selection pressures are acting equally on adults and juveniles. If social dominance were the main operating factor, we would expect juvenile males to occur in lower pro- portions than adult males in the more northern areas. Furthermore, the sex ratio of adults should change as food availability decreases and/or as hawk densities change, as would be expected by the social-dominance hypothesis. However, the sex ratios changed very little between years of extreme- ly low densities and presumably limited food (1995-96 pers. obs.), and extremely high wintering densities with abundant food (1998-99 pers. obs.) in Montana. Indeed, although Russell (1981) fa- vored the social-dominance hypothesis for explain- ing differential migration by sex in Rough-legged Hawks, he suggested that the migration patterns may be flexible, varying as regional environmental conditions vary. We propose that the most influential factor reg- ulating differential winter distribution in the Rough-legged Hawk is thermoregulation and tol- erance of more extreme winter conditions, i.e., the body-size hypothesis (Ketterson and Nolan 1976, Searcy 1980). In Montana, we detected the highest proportions of adult females on December and January surveys, and the highest proportions of adult males on the first and last surveys, during the two coldest winters (1995-96 and 1996-97). More- over, the mean ratio of adult females to adult males in Montana was significantly inversely correlated with average temperature, and less-strongly corre- lated with average snowfall, among the four win- ters. Cade (1955) found no overlap in body mass between sexes of Rough-legged Hawks, although the sample sizes were small. When considering all morphological measurements, Cade and Palmer (1988) both estimated a minimum of 75% non- overlap between the sexes. So, female Rough-leg- ged Hawks are clearly larger on average than males. Herreid and Kessel (1967) determined for 31 species of birds that larger individuals have rel- atively heavier plumage and more effective insula- tion than smaller birds. Finally, Root (1988) sug- gested that larger body size increases potential energy stores and therefore enables longer periods of fasting, and further claimed that energy con- straints eventually limit the distribution and abun- dance of species. If this is true for Rough-legged Hawks, then females may be more capable than males of withstanding colder temperatures and fasting during periods of deep snow and low prey availability. Therefore, we believe thermoregulato- ry constraints may be an important factor contrib- uting to the differential latitudinal winter distri- bution of the sexes in the Rough-legged Hawk. Because the predictions of the social-dominance hypothesis overlap with those of the body-size hy- pothesis, it is difficult to completely disprove one or the other hypothesis. Clearly, further research is needed on the differences between the sexes in thermal conductance and the behavioral differenc- es among the ages and sexes in territoriality. Other suggested possibilities explaining female hawks wintering farther north than males, include greater prey-switching capability, interspecific com- petition or both (T. Swem pers. comm.). Because females are larger overall, they should be more ca- pable of switching to alternative prey-types during periods of deep snow and subsequently low prey availability. Rough-legged Hawks are recognized as small mammal specialists; however, a variety of small and medium birds have been recorded at nests (Swem 1996), and road-killed carrion was commonly fed upon in Idaho (Watson 1984). Al- though neither of these ideas was specifically ex- amined in this study. Rough-legged Hawks were seen foraging almost exclusively on small mam- mals, even throughout periods of deep (>10 cm) snow cover (Olson unpubl. data) . Additionally, in- terspecific competition involving prey was likely much less than observed with hawks feeding on carrion in Idaho, because of the smaller size, faster consumption times and overall greater abundances usually associated with small mammals as prey. Therefore, these potential benefits for the larger sex may be in addition to, but probably are not, the actual operating factors. Finally, we expected a greater proportion of males in Montana early and late in the season, es- pecially during migration. Although we observed the highest proportion of males during November September 2000 Rough-legged Hawk Winter Distribution 165 and April, this was not significantly different from the rest of the winter. Russell (1981) also noted that sex ratios remained relatively unchanged dur- ing a winter. Thus, we suspect that migration, es- pecially during fall, may be rapid and relatively continuous in birds wintering farther south, there- by explaining why we did not observe greater num- bers of adult males stopping over in the Mission Valley during migration. Acknowledgments We thank D. Becker and the Confederated Salish and Kootenai Tribes for supporting the research on the Flat- head Indian Reservation. Funding for the Montana field- work was provided by HawkWatch International, Flathead Audubon Society, Bureau of Land Management, Avian Power Line Interaction Committee (APLIC), Montana Power Company, Mission Valley Power, USFWS Migratory Bird Office and National Bison Range Complex, and Montana Fish, Wildlife and Parks. Additionally, we thank University of Washington Burke Museum, Charles R. Conner Natural History Museum-Washington State Uni- versity, Michigan Museum of Zoology-University of Mich- igan, James R. Slater Museum of Natural History-The University of Puget Sound, Idaho State University-Zoo- logical Museum, Monte L. Bean Life Sciences Museum- Brigham Young University, Peabody Museum of Natural History, Dallas Museum of Natural History, and the Phil Wright Zoological Museum-University of Montana. Also, we thank the many volunteers from the first year, but especially J. Haskell, and field assistants K. Lucas and S. Osborn. K.L. Bildstein, S. Houston, J. Marks, S. Osborn, T. Swem, J.W. Watson, and C. White provided helpful reviews of the manuscript. Literature Cited American Ornithologists’ Union. 1998. Checklist of North American birds, 7th ed. Am. Ornithol. Union, Washington, DC U.S.A. Baker, J.A, and R.J. Brooks. 1981. Raptor and vole pop- ulations at an airport./. Wildl. Manage. 45:390-396. Bent, A.C. 1937. Life histories of North American birds of prey. U.S. Natl. Mus. Bull. 167:1-398. Bildstein, K. 1987. Behavioral ecology of Red-tailed Hawks {Buteo jamaicensis) , Rough-legged Hawks (Buteo lagopus), Northern Harriers (Circus cyaneus), and American Kestrels (Falco sparverius) in south central Ohio. Ph.D. dissertation, Ohio State Univ., Columbus, OH U.S.A. Brown, L. and D. Amadon. 1968. Eagles, hawks and fal- cons of the world. McGraw-Hill, New York, NYU.S.A. Cade, TJ. 1955. Variation of the common Rough-legged Hawk in North America. Cowcfor 57:313-346. Clark, W.S. and B.K. Wheeler. 1987. A field guide to hawks: North America. Houghton Mifflin Company, Boston, MA U.S. A. Gauthreaux, S.A., JR- 1985. Differential migration of raptors: the importance of age and sex. Pages 99-106 in M. Harwood [Ed.], Proc. Hawk Migration Confer- ence IV, Rochester, NY U.S.A. Herreid, C.F., II and B. Kessel. 1967. Thermal conduc- tance in birds and mammals. Comp. Biochem. Physiol 21:405-414. JOHNSGARD, P.A. 1990. Hawks, eagles, and falcons of North America: biology and natural history. Smithson- ian Institution Press, Washington, DC U.S.A. Kerlinger, P. and M.R. Lein. 1986. Differences in winter range among age-sex classes of Snowy Owls Nyctea scandiaca in North America. Omis Scand. 17:1-7. Ketterson, E.D. and V. Nolan, Jr. 1976. Geographic var- iation and its climatic correlates in the sex ratio of eastern-wintering Dark-eyed Juncos (Junco hyemalis hye- malis). Ecology 57:679-693. King, J.R., D.S. Earner, and L.R. Mewaldt. 1965. Sea- sonal sex and age ratio in populations of White- crowned Sparrow of the race gambelii. Conrfor 67: 489- 504. Kjellen, N. 1994. Differences in age and sex ratio among migrating and wintering raptors in southern Sweden. Auk 111:274-284. Koplin, J.R. 1973. Differential habitat use by sexes of American Kestrels wintering in northern California Raptor Res. 7:39-40. Mills, G.S. 1976. American Kestrel sex ratios and habitat separation. Auk 93:740-748. Mindell, D.P. and C.M. White. 1987. Breeding popula- tion fluctuations in some raptors. Oecologia 72:382- 388. Mvers, J.P. 1981. A test of three hypotheses for latitudinal segregation of the sexes in wintering birds. Can. J Zool. 59:1527-1534. Newton, I. 1979. Population ecology of raptors. T. & A.D Poyser, Berkhamsted, U.K. Palmer, R.S. [Ed.]. 1988. Handbook of North American birds. Vol. 5. Yale Univ. Press, New Haven, CT U.S.A Potapov, E.R. 1997. What determines the population density and reproductive success of rough-legged buz- zards, Buteo lagopus, in the Siberian tundra? Oikos 78: 362-376. Root, T. 1988. Energy constraints on avian distributions and abundances. Ecology 69:330-339. Russell, K.B. 1981. Differential winter distribution by sex in birds. M.S. thesis, Clemson Univ., Clemson, SC U.S.A. Searcy, W.A. 1980. Optimum body size at different am- bient temperatures: an energetics explanation of Bergmann’s rule. J. Theor. Biol. 83:579-593. Swem, T.R. 1996. Aspects of the breeding biology of Rough-legged Hawks along the Colville River, Alaska. M.S. thesis, Boise State Univ., Boise, ID U.S.A. Temeles, E.J. and T.I. Wellicome. 1992. Weather-depen- dent kleptoparasitism and aggression in a raptor guild. Auk 109:920-923. Virkkala, R. 1992. Fluctuations of vole-eating birds of prey in northern Finland. Ornis Fenn. 69:97—100. 166 Olson and Arsenault VoL. 34, No. 3 Wallin, K., M. Wallin, T.J. Joras, and P. Strand vik. 1985. Leap-frog migration in the Swedish kestrel Falco tinnunculus population. Pages 213-222 in M.O.G. Er- iksson [Ed.], Proc. Fifth Nordic Ornithol. Congress, Onsala, Sweden. Watson, J.W. 1984. Rough-legged Hawk winter ecology in southeast Idaho. M.S. thesis, Montana State Univ., Bozeman, MT U.S.A. Wheeler, B.K. and W.S. Clark. 1995. Photographic guide to North American raptors. Houghton Mifflin Company, Boston, MA U.S.A. Wilkinson, L., G. Blank, and C. Gruber. 1996. Desktop Data Analysis with SYSTAT. Prentice Hall, Englewood Cliffs, NJ U.S.A. Received 30 October 1999; accepted 22 May 2000 J. Raptor Res. 34 (3): 167-1 74 © 2000 The Raptor Research Foundation, Inc. AVAILABILITY AND INGESTION OF LEAD SHOTSHELL PELLETS BY MIGRANT BALD EAGLES IN SASKATCHEWAN Michael J.R. Miller^ Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2 Canada Mark E. Wayland Environment Canada, Prairie and Northern Region, 115 Veterinary Road, Saskatoon, SK S7N 0X4 Canada Elston H. Dzus^ and Gary R. Bortolotti Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2 Canada Abstract. — ^We determined food habits and prevalence of ingested shotshell pellets in a population of Bald Eagles (Haliaeetus leucocephalus) at a waterfowl staging area on the Canadian prairies. Food habits were ascertained through examination of prey remains and regurgitated castings, and by direct obser- vation. Shotshell pellet ingestion was determined by radiography of regurgitated castings and by fluo- roscopy of live-trapped eagles. In addition, we collected moribund and dead waterfowl to determine prevalence of lead shotshell pellets within their tissues. Waterfowl formed the bulk of the diet (>70% of prey items). Of 123 waterfowl carcasses examined, 47% contained shotshell pellets ranging in number from 1-7 per bird. Of 118 shotshell pellets removed, 87% were composed of lead, the remainder steel. Less than 2% of regurgitated eagle castings collected {N = 509) contained lead shotshell pellets. In- gested shotshell pellets were found in 9% (6 of 66) of trapped eagles. These conditions should amelio- rate with the ban on use of lead shotshell pellets for hunting waterfowl in Canada that was instituted in 1999. Key Words: Bald Eagle; Haliaeetus leucocephalus; food habits; lead shotshell pellets; lead exposure; Saskatch- ewan. Disponibilidad e ingestion de perdigones de plomo en aguilas calvas migratorias en Saskatchewan Resumen. — Determinamos los habitos alimenticios y la prevalencia de perdigones ingeridos en una poblacion de aguilas calvas {Haliaeetus leucocephalus) en un area de aves acuaticas en las praderas de Canada. Los habitos alimenticios fueron evaluados a traves del examen de restos de presas, egagropilas y observacion directa. La ingestion de perdigones fue determinada por radiografias de egagropilas y por fluoroscopia de aguilas atrapadas vivas. Adicionalmente, recolectamos aves acuaticas moribundas para determinar la prevalencia de perdigones de plomo dentro de sus tejidos. Las aves acuaticas con- forman la mayoria de la dieta (>70% de las presas). De los 123 cadaveres de aves acuaticas examinadas, 47% contenian perdigones en un rango de 1-7 por ave. De los 118 perdigones removidos, 87% eran de plomo y el resto de acero. Menos del 2% de las egagropilas recolectadas {N = 509) contenian perdigones de plomo. Los perdigones ingeridos fueron encontrados en el 9% (6 de 66) de las aguilas atrapadas. Estas condiciones deben aminorarse con la prohibicion del uso de perdigones de plomo en la caza de aves acuaticas en Canada, instaurada en 1999. [Traduccion de Cesar Marquez] The presumed major source of lead for raptors is that obtained through ingestion of shotshell pel- ^ Present address: lolaire Ecological Consulting, 210- 112* St., Saskatoon, SK S7N 1V2 Canada. ^ Present address: Forest Ecology Program Manager, Al- berta Pacific Forest Industries, Inc., Box 8000, Boyle, AB TOA OMO Canada. lets or bullet fragments present in tissues of prey animals (Redig et al. 1980, Pattee and Hennes 1983, U.S. Fish and Wildlife Service 1986, Gill and Langelier 1994). Bald Eagles {Haliaeetus leucoce- phalus) are particularly at risk to lead poisoning because they often rely on wounded prey or car- rion likely to contain lead shotshell pellets (Pattee and Hennes 1983, Gerrard and Bortolotti 1988). 167 168 Miller et al. VoL. 34, No. 3 Thus, lead toxicosis has been documented more frequently in Bald Eagles than in any other non- waterfowl species (Locke and Friend 1992). In addition to unrecovered birds shot by hunt- ers, free-flying waterfowl often harbor shotshell pellets embedded in body tissues (U.S. Fish and Wildlife Service 1986, Scheuhammer and Norris 1995). Wintering and migrant Bald Eagles fre- quently use locally abundant food sources such as waterfowl (Steenhof 1976, Sabine and Klimstra 1985, Hennes 1985, Lingle and Krapu 1986, Ger- rard and Bortolotti 1988) . Thus, it is generally be- lieved that the presence of waterfowl hunting and eagles in a localized area predetermine a high risk of lead poisoning for scavenging eagles (Pattee and Hennes 1983). In Canada, approximately 1500 metric tonnes of lead shotshell pellets are depos- ited annually into the environment by hunters shooting waterfowl, upland game birds and small mammals (Scheuhammer and Norris 1995). Lead exposure and poisoning have been docu- mented in both Bald and Golden Eagles {Aquila chrysaetos) from specimens collected on the Cana- dian prairies (Wayland and Bollinger 1999). Be- cause of intense, localized waterfowl hunting in the southern portions of the Canadian prairies during the autumn and the concurrent passage of Bald Eagles with numerous waterfowl, eagles in this area have a high potential for lead exposure and poi- soning. The purpose of this investigation was to determine the prevalence of lead shotshell pellets in potential prey items and to document the prev- alence of ingestion of lead shotshell pellets by Bald Eagles at a waterfowl staging area under heavy hunting pressure. Study Area We examined a congregation of Bald Eagles and wa- terfowl at Galloway Bay (50°48'N, 108°27'W), an im- poundment located on the South Saskatchewan River in southwestern Saskatchewan, Canada. During the fall, in addition to attracting large numbers of Bald Eagles, the river and surrounding submerged floodplain together create favorable staging habitat for up to 700 000 geese and cranes (Roy 1996). The 10' block (10' latitude X 10' longitude) containing Galloway Bay is also among the most heavily used goose-hunting areas in Canada accord- ing to the Canadian Wildlife Service’s National Harvest Survey (Canadian Wildlife Service unpubl. data). Methods From September-November 1992-95, ancillary to trap- ping and blood sampling Bald Eagles to estimate lead exposure (Miller et al. in press), we collected data per- taining to food habits. We determined percent occur- rence of food items using three techniques: analysis of regurgitated castings, collection of prey remains and di- rect observation. Each technique potentially under- or overrepresented certain prey items; therefore, we used all three methods simultaneously (Simmons et al. 1991, Mersmann et al. 1992). Throughout the study area, whole or partially con- sumed carcasses were salvaged individually, while we com- piled smaller items such as feathers or bones. The fre- quency of occurrence was determined for each species found in a particular day’s collection. Prey remains not readily identified were compared with museum reference specimens (University of Saskatchewan and Royal Ontar- io Museum, Toronto, Ontario, Canada). Avian remains were identified to the lowest taxonomic category possi- ble; all other remains were designated only to class. Regurgitated castings were placed in separate bags and later fluoroscoped to determine prevalence of metallic shot. Castings were then air-dried at room temperature and examined under a dissecting microscope. A sample of approximately five similar feathers was examined un- der a compound microscope to determine downy bar- bule configuration as an aid in identification (Brom 1991) before using a reference collection or feather key (Broley 1950). Under scientific and salvage permits acquired from En- vironment Canada, physically injured or moribund wa- terfowl were captured by hand and euthanized. Carcasses were frozen and later fluoroscoped in the laboratory to ascertain the presence of shotshell pellets. Shot-positive carcasses were radiographed frozen and left to thaw over- night. Shotshell pellets were excised and the tissue type and anatomical location from each embedded pellet or fragment noted. Lead and steel shotshell pellets were dif- ferentiated with a magnet. We observed eagles hunting and eating. When possi- ble, prey remains were retrieved after eagles had ceased feeding or after being flushed by an observer. In 1994 and 1995, we used a Xi Scan 1000 Portable Radiographic and Fluoroscopic System (Xi Tech, Wind- sor Locks, CT U.S.A.) to examine the gastrointestinal tract of captured eagles to determine the prevalence of shotshell pellet ingestion (Miller et al. in press). Lead shotshell pellets could not be differentiated from steel or other nontoxic pellets, nor was the size of shotshell pel- lets determined. Three eagles recaptured and fluoroscoped in the same season were included in analyses. Unlike blood lead (PbB) concentrations which may take several weeks to return to preexposure levels (Pain 1996), we considered initial and recapture dates independent, as shotshell pel- lets are likely not retained for long (Hoffman et al. 1981). Unless indicated, nonparametric statistics were used throughout based on methods presented by Siegel and Castellan (1988). The Y-subscript following tests indi- cates that a Yates’ correction for continuity has been ap- plied; the c-subscript following test statistics and z-values indicate that these values have been corrected for tied observations (Siegel and Castellan 1988). Results Seventy-two collections were made during 1992- 95. Avian remains were found in 97% of all collec- September 2000 Lead Shot in Bald Eagles 169 Table 1. Comparison of prey identification techniques for Bald Eagles at Galloway Bay, Saskatchewan, 1992-95. Prey Direct Obser- vation^ Prey Re- mains'’’'^ Cast- INGS'"’'* Unknown 22.8 — — Avian White-fronted Goose 28.1 66.7 49.0 Canada Goose 5.3 20.8 0.7 White Goose‘s 5.3 19.4 3.5 Anser spp. 7.0 22.2 5.6 American Coot 3.5 31.9 27.3 Mallard Duck^ 3.5 19.4 13.3 Unidentified duck 3.5 13.9 27.3 Unidentified waterfowl 14.0 — — Mammals 1.8 8.3 8.4 Fish 5.3 9.7 2.8 ^ % of all observations {N = 57), % occurrence in all castings {N — 143) or collections (N — 72). **0068 not total 100% as some items were found in occurrence with other items within the same casting or collection period. Snow Geese {Chen caerulescens) and Ross’ Geese (C. rossii). ^ Anas platyrhynchos. tions (70 of 72), while mammals and fish were only found in six and seven (8 and 10%) collections, respectively (Table 1). White-fronted Geese {Anser albijrons) were the most common bird and were found in 48 of 72 (67%) collections; American Coots {Fulica americana) were the next most com- mon avian prey and occurred in 32% of all collec- tions (Table 1). Of the 509 castings collected during 1994—95, 143 were examined to determine prey composi- tion. Castings generally consisted of either one spe- cies or class (62%), although up to four species were identified in several pellets (3%). Of the three broad categories of prey items, fish and mammals were observed least often and were only found in 2.8% and 8.4% of castings, respectively (Table 1). Birds were the most common prey and were found in all regurgitated castings; six species and three genera were identified (Table 1). Since observations of foraging eagles were gen- erally made at a distance, assessing diet through feeding observations provided the least opportu- nity for identification of prey to the lowest taxon (Table 1). Seventy-five percent (43 of 57) of obser- vations were of eagles eating; the remainder were of eagles hunting with no consumption of prey. Birds accounted for at least 71% of all items that were consumed or actively pursued; fish and mam- mals combined accounted for only 7% of obser- vations (Table 1). Of note, however, was the response of eagles in 1995 to an avian cholera epizootic. Waterfowl mor- tality was noted on 22 October and we speculated that the outbreak began six days before on 16 Oc- tober based on changes in the number of eagles that were observed feeding on the ground from population counts during the same period (Change-point test, z = —3.62, P< 0.001) (Miller 1999). Of 123 fluoroscoped waterfowl carcasses of nine species, greater than 91% retrieved were geese; of these, 81% were White-fronted Geese (Table 2). Ducks, Sandhill Cranes {Grus canadensis) and American Coots accounted for only 9% of birds retrieved (Table 2). Ninety carcasses were dissected in the laboratory. The remaining 33 birds salvaged from the avian cholera epizootic in 1995 were fluo- roscoped on site, and only the number of shotshell pellets present was recorded, as anatomical loca- tion could not be determined. Significantly more birds with embedded shot- shell pellets were obtained through sacrificing in- jured birds (40 of 68) than from specimens found dead through salvage (8 of 55) (x\ = 23.226, P < 0.001). Geese {N — 112) had a significantly larger median number of embedded shotshell pellets, or burdens, than an aggregate sample of ducks, Sand- hill Cranes, and American Coots {N = 11) (Wil- coxon-Mann-Whitney, = —2.992, P = 0.0028). Embedded shotshell pellets were found in 40% of carcasses and in three of the nine species ex- amined; among these three species, the median number of embedded shotshell pellets did not vary significantly (Table 2) (Kruskal-Wallis one-way AN- OVA, df = 2, Hf. = 1.243, P = 0.54). The number of pellets per carcass ranged from 1-7 (Table 2). We could not detect a difference in median shot- shell pellet burden per anatomical region among carcasses with shotshell pellets (Kruskal-Wallis one- way ANOVA, df = 2, P > 0.10) (Table 2). No evidence suggested a temporal increase in embedded shotshell pellet burdens in all species combined (Kendall’s rank-order correlation, = 0.059, = 0.961, N = 123, P = 0.34). Neither did evidence support an increase among White-front- ed Geese alone (Kendall’s rank-order correlation, = -0.021, Zc "" -0.294, A= 91, P = 0.39) nor Canada Geese {Branta canadensis) (Kendall’s rank- 170 Miller et al. VoL. 34, No. 3 Table 2. Summary of anatomical location and number of shotshell pellets excised from waterbirds at Galloway Bay, 1994-95. Anatomical Location of Shotshell Pellet‘d Shotshell „ Body Region Species (N) Present? No./ SUB- CUTAN.*^ Gizzard Muscle^* Thor.*' Abdom.^ Legss Wings Bone^ N Y Carcass White-fronted Goose (91) 52 39 1-7 21,5 8,0 20, 1 6, 0 8,2 5,1 25,3 Canada Goose (14) 6 8 1-4 2,0 0,1 3,0 3, 0 0,2 2,0 4,1 Snow Goose (3)* 1 2 1-5 3 0 1 0 0 0 1 Ross’ Goose (5)J 4 0 — 0 0 0 0 0 0 0 Sandhill Crane (1) 1 0 — 0 0 0 0 0 0 0 Mallard Duck (5) 5 0 — 0 0 0 0 0 0 0 American Coot (3) 3 0 — 0 0 0 0 0 0 0 Green-winged TeaP (1) 1 0 — 0 0 0 0 0 0 0 Northern Shoveled (1) 1 0 — 0 0 0 0 0 0 0 ® The two numbers represent the number of shotshell pellets per location in birds that were collected live or found dead, respectively. ^ Shotshell pellets just beneath the skin. Shotshell pellets within the lumen of the ventriculus or within the ventricular wall. Shotshell pellets within muscle mass throughout the body excluding the legs and wings. Shotshell pellets within the thoracic region. * Shotshell pellets within the abdominal region. s Shotshell pellets within muscle and bone of the legs. Shotshell pellets within the bones and muscles of the wings and larger bones of the body were considered nonavailable to eagles. ‘ Birds were found dead. J One specimen was not fluoroscoped. Anas crecca. * Anas clypeata. order correlation, — 0.269, z^. = 1.339, N = 14, 0.090). Of all shotshell pellets excised {N = 118), 87.3% were composed of lead; the remainder were steel. Individual carcasses harbored either lead {N= 40), steel {N = 2) shotshell pellets, or both {N = 6). Lead shotshell pellets ranged in size from #6 to size BBB; steel shotshell pellets varied from #2 to size T. During 1994—95, 509 castings were collected. All castings were fluoroscoped to determine if metallic shotshell pellets were present; 10 castings con- tained one metallic shotshell pellet of undeter- mined size. Four of 248 (1.6%) and four of 261 (1.5%) castings collected in 1994 and 1995 respec- tively, contained lead shotshell pellets, while the remaining two castings with shotshell pellets from 1995 contained steel shotshell pellets (2 of 261, or 0.8%). Contrary to our hypothesis, we did not de- tect an increase in the incidence of shotshell pos- itive castings over the nine week period (16 Sep- tember-16 November 1994-95) (x^ = 2.765, df — 3, P= 0.22). Intragastrointestinal shotshell pellets were ob- served in six of 69 eagles (8.7%). The 7.8% prev- alence of lead exposure as determined from PbB concentrations (Miller et al. in press) was not sig- nificantly different from the exposure prevalence ascertained from ingestion of shotshell pellets (x\ = 0.001, P = 0.96). The number of ingested shot- shell pellets per eagle ranged from 1-2. Four of the six eagles had shotshell pellets located in the abdomen, while the remaining two eagles each had single shotshell pellets present near the crop. Discussion Waterfowl were the most common food of Bald Eagles at Galloway Bay. This dependence on water- fowl is typical for Bald Eagles wintering in the west- ern United States (Steenhof 1976, Hennes 1985, Sabine and Klimstra 1985, Lingle and Krapu 1986). White-fronted Geese, the most abundant species at Galloway Bay, were also the most common species consumed. The second-most common prey items were ducks and American Coots, found in 41 and 27%, respectively, of all castings, and 32 and 39%, respectively, of all prey remains. Occurring in <10% of prey remains, observa- tions or castings, mammals and fish were uncom- September 2000 Lead Shot in Bald Eagles 171 mon in the diet. However, we may have under- estimated the proportion of each owing to differences in detectibility (Frenzel and Anthony 1989, Mersmann et al. 1992, Watson et al. 1992) . The occurrence of shotshell pellets in 40% of debilitated or dead waterfowl at Galloway Bay is similar to the 20-30% reported for free-flying and apparently healthy waterfowl throughout the Unit- ed States and Canada (U.S. Fish and Wildlife Ser- vice 1986, Scheuhammer and Norris 1995). Waterfowl sampled late in or after the hunting season and individuals that have survived succes- sive hunting seasons will often harbor large amounts of embedded shot (Pattee and Hennes 1983, Hennes 1985, U.S. Fish and Wildlife Service 1986). Differences in shotshell pellet burden in wa- terfowl have also been shown to exist among spe- cies (U.S. Fish and Wildlife Service 1986). In gen- eral, larger species usually carry greater shotshell pellet burdens than smaller species (U.S. Fish and Wildlife Service 1986), a phenomenon also sug- gested by our results. The anatomical location of embedded shot in waterfowl at Galloway Bay was similar to what has been previously reported in other waterfowl spe- cies (Perry and Geisler 1980, Hennes 1985). The location of embedded shot may influence the avail- ability of lead for foraging eagles. For example, Sabine and Klimstra (1985) and Hennes (1985) found that nonedible prey remains retrieved from eagle kill sites generally consisted of feathers and bones of the wings, pelvis, and vertebral column. Based on this and on observations of feeding ea- gles, Hennes (1985) estimated that 75-85% of em- bedded shot was available to eagles; the remaining shot, such as that deeply embedded into large bones, were considered unavailable as eagles rarely consumed these parts. Our results suggested a sim- ilar phenomenon, where 73% of embedded shot- shell pellets were considered available to eagles. Eagles may also secondarily consume lead shot- shell pellets that were originally ingested by water- fowl (Locke and Thomas 1996). Although it was difficult to determine whether shotshell pellets in the lumen resulted from gunshot or ingestion (Lu- miej and Scholten 1989), data from dead or mor- ibund waterfowl at Galloway Bay indicated a low prevalence of shot in the ventriculus. In Saskatch- ewan, the proportion of waterfowl with ingested lead shotshell pellets have been reported as gen- erally low (<4%) (Hochbaum 1993, Scheuhammer and Norris 1995). Field hunting, wide dispersal of hunters, and annual cultivation of fields, as occur at Galloway Bay, all act to decrease the availability of lead shot pellets for waterfowl (Hochbaum 1993). Waterfowl in Saskatchewan do not appear to be overly exposed to lead based on surveys of lead content in wing bones (Dickson and Scheu- hammer 1993). Therefore, it seems unlikely that eagles at Galloway Bay secondarily consume shot- shell pellets originally ingested by waterfowl. In comparison to other studies that have exam- ined the castings of Bald Eagles that have been feeding on waterfowl (e.g., Griffin et al. 1982, Bengston 1984, Hennes 1985, Nelson et al. 1989), the frequency of castings with shotshell pellets at Galloway Bay was relatively low. While Bengston (1984) argued that castings with shotshell pellets are the best indicators of lead exposure for raptors, Hennes (1985) suggested that shotshell pellets in eagle castings represent a minimum estimate of the true ingestion rate. Pain et al. (1993 and 1997) and Mateo et al. (1999) noted that the prevalence of lead shotshell pellets in castings of Marsh Harriers ( Circus aeru- ginosus) increased with the progression of the hunting season and was higher within than outside the hunting season. However, no temporal trend was detected at Galloway Bay or by Hennes (1985). Hennes (1985) suggested that multiple castings which may be regurgitated by individual eagles af- ter feeding on larger carcasses such as geese may “dilute” the prevalence of ingestion of shotshell pellets and may have masked seasonal increases (Hennes 1985). The relatively high prevalence of lead shotshell pellets found in waterfowl carcasses and thus, the potential for consumption by eagles contrasted with the apparent low rate of ingestion of shotshell pellets. Hennes (1985) suggested that the rate of ingestion by Bald Eagles would not equal the prev- alence embedded in carcasses because of unavail- ability due to anatomical location; this may have occurred at Galloway Bay. Alternatively, eagles may have been able to detect embedded shotshell pel- lets within the prey item and avoid them (cf. Sten- dell 1980). Possible evidence for this occurring at Galloway Bay was observed in one salvaged carcass of a White-fronted Goose that was almost com- pletely defleshed, yet contained several (N — 4) shotshell pellets lying between bones in the ventral aspect of the synsacrum and vertebral column. In an early review of the cases of lead poisoning in Bald Eagles, Feierabend and Myers (1984) in- 172 Miller et al. VoL. 34, No. 3 dicated that despite definitive diagnoses of lead toxicosis, only 14% of Bald Eagles necropsied in the United States had lead shotshell pellets present in the gastrointestinal tract. Therefore, lead toxic- ity or exposure in raptors cannot be ruled out sole- ly on the basis of radiographic evidence (Janssen et al. 1986, Langelier et al. 1991), nor can the pres- ence or absence of lead in the ventriculus be used to estimate quantitative lead concentrations (Kra- mer and Redig 1997). Since ingested shotshell pel- lets may rapidly erode, dissolve or be voided in the feces leaving no direct evidence of recent ingestion (Bellrose 1959, Scanlon et al. 1980), estimates of shotshell pellet ingestion determined from fluo- roscopy likely represent a minimum estimate of ac- tual prevalence and subsequent severity of expo- sure (Anderson and Havera 1985). Given the relatively low prevalence of lead ex- posure (Miller et al. in press) and ingestion of shotshell pellets at Galloway Bay, eagles may be consuming more uncontaminated prey than indi- cated by our results (Miller et al. 1998). For ex- ample, nonanserid species such as American Coots are hunted less intensively and generally have a low prevalence of tissue-embedded shotshell pellets (U.S. Fish and Wildlife Service 1986). Therefore, the lower prevalence of lead ingestion by eagles at Galloway Bay may be partially attributable to the presence of a high proportion of coots in the diet. Moreover, in 1992 and 1995, eagles extensively fed upon moribund or dead waterfowl resulting from an avian cholera epizootic, a source likely to con- tain less lead shotshell pellets than waterfowl shot by hunters (Miller et al. 1998). Median PbB con- centrations in eagles from 1992-95 did not, how- ever, yield any significant differences between years (Miller et al. in press) . Reducing availability of lead shotshell pellets for raptors has long been the focus of management strategies for abating lead exposure amongst these species (Pattee and Hennes 1983, Feierabend and Myers 1984, U.S. Fish and Wildlife Service 1986, Pain et al. 1997). However, in light of recent find- ings (Kramer and Redig 1997, Miller et al. 1998), other sources of lead such as fragments from rifle bullets, fishing sinkers and lead shotshell pellets in upland game birds may be important. To accurate- ly assess the effect on raptors of banning lead shot- shell pellets for waterfowl hunting in the United States in 1991 and Canada in 1999, the importance of other potential sources of lead must be resolved (Elliott et al. 1992). Acknowledgments Environment Canada provided the major funding and technical support for this project. Additional funding and technical support was provided by the Wildlife Tox- icology Fund of the World Wildlife Fund (Canada), a Natural Sciences and Engineering Research Council of Canada grant to G.R. Bortolotti, Saskatchewan Environ- ment and Resource Management, and the Department of Veterinary Pathology, Western College of Veterinary Medicine (WCVM). A University of Saskatchewan Grad- uate Teaching Fellowship, and support from General Mills Canada and Nature Saskatchewan provided finan- cial assistance to M.J.R. Miller. H. Levesque kindly pro- vided hunting statistics from the National Harvest Survey of Canada, Canadian Wildlife Service. A. Lang and R. Peck of the Royal Ontario Museum are acknowledged for their valuable advice in identifying prey specimens. E. Dewhurst of the Department of Medical Imaging, Royal University Hospital in Saskatoon, kindly donated his time to radiograph all of the prey specimens. Members of the Department of Veterinary Pathology, WCVM, are thanked for their assistance in the post-mortem room. We thank landowners A. Braaten and R. Stuart for allow- ing us to work on their properties. We also extend our gratitude to all of the field assistants who helped with data collection: E. Bayne, C. Dzus, D. Grier, J, Hochbaum, B. Holliday, S. Neis, K. Skelton, D. Zazelenchuk, and par- ticularly I. Welch, who examined a large proportion of castings, R. Dawson, T, Grubb, and G. Hunt provided valuable comments on earlier drafts of the manuscript. Literature Cited Anderson, W.L. and S.P. Havera. 1985. Blood lead, pro- toporphyrin, and ingested shot for detecting lead poi- soning in waterfowl. Wildl. Soc. Bull. 13:26-31. Bellrose, F.C. 1959. Lead poisoning as a mortality factor in waterfowl populations. III. Nat. Hist. Surv. Bull. 27: 235-288. Bengston, F.L. 1984. Studies of lead toxicity in Bald Ea- gles at the Lac Qui Parle Wildlife Refuge. M.S. thesis, Univ. 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Dietary exposure of kestrels to lead. /. Wildl. Manage. 44:527-530. U.S. Fish and Wildlife Service. 1986. Use of lead shot for hunting migratory birds in the United States: final supplemental environmental impact statement. U.S. Dep. Inter., Fish and Wildl., Washington, DC U.S.A. Watson, J., A.F. Leitch, and R.A. Broad. 1992. The diet of the Sea Eagle Haliaeetus albicilla and Golden Eagle Aquila chrysaetos in western Scotland. Ibis 134:27-31. Wayland, M. and T. Bollinger. 1999. Lead exposure and poisoning in Bald Eagles and Golden Eagles in the Canadian prairie provinces. Environ. Pollut. 104: 341-350. Received 2 December 1999; accepted 23 May 2000 J. Raptor Res. 34(3): 175-1 86 © 2000 The Raptor Research Foundation, Inc. STAND STRUCTURES USED BY NORTHERN SPOTTED OWLS IN MANAGED FORESTS Larry L. Irwin ^ and Dennis R Rock National Council of the Paper Industry for Air and Stream Improvement (NCASI), P. O. Box 458, Corvallis, OR 97339 U.S.A. Gregory R Miller^ U.S. Department of Interior, Bureau of Land Management (BLM), Eugene, OR 97408 U.S.A. Abstract. — We compared vegetative structures in 4— 16-ha patches in forest stands used by 12 pairs of Northern Spotted Owls {Strix ocddentalis caurina) for nesting {N = 44) and foraging (A^ = 38) with habitat structures in 50 stands located randomly throughout annual home ranges in a young and mid- successional forest landscape (25-79 yr-old stands) in the foothills of the western Cascades in Oregon. Forest stand structures influenced selection for stands used for foraging and nesting by Spotted Owls, and abundance of these structures varied with successional development as represented by five age classes. Conifer saplings (10-19 cm in diameter at breast height [dbh]) and trees 50-79 cm dbh were more abundant in foraging areas than nest sites or random sites. Large snags (>40 cm dbh) tended to be more abundant, down woody debris was more abundant, and cover of herbs and low-growing shrubs (<0.5 m) was lower in stands in which owls hunted frequently than in randomly located stands of the same age classes. Owls nested in trees as young as 41 yr old, although 65% of nest trees were older than 120 yr of age. We found 22 (50%) nests in forest stands 46—79 yr of age, whereas owls repeatedly foraged in stands as young as 27 yr of age. Silviculturists should be able to create foraging habitat for Northern Spotted Owls in managed forests by emphasizing control of tree densities and form, woody debris, and understory vegetation. Suitable nesting habitat might best be facilitated via retaining legacy trees. Future research should determine the relative contribution of managed forests to owl conservation. Keywords: Northern Spotted Owl; Strix ocddentalis caurina; foraging habitat; managed forests', nesting hab- itat, Oregon. Estructuras de arboles utilizadas por Strix ocddentalis caurina en bosques manejados Resumen. — Comparamos las estructuras vegetales de 4-16 parches de bosques utilizados por 12 parejas de Strix ocddentalis caurina en habitats de anidacion {N = 44) y forrajeo {N = 38), en estructura de habitats de 50 parcelas de arboles ubicados al azar a lo largo de los rangos de hogar anuales en paisajes de sucesiones de bosques jovenes (25-79 anos), los cuales estaban ubicados en el piedemonte al oeste de Cascadas en Oregon. Las estructuras de arboles influenciaron la seleccion de arboles utilizados para el forrajeo y anidacion de los buhos. La abundancia de estas estructuras vario con el desarrollo suce- sional representado por 5 clases de edad. Las muestras de coniferas (10-19 cm) de diametro a la altura del pecho (dap) y de arboles 50-79 cm dap fueron mas abundantes en areas de forrajeo que en los sitios de anidacion o los sitios escogidos al azar. Los troncos grandes (>40 cm dap) tendian a ser mas abundantes, la cobertura de hierbas y arbustos del sotobosque (<0.5 m) fue menor en los fragmentos de arboles en los que los biihos cazaban con frecuencia que en las estructuras de la misma clase de edad ubicadas al azar. Los buhos anidaron en arboles jovenes de 41 anos de edad, aunque el 65% de los arboles con nidos fueron de mas de 120 anos de edad, mientras que los buhos forrajearon repeti- damente en arboles de 27 anos de edad. Los silviculturistas podrian crear habitat de forrajeo para los buhos en bosques manejados enfatizando el control de las densidades de arboles, su forma, y de la vegetacion del sotobosque. El habitat de anidacion apropiado puede ser implementado protegiendo los arboles valiosos. Las investigaciones futuras deben determinar la relativa contribucion de los bosques manejados a la conservacion de los buhos. [Traduccion de Cesar Marquez] Field studies have repeatedly demonstrated that Northern Spotted Owls (Strix ocddentalis caurina) ^ Present address: P.O. Box 68, Stevensville, MT 59870 U.SA 2 Present address: 3165 10^*^ Street, Baker City, OR 97814 U.S.A. selectively use late-successional and old-growth (LS/OG) forest stands (Forsman et al. 1984, Carey et al. 1990, Hunter et al. 1995), and that vegetative structures within such stands likely influence selec- tion of foraging habitats (Solis and Gutierrez 1990, Call et al. 1992) and nest sites (Forsman et al. 1984, 175 176 Irwin et al. VoL. 34, No. 3 Buchanan et al. 1993, Buchanan and Irwin 1995, LaHaye and Gutierrez 1999). North et al. (1999) documented that forest stand structures influ- enced selection of foraging sites used by Northern Spotted Owls in unharvested forests in Washing- ton. Forest stand structures, including large trees and snags, multiple canopy layers, downed woody debris and shrubs, have been hypothesized to pro- vide favorable microclimates, nest sites, cover from predators, and/or habitat for the owl’s prey (Carey 1985, Carey and Johnson 1995, Carey and Peeler 1995). Forest stand structures influence small mammal diversity and abundance (Carey 1995), and many aspects of Spotted Owl biology are influ- enced by prey abundance, diversity and biomass (Carey et al. 1992, Carey and Peeler 1995, Ward et al. 1998, Carey et al. 1999). There are no detailed measures of forest stand structures and other habitat attributes in young or managed forests occupied by Northern Spotted Owls. Investigators who have documented North- ern Spotted Owl presence in young and mid-suc- cessional (Y/MS) forests (defined herein as those 25-79 yr of age) have speculated that such occu- pancy probably is related to structural legacies from previous, older forests (e.g., Forsman et al. 1977, Irwin et al. 1989). Information on density or abundance of vegetative structures associated with use of Y/MS forests by Northern Spotted Owls could be used for crafting silvicultural prescrip- tions for producing or enhancing habitat in man- aged forests, if a breeding population of owls could be found occupying a Y/MS forest landscape. We located such a Y/MS landscape occupied by North- ern Spotted Owls at the foot of the Cascade Range in western Oregon, where surveys identified 57 ter- ritories occupied by 42 owl pairs and 15 single owls (with annual variation) near Springfield, Oregon in a managed landscape that contained <10% LS/ OG forests. Owl pairs at 29 of the 42 sites success- fully fledged young 1 yr from 1992-99, providing an opportunity to examine forest stand structure at foraging and nest sites. The scale for comparing used and available hab- itats determines the range of inferences from hab- itat selection studies (Johnson 1980, Porter and Church 1987). Previous investigators (Laymon and Reid 1986, Carey and Peeler 1995) found that Northern Spotted Owls often concentrated their searches for prey repeatedly in small “pockets” (<16 ha) of forests, and Bingham and Noon (1997) recommended sampling habitat conditions within core areas (Samuel et al. 1985), or those areas within home ranges that receive dispropor- tionate use. Quantifying habitat components in fre- quently-used stands, which are most likely to occur within core areas, may help identify consistent as- pects of the environment that trigger the owl’s hab- itat selection response and influence its survival and reproduction (Bingham and Noon 1997). Thus, our primary goal was to evaluate stand struc- tural factors associated with forests used for nesting and foraging in frequently-used areas within owl home ranges. We wanted to learn if densities of forest stand-structures and other habitat descrip- tors differed across a successional gradient and among nest sites, foraging areas, and random lo- cations within owl home ranges. Study Area The study area was bordered by the Willamette Nation- al Forest on the east and forests adjacent to Interstate Highway-5 on the west, and extended south from Browns- ville in Linn County to Dorena Reservoir in Lane County, Oregon. About 10% of the land was administered by the USDI Bureau of Land Management (BLM). The remain- der was owned by private timber companies or occurred as rural residential areas and farmlands. Forests in the northern and western portions of the study area regen- erated following timber harvests that often left scattered nonmerchan table trees or seed trees, many of which were >80 cm in diameter. Forests in the eastern parts of the study area regenerated following extensive wildfires about the turn of the century (Teensma 1987). The 57 owl territories that we identified lay below 915 m in elevation in the foothills of the McKenzie River drainage. The area was in the Western Hemlock Zone (Franklin and Dyrness 1981), and the forests were pre- dominantly coniferous trees such as Douglas-fir {Pseudot- suga menziesii) , western hemlock ( Tsuga heterophyllo) , and western redcedar {Thuja plicata). Common hardwoods included Pacific dogwood ( Cornus nuttallii) , big leaf ma- ple {Acer macrophyllum) , and red alder {Alnus rubra) . Less common species included golden chinquapin {Castanop- sis chrysophylla) and Pacific yew {Taxus brevifolia). Com- mon understory species included swordfern {Polystichum munitum) , salal ( Gaultheria shallon) , vine maple (Acer cir- cinatum), and Oregon grape {Berberis nervosa). Methods Radiotracking of 26 owls in the Springfield population provided an opportunity to examine habitat structures at areas of concentrated use for foraging. We also examined forest stand structures at nest sites. Capturing and radio- tracking Spotted Owls followed procedures described by Carey et al. (1989, 1990) and Guetterman et al. (1991) To ensure statistical independence, only telemetry loca- tions separated by 72 hr were used in the analysis (Guet- terman et al. 1991). This criterion was met by field crews locating radio-tagged owls 2-3 times per week. We used only owls for which telemetry data were gathered contin- September 2000 Spotted Owl Habitat in Oregon 177 uously according to that schedule for >1 yr (13-27 mo), to provide estimates of year-round use patterns within home ranges. Nocturnal telemetry locations (when owls foraged most frequently) were initially mapped in the field on 7.5-min U.S. Geological Survey quadrangle maps and on aerial photographs. We subsequently mapped owl home ranges and identified core areas using the adaptive kernel (ADK) method (Worton 1989, 1995). Although core areas of Northern Spotted Owls may include up to 75% of the telemetry locations of an individual or pair (Bingham and Noon 1997), we used the 60% ADK iso- pleth to estimate core area. Using aerial photographs, we identified forest stands for sampling stand-structural measurements using three criteria: the radio-tagged owls involved were members of pairs of territorial Spotted Owls, at least one of which was monitored for 1 yr; the pairs nested successfully ^ 1 time during the study; and the stands received repeated or disproportionate use by radio-tagged owls for foraging, which we arbitrarily defined as 4% of the total telemetry locations in areas that comprised 1 % of the annual ADK home range. Due to the concentration of use near the center of the home ranges (Rosenberg and McKelvey 1999), such repeatedly-used foraging areas were located within core areas. Sizes of foraging areas sampled varied with the number of telemetry locations and size of error polygons from telemetry, and ranged from 5-15 ha, usu- ally 10 ha. We specified the maximum sampling area at 15 ha based upon similar observations by Laymon and Reid (1986) and Carey and Peeler (1995), as well as our own observations. Also, we specified the minimum for- aging area to be at least twice the size of average telem- etry-error polygons (1. 5-2.0 ha), which we estimated by comparing triangulations with actual (walk-in) observa- tions {N = 75) of radio-tagged birds. Although our choice of 4% of telemetry points in 1% of home ranges was arbitrary, the design was similar to that of North et al. (1999), who used 3-9% of telemetry locations to des- ignate “moderately-used” stands and 10% for very high- ly-used stands. However, they sampled stands 40-80 ha in size, whereas we sampled within much smaller areas that contained a comparatively high density of telemetry points. We sampled 2-4 frequently-used foraging areas within each core area; few home ranges contained >4 repeat- edly-used foraging areas. Thus, the foraging area (or nest site) was the sampling unit, not each owl. North et al. (1999) found that variance in stand structure estimates stabilized at 3-4 plots per stand in homogeneous stands. Thus, we sampled 2 plots in each foraging area or ran- dom site, but opted for five plots when we encountered additional variation, as was found in the largest stands sampled (15 ha) and also in those with large-tree legacies from previous stands. Data presented are averages from 104 plots sampled in 38 frequently-used foraging areas within home ranges of 12 pairs of Northern Spotted Owls, either from combined home ranges of both pair members or from one member of a pair. In addition, we collected data from 44 nest stands, using the nest tree as the center of a single plot. Several owl pairs used more than one nest tree; alternate nest trees were sampled only if they were found in different stands. Specific locations of plots to be sampled within forag- ing areas and in comparison areas that contained zero or low densities of telemetry locations were established us- ing random coordinates on grid maps (100-m grid inter- vals) and found in the field using a global positioning system. Statistical comparisons of data from nests and for- aging areas were made with data gathered from 50 stands (averaged from three plots/ stand) that were selected ran- domly. The 2-4 foraging stands sampled within individ- ual home ranges were >200 m apart to ensure a broad distribution and sampling of the range of types within home ranges, and we also assumed that the random sites within the 12 home ranges represented the range of var- iation in habitat conditions used by Spotted Owls in the study area. Examples of home ranges, core areas, and sampling design for estimating habitat structures at fre- quently-used foraging sites and random sites are shown in Fig. 1. We sampled several variables associated with four ma- jor stand-structural features that are believed to be im- portant to Spotted Owls and/or their prey: densities and sizes of live trees; coarse woody debris, including fallen logs and snags; understory vegetation; and forest canopy structure. Our sampling design employed nested circular plots, following procedures used in Spies (1989) and North et al. (1999), in which the minimum vegetation structure size sampled increased with plot size. These procedures provided tallies of large, infrequently occur- ring items such as snags and old-growth trees without over-sampling small, less variable structures. Each plot in- cluded three nested circular sub-plots: 0.05-, 0.1 0-, and 0.20-ha in size. Beginning 2 m from the site center, we made ocular estimates of cover (to the nearest percent) for shrubs and herbs in three height classes (<0.5, 0. 5-2.0, and >2.0 m) in four 4-m^ quadrats placed in the cardinal directions We counted all living trees and all snags (>10 cm dbh) and estimated abundance and length of downed woody debris (pieces >10 cm diameter) within the 0.05-ha sub- plot. In the 0.1-ha plot, we tallied living trees 51-80 cm dbh and all downed logs (large and small diameter and length). Finally, in the 0.2-ha plot, we recorded the num- ber of large snags (50 cm dbh) and large living trees (80 cm dbh). We also estimated stand age (from annual growth rings) , average crown depth (using a clinometer) , and average crown volume (VsTTr^ X height) based upon six living dominant or codominant trees that we judged to typify the dominant canopy trees in each stand sam- pled. We estimated canopy cover using a concave densi- tometer (after this study was well underway, we learned that this tool inflates estimates in high closure classes, see Cook et al. 1995). Distance from the ground level to the lower canopy provided an index to flying space under the primary canopy. We sampled only those stand-age classes that owls used for nesting or that radio-tagged owls used repeatedly for foraging. Thus, we discarded random points that fell on non-forested areas or forest age-classes that were not used. For statistical comparisons, we grouped stands into five age classes that approximat- ed a successional gradient: 25-39, 40-59, 60-79, 80-119, and >120 yr. We designated the first three age classes as Y/MS or managed forests and the older two as LS/OG forests. After evaluating stand structure variables to assess nor- 178 Irwin et al. VoL. 34, No. 3 o Figure 1. Examples of sampling design for comparing habitat structure at frequently-used foraging areas (large circles) within core areas (dotted lines) of a pair of Northern Spotted Owls (A) and an individual Spotted Owl (B) vdth that at randomly-located areas (squares). Radiotelemetry points are denoted by small circles and 95% adaptive kernel home ranges are enclosed by solid lines. Both members of the pair in A used two core areas that were separated by unusable habitat. Table 1. Number of forest stand samples by age class for repeatedly-used foraging sites and nesting sites of Northern Spotted Owls and random sites within Spotted Owl home ranges, western Oregon. Age classes 25-39, 40-59, and 60-79 yr were classified as young or mid-suc- cessional (Y/MS) stands and classes 80-119 yr and >120 yr were late-successional and old-growth (LS/ OG) stands. Forest Stand Age Class (yr) 25-39 40-59 60-79 80-119 >120 Total Foraging 5 16 5 8 4 38 Nesting 0 11 11 18 4 44 Random 19 10 7 9 5 50 mality of distributions and possible correlations, we test- ed for effects of succession with a two-way, fixed effects analysis of variance (ANOVA). For comparisons that were statistically significant, Fisher’s least significant difference test was used to determine which levels differed. Com- parisons among random, foraging, and nesting sites were made using fixed effects ANOVA. In general, we consid- ered comparisons statistically significant if Type-I error levels were <0.05. Results Descriptive Data. Core areas of Northern Spot- ted Owls for which we obtained sufficient teleme- try data averaged 372 ha (SE = 67.6 ha) in size for 18 individuals and 417 ha (SE = 128.9 ha) in size for 6 pairs, and occupied <25% of annual ADK home ranges among individuals and pairs. The 44 nests were in stands that ranged in age from 46- 168 yr, half (22) of which were in LS/OG forests and half of which were in Y/MS forests (Table 1). These included 11 nests in stands 46-60 yr old. Trees with owl nests were mostly Douglas-firs (86%) of large size (73% >80 cm dbh) and rela- tively old age (65% >120 yr). Such trees clearly were legacies from previous stands. All but four nests were in living trees. Four nest trees were <60 yr old and <50 cm dbh, with the youngest being 41 yr. The nest structures that we could identify were either cavities (N = 17) or debris platforms (N = 22) on large limbs or in tree crotches. Owls foraged in stands with a wider age range than was found at nest sites. Repeatedly-used for- aging areas ranged from 27->200 yr in age. Twen- ty-six Y/MS stands and 12 LS/OG stands were used repeatedly for hunting (Table 1). Five stands 25- 40 yr of age were used repeatedly for foraging. Ra- dio-tagged owls made very little use of stands <25 yr of age. Stand composition was similar to that of September 2000 Spotted Owl Habitat in Oregon 179 25-39 40-59 60-79 80- 1 1 9 > 1 1 9 Trees/ Hectare 25-39 40-59 Trees 20-35 cm 60-79 80-119 >119 250 - 200 - 150 - 100 - 25-39 40-59 Trees 51-80 cm I I I 60-79 80-119 >119 250 - 200 - Trees 36-50 cm 150 - 25-39 40-59 60-79 80-119 >119 Age class (yr) Figure 2. Successional patterns of tree densities by size- and age-class in stands frequently used for foraging or nesting or at random locations within home ranges of Northern Spotted Owls. Vertical lines above bars indicate standard errors. Douglas-fir forests of western Oregon in that stands typically consisted of abundant, small-diameter western hemlock seedlings and trees (<20 cm dbh) with Douglas-fir tending to be the large-di- ameter trees. Density of Live Trees. Average densities of trees seemed to differ among the five classes that we used to express successional gradients. Stands 25- 39 yr of age contained highest densities of trees <35 cm dbh. Stands 40-79 yr of age contained moderate densities (>40/ha) of trees >50 cm dbh and mature and older stands (80 yr old) contained relatively high densities of large trees with >19 trees/ha >80 cm dbh (Fig. 2). In general, densities of trees in the three diameter classes <50 cm de- clined with advancing age and densities of trees >50 cm dbh increased. Nearly all stands sampled contained more than one large (>80 cm dbh) tree/ha. We found relatively few differences in densities of trees of five diameter classes among nesting, for- aging, or random sites within owl home ranges (Ta- ble 2) . Foraging sites contained more sapling trees (10-19 cm dbh) and more 51-80 cm dbh trees than either nesting or random sites. In turn, nest sites contained the most trees in the 20-35 cm dbh class and fewest in the 51-80 cm dbh class. Forag- ing sites tended to contain a few more large trees (>80 cm dbh) than random or nesting sites. Snags and Downed Wood Debris. We found suc- cessionally-related gradients in densities of large snags in comparisons that included all stands that we sampled (Table 3). Large snags increased and small snags tended to decrease with advancing 180 Irwin et al. VoL. 34, No. 3 Table 2. Comparisons of tree densities by size class among nesting, foraging, and random locations within Northern Spotted Owl home ranges, western Oregon. Row values with different superscripts are statistically dif- ferent at the indicated level of probability, based on AN- OVA. Tree Size Class ( dbh . Tree Density (No. /ha ± SE) in cm) Random Foraging Nesting pa 10-19 120^ ± 16 186'^ ± 19 162^ ± 17 0.041 20-35 164^ ± 13 142*’ ± 16 188^^ ± 14 0.109 36-50 87 ± 7 84 ± 8 79 ± 8 0.814 51-80 56^ ± 4 62"^ ± 5 43*’ ± 4 0.018 >80 15 ± 2 19 ± 2 15 ± 2 0.201 stand age and large snags generally were more abundant at foraging and nesting sites than at ran- dom, although the differences were not consistent among all age classes. There were no differences in densities of small-diameter snags among forag- ing, nesting, and random locations. There were no clear successional gradients in the densities or volumes of downed woody debris (Table 4), although the youngest stands usually contained the least amount of woody debris. For- aging areas contained greater densities and vol- umes of both large and small woody debris than random sites. Foraging areas also contained as much as 50% more downed trees than nest sites or random locations within home ranges. The volume of large woody debris was greater at nest sites than random sites and several significant comparisons occurred within age classes at foraging and nesting sites and random locations. Although estimates of the volume of woody debris were more variable than density estimates, foraging sites in managed stands contained from 150-200% more debris vol- ume than random sites of the same age classes. Canopy Structure. Canopies of all stands were dense, averaging >80% closure. Average crown volume increased with advancing stand age, but did not differ among foraging, random or nesting locations within home ranges, except that trees in the five foraging stands sampled that were 60-79 yr of age contained smaller crown volumes than those at random sites (Table 5). Tree crown vol- ume was significantly lower at foraging sites than at random sites in stands <40-yr old. Average crown depth of trees at foraging sites was less than that in nest sites or random locations for stands <80 yr of age (i.e., Y/MS stands). The index of flying space beneath the forest can- opy increased with advancing stand age and was significantly less at foraging sites than at random sites within home ranges over all age classes com- Table 3. Snag densities at Northern Spotted Owl foraging, nesting, and random locations, western Oregon. Ar.F P,T ASS Snag Densities (No. /ha ± SE) (yrs) Foraging Nesting Random pa Overall Large Snags (^50 cm dbh) 25-39 4.4 ± 1.4 n.d.*’ 2.1 ± 0.6 0.1461 3.0 ± 1.3 40-59 2.5 ± 1.5 5.5 ± 1.9 6.1 ± 1.8 0.271 4.1 ± 1.1 60-79 7.0 ± 3.4 7.7 ± 2.3 2.6 ± 2.9 0.378 6.1 ± 1.3 80-119 12.0 ± 2.1 6.1 ± 1.3 9.6 ± 1.9 0.0575 8.3 ± 1.1 >120 17.6 ± 4.1 12.5 ± 4.1 5.3 ± 3.7 0.1277 11.4 ± 1.7 Overall 7.0 ± 1.1 7.0 ± 1.0 4.7 ± 0.9 0.0165 Small Snags (<50 cm dbh) 25-39 129 ± 39 n.d.*’ 125 ± 18 0.9377 133 ± 16 40-59 112 ± 24 124 ± 29 171 ± 31 0.5442 130 ± 13 60-79 91 ± 13 91 ± 13 53 ± 16 0.5076 79 ± 16 80-119 111 ± 25 92 ± 17 77 ± 24 0.4722 88 ± 13 120 79 ± 30 70'± 26 52 ± 23 0.5099 66 ± 21 Overall 108 ± 14 100 ± 12 126 ± 13 0.5012 ^ Probability values in same row do not differ, as determined from ANOVA. No data. September 2000 Spotted Owl Habitat in Oregon 181 Table 4. Average density and volume of large (>50 cm diameter) woody debris and volume of small (10-50 cm diameter) woody debris in Northern Spotted Owl foraging, nesting, and random sites, western Oregon. Age Class ( yr) Foraging Nesting Random pa Overall Density of Large Woody Debris (No. /ha ± SE) 25-39 86 ± 27 n.d.b 65 ± 12 0.4816 77 ± 12 40-59 113 ± 16 73 ± 18 62 ± 19 0.1022 82 ± 10 60-79 147 ± 29 79 ± 19 66 ± 24 0.0987 95 ± 12 80-119 111 ± 21 76 ± 13 82 ± 19 0.3893 91 ± 10 120 139^ ± 22 55 ± 22 65 ± 20 0.0435 86 ± 16 Overall 117^ ± 10 74 ± 9 68 ± 8 0.0003 Volume of Large Woody Debris (m^/ha ± SE) 25-39 184 ± 55 n.d.'’ 125 ± 25 0.3377 186 ± 35 40-59 278 ± 41 143 ± 41 159 ± 50 0.0757 193 ± 28 60-79 368^ ± 73 197'^ ± 49 115" ± 62 0.0476 216 ± 35 80-119 243 ± 65 218 ± 40 103 ± 57 0.1932 197 ± 29 120 345 ± 132 344 ± 132 88 ± 114 0.2821 252 ± 47 Overall 28D ± 28 2061’ + 25 123" ± 23 0.0002 Volume of Small Woody Debris (m^/ha : ± SE) 25-39 28^ ± 4 n.d.i* 17 ± 2 0.0336 20 ± 3 40-59 19 ± 4 23 ± 4 16 ± 4 0.4706 19 ± 2 60-79 31 ± 6 19 ± 4 21 ± 5 0.2884 24 ± 3 80-119 39^ ± 6 171’ ± 4 231’ + 5 0.0163 25 ± 92 120 39 ± 9 12 ± 9 16 ± 8 0.1357 22 ± 4 Overall 28^ ± 2 191’ + 2 lOb ± 2 0.0031 ® Probability values in same row do not differ, as determined by ANOVA. Row values with different superscripts are significant at the level of probability indicated. ‘’No data. Table 5. Comparison of canopy structure in stands used for foraging and nesting with random locations within Northern Spotted Owl home ranges, western Oregon. Age Class (yr) Foraging Nesting Random pa Overall Average Crown Volume (m^ ± SE) 25-39 197^ ± 61 n.d.'’ 303 ± 31 0.0337 226 ± 47 40-59 253 ± 30 228 ± 98 352 ± 49 0.1309 282 ± 38 60-79 292^ ± 89 373b ± 88 57P ± 75 0.0369 424 ± 47 80-119 489 ± 84 477 ± 69 491 ± 79 0.9857 487 ± 39 120 716 ± 112 246 ± 147 641 ± 101 0.6344 536 ± 63 Overall 349 ± 36 376 ± 38 418 ± 32 0.1564 Average Crown Depth (m ± SE) 25-39 12.7^ ± 1.4 n.d.'’ 17.0 ± 0.7 0.0113 15.4 ± 1.0 40-59 14.0^ ± 0.5 17.1‘’ ± 1.1 17.2*’ ± 0.7 0.0012 16.0 ± 1.1 60-79 14.4^^ ± 1.2 18.6*’ ± 2.5 21.3*’ ± 1.0 0.0013 18.0 ± 1.0 80-119 18.6 ± 1.1 20.2 ± 2.0 19.0 ± 1.5 0.843 19.0 ± 1.1 120 20.4 ± 1.6 14.5 ± 4.0 20.2 ± 1.5 0.9161 18.1 ± 1.5 Overall 15.5^ ± 0.6 18.3*’ ± 1.3 18.3*’ ± 0.5 0.0006 ^ Probability values do not differ, as determined from ANOVA. No data. 182 Irwin et al. VoL. 34, No. 3 Table 6. Average distance from ground to lowermost whorls of branches on trees at Northern Spotted Owl foraging, nesting, and random locations, western Oregon. Age Class ( yr) Average Distance (m ± SE) P Overall Foraging Nesting Random 25-39 13.0 ± 2.0 n.d.'’ 16.2 ± 1.0 0.165 12.3 ± 1.1 40-59 13.8^ ± 0.9 16.4” ± 1.3 20.2^ ± 1.2 0.0003 16.6 ± 0.8 60-79 18.3 ± 2.7 15.7 ± 1.5 19.9 ± 2.3 0.657 17.9 ± 1.1 80-119 22.2^ ± 1.8 17.4” ± 1.1 +1 u o (M 0.0148 22.1 ± 0.9 >120 21.2 ± 3.5 22.9 ± 2.4 31.4 ± 3.1 0.0681 25.3 ± 1.4 Overall 16.8^ ± 1.1 17.4^ ± 1.2 21.3” ±1.0 0.0026 ® Probability foraging, nesting, and random values do not differ, as determined by ANOVA. ^ No data. bined and for stands in the 40-59 and 80-119 year categories (Table 6). The same was true for nest sites in overall comparisons with flying space tend- ing to be less at nest sites. Understory Vegetation. We found no clear suc- cessional trends in understory vegetation cover. Cover of understory vegetation <0.5-m tall was sig- nificantly less at foraging locations than at random locations for most age classes (46.0 vs. 65.3%, P = 0.001) , but understory vegetation cover at nest sites generally did not differ from that at random loca- tions (Fig. 3, 66.2 vs. 65.3%, P = 0.894). Understo- ry cover in the other two height classes was more variable. In separate ANOVA comparisons that pooled stands in the two broader classes of Y/MS and LS/OG forests, foraging locations contained 100 80 60 40 20 A. Herbs and shrubs <0.5-m tall Figure 3. Comparisons by ANOVA of successional trends among foraging areas (squares), nest sites (triangles), and random locations (dots) for three understory cover classes within Northern Spotted Owl home ranges. Superscripts indicate within-age class comparisons that were statistically different at Type-I error probabilities of <0.05 (a) and 0.05-0.10 (b). September 2000 Spotted Owl Habitat in Oregon 183 less understory vegetation cover 2.0 m in height than did nest sites and random locations in Y/MS forests (64.3% vs. 89.2% and 89.6%, P< 0.040). Understory cover at nest sites did not differ from random locations within Y/MS and LS/OG classes. Discussion Most forest stand structures increased in abun- dance with advancing forest succession and prob- ably influenced the choice of Y/MS forests by Northern Spotted Owls for nesting and foraging habitats. The most important stand structures in influencing habitat use were the amount of woody debris and, less consistendy, the number of large snags at foraging sites and large-diameter trees at nest sites. The direct connection of standing and downed dead trees to owl biology probably occurs through the relationship between dead wood and the owl’s prey. This appears particularly likely for northern flying squirrels {Glaucomys sabrinus), which are associated with snags (Carey 1995) and are the primary prey for owls in forests similar to those we studied (Forsman et al. 1984). Northern flying squirrel abundance in Y/MS forests may equal that of LS/OG forests if old-forest legacies (i.e., large trees and snags and downed wood de- bris) are present and understory vegetation is rel- atively well-developed (Carey 1995). Many other small forest mammal prey of Spotted Owls also are associated with coarse woody debris on the forest floor (Maser and Trappe 1984, Carey 1995, Carey and Johnson 1995), such as woodrats {Neotoma spp.), deer mouse {Peromyscus maniculatus) , Town- send’s chipmunk {Tamias townsendii), and western red-backed vole ( Clethrionomys occidentalis ) . Although owl foraging occurred in a broad array of structural conditions across all successional spec- tra, conditions of nesting sites were more specific. For example, foraging occurred in stands as young as 27 yr, whereas nesting occurred in stands >45 yr. Further, 50% of the nests were in LS/OG stands, which comprised <10% of the study area, and trees containing nests in Y/MS stands were of- ten much older than trees that typified the nest stands. Finally, understory vegetation <2.0-m tall did not influence nest-site choice but did influence use of foraging sites. Densities of live trees and small and large snags varied with advancing succession at sites used fre- quently for foraging, which was expected due to competition among trees during the course of for- est development (Oliver and Larson 1990). There- fore, most of the stands we sampled were classified as within the stem-exclusion or understory reinitia- tion phases (Oliver and Larson 1990) of forest suc- cession. However, most of the repeatedly-used for- aging stands also contained structural legacies from previous forests, including large trees, large snags and large woody debris, and many nesting sites classified as being in 60-, 80-, or 120-yr old stands met several of the structural components defining old-growth forests in the Western Hem- lock Zone (Franklin et al. 1981, Old-Growth Defi- nition Task Group 1986). Similarly, densities of trees 80 cm dbh in most of the stands >80 yr of age met the large-tree criterion of the definition of old-growth forests, or 20 such large trees/ha (Franklin et al. 1981, Old-Growth Definition Task Group 1986). In fact, some of the stands that were 60-79-yr old also contained enough trees 80 cm dbh to meet the large-tree criterion used to define old-growth forest. This was particularly true for 60- 79-yr old, repeatedly-used foraging stands which av- eraged 19 large trees/ha. Such large-diameter trees were not necessarily old, although some were old-growth residuals from previous stands, and oth- ers were broken-topped, old-growth western hem- lock trees that did not protrude through the over- story canopy. Because sites that we measured were used fre- quently for foraging or for nesting and were within core areas (i.e., areas disproportionately used with- in home ranges), structural features of stands might be important determinants of habitat selec- tion of Northern Spotted Owls. Indeed, several var- iables exhibited little variation across all age classes of stands within core areas. All stands that were repeatedly used contained dense forest canopies (>80% cover, as estimated by a spherical densitom- eter) and had well-developed understory vegeta- tion. All but the youngest sites contained large vol- umes of coarse woody debris, 1 large snag/ha, and at least a few live trees >80 cm in diameter. “Flying space,’’ which varied as expected with advancing succession, was consistently lower at foraging and nesting sites than at random locations. We were not certain why “flying space’’ was low- er at foraging sites, even though tree diameters and crown volumes were the same as at random locations. It was possible that the lower-slope posi- tions and east and northern aspects of foraging sites may have influenced the development of tree crowns there because of the limited amount of sun- light they receive. In such topographic conditions. 184 Irwin et al. VoL. 34, No. 3 trees do not self-prune as rapidly as in other to- pographic settings (Oliver and Larson 1990), so fly- ing space would be lower. In this case, the reduced flying space in foraging sites was simply a conse- quence of their use of lower topographic locations in the habitat. We are also unsure what can be inferred from the information on understory vegetation cover, the total of which generally was less at foraging sites than at random and nesting locations. The differences did not appear to be caused by varia- tion in sampling nest sites. Our results were con- trary to those of Carey (1995) who suggested use of silvicultural manipulations to increase erica- ceous shrubs which would accelerate growth of Northern Spotted Owl habitat in areas where LS/ OG is lacking, but they were similar to those of Solis and Gutierrez (1990) who found less shrub and herb cover at frequently-used Northern Spot- ted Owl foraging sites in northern California and those of Call et al. (1992) who found less herba- ceous cover at owl sites than random locations for California Spotted Owls (5. o. occidentalis) . We pre- sume that Spotted Owl response to understory veg- etation may be unimodal or asymptotic with gra- dients of understory vegetation cover and with variation in abundance or access to small mammal communities. There is evidence of such nonlinear responses by small mammals to gradients of un- derstory vegetation density and composition (Ca- rey 1995). If so, it seems possible that understory vegetation can be either too sparse, resulting in low prey densities, or too dense, thereby impeding access by owls to prey. The management applica- tion of this is to maintain patchy understories pro- viding prey that are both abundant and accessible to owls. Northern Spotted Owls used Y/MS forests sub- stantially more frequently than reported by Fors- man et al. (1984) and Carey et al. (1990) for Spot- ted Owl home ranges elsewhere in western Oregon. Such differential use of habitats by raptors may be due to local and structural differences in preferred habitats (Mosher et al. 1986). In the managed-forest landscape that we studied, stand structural differences were the most important habitat features determining use by Northern Spot- ted Owls. For example, turn-of-the-century wild- fires left large legacy trees and timber harvesting about 60 yr prior to our study left cull or seed trees across the landscape. Both types of disturbance provided numerous snags and downed structural legacies. Also, the area contained frequent pockets of root-rot {Armillaria spp.) that resulted in large piles of downfall. We believe our information merits judicious ap- plication in forest management strategies, which increasingly strive to protect wildlife by applying information from stand- to landscape-levels. Re- cent examples include the conservation strategy for federal timberlands in the range of the North- ern Spotted Owl (Thomas et al. 1993) and that described by Hicks et al. (1999) for managed, pri- vate timberlands. Doing so requires an understand- ing of both the diversity of forest stand structures used by owls and silvicultural procedures than can create them within the context of natural distur- bance and timber management. Northern Spotted Owls apparently discriminate and select among Y/ MS stands on the basis of stand-structural differ- ences; therefore, providing these structures should be important parts of prescriptions for enhancing the value of young stands. Our information could help forest managers assess the value of future hab- itat, allowing them to schedule management activ- ities across landscapes. We believe that extensively- managed Y/MS landscapes could contribute significantly to the long-term persistence of North- ern Spotted Owls. Until such contributions are demonstrated to support viability, we strongly cau- tion against drawing the inference that Y/MS for- ests with structural legacies might be an equivalent substitute for LS/OG forests. Solis and Gutierrez (1990) predicted that studies of Northern Spotted Owls in managed landscapes would show use of habitats that structurally resem- ble old-growth forests. Indeed, we found that Spot- ted Owls selected large, old trees for nests and that they selected foraging areas on the basis of coarse woody debris and understory vegetation in a man- aged landscape dominated by Y/MS stands. This information provides additional support for habi- tat restoration as part of a strategy for recovery of the Northern Spotted Owl (Carey 1995) and for blending goals of a forest-based economy with those of a healthy biotic community. Silvicultural prescriptions could accelerate de- velopment of habitat for owls and perhaps other species that frequent LS/OG forests. We suggest that foraging habitat should contain seven large (40 cm dbh) snags/ha and 280 m^/ha of coarse woody debris, based on averages for 26 repeatedly- used sites in Y/MS forests in forest patches 16 ha in size. These values are similar to those of North September 2000 Spotted Owl Habitat in Oregon 185 et al. (1999), who worked with Northern Spotted Owls in unmanaged forests and those of Buchanan et al. (1999), who recommended some 10 large snags/ha based upon 16 telemetry points in young forests in western Washington. Noting that both small- and large-diameter woody debris apparently influenced use for foraging, we wonder if equiva- lent amounts of small-diameter logging residue might be piled to create woody debris. Doing so would constitute a topic for experimental research. Foraging success by Northern Spotted Owls may be optimal in stands with a mix of canopy gaps and patchy ground cover (Carey 1995). Thus, precom- mercial thinnings in patches might support forag- ing in such areas by maintaining understory vege- tation (Omule 1988, Carey and Curtis 1996), as long as total understory cover does not exceed about 75-80%. Skillful applications are required in our area because salal {Gaultheria shallon) may quickly form dense patches that exclude both her- baceous and tree-seedling establishment (Huffman et al. 1994). Nesting habitat involves more ad- vanced successional development. Silvicultural pre- scriptions for providing suitable nest sites in man- aged forests could be facilitated by thinning to low densities (Tappeiner et al. 1997) and retaining small patches (perhaps 4 ha) that include large leg- acy trees. We recommend prescriptions that can ensure presence of 4 such trees/ha after a stand age of 40 yr, based upon the observation that only a few nesting stands contained <3 trees/ha >80 cm dbh. Because physical features such as topog- raphy and elevation influence use of foraging sites by Spotted Owls (Haufler and Irwin 1993), silvi- cultural manipulations should vary with topo- edaphic conditions. For example, we found that Spotted Owls used areas on the lower half of slopes and near riparian areas most often for foraging (Ir- win 1994). Carey and Peeler (1995) also found sig- nificant use of lower-slope positions by Northern Spotted Owls in western Oregon. Therefore, man- agement of these areas should be site-specific to ensure their integrity. Acknowledgments This study was funded by Northwest Forest Resource Council, Association of O &: C Counties, Bureau of Land Management, and NCASI. We expressly thank R. Doer- ner, L. Lauritzen, and D. Robertson for helping to secure financial support. R.J. Anderson and D. Woodworth fa- cilitated home range analyses. L. Diller, E. Forsman, and two anonymous reviewers provided helpful criticisms of previous drafts. Literature Cited Bingham, B.B. and B.R. Noon. 1997. Mitigation for hab- itat “take”: application to habitat conservation plan- ning. Conserv. Biol. 11:127-139. Buchanan, J.B. and L.L. Irwin. 1995. Within-stand nest site selection by Spotted Owls in the eastern Washing- ton Cascades./. Wildl. Manage. 59:301-310. , , and E.L. McCutCHEN. 1993. Character- istics of Spotted Owl nest trees on the Wenatchee Na- tional Forest./. Raptor Res. 27:1-7. , J.C. Lewis, D.J. Pierce, E.D. Forsman, and B.L. Bismtul. 1999. Characteristics of young forests used by Spotted Owls on the western Olympic Peninsula, Washington. Northwest Sci. 73:255-263. Call, D.R., R.J. Gutierrez, and J. Verner. 1992. Foraging habitat and home-range characteristics of California Spotted Owls in the Sierra Nevada. Condor 94:880- 888 . Carey, A.B. 1985. A summary of the scientific basis for Spotted Owl management. USDA For. Serv. Gen. Tech. Rep. PNW-185, Portland, OR U.S.A. . 1995. Sciurids in Pacific Northwest managed and old-growth forests. Ecol. Applic. 5:648-661. and R,0. Curtis. 1996, Conservation of biodiver- sity: a useful paradigm for forest ecosystem manage- ment. Wildl. Soc. Bull. 24:610-620. AND M.L. Johnson. 1995. Small mammals in man- aged, naturally young, and old-growth forests. Ecol Applic. 5:336-352. AND K. Peeler. 1995. Spotted Owls: resource and space use in mosaic landscapes./. Raptor Res. 29:223- 239. , J.A. Reid, and S.P. Horton. 1990. Spotted Owl home range and habitat use in southern Oregon coast ranges. /. Wildl. Manage. 54:11-17. , S.P. Horton, and B.L. Biswell. 1992. Northern Spotted Owls: influence of prey base and landscape character, Ecol. Monogr. 62:223—250. , , AND J.A. Reid. 1989. Optimal sampling for radiotelemetry studies of Spotted Owl habitat and home-range. USDA For. Serv. Res. Pap. PNW-RP-416, Portland, OR U.S.A. , J. Kershner, B. Biswell, and L. Domingues De Toledo. 1999. Ecological scale and forest develop- ment: squirrels, dietary fungi, and vascular plants in managed and unmanaged forests. Wildl. Monogr. No. 142. Cook, J.G., TW. Stutzman, C.W. Bowers, K.A. Brenner, and L.L. lRW^N. 1995. Spherical densitometers pro- duce biased estimates of forest canopy cover. Wildl Soc. Bull. 23:711-717. Forsman, E.D., E.C. Meslow, and MJ, Strub. 1977. Spot- ted Owl abundance in young versus old-growth for- ests. Wildl. Soc. Bull. 5:43-47. , , AND H.M. Wight. 1984. Distribution and 186 Irwin et al. VoL. 34, No. 3 biology of the Spotted Owl in Oregon. Wildl. Monogr. No. 87. Franklin, J.R and C.T. Dyrness. 1981. Natural vegetation of Oregon and Washington. Oregon State Univ. Press, Corvallis, OR U.S.A. , K. Cromack, Jr., W. Denison, A. McKee, C. Ma- ser, J. Sedell, F. Swanson, and G. Juday. 1981. Eco- logical characteristics of old-growth Douglas-fir for- ests. USDA For. Serv. Gen. Tech. Rep. PNW-118, Portland, OR U.S.A. Guetterman, J.H., J.A. Burns, J.A. Reid, R,B. Horn, and C.C. Foster. 1991. Radio telemetry methods for studying Spotted Owls in the Pacihc Northwest. USDA For. Serv. Gen. Tech. Rep. PNW-272, Portland, OR U.S.A. Haufler, J.B. and L.L. Irwin. 1993. An ecological basis for forest planning for biodiversity and resource use. Proc. Int. Union Game Biol. 21:73-81. Hicks, L.L. , H.C. Stabins, and D.R. Herter. 1999. De- signing Spotted Owl habitat in a managed forest. /. Forest. 97:20-25. Huffman, D.W., J.G. Tappiener, II, and J.G. Zasada. 1994. Regeneration of salal {Gaultheria shallon) in the cen- tral Coast Range of Oregon. Can. J. Bot. 72:39-51. Hunter, J.E., RJ. Gutierrez, and A.B. Franklin. 1995. Habitat configuration around Spotted Owl sites in northwestern California. Condor 97:684-693. Irwin, L.L. 1994. A process for improving wildlife habitat models for assessing forest ecosystem health. J. Sus- tain. Forestry 2:293-306. , S. Self, and L. Smith. 1989. Status of Northern Spotted Owls in managed forestlands in northern Cal- ifornia. Timber Assoc, of Calif., Unpubl. Rep. Sacra- mento, CA U.S.A. Johnson, D.H. 1980. The comparison of usage and avail- ability measurements for evaluating resource prefer- ence. Ecology 61:65-71. LaHaye, W.S. and RJ. Gutierrez. 1999. Nest site selec- tion and nesting habitat of the Northern Spotted Owl in northwest California. Condor 101:324-330. Laymon, S.A. and J.A. Reid. 1986. Effects of grid-cell size on tests of a Spotted Owl HSI model. Pages 93-96 in J. Verner, M.L, Morrison, and C.J. Ralph [Eds.], Wild- life 2000: modeling habitat relationships of terrestrial vertebrates. Univ. Wisconsin Press, Madison, WI U.S.A. Maser, C. and J.M. Trappe. 1984. The seen and unseen world of the fallen tree. USDA For. Serv. Gen. Tech. Rep. PNW-285, Portland, OR U.S.A. Mosher, J.A., K. Titus, and M.R. Fuller. 1986. Devel- oping a practical model to predict nesting habitat of woodland hawks. Pages 31-35 in]. Verner, M.L. Mor- rison, and C.J. Ralph [Eds.], Wildlife 2000: modeling habitat relationships of terrestrial vertebrates. Univ. Wisconsin Press, Madison, WI U.S.A. North, M.P., J.F. Franklin, A.B. Carey, E.D. Forsman, and T. Hamer. 1999. Forest stand structure of the Northern Spotted Owl’s foraging habitat. For. Sci. 45: 520-527. Old-Growth Definition Task Group. 1986. Interim def- initions for old-growth Douglas-fir and mixed-conifer forests in the Pacific Northwest and California. USDA For. Serv. Res. Note PNW-447, Portland, OR U.S.A. Oliver, C.D. and B.L. Larson. 1990. Forest stand dynam- ics. McGraw-Hill, Inc., New York, NYU.S.A. Omule, S.A.Y. 1988. Growth and yield 35 years after com- mercially thinning 50-year old Douglas-fir. British Co- lumbia Ministry Forests and Lands. For. Resource De- velop. Agree. Rep. 021, Victoria, BC Canada. Porter, W.F. and K.E. Church. 1987. Effects of environ- mental pattern on habitat preference analysis./. Wildl. Manage. 51:681—685. Rosenberg, D.K. and K.S. McKelvey. 1999. Estimation of habitat selection for central-place foraging animals./. Wildl. Manage. 63:1028-1038. Samuel, M.D., DJ. Pierce, and E.O. Garton. 1985. Iden- tifying areas of concentrated use within the home range./. Anim. Ecol. 54:711-719. Solis, D.M., Jr. and RJ. Gutierrez. 1990. Summer hab- itat ecology of Northern Spotted Owls in northwest- ern California. Cowtior 92:739-748. Spies, T.A. 1989. Characterization of old-growth Douglas- fir forests of western Oregon and Washington. Un- publ. study plan. U.S. Forest Service, Corvallis, OR U.S.A. Tappeiner, J.C., D. Huffman, D. Marshall, T.A. Spies, AND J.D. Bailey. 1997. Density, ages, and growth rates in old-growth and young-growth forests in coastal Oregon. Can. J. For. Res. 27:638-648. Teensma, P.d. 1987. Fire history and fire regimes of the central western Cascades of Oregon. Ph.D. disserta- tion, Univ. Oregon, Eugene, OR U.S.A. Thomas, J.W., M.G. Raphael, R.G. Anthony, E.D. Fors- man, A.G. Gunderson, R.S. Holthausen, B.G. Mar- cot, G.H. Reeves, J.R. Sedell, and D.M. Solis. 1993. Viability assessments and management considerations for species associated with late-successional and old- growth forests of the Pacific Northwest. The report of the Scientific Analysis Team, USDA For. Serv., Port- land, OR U.S.A. Ward, J.P., Jr., R.J. Gutierrez, and B.R. Noon. 1998. Habitat selection by Northern Spotted Owls: the con- sequences of prey selection and distribution. Condor 100:79-92. WORTON, BJ- 1989. Kernel methods for estimating the utilization distribution in home-range studies. Ecology 70:164-168. . 1995. Using Monte Carlo simulation to evaluate kernel based home range estimators. /. Wildl. Manage 59:794-800. Received 2 September 1999; accepted 18 March 2000 J. Raptor Res. 34(3):187-195 © 2000 The Raptor Research Foundation, Inc. POPULATION FLUCTUATIONS OF THE HARRIS’ HAWK {PARABUTEO UNICINCTUS) AND ITS REAPPEARANCE IN CALIFORNIA Michael A. Patten Department of Biology, University of California, Riverside, CA 92521 U.S.A. Richard A. Erickson LSA Associates, One Park Plaza, Suite 500, Irvine, CA 92714 U.S.A. Abstract. — The Harris’ Hawk {Parabuteo unicinctus) was considered extirpated from California in the mid-1960s. Most sightings in the past 30 years were, therefore, considered to be escaped or released birds. The species has recently staged an incursion into southern California and northern B^a California in the 1990s, involving nearly 50 individuals and local breeding. This incursion was apparently another in a long-term series of population fluctuations of the Harris’ Hawk, each bringing large numbers to the north and west of its established range in Arizona and Baja California. Although first recorded at the state border in the 1850s, the Harris’ Hawk was not recorded as a breeder until an incursion in the late 1910s and 1920s brought hundreds to the state, including the first known breeders. Numbers declined again in the 1940s, built up again in the 1950s, and thereafter drastically declined to the point of their absence by the mid-1960s. Therefore, the recent incursion was not anomalous but rather follows historical patterns of occurrence, indicating that California is on the fringe of the natural range of the Harris’ Hawk, with emigration bringing birds into the state and subsequent population decreases leading again to “extirpation.” Keywords: Harris’ Hawk, Parabuteo unicinctus; Baja California', California', population fluctuations. Fluctuaciones poblacionales de Parabuteo unicinctus y su reaparicion en California Resumen. — El gavilan de harris {Parabuteo unicinctus) fue considerado como extirpado de California a mediados de 1960. La mayoria de los avistamientos de los ultimos 30 ahos fueron considerados como aves escapadas o liberadas. La especie ha incursionado en el sur de California y norte de Baja California en los anos 90, incluyendo unos 50 individuos y algunos eventos de reproduccion locales. Esta incursion es aparentemente una mas de las ocurridas a largo plazo por esta especie. Cada una trayendo grandes numeros de individuos al norte y oeste de su rango establecido en Arizona y Baja California. Aunque por primera vez fue registrado en el horde del estado en 1850, el gavilan de harris no fue reportado en reproduccion hasta su incursion en 1910 y 1920 con cientos de individuos incluyendo los primeros registros de reproduccion. Los numeros de individuos declinaron otra vez en 1940, aumentaron en 1950, y declinaron drasticamente hasta considerados ausentes en 1960. Por lo tan to, la reciente incur- sion no es anomala, al contrario, sigue los patrones de ocurrencia indicando que California esta en el limite del rango natural del gavilan de harris, con su emigracion trayendo aves dentro del estado y la subsecuente declinacion la cual conlleva a su extirpacion. [Traduccion de Cesar Marquez] The Harris’ Hawk {Parabuteo unicinctus) ranges from the southwestern United States southward through Central America to central Chile and cen- tral Argentina, with a geographically disjunct pop- ulation on the Baja California peninsula. In the United States, it occurs from southern Arizona, southeastern New Mexico, and central Texas south- ward (Fig. 1; American Ornithologists’ Union 1998). Its range in Arizona, New Mexico, and Tex- as has been expanding northward in recent years (Bednarz etal. 1988, Bednarz 1995, Dawson 1998). In California, the Harris’ Hawk was found formerly throughout the lower Colorado River Valley and in the Imperial Valley south of the Sal ton Sea (Grin- nell and Miller 1944). By the mid-1950s, it was ex- tirpated from California as a breeder (Remsen 1978, Walton et al. 1988), with the last definite wild bird recorded north of Blythe on 28 November 187 188 Patten and Erickson VoL. 34, No. 3 Figure 1. The northwestern portion of the current range (the shaded area) of the Harris’ Hawk {Parabuteo um- anctus), modified from Bednarz (1995) and Dawson (1998). The dashed line signifies the former westerly limits of its range in southwestern Arizona and southeastern California. September 2000 Harris’ Hawk in California 189 1964 (Garrett and Dunn 1981, Rosenberg et al. 1991). A reintroduction project for the Harris’ Hawk was initiated in California in 1979 by various state, federal, and private groups (Stewart 1979, 1982, Walton et al. 1988). Eight birds were released that year and several more were released each year un- til 1989, for a total of 222 releases (Linthicum 1989, Linthicum pers. comm.). The first pair nest- ed successfully in 1983, three pairs bred success- fully in 1986 (Walton et al. 1988, Rosenberg et al. 1991), and five nested in 1989 (Linthicum 1989, Bednarz 1995). However, it is unlikely that this population is viable, as birds are now infrequently noted (Rosenberg et al. 1991, Patten pers. obs.). Since the mid-1960s, virtually all recent records of the Harris’ Hawk in California are of birds con- sidered to have escaped from falconers (Garrett and Dunn 1981, Unitt 1984). In some cases, birds have been observed with Jesses and clearly came from this source. In other cases, there appears to be some tendency for natural occurrence such as sightings of immatures along the Colorado River near Blythe in September (Roberson 1980) and December 1978 (Rosenberg et al. 1991) and at the south end of the Salton Sea on 25 June 1989 (McCaskie 1989). Nevertheless, records of individ- ual birds are perhaps always suspect given that the species remains popular with falconers and reha- bilitated birds are occasionally released, as were a few around the Salton Sea in the 1970s and 1980s (Walton et al. 1988). Herein, we document a major increase in sightings beginning in April 1994 that was apparently a natural influx involving nearly 50 individuals throughout southern California and northern Baja California. Further, we hypothesize that such incursions are the rule rather than the exception for the occurrence of this species in Cal- ifornia. Methods For the recent incursion, we gathered records and doc- umentation from various field observers (see Acknowl- edgments) and from files of the California Bird Records Committee. All specific data gathered are on file at the Western Foundation of Vertebrate Zoology (WFVZ), Camarillo, California U.S.A. Recent and historical data were gathered from seasonal reports for the Southern Pacific Coast Region published in Field Notes (now North American Birds) , Christmas Bird Counts and specimens at the San Diego Natural History Museum (SDNHM), San Diego, California U.S.A., National Museum of Natural History (USNM), Washington, D.C. U.S.A. and WFVZ. We tabulated and mapped these data to obtain an esti- mate of the magnitude of the incursion and to examine its geographic extent. The 1994 Incursion Despite an annual “background” escape/release rate throughout California of >3 Harris’ Hawks (Bloom pers. comm., Walton pers. comm.), a dif- ferent phenomenon began 15 April 1994, when J. Rudley, R Jorgensen, and M. Jorgensen observed three adults together in Borrego Valley. Between 1994—96, at least 34 individuals had been found in southern California (Table 1; McCaskie 1995). The largest groups of birds consisted of at least eight individuals in the Borrego Springs region of the Anza-Borrego Desert and up to five individuals both at the former George Air Force Base near Victorville and at Boulevard (Table 1 ) . During this apparently natural incursion (Bednarz 1995, Mas- sey 1997, Walton pers. comm.), Harris’ Hawks were found north of their historical range as far as Vic- torville in the Mojave Desert, with scattered indi- viduals reported around the Salton Sea and else- where (Fig. 2). Additional birds in cismontane valleys at Riverside and in central San Diego Coun- ty may or may not have been naturally occurring, with individuals far west in coastal Orange County and in the Antelope Valley being particularly sus- pect given the apparent geographic extent of the influx (Fig. 2). Indeed, the Orange County bird showed signs of being in captivity (Bloom pers. comm., Daniels pers. comm.). This influx into southern California was con- comitant with at least 22 individuals well north of the species’ normal range in northern Baja Cali- fornia (Table 2; Radamaker pers. comm., Wurster pers. comm.) and in adjacent northwestern Sonora (Russell and Monson 1998). During this period, Harris’ Hawks bred in California at Borrego Springs (Massey 1997), Boulevard (Unitt pers. comm.) and Laguna Dam (McCaskie 1996, Massey 1997), and in northern Baja California at Valle San Telmo (Bloom pers. comm.). Small numbers have persisted in Borrego Valley as recently as 7 March 1999 (Jorgensen pers. comm.) and in Valle San Telmo on 31 January 1999 (Patten pers. obs.). Historical Trends and Current Status The historical distribution of the Harris’ Hawk in California is not clear. The species was first re- corded along the Colorado River on the Arizona side in February 1854 (Kennerly 1859, Swarth 1914), but Elliot Coues never recorded the species 190 Patten and Erickson VoL. 34, No. 3 Table 1. California records of the Harris’ Hawk {Parabuteo unidnctus) from spring 1994 through winter 1996-97 (Fig. 2), arranged chronologically. Birds nested at Boulevard (1994) and Laguna Dam (1996), and exhibited nesting behavior (copulations, carrying sticks and food) at Borrego Valley (1994-95), with immatures observed in 1995. Data are on file with the CBRC. Date(s) Location Maximum 15 April 1994-January 1999-1- San Diego County; Borrego Valley 8 1 June 1994-31 October 1995 San Diego County; Boulevard 5 26 November 1994-29 January 1995 San Diego County; Santee 2 ? December 1994 Riverside County; Blythe 1 7-18 December 1994 Imperial County; Westmorland 2 10-12 December 1994 Orange County; Irvine 1 31 December 1994-29 January 1995 Riverside County; n. end Salton Sea 1 2-21 January 1995 San Bernardino County; Victorville 5 27 June-23 July 1995 Riverside County; Riverside 1 6-10 July 1995 San Diego County; Carrizo Canyon 2 3 April 1996 San Diego County; Escondido 1 5 April 1996 San Bernardino County; Vidal Wash 1 25 March-30 December 1996 Los Angeles County; Antelope Valley 1 29 March-April 1996 Imperial County; Laguna Dam 2 31 March 1996 San Diego County; Spring Valley 1 during his extensive surveys of the lower Colorado River Valley in the 1870s and 1880s. It apparently was not recorded at the Colorado River again until August (Stephens 1903) and December 1902 (Wil- der 1916), when individuals were noted on both sides of the river. Two specimens collected in the Rio Colorado delta of northeastern Baja California bracket these records, a male along the Rio Alamo southwest of Pilot Knob on 7 April 1894 (USNM 133726) and a subadult along the Rio Hardy on 16 April 1905 (USNM 197921). Thus, a few birds were in the area from the mid-1890s until the early 1900s; however, following the few noted in 1902, the species again went unrecorded in California for a decade. For example, Joseph Grinnell and party did not find the Harris’ Hawk during their exhaustive survey of the length of the lower Colo- rado River Valley 14 February-15 May 1910 (Grin- nell 1914). Given the paucity of records through this period, Grinnell (1915) considered the species to be only a “summer visitant” to the Colorado River, based solely on Stephens’ (1903) records. The Harris’ Hawk was not documented as a breeder in southeastern California until the late 1910s, with the first evidence found on 25 July 1916 (Wiley 1917, Bancroft 1920); the first breeding ev- idence for northeastern Baja California was con- comitant (WFVZ 83655). Thus, it is probable that the species had only recently expanded its range into the area. These breeding records were also the first for the lower Colorado River Valley, as Cooper (1870) made no specific mention of encountering this species. By the mid-1940s, it was “locally com- mon” in California (Grinnell and Miller 1944). There were occasional records of large numbers, although reports of 400-500 between Calexico and Heber, Imperial County, on 22 October 1920 (Chambers 1921) and 250 near Calexico on 28 Au- gust 1923 (Chambers 1924) are perhaps best con- sidered tentative given that the species does not travel in large flocks (Bednarz pers. comm.). The few records of the Harris’ Hawk prior to the late 1910s may have involved occasional strays to the west of its established range given its apparent spread into western Arizona. This species “has a reputation for being somewhat nomadic” (Bed- narz et al. 1988), with strays being recorded north to Ohio (Earl 1918) and Kansas (Bunker 1919, Sny- der 1919), east to Louisiana (Coombs 1892), and west to Utah and Nevada (Palmer 1988), The spe- cies has bred opportunistically even at the fringes of its range, including occasional nesting in Kansas (Parmalee and Stephens 1964) and Louisiana (Bai- ley and Wright 1931). On a smaller scale, groups of Harris’ Hawks have been documented to invade and subsequently nest in several regions in south- ern Arizona east of its normal range (Bednarz 1995). Furthermore, there are two historical re- cords of the Harris’ Hawk for coastal San Diego County, California: one collected at Mission Valley September 2000 Harris’ Hawk in California 191 California Colorado River *^•0^ • 1 individual • 2- 3 individuals # 4'*- individuals Approximate northern * limit of range (Wilbur 1987) Figure 2. Records of the Harris’ Hawk {Parabuteo unidnctm) in southern California and northern Baja California since April 1994. The double line identifies the apparent geographic limits of the 1994 incursion. Records within this line are best considered naturally occurring, records falling on the line are debatable, and records well to the west or east are problematic (see text) . Shading represents urban /agricultural areas. on 17 November 1912 (Grey 1913, SDNHM 1842; the second record for California) and one ob- served at Oceanside from 1-6 November 1942 (Kent 1944). Although there are no long-term population census data, available data suggest that the Harris’ Hawk has undergone four influxes into California during the 20‘^ century (Fig. 3). The first major northwesterly expansion was around the turn of the century when “10-20 [were] in the air at a time’’ along the lower Colorado River between 1- 3 December 1902 (Wilder 1916). These numbers followed many decades of no records for the lower Colorado River Valley. Elliot Coues never recorded the species during many years of work at Yuma and the species was apparendy absent again by 1910 (Grinnell 1914). This dearth was followed by an influx in the late 1910s and early 1920s that was apparendy an order of magnitude larger than the incursions of 1902 or 1994, as evidenced by reports of large numbers in the Imperial Valley (Chambers 1921, 1924), a new westerly outpost for the species. 192 Patten and Erickson VoL. 34, No. 3 Table 2. Baja California records of the Harris’ Hawk {Parabuteo unicinctus) north of its normal range from fall 1993 through fall 1995 (Fig. 2). Records are arranged chronologically. Breeding has been documented in the Valle San Telmo, where at least one was still present as of 31 January 1999 (Patten pers. obs.); in addition, an adult was still present at Leyes de Reforma on 7 November 1998 (Erickson pers. obs.) . For the sake of completeness we also include one record from this timeframe for the Rio Colorado in extreme northwestern Sonora (Russell and Monson 1998). See Methods for data sources (now on file at AVFVZ). Date(s) Location Maximum 5 September 1993— fall 1995 + Valle San Telmo 2 20 February 1994 20 km s. of San Quintin 3 9 April 1994 El Doctor (Sonora) 1 10 April 1994 Valle las Palmas 1 23 April 1994 Laguna Hanson 1 21 May 1994 Campo Christiano 3 21 May 1994-5 March 1995 Valle San Matias 5 30 May 1994 Ejido Sinaloa 1 13 November 1994-fall 1995+ Leyes de Reforma 2 13 November 1994 Valle Trinidad 1 26 March 1995 La Rumorosa 1 10 November 1995 Heroes de la Independencia 1 Figure 3. Timeline of the fluctuating occurrence of the Harris’ Hawk {Parabuteo unicinctus) in California and the lower Colorado River Valley. September 2000 Harris’ Hawk in California 193 There was apparently another influx of Harris’ Hawks into California during the late 1940s and early 1950s (Bednarz 1995). During this period numbers again built to double digits (e.g., 30 at Havasu National Wildlife Refuge on 27 December 1950) following two decades of only a few individ- uals being regularly recorded (Rosenberg et al. 1991). Two major factors have been implicated in caus- ing the extirpation of this species in California. First, the sport of falconry had an upsurge in pop- ularity in the 1950s, and the Harris’ Hawk was and remains a favored bird (White 1988, 1989). Rem- sen (1978) suggested that nestlings were taken in California until the population was completely de- pleted, but there is no evidence that falconers ever harvested Harris’ Hawks in California (Walton pers. comm.). Instead, birds were harvested in Ar- izona and Texas and most flown now are from cap- tive breeding. Shooting was undoubtedly common and may also have contributed somewhat to its de- cline. Second, habitat loss along the Colorado River from agricultural clearing and water diversion pro- jects was extensive between 1930-60 (Whaley 1986) and similarly occurred during this time in the Im- perial Valley (Steere 1952). In addition to direct clearing, erratic water levels led to periodic flood- ing and desiccation, killing most suitable nest trees. Throughout its range, the Harris’ Hawk inhabits savannah-type habitats in arid and semiarid areas, including open woodland, open scrub, mesquite {Prosopis spp.) woodland, and riparian woodland bordering open spaces. Trees, especially cotton- woods {Populus spp.), or large cacti such as the sa- guaro {Carnegiea gigantea), are used for nesting; however, this species will use utility poles and other artificial structures. In recent years, this species has been steadily increasing its range in southeastern Arizona (Bednarz 1995, Dawson 1998) where it has become more tolerant of human settlements. In- deed, Dawson (1998) noted that “the willingness of Harris’ Hawk to nest in urban areas offers some hope of mitigating habitat loss to development,” although post-fledging survival of such birds is low (Bednarz pers. comm.). Perhaps such tolerance for urban setting is a re- cent advent, for if it were always the case then the Harris’ Hawk may have persisted in many areas where it formerly occurred. However, we feel that whereas this urban tolerance may play some small role in the recent incursion into southern Califor- nia and northern Baja California, it explains nei- ther the magnitude nor the rapidity of the 1994 event. Instead, our investigation supports the hy- pothesis that the species undergoes periodic pop- ulation fluctuations that result in rapid range ex- pansions followed by adventitious breeding and, typically, slow range contraction (Millsap 1981, Bednarz et al. 1988). Each expansion-retraction cy- cle differs in magnitude and may bring individuals into areas where they had not been recorded pre- viously, such as the Mojave Desert. The breeding biology of the Harris’ Hawk promotes rapid expan- sion in numbers when conditions allow. While most nest in spring (March-June) , it is able to breed year-round in temperate-climate desert hab- itats in North America and may produce second and third clutches (Bednarz 1987, 1995), We be- lieve that most birds observed during the 1994 event originated in northern Baja California, where rainfall totals at Ensenada were 140% of av- erage during winter 1991-92 and 168% in 1992- 93, but were 90% average in 1993-94 (Mellink pers. comm.). Perhaps two years of favorable con- ditions allowed for an increase in numbers suffi- cient to send birds far afield during less favorable conditions in 1993-94, although causes are likely more complex. In summary, the available evidence suggests that the Harris’ Hawk has always been on the fringe of its natural range in California, with occasional ir- ruptive occurrences into the state every few de- cades. Many stay to breed or linger for significant periods, but eventually numbers decline as ap- peared to be happening already in the wake of the influx of 1994. As noted above for Louisiana and Kansas, this species is capable of adventitious breeding following a lengthy dispersal. Further- more, the more general pattern of range expan- sion and contraction has been documented re- peatedly in Arizona and New Mexico (Bednarz 1995, Dawson 1998), although it is perhaps more dramatic in California given that the species may not occur in the state for years at a time. Acknowledgments We are indebted to P.D. Jorgensen, K.A. Radamaker, R. Theriault, and T.E. Wurster for graciously providing extensive summaries of field observations of the Harris’ Hawk in southern California and northern Baja Califor- nia. P.H. Bloom, B.E. Daniels, G. McCaskie, E. Mellink, J. Linthicum, P. Unitt, and B.J. Walton supplied unpub- lished information and shared their views of this incur- sion. California Bird Records Committee files (housed at 194 Patten and Erickson VoL. 34, No. 3 WFVZ) were an invaluable resource for information about recent occurrences. R. Corado and J. Fisher (WFVZ), J.R Dean and C. Ludwig (USNM), and P. Unitt (SDNHM) provided data about and/or allowed access to specimens in their care. We thank J.C. Bednarz, P.H. Bloom, B.J. Walton, and S.R. Wilbur for their careful re- views of the manuscript. Literature Cited American Ornithologists’ Union. 1998. Check-list of North American Birds, 7th ed. Am. Ornithol. Union, Washington, DC U.S.A. Bailey, A.M. and E.G. Wright. 1931. Birds of southern Louisiana. Wilson Bull. 43:190-219. Bancroft, G. 1920. The Harris Hawk as a breeder in California. Cowcfor 22:156. Bednarz, J.C. 1987. Pair and group reproductive success, polyandry, and cooperative breeding in Harris’ Hawk. Auk 104:393-404. . 1995. Harris’ Hawk (Parabuteo unidnctus). In K. Poole and F. Gill [Eds.], The birds of North America, No. 146. Acad. Nat. Sci., Philadelphia, PA and Am. Ornithol. Union, Washington, DC U.S.A. , J.W. Dawson, and W.H. Whaley. 1988. Harris’ Hawk. Pages 71-82 in R.L. Glinski, B.G. Pendleton, M.B. Moss, M.N. LeFranc, Jr., B.A. Millsap, and S.W. Hoffman [Eds.], Proc. Southwest Raptor Manage- ment Symposium and Workshop. Natl. Wildl. Fed. Sci. Tech. Ser. 11. Bunker, C.D. 1919. Harris’ Hawk {Parabuteo unidnctus harrisi) in Kansas. Auk 36:285. Chambers, W.L. 1921. A flight of Harris’ Hawks. Condor 23:65. . 1924. Another flight of Harris’ Hawks. Condor 26:75. Coombs, F.E. 1892. Notes on a few Louisiana birds. Auk 9:204-206. Cooper, J.G. 1870. The naturalist in California. Am. Nat. 3:470-481. Dawson, J.W. 1998. Harris’ Hawk. Pages 77-81 in R.L. Glinski [Ed.], The raptors of Arizona. Univ. Ariz. Press, Tucson, AZ U.S.A. Earl, J.M. 1918. Harris’ Hawk in Ohio. Wilson Bull. 30: 15-16. Garrett, K. and J. Dunn. 1981. Birds of southern Cali- fornia: status and distribution. Los Angeles Audubon Soc., Los Angeles, CA U.S.A. Grey, H. 1913. Harris’ Hawk in California. Condor 15:12,8. Grinnell, J. 1914. An account of the mammals and birds of the lower Colorado Valley, with especial reference to the distributional problems presented. Univ. Calif. Publ. Zool. 12:51-294. . 1915. A distributional list of the birds of Califor- nia. Pac. Coast Avifauna 1 1 . AND A.H. Miller. 1944. The distribution of the birds of California. Pac. Coast Avifauna 27. Kennerly, C.B.R. 1859. Route near the thirty-fifth paral- lel, explored by Lieutenant A.W. Whipple, topograph- ical engineers, in 1853 and 1854: No. 3, report on birds collected on the route. Pac. Railroad Rep. 10:19— 35. Kent, W.A. 1944. Rare birds seen in southern California. Condor 46:129-130. Linthicum, J. [Ed.]. 1989. Peregrine Falcon monitoring, nest managment, hack site, and cross-fostering efforts, 1989, including information regarding other field and laboratory activities. Ann. Activity Statement, San- ta Cruz Predatory Bird Res. Group, Univ. Calif., Santa Cruz, CA U.S.A. Massey, B.W. 1997. Guide to birds of the Anza-Borrego Desert. Anza-Borrego Desert Nat. Hist. Assoc., Bor- rego Springs, CA U.S.A. McCaskie, G. 1989. Southern Pacific Coast Region. Am. Birds 43:1366-1369. . 1995. Southern Pacific Coast Region. Field Notes 49:195-201. . 1996. Southern Pacific Coast Region. Field Notes 50:330-334. Millsap, B.A. 1981. Distributional status of falconiformes in west-central Arizona: with notes of ecology, repro- ductive success, and management. Bureau Land Man- age. Tech. Note 355. Palmer, R.S. 1988. Bay-winged Hawk. Pages 390-394 in R.S. Palmer [Ed.], Handbook of North American birds. Vol. 4. Yale Univ. Press, New Haven, CT U.S.A. Parmalee, P.F. and H.A. Stephens. 1964. Status of the Harris’ Hawk in Kansas. Condor 66:443-445. Remsen, J.V., Jr. 1978. Bird species of special concern in California: an annotated list of declining or vulnera- ble bird species. Calif. Dept. Fish and Game, Wildl. Manage. Branch Admin. Rep. 78-1. Roberson, D. 1980. Rare birds of the West Coast. Wood- cock Publ., Pacific Grove, CA U.S.A. Rosenberg, K.V., R.D. Ohmart, W.C. Hunter, and B.W. Anderson. 1991. Birds of the Lower Colorado River Valley. Univ. Ariz. Press, Tucson, AZ U.S.A. Russell, S.M. and G. Monson. 1998. The birds of So- nora. Univ. Ariz. Press, Tucson, AZ U.S.A. Snyder, L. 1919. Harris’ Hawk in Kansas. Auk 36:567. Steere, C. H. 1952. Imperial and Coachella Valleys. Stan- ford Univ. Press, Stanford, CA U.S.A. Stephens, F. 1903. Bird notes from eastern California and western Arizona. Condor 5:75— 18. Stewart, G.R. 1979. Re-establishing the Harris’ Hawk on the Lower Colorado River. Unpubl. job report (proj. W-54-R-12, job II-7), Bureau Land Manage., Yuma, AZ U.S.A. . 1982. Re-establishing the Harris’ Hawk on the Lower Colorado River: annual report for fiscal 1982. Unpubl. job report (proj. W-54-R-14, job 11-7), Bureau Land Manage., Yuma, AZ U.S.A. Swarth, H.S. 1914. A distributional list of the birds of Arizona. Pac. Coast Avifauna 10. Unitt, P. 1984. The birds of San Diego County. San Diego Soc. Nat. Hist. Mem. 13. September 2000 Harris’ Hawk in California 195 Walton, B,, J. Linthicum, and G. Stewart. 1988. Re- lease and re-establishment techniques developed for Harris’ Hawks-Colorado River 1979-1986. Pages 318- 320 in R.L. Glinski, B.G. Pendleton, M.B. Moss, M.N. LeFranc, Jr., B.A. Millsap, and S.W. Hoffman [Eds..], Proc. Southwest Raptor Management Symposium and Workshop. Natl. Wildl. Fed. Sci. Tech, Ser, 11. Whaley, W.H. 1986. Population ecology of the Harris’ Hawk in Arizona. Raptor Res. 20:1-15. White, B. 1988. Report on raptor propagators in the United States — 1987. Unpubl. report, U.S. Fish and Wildl. Serv., Washington, DC U.S.A. . 1989. Report on raptor propagators in the Unit- ed States — 1988. Unpubl. report, U.S. Fish and Wildl. Serv., Washington, DC U.S.A. Wilder, H.E. 1916. Some distributional notes on Califor- nia birds. Condor 18:127-128. Wiley, L. 1917. Nesting of the Harris’ Hawk in south- eastern California. Condor 19:142. Received 30 October 1999; accepted 14 March 2000 J Raptor Res. 34(3):196-202 © 2000 The Raptor Research Foundation, Inc. THE FOOD HABITS OF SYMPATRIC FOREST-FALCONS DURING THE BREEDING SEASON IN NORTHEASTERN GUATEMALA Russell Thorstrom The Peregrine Fund, 5666 West Flying Hawk Lane, Boise, ID 83709 U.S.A. Abstract. — The food habits of Barred {Micrastur ruficollis) and Collared Forest-Falcons (M. semitorquatus) were studied in Tikal National Park, Guatemala. On a numerical basis for 405 identified prey for Barred Forest-Falcons, lizards { Anolis spp., Ameiva or Cnemidophorus spp., Laemanctus spp., and Corytophanesspp.) were the most numerous prey type comprising 61.5% of the diet. For Collared Forest-Falcons, on a numerical basis of 170 identified prey, mammals represented the greatest proportion at 45.9%. On a biomass basis, lizards (37.3%) and birds (36.8%) were equally important in the diet of Barred Forest- Falcons but, for Collared Forest-Falcons, mammals (47%) and birds (45.4%) were the most important prey. Food-niche overlap was 0.49 between the two forest-falcons and prey that overlapped were mice, rats, bats, birds {Momotus spp., Dendrocinda spp.) , and lizards ( Corytophanes spp.) . The wider food breadth of the Collared Forest-Falcon was probably attributable to the greater diversity of bird species in its diet. The Collared Forest-Falcon is approximately 3 times the size of Barred Forest-Falcons but the mean weight of its prey (MWP) was 10 times greater (x = 239 g) than that of Barred Forest-Falcons (x = 24 g). Key Words: Barred Forest-Falcon; Micrastur ruficollis; Collared ForestFalcon; Micrastur semitorquatus; food habits', niche overlap', niche breadth. Habitos alimenticios de dos halcones de bosque simpatricos durante la estacion reproductiva en el noreste de Guatemala Resumen. — Los habitos alimenticios de Micrastur ruficollis y Micrastur semitorquatus fueron estudiados en Parque Nacional Tikal, Guatemala. En una base numerica de 405 presas identificadas para Micrastur ruficollis, las lagartijas {Anolis spp., Ameiva o Cnemidophorus spp., Laemanctus spp., y Corytophanes spp.) fueron el tipo de presa mas numeroso o sea el 61.5% de la dieta. Para Micrastur semitorquatus, en una base numerica de 170 presas identificadas, los mamiferos representaron la proporcion mayor con el 45.9%. En relacion a la biomasa, las lagartijas (37.3%) y aves (36.8%) fueron igualmente importantes en la dieta de Micrastur ruficollis, pero para Micrastur semitorquatus, los mamiferos (47%) y aves (45.4%), fueron las presas mas importantes. El traslape del nicho alimenticio fue de 0.49 entre los dos halcones de bosque y las presas que se traslaparon fueron ratones, ratas, murcielagos, aves {Momotus spp., Den- drodncla spp.), y lagartijas {Corytophanes spp.). El espectro mas amplio de la dieta de Micrastur semitor- quatus fue probablemente atribuible a la mayor diversidad de especies de aves en su dieta. Micrastur semitorquatus es 3 veces el tamano de Micrastur ruficollis pero su peso medio fue 10 veces mayor (x = 239g) que el de Micrastur ruficollis (x = 24 g), [Traduccion de Cesar Marquez] Neotropical birds of prey are poorly known, es- pecially the forest-dependent species which are in- conspicuous in their habits. The secretive forest raptors of the genus Micrastur are among the least- studied raptors and most accounts of their diets come from stomach contents of museum speci- mens or incidental observations (Dickey and van Rossem 1938, Friedmann 1948, Smith 1969, Izawa 1978, Mader 1981, Willis et al. 1983, Mays 1985, Trail 1987, Rappole et al. 1989, Thorstrom et al. 1990) . The most detailed account of the food hab- its of this genus is given hy Robinson (1994), but it too is limited to incidental observations. The Barred Forest-Falcon (Micrastur ruficollis) is perhaps the most common raptor in Neotropical forests. It has the widest distribution of any forest- falcon, occurring from southeastern Mexico to northern Argentina, Paraguay, and east through Brazil and the Guianas (Brown and Amadon 1989, del Hoyo et al. 1994). It ranges from humid low- land and foothill forests to higher subtropical and montane forests reaching its limit near 2500 m. In- 196 September 2000 Food Habits of Forest-Falcons 197 formation on the diet of the Barred Forest-Falcon suggests that it feeds mainly on lizards (Thorstrom et al. 1990, Thorstrom 1993, del Hoyo et al. 1994). The Collared Forest-Falcon (M. semitorquatus) also has a broad distribution, ranging from central Mexico to eastern Bolivia, northern Argentina, and Paraguay (Brown and Amadon 1989). It occupies dense primary and secondary forests from sea level to 2500 m. A recent sighting in Texas (Lasley et al. 1994) extended its northern distribution to the southwestern U.S. Food of the Collared Forest-Fal- con includes birds, mammals, lizards, snakes, and insects (Brown and Amadon 1989, Thorstrom 1993). In this paper, I compare the diet of Barred For- est-Falcons and Collared Forest-Falcons based on several years of nest observations of prey deliveries, and direct observations at and away from nests dur- ing breeding seasons from 1988-92 in northeast- ern Guatemala. My objectives were to compare prey frequency and biomass and to assess the amount of overlap in diet among the two species and compare food-niche parameters and differenc- es as potential mechanisms for coexistence of these two forest-falcons. Study Area and Methods I studied Barred and Collared Forest-Falcons in Tikal National Park, Peten, Guatemala from 1988-92. The park encompasses 576 km^ in northeastern Guatemala and its center lies at 17°13'N, 89°36'W. Vegetation in the park is semideciduous tropical forest with lowland rolling hills ranging from 200-450 m elevation. Schulze and Whitacre (1999) described several forest types that occur along topographical drainage, soil type, and moisture gradients within the park. The two ex- tremes of this forest-type continuum are upland or high- ground forests (tall, semi-evergreen forests on well- drained, shallow soils) and “bajo” forests (low in stature, with open canopy and dense understory, occurring in low-lying sites of deep, clay-rich soils subject to seasonal flooding and drought). Tikal National Park is covered mostly by unbroken primary forest, except for some areas where light selective logging occurred prior to 1969. The climate has pronounced wet and dry seasons with rains usually beginning in May or June and ending by December. Between 1989-95, monthly precipitation ranged from 1.0 mm in April to 302.5 mm during Sep- tember with an annual mean rainfall of 1309 mm (pers. obs.). Mean monthly temperatures ranged from a low of 15°C in January to a high of 35°C in May. The forest and known forest-falcon territories were searched daily from February through August to docu- ment nesting activity and potential breeding pairs. Nests of Barred Forest-Falcons were observed primarily from the ground and those of the Collared Forest-Falcon were occasionally observed from tree platforms. Observations were made using 7-10 X binoculars at distances of 25-50 m. During the breeding season, observations of prey items were recorded during prey deliveries and away from nests during radiotracking sessions. All prey was identified to the most accurate taxonomic level possible with the exception of amphibians and insects, which were not identifiable to the species level and were assigned to larger taxonomic groupings. The resulting tabulation produced a total of 37 prey categories for both species. Only observed prey delivered and captured were includ- ed in biomass estimates to avoid possible bias from prey found in nests (Snyder and Wiley 1976, Wiley and Wiley 1981, Marti 1987). Anolis lizards were separated in small (<20 cm) and large catagories (>20 cm). To estimate mean weight of prey (MWP), I multiplied each prey item by its average weight (Table 1), summed the products and divided the sum by the total number of prey observed. Mammal weights follow Emmons and Feer (1997), bird weights come from Smithe (1966) and Dunning (1993), and reptile weights were taken in the field. Food-niche breadths (FNB) were calculated using Lev- ins’ (1968) equation: FNB = 1 /SPj^, where P, is the proportion of the ith prey category of species / For com- parison among raptors with different number of prey cat- egories, a standardized niche breadth value (FNBs) was also calculated as follows: FNBs = (FNB — l)/(n — 1), where n is the number of prey categories (Levins 1968) Niche overlap was calculated using Schoener’s (1970) in- dex of symmetrical overlap: overlap = 1 — (%) (S|Py — Piii\), where P^ is the proportion of the ith prey category for species J and h. Linton et al. (1981) found this overlap formula to be the only index that accurately measures real overlap between 7-85%, The Collared Forest-Falcon is the largest of the two species with a body mass of 467-511 g for males (Dickey and van Rossem 1938) and 556-750 g for unknown sexes (Haverschmidt 1968), Males I weighed averaged 587 ± 17.6 g (±SD, range = 563-605 g, = 4) and females averaged 869 g ± 63 g (range = 792-940 g, A = 6) Barred Forest-Falcons averaged 167.8 ± 10.6 g (range = 144-184 g, A = 25) for males and 233.2 g ± 23.9 (range = 200-322 g, A = 34) for females. Results Barred Forest-Falcon. I recorded lizards {Anohs spp., Ameiva spp. or Cnemidophorus spp., Laemanctus spp., and Corytophanes spp.), birds {Momotus spp., Aulacorhynchus spp., Turdus spp., Leptotila spp., Den- drocinda spp., Thryothorus spp., and Tyrannidae), amphibians, mammals, snakes, and insects (Blatti- dae) in the diet of Barred Forest-Falcons during the nesting season. I observed a total of 600 prey items being deliv- ered to females, nestlings, and fledglings from 1988-92. On a numerical basis, reptiles were the predominant prey comprising 61,5% of the diet (249 prey items), followed by birds 22% (89), in- sects 8.2% (33), mammals 5.9% (24), and amphib- ians 2.5% (10) (Fig. 1). Nearly one third (195) of 198 Thorstrom VoL. 34, No. 3 Table 1. Weights used to estimate prey biomass of Barred and Collared Forest-Falcons at Tikal National Park, Guatemala. Prey Weight (g) Source Insects Blattaria 1.5 This study Reptiles Anolis <20 cm 3.9 This study Anolis large >20 cm 13.8 This study Ameiva or Cnemidophorus 25 This study Laemanctus 15 This study Corytophanes 45 This study Birds Crypturellus 440 Smithe 1966 Penelope 600 Smithe 1966 Crax 500 Smithe 1966 Ortalis 450 Smithe 1966 Agriocharis 3000 Smithe 1966 Odontophorus 300 Smithe 1966 Leptotila 160 Smithe 1966 Ciccaba 240 Smithe 1966 Momotus 133 Dunning 1993 Ramphastos 350 Dunning 1993 Pteroglossus 220 Dunning 1993 Aulacorhynchus 150 Smithe 1966 Melanerpes 81 Dunning 1993 Celeus 85 Dunning 1993 Tyrannidae 15 Smithe 1966 Cyanocorax 200 Dunning 1993 Troglodytidae 15 Smithe 1966 Muscicapidae 75 Smithe 1966 Mammals Sciurus small 205 Emmons and Feer 1997 Sciurus large 400 Emmons and Eeer 1997 Artibeus 50 Emmons and Eeer 1997 Unidentified bat 20 This study Unidentified mouse (Heteromys) 76 This study, Emmons and Feer 1997 Unidentified rat {Rattus, Oryzomys, Sigmodon) 150 This study, Emmons and Feer 1997 the items were unidentified, especially late in the nestling period, because male forest-falcons flew secretively into their nests without calling their mates to receive prey, and females flew into the nests quickly and directly without vocalizations. It was unlikely, however, that the unidentified prey items differed from those actually identified. The most detailed dietary information was obtained during 1989 when 267 of 380 items delivered to nests were identified. Again, most (64.0%, N = l7l) were lizards and were represented by 57 small Anolis spp., 21 large Awofospp., 28 teiids (most like- ly Ameiva spp. or Cnemidophorus spp.), 11 Laemanc- tus spp., 5 Corytophanes spp., and 49 unidentified lizards. Snakes included 1 coral snake or mimic {Lampropeltis sp. or Micrurus sp.) and 2 other snakes. Eleven of the 267 identified prey (4%) were frogs {Rana spp. and/or Hyla spp.). Only 21 arthropods (8 cockroaches and 13 other items in- cluding spiders and beetles, 8% of the diet) were identified. Birds contributed 52 prey items (19.5 % of the diet) and included five Blue-crowned Mot- mots {Momotus momota), two flycatchers (Tyranni- dae) , two Emerald Toucanets {Aulacorhynchus pra- September 2000 Food Habits of Forest-Falcons 199 a) Barred Forest-Falcon (n=267) Collared Forest-Falcon {n=1 70) Mammals I Birds iS Reptiles Amphibians Insects b) Barred Forest-Falcon biomass Collared Forest-Falcon biomass Mammals I Birds 3 Reptiles Amphibians Insects Figure 1. Comparison of the diets of Barred Forest-Falcons and Collared Forest-Falcons as (a) the percent prey of individuals and (b) the biomass composition (% weight of prey individuals). sinus), one Gray-fronted Dove {Leptotila rufaxiUa), one woodcreeper {Dendrodncla sp.), one Spot- breasted Wren (Thryothorus macuUpectus) , and one Clay-colored Robin ( Turdus grayt) . Birds taken ranged in size from an unidentified warbler (Den- droica sp.) at 9 g to a Gray-fronted Dove at 160 g (Smithe 1966, Dunning 1993). The nine mammals 1 identified represented only 3% of the diet. Among them were seven rodents, one bat, and one other mammal. The rodents were possibly mem- bers of the genera Heteromys and Oryzomys. Snakes accounted for 3 prey items or 1.1% of the diet. Biomass estimates were made for 267 identified prey items delivered during the 1989 breeding sea- son. On a biomass basis, reptiles (37.3%), birds (36.8%), and mammals (20.2%) comprised 94.3% of the estimated biomass (Fig. 1). Males delivered more prey items and prey biomass than females during the breeding season. Of the 267 identified prey delivered in 1989, five males brought in 3.8 kg (75.7%) and five females delivered 1.2 kg (24.3%) of the biomass during the breeding sea- son. Collared Forest-Falcon. I found squirrels {Sciu- rus spp.), bats {Artibeus spp.), rats (Sigmodon spp.), mice {Heteromys spp.), birds {Crypturellus spp., Pe- nelope spp., Crax spp., Ortalis spp., Agriocharis spp., Odontophorus spp., Leptotila spp., Ciccaba spp., Mom- otus spp., Ramphastos spp., Pteroglossus spp., Aulaco- rhynchus spp., Melanerpes spp., Celeus spp., Cyanocor- ax spp., Dendrocolaptidae) , snakes {Coluber sp.), and lizards {Corytophanes From 1990-92, 222 prey items were delivered to females, nestlings, and fledglings and 170 of these were identified. On a numerical basis, 45.9% were mammals (78 prey items), 34.7% birds (59), 18.8% reptiles (13 lizards and 19 snakes), and 0.6% am- phibians (1 frog) (Fig. 1). The 52 unidentified 200 Thorstrom VoL. 34, No. 3 prey items were presumed to have been similar to those that were identified. In addition, 36 items were given to two fledglings by an extra adult be- lieved to be a male. This male specialized in catch- ing toucans so I calculated the diet of Collared For- est-Falcons both with and without this male’s contribution. Prey of Collared Forest-Falcons ranged in size from a frog estimated at 20 g to an Ocellated Tur- key {Agriocharis ocellata) weighing about 3 kg. The two largest prey were the adult female turkey and a young Crested Guan {Penelope purpurascens) . Of the 13 lizards taken, 12 were in species belonging to the genus Corytophanes. The 19 snakes I ob- served were most likely colubrids. The 78 mam- mals identified included 42 Deppe’s squirrels (Sciu- rus deppei; 190-220 g), 11 Yucatan squirrels (5. yucatanensis] 420 g), two fruit bats {Artibeus spp.), 14 unidentified bats, 7 rat-sized rodents including the hispid cotton rat {Sigmodon hispidus), and 2 mice believed to be spiny pocket mice {Heteromys spp.). Among the 59 birds identified, the most nu- merous were Collared Aracari {Pteroglossus torqua- tus, N = 9), Plain Chachalaca {Ortalis vetula, N = 7), Great Curassow {Crax rubra, N — 7), Keel-billed Toucans {Ramphastos sulfuratus, N = 6), Ruddy Woodcreepers {Dendrocincla homochroa, N = 4), Tinamous {Crypturellus spp., A = 3) , and Brown Jays {Cyanocorax morio, N — S). In 1990, a third adult forest-falcon, probably a male, began delivering prey items to two young, 4 wk after they fledged. We observed this adult de- liver 36 prey items until 11 weeks after fledging. It appeared to prefer Keel-billed Toucans delivering 27 toucans, two Collared Aracari, two unidentified birds, four squirrels (5. deppei), and one unidenti- fied prey item. Sometimes it delivered two Keel- billed Toucans a day. When this contribution was included in the overall diet of Collared Forest-Fal- cons, the diet was dominated by birds (43.9%, 90 individuals) followed by mammals (40.0%, 82), reptiles (15.6%, 32), and amphibians (0.5%, 1). In terms of biomass, this extra adult delivered 12.6 kg of prey during the post-fledging period. Biomass estimates were based on the 170 iden- tified prey items delivered during the breeding sea- sons. On this basis, 47.0% of the prey were mam- mals, 45.4% birds and 6.5% reptiles (Fig. 1). Squirrels represented 66.7% of the mammalian biomass. Males delivered 11.4 kg (65.7%) and fe- males 5.9 kg (34.3%) of the biomass. Food-niche Parameters. Lizards, especially Anolis Table 2. Food-niche breadth, dietary overlap, and esti- mated mean weights (g) of prey (MWP) and of birds (MW) of Barred and Collared Forest-Falcons during the nesting season. All calculations based on prey at the ge- neric or family level. Mean ± SE (N). Food-niche Parameters Barred Forest- Falcon Collared Forest- Falcon Total identified prey items 267 170 Mammal species richness 3 6 Bird species richness 7 15 Lizard species richness 5 1 MWP 23.7 ± 2.5 238.9 ± 18.9 (267) (170) MW birds 62.1 ± 15.3 373.4 ± 49.5 (52) (59) FNB 7.9 13.8 FNBs 0.33 0.49 Dietary overlap 0.49 spp., dominated the Barred Forest-Falcon diet and, as a result, it had a narrower niche breadth than did the Collared Forest-Falcon. Collared Forest-Fal- cons took a higher richness of bird and mammal species (Table 2). The standardized FNB of the Barred Forest-Falcon was lower (0.33) than the Collared Forest-Falcon (0.49). Dietary overlap be- tween the two forest-falcons was 0.49. Estimated MWP captured by Collared Forest-Falcons was sig- nificantly heavier than that of Barred Forest-Fal- cons (Table 2). The larger Collared Forest-Falcon captured larger avian (x = 373.9 ± 49.5 g, ±SE, N - 59) and mammalian (x = 179 ± 12.5, N = 78) prey than did the Barred Forest-Falcon which took mostly lizards {x — 13.8 ± 0.6, N = 122) and birds (x = 62.1 ± 4.9, A - 52). Discussion Barred and Collared Forest-Falcons are moder- ately dimorphic with Collared Forest-Falcons 3-4 times larger than Barred Forest-Falcons. Optimal foraging theory predicts that larger predators should have a wider food niche than smaller ones (Schoener 1970). I found this to be true for these two forest-falcons. Collared Forest-Falcons cap- tured a higher proportion of medium-sized mam- mals, especially squirrels, and they had a greater diversity of birds in their diet giving them a broad- er food-niche breadth (13.8) compared to Barred September 2000 Food Habits of Forest-Falcons 201 Forest-Falcons (7.9) . Barred Forest-Falcons preyed predominantly on lizards, mainly Anolis spp., con- tributing to its narrower food-niche breadth, and birds were of secondary importance in their diet. Collared Forest-Falcons preyed on a wider range of animal sizes, ranging from a small frog (20 g) to large birds (3 kg) whereas Barred Forest-Falcons caught prey ranging in size from insects (1.5 g) to a dove (160 g). In terms of biomass. Barred Forest-Falcons cap- tured nearly equal proportions of lizards (37.3%) and birds (36.8%) during the breeding season. This was attributed to the smaller mean weight of lizards (13.8 g) vs. the mean weight of birds (93.5 g). Birds were approximately seven times heavier but three times fewer in numbers. Prey biomass of Collared Forest-Falcons was distributed nearly equally between mammals (47%) and birds (45.4%), but the mean weight of birds (368 g) was twice that of mammals (179 g). However, fewer birds (59) than mammals (78) were delivered dur- ing the nesting season, contributing to the nearly equal frequency of prey biomass of Collared For- est-Falcons. The food-niche overlap was relatively high be- tween these two congeners and almost near the competition threshold level of 0.6 which was pro- posed as biologically significant by Zaret and Rand (1971). Schoener (1984) and Temeles (1985) pre- dicted that similar morphological features of rap- tors can be found among congeners which affect their hunting ability and food habits. However, Bo- sakowski and Smith (1992) showed that larger dif- ferences in body size limit food overlap below the competition threshold. Thus, while the two forest- falcons exhibited overlap on a few prey species, I suspect that the effect on overall prey availability was probably insignificant. Both species have a broad diet with Barred Forest-Falcons relying more on lizards and Collared Forest-Falcons preying mainly on squirrels. The Barred Forest-Falcon is dependent on ma- ture forests while the Collared Forest-Falcon oc- cupies mature forests, forest edge, and secondary woodlands and thickets. Both species use a short stay “perch-hunting” technique, a common meth- od found in forest or woodland-adapted species (Kenward 1982, Newton 1986). The higher con- sumption of avian prey by the Collared Forest-Fal- con may be enhanced by its great maneuverability, owing to its long legs and long-arched tail which are morphological adaptations for chasing prey by foot. Collared Forest-Falcons were observed chas- ing prey by running on the ground, around tree trunks, and along large branches, whereas Barred Forest-Falcons usually attacked prey by surprise from concealed perches. The information provided here is limited to ob- servations during the nesting season and may not accurately reflect the overall diet of these two spe- cies. There may be seasonal shifts in the diet of these forest-falcons or certain prey types may be taken preferentially due to experience or ability as observed in the extra adult Collared Forest-Falcon that delivered 75% of its prey as Keel-billed Tou- cans. This particular bird apparently had a special ability or learned behavior for capturing toucans. More information is needed from other regions in the Neotropics and during the nonbreeding sea- son to determine the extent of niche breadth and dietary overlap between these two species. Acknowledgments This study was part of The Peregrine Fund’s Maya Pro- ject, in cooperation with the Instituto Nacional de Antro- pologia y Historia (IDAEH) , Centro de Estudios Conser- vationistas (CECON), Guatemala, and Consejo Nacional de Areas Protegidas (CONAP), Guatemala. A special thanks to B. Burnham, J.P. Jenny, L. Kiff, and D. Whitacre of The Peregrine Fund. Thanks to Boise State University for providing assistance. I kindly thank the staff of Tikal National Park, Guatemala for their assistance. For assist- ing in the field I would like to thank E.M. Ramirez, J.D. Ramos, C.M. Morales, J.M. Castillo, H. de J.G. Manzane- ro, and C.S. Mateo. Literature Cited Bosakowski, T. and D.G. Smith. 1992. Comparative diets of sympatric nesting raptors in the eastern deciduous forest biome. Can. J. Zool. 70:984—992. Brown, L. and D. Amadon. 1989. Eagles, hawks, and fal- cons of the world. Wellfleet Press, Seacaucus, NJ U.S.A. Dickey, D.R. and AJ. van Rossem. 1938. The birds of El Salvador. Zool. Ser. 23, Eield Mus. Nat. Hist., Chicago, IL U.S.A. Dunning, J.B., Jr. 1993. CRC handbook of avian body masses. CRC Press Inc., Boca Raton, FL U.S.A. Emmons, L.H. and F. Feer. 1997. Neotropical rainforest mammals. Univ. Chicago Press, Chicago, IL U.S.A. Friedmann, H. 1948. Birds collected by the National Geo- graphic Society’s Expedition to northern Brazil and southern Venezuela. Proc. U.S. Natl. Mus. 97:373-569 Haverschmidt, F. 1968. Birds of Surinam. Oliver 8c Boyd, London, U.K. DEL HOYO, J., A. Eliot, and J. Saragatal. 1994. Hand- book of the Birds of the World. Vol. 2. New World 202 Thorstrom VoL. 34, No. 3 vultures to guineafowl. Lynx Edicions, Barcelona, Spain. IzAWA, K. 1978. A field study of the ecology and behavior of the black-mantle tamarin {Sanguinus nigricollis) . Fo- lia Primates 19:241-274. Kenward, R.E. 1982. Goshawk hunting behaviour and range size as a function of food and habitat availabil- ity, y. Anim. Ecol. 51:69-80. Lasley, G.W., C. Sexton, and G.D. Luckner. 1994. Win- ter season, December 1, 1993-February 28, 1994, Tex- as Region. Natl. Audubon Soc. Field Notes 48:224-228. Levins, R. 1968. Evolution in changing environments. Princeton Univ. Press, Princeton, NJ U.S.A. Linton, L.R., R.W. Davies, and F.J. Wrona. 1981. Re- source utilization indices: an assessment. J. Anim. Ecol. 50:283-292. Mader, W. 1981. Notes of nesting raptors in the llanos of Venezuela. Condor 83:48-51 . Marti, C.D. 1987. Raptor food habits studies. Pages 67- 79 in B.G. Pendleton, B.A. Millsap, K.W. Kline, and D.A. Bird [Eds.], Raptor management techniques manual. Natl. Wildl. Fed. Sci. Tech. Sen No. 10. Na- tional Wildlife Federation, Washington, DC U.S.A. Mays, N.M. 1985. Ants and foraging behavior of the Col- lared Forest-Falcon. Wilson Bull. 97:231-232. Newton, 1. 1986. The Sparrowhawk. T. & A.D. Poyser, Gallon, U.K. Rappole, J.H, M.A. Ramos, and K. Winker. 1989. Win- tering wood thrush movements and mortality in southern Veracruz. Auk 106:401-410. Robinson, S.K. 1994. Habitat selection and foraging ecol- ogy of raptors in Amazonian Peru. Biotropica 26:443- 458. Schoener, T.W. 1970. Nonsynchronous spatial overlap of lizards in patchy habitats. Ecology 51:408-418. . 1984. Size differences among sympatric bird-eat- ing hawks: a worldwide survey. Pages 254-281 m D.R. Strong, D. Simberloff, L.G. Abele, and A.B. Thistle [Eds.], Ecological communities conceptual issues and the evidence. Princeton Univ. Press, Princeton, NJ U.S.A. Schulze, M. and D.F. Whitacre. 1999. A classification and ordination of the tree community of Tikal Na- tional Park, Peten, Guatemala. Bull. Ela. Mus. Nat. Hist. 41:169-297. Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size dimor- phism in hawks and owls of North America. Ornithol Monogr. 20. Smith, N.G. 1969. Provoked release of mobbing — a hunt- ing technique of Micrastur fzlcons. Ibis 111:241-243. Smithe, F.B. 1966. The birds of Tikal. The Natural His- tory Press, Garden City, NY U.S.A. Temeles, E.J. 1985. Sexual size dimorphism of bird-eating hawks and the effect of prey vulnerability. Am. Nat. 125:485-499. Thorstrom, R.K. 1993. Breeding ecology of two species of forest-falcons {Micrastur) in northeastern Guate- mala. M.S. thesis, Boise State Univ., Boise, ID U.S.A. , C.W. Turley, EG. Ramirez, and B.A. Gilroy. 1990. Description of nest, eggs, and young of the Barred Forest-falcon {Micrastur ruficollis) and of the Collared Forest-falcon {Micrastur semitorquatus) . Con- dor 90:237-239. Trail, P.W. 1987. Predation and antipredator behavior at Guiana. Auk 104:495-507. Wiley, J.W. and B.N. Wiley. 1981. Breeding season ecol- ogy and behavior of Ridgway’s Hawk {Buteo ridgwayi). Condor 83:132-151. Willis, E.O., D. Wechsler, and EG. Stiles. 1983. Forest- falcons, hawks, and pygmy-owl as ant followers. Rev. Bras. Biol. 43:23-28. Zaret, T.M. and A.S. Rand. 1971. Competition in tropical stream fishes: support for the competitive exclusion principle. Ecology 52:336-342. Received 19 July 1999; accepted 19 March 2000 /. Raptor Res. 34(3):203-209 © 2000 The Raptor Research Foundation, Inc. A COMPARISON OF RAPTOR DENSITIES AND HABITAT USE IN KANSAS CROPLAND AND RANGELAND ECOSYSTEMS Christopher K. Williams Department of Wildlife Ecology, University of Wisconsin, Russell Labs, 1 630 Linden Drive, Madison, WI 53706-1598 US. A. Roger D. Applegate Department of Wildlife and Parks, Research and Survey Office, P.O. Box 1525, Emporia, KS 66801-1525 US. A. R. Scott Lutz and Donald H. Rusch Department of Wildlife Ecology, University of Wisconsin, Russell Labs, 1630 Linden Drive, Madison, WI 53706-1598 US. A. Abstract. — We counted raptors on line transects along roads to assess densities, species diversity, and habitat selection of winter raptors between cropland and rangeland habitats in eastern Kansas. We conducted counts every 2 wk between September-March 1994-98. Species diversity indices did not differ between the two habitats {P = 0.15). We calculated density estimates and cover type selection for Red- tailed Hawks {Buteo jamaicensis) , Northern Harriers (Circus cyaneus), and American Kestrels (Falco sparv- erius) . Red-tailed Hawks and Northern Harrier densities were higher in cropland, while kestrel densities did not differ between the two habitats. All three species across both habitats had a general preference for idleland habitat. We believe three factors could explain the higher raptor densities in cropland: increased prey abundance, increased visibility of prey associated with harvested agriculture fields, and/ or a higher relative amount of preferred hunting habitat. Key Words: Northern Harrier, Circus cyaneus; Red-tailed Hawk, Buteo jamaicensis; American kestrel, Falco sparverius; cropland', cover type selection', density, line transect, rangeland. Una comparacion de densidades de aves rapaces y uso de habitat en tierras agricolas y ecosistemas de pastizales en Kansas Resumen. — Contamos las aves rapaces en transectos lineares a largo de carreteras para evaluar las den- sidades, la diversidad de especies y la seleccion de habitat de las rapaces que pasan el invierno entre las tierras agricolas y los habitats de pastizales en el este de Kansas. Hicimos conteos cada 2 semanas entre septiembre y marzo 1994—98. Los indices de diversidad de especies no difirieron entre los dos habitats (P = 0.15). Calculamos las densidades y la seleccion de cobertura para Buteo jamaicensis. Circus cyaneus, y Falco sparverius. Las densidades de Buteo jamaicensis y Circus (yaneus lueron mayores en las areas de cultivos, mientras que las densidades de Falco sparverius no difirieron entre los dos habitats. Las tres especies a lo largo de ambos habitats tuvieron una preferencia general por el habitat de tierras sin trabajar. Creemos que tres factores pueden explicar la mayor densidad en tierras cultivadas; aumento de la abundancia de presas, aumento de la visibilidad de presas asociada a las areas de tierras cosechadas, y/o a un aumento relativo de la cantidad de habitat de caza. [Traduccion de Cesar Marquez] Eastern Kansas is the wintering range for 1 1 spe- cies of diurnal raptors. In addition, three species of diurnal raptors migrate through eastern Kansas to wintering and breeding ranges (American Or- nithologists’ Union 1998). Eastern Kansas Audu- bon Society Christmas Bird Counts average 41—100 individual falconiform birds per count in 1986 (Johnsgard 1990). Although there is a large amount of research on the basic winter ecology of many species of raptors (e.g., Craighead and Craighead 1956, Collopy 19'73, Bohall and Collopy 1984, Collopy and Bild- stein 1987, Temeles and Wellicome 1992, Ardia and Bildstein 1997), little research has examined the effects of different landuse regimes (e.g., ag- riculture or grazing) on winter raptor ecology. 203 204 Williams et al.. VoL. 34, No. 3 Consequently, we estimated densities, species di- versity, and habitat selection of winter raptors in cropland and rangeland ecosystems in eastern Kansas. Study Areas We conducted raptor surveys in both an agricultural- and rangeland-dominated landscape in southern Lyon County, Kansas, where there was narrow transition zone between rangeland (western) and cropland (eastern) ecosystems. We selected study areas within this transition zone to ensure that the distance between study areas would reduce confounding climatic differences yet min- imize migration between study areas. Both study areas were approximately 2849 ha of private land and separat- ed by 20 km. The cropland study area (CSA) was 3 km west of Hartford, Kansas, and the rangeland study area (RSA) was 7 km west of Olpe, Kansas. Because the study areas were large, we could not spatially replicate our land- scapes. Methods The percent coverage of cover types on our study areas was calculated areas using aerial photographs from 1990 and ArcView Geographic Information System (Version 3 1, 1998). The CSA included 49% cropland (e.g., soy- beans, sorghum, corn, and winter wheat), 19% native hayland, 16% native tallgrass pasture, 12% idle grassland (e g.. Conservation Reserve Program grasses, grassy wa- terways, roadsides), and 4% woody cover (e.g., treelines, wooded drainage ways). We identified 65 discrete units of woody cover on CSA, each measuring on average 1.75 ha Percent coverage of cover types within CSA was sim- ilar to agricultural areas within eastern Lyon County (By- ram 1996). The composition of RSA was 72% native tallgrass pas- ture, 8% hayland, 8% idle grassland, 8% cropland, and 3% woody cover. We identified 28 discrete units of woody cover on RSA, each measuring on average 3.05 ha. As compared to CSA, woody cover units were larger and more fragmented from each other. Percent coverage of cover types within RSA was similar to rangeland areas within the Flint Hills region (Kollmorgan and Simonett 1965), and grazing and burning dominated land use practices (every 1-4 yr). Landowners reported the aver- age annual grazing pressure on RSA was 1 steer/0.81 ha, which was considered overgrazed (Launchbaugh and Owensby 1978, Owensby et al. 1988). To measure relative diurnal raptor species diversity be- tween study areas, we used the Shannon-Wiener diversity index (Zar 1984) on raw observations of species. By using raw observations, we assumed detectability functions were equal across all species and individuals. We used a two- way ANOVA {P < 0.05) to compare diversity indices among years and between study areas. We established a single line transect on roads travers- ing CSA and RSA (Andersen et al. 1985). An assumption of line transect sampling is that the distribution of ob- served species is not influenced by the transect lines (Buckland et al. 1993). We feel any violation of this as- sumption was reduced because roads were generally one lane, unpaved, and had low traffic and telephone and power poles that could influence raptor abundance were present along 50% of the RSA transect and 55% of the CSA transect (Andersen et al. 1985). Transect length was 31.40 km on CSA and 28.94 km on RSA. We ran transect routes every 2 wk between 15 September-31 March 1994—98. With two observation vehicles, each containing two individuals, we sampled each route on the same day starting approximately 1 hr after sunrise. At each sight- ing, we stopped the vehicle at approximately a perpen- dicular angle from where the raptor was first observed perched or flying. We recorded the species, major land use the raptor was occupying, and estimated the distance from car to raptor using rangefinders. We estimated den- sities with five possible detection functions (HNormal Hermite, Uniform Polynomial, HNormal Cosine, Uni- form Cosine, and Hazard Cosine) using program DIS- TANCE (Laake et al. 1993). The best fit detection func- tion and density was chosen by program DISTANCE (P < 0.05). We used repeated measures ANOVA to compare density estimates within and among years within study areas and between study areas. We performed compositional analyses for individual species across all surveys within a given year using log- ratio differences between cover type use and availability (Aebischer et al. 1993). We considered cover type use as the percent of all cover types a species was observed oc- cupying. We considered cover type availability as the per- cent of all cover types within the study area boundaries. We defined cover type “selection” as the difference be- tween cover type use and availability. We first tested whether all cover type selection was random using Wilk’s lambda statistic (P^ 0.05). We then used 1-sample Kests to rank the selection of cover types (Aebischer et al. 1993). If cover type selection occurred significantly great- er than random, we defined the cover type as “pre- ferred.” If cover type selection occurred significantly less than random, we defined the cover type as “avoided.” To compare relative cover type selection between study areas among years, we used 2-way ANOVA. Results Species diversity indices did not differ among years within study areas (i^s ^s ~ 1.51, P = 0.22) or between study areas (Pyes ~ 3.04, P = 0.09) (Table 1). Due to low sample sizes (mean N < 10 per year) , we only estimated density and cover type se- lection for Red-tailed Hawks {Buteo jamaicensis, CSA: mean A = 127, RSA: mean A = 127), North- ern Harriers (Circus cyaneus, CSA: mean N = 36, RSA: mean N — 20) , and American Kestrels (Falco sparverius, CSA: mean N= 18, RSA: mean N — 19). Red-tailed Hawk densities did not differ within and among years in both CSA or RSA (F i q = 2.79, P = 0.15), so data were pooled within each study area. Densities were three times higher on CSA than on RSA (Pi ^ = 14.81, P < 0.01) (Table 2). Habitat use did not differ among years vdthin both study areas (P 3 70 < 142, P > 0.24) and was pooled within study areas. On both study areas, overall cov- Table 1. Number of observed diurnal raptors, by species, and species diversity index across the CSA and RSA, Lyon Co., Kansas, winter 1994-95. September 2000 Kansas Raptor Ecology 205 05 Oi O H 00 03 cA 03 03 I m 03 05 4 o o o O o I o o H O H 00 o U 4 o o o o ^ o ^ 4 o o lO o I,— I010'^1>CC(MO 00 J> GM I-H Tfl ^ CO eo lO C^f OOOoO(Mi>cOOOO 00 J> ^^OOi>^^^oOOOO lO^’^O'TSr— 1| — I OOOOi-HOOi— iC^OOOC^f yo CM COO'— iMOOCM^SMCyOO O ^ r— I m.-HoocDOOccf®coo 00 C^J I-H OCM000300-^iO)000 00 (M 4> O J> ^ ^ OO C^l 03 03 CM 00 OO CO O GO 00 o ^ o 00 xn ^ O VO OO o o o T— I T— I T— I ^0 0> 05 CM O O 1-H ■of' 1> 00 CD 00 o m o ■-H J> CM J> 03 I— I 03 (M 00 03 t-H 0> J> CD J> CM OO O o d 03 ^ OO o d d 00 J> o t- OO o d d VO i> 00 m GO q d d 00 CD O CO ^ q d d i> o O CM OO O d d 1> CM o ^ OO O d d CM O d d 00 t-h CO OO O d d O VO VO OO GO O d d Table 2. Winter density estimations of Red-tailed Hawks, Northern Harriers, and American Kestrels in cropland and rangeland study areas, Lyon Co., Kansas, winter 1994-98. Detection functions (Det. Tunc.) are reported as HC (Hazard Cosine), HNC (Hnormal Cosine), UP (Uniform Polynomial), HNH (HnormalHermite), or UC (Uniform Cosine). VoL. 34, No. 3 206 Williams et al. H Func. u u u u U U PJ Q K X X K X X , ^ , ^ ^ Cl CO 00 rH IC W CD CM CM rH q (/) CD d d d d I-H — ' Hr- — ' ■ — ' CM s CM Cl CD 50 C<5 Cl q 00 q eo d d d CM CM IT) CD 0 CM J> CO rH CM CM rH rH CM H Func. u U u fP u u u Q X X X D X G^r rH CM CM 00 01 w csr d rH d rH d 00 d 1 -H P 1 'r.— ^ (M CTi s CM J> 0 0 0 m M Cl CD CO 00 CO 00 TJH d d d CM 10 cO 0 CM J> 00 t-H CM CM rH I — 1 CM H U 0 U U Ph Clh IP W Q L K P P P , , . ^ . ^ , — . 00 CO M> lO Cl w c/5 q CO d CO d 0 d 00 d T d ci 01 ' — ' ' — ' ' — ' CM Cl g CM 00 M> I-H q q CM 00 d rH d 1 -H d 0 Cl i> CO rH CM I-H d u M z u U U U U Q p Ph X P P 0 1 -H rH CO 1 M> in 00 CD 00 00 Cl 1 C/D rH d d d d ci iC — ■ — ■ '' — ^ ' — ■ ^ ^ Cl CM g Cl m 1 T 5 00 m:^ CM 00 tC 50 q q CO d !-H rH rH P CO 00 iD lO CO rH CM rH rH d u z u u u z u u Q p Ph X X d: K X p ^ ^ ^ ^ Ifl Cl 4 . — ' CTl 00 c. w Cl 50 0 0 d d d d d '• — ^ '•-r' '■ — ' — ' Cl CM Cl s Cl 0 TfH i> 00 Cl 00 1— H tn 1 CM 00 1 -H CO a ‘C X d m d 00 a; b (yi lO ^H rH 00 < 0 rH G ■TtH G cd CM > p < % X u 'C Li tj C w u < < < H C /5 < Pi c/5 u 0 z CZJ U C /5 Pi 1 c/5 P er type selection departed from random selection (CSA: A < 0.53, > 44.00, P < 0.01). On CSA, Red-tailed Hawks preferred idle grassland and woody cover (^40 > 2.33, P < 0.03) while avoiding hayland, cropland, and pasture (^40 > 3.81, P < 0.01) (Fig. 1). On RSA, they used pasture equally with availability (/gg = 1.95, P — 0.06), preferred woody cover (^g = 12.48, P < 0.01), and avoided pasture, hayland, and cropland > 3.91, P < 0.01) (Fig. 1). We found Red-tailed Hawks selected hayland and cropland equally between CSA and RSA (F) 70 < 0.47, P > 0.50). However, they selected pasture and woody cover less on RSA than CSA (i^i 70 ^ 5.48, P < 0.02) while they selected idle grassland more on RSA than CSA (i^s ^o = 28.34, P < 0.01). Northern Harrier densities did not differ within or among years in both CSA or RSA (F\ g = 0.62, P = 0.46) , so data were pooled within study areas. Densities were twice as high on CSA than on RSA (F\ g = 4.22, P - 0.09) (Table 2). Habitat use did not differ among years in either study area (7% gg < 1.53, P > 0.22) and was pooled within study ar- eas. On CSA overall cover type selection did not depart from random selection (CSA: A = 0.96, x ^4 = 8.26, P < 0.08) whereas selection on RSA did (RSA: A = 0.73, x\ = 12.87, P < 0.01). On RSA, Northern Harriers used idle grassland equally with its availability (^g = 1.00, P = 0.32) while avoiding woody cover and hayland (% > 2.86, P < 0.01) and preferring pasture and cropland (^g > 2.58, P < 0.02) (Fig. 1). We found Northern Harriers selected hayland, idle grassland, woody cover, and cropland equally between CSA and RSA (F'l gg < 3.45, P > 0.07). However, they selected pasture more on RSA than CSA (Fi,58 = 9.17, P< 0.01). American Kestrel densities did not differ within or among years in both CSA or RSA (F^ g = 1.90, P — 0.22) or between study areas (Fj g = 0.02, P = 0.90) (Table 2). For kestrels on both study areas, habitat use did not differ among years (Fg 4 ^ < 2.71, P > 0.06) and was pooled within study areas. On both study areas, overall cover type selection departed from random selection (A < 0.56, x ^4 > 24.01, P < 0.01, RSA). On CSA, kestrels used idle grassland and cropland equally with their avail- ability (^4 < 1.33, P> 0.20), preferred woody cov- er (^4 = 6.48, P < 0.01), and avoided pasture and hayland (^4 > 3.01, P < 0.01) (Fig. 1). On RSA, they used pasture and cropland equally with their availability (^3 < 1.43, P> 0.17), preferred woody LOG-RATIO COVER TYPE SELECTION VALUE September 2000 Kansas Raptor Ecology 207 RED-TAILED HAWK CROPLAND WOODLAND IDLE GRASSLAND NORTHERN HARRIER IDLE GRASSLAND HAYLAND WOODLAND PASTURE CROPLAND -4 J 6 n 4 2 - 0 -2 - -4 - -6 - PASTURE AMERICAN KESTREL HAYLAND □ CROPLAND STUDY AREA ■ RANGELAND STUDY AREA IDLE GRASSLAND CROPLAND WOODLAND Figure 1. Relative cover type selection given availability (±SE) by Red-tailed Hawks, Northern Harriers, and Amer- ican Kestrels in CSA and RSA, Lyon County, Kansas, 1994-98. Log-ratio cover type selection values above zero indicate relative preference whereas values below zero indicate relative avoidance. 208 Williams et al. VoL. 34, No. 3 cover (^24 = 5.36, P < 0.01), and avoided hayland and idle grassland (^4 > 14.30, P< 0.01) (Fig. 1). We found that American Kestrels selected hay- land, woody cover, and cropland equally between CSA and RSA (F\ 41 < 3.20, P > 0.08). However, they selected pasture more on RSA than CSA (F\ 41 = 23.05, P < 0.01) and they selected idle grassland less on RSA than CSA (Fj 41 = 4.25, P> 0.05) (Fig. 1). Discussion In the four years of our study, we found stable populations of Red-tailed Hawks, Northern Harri- ers, and American Kestrels. While long-term data (1959-88) from Kansas Christmas Bird Counts (Sauer et al. 1996) suggest that Red-tailed Hawk populations have remained stable, they also found Northern Harriers have declined while American Kestrels have increased. Our finding that local densities of Red-tailed Hawks and Northern Harriers were higher on CSA is similar to Fitch et al. (1973) who found higher raptor populations in eastern Kansas (similar to CSA) than in the Flint Hills Region (RSA) between 1950-63. We believe several factors could explain higher raptor densities on CSA including prey abundance, prey visibility, and/or the relative amount of preferred hunting habitat. Relative local prey abundance can affect local raptor densities (Craighead and Craighead 1956, Grant et al. 1991). In a study of Eurasian Kestrels {Falco tinnunculus) in cropland and grassland, Vil- lage (1989) found kestrel numbers were higher and less variable in cropland ecosystems because of the greater diversity of stable prey populations. Both Red-tailed Hawk and Northern Harrier choice of prey includes small- and medium-sized mammals (mainly rodents), reptiles and small- to medium-sized birds (Preston and Beane 1993, MacWhirter and Bildstein 1996). Additionally, both are known to consume Northern Bobwhite {Coli- nus virginianus) (Errington and Breckinridge 1938, Selleck and Glading 1943). Williams (1996) found that Northern Bobwhite densities were significantly higher on the CSA than on the RSA, potentially indicating a larger prey base on CSA, which in turn could promote a higher abundance of raptors. Secondly, raptor densities could have been high- er on CSA because of the increased visibility of prey associated with harvested agriculture fields. Wakeley (1978) and Bechard (1982) found that se- lection of hunting sites by Swainson’s Hawks {Buteo swainsoni) and Ferruginous Hawks {Buteo regalis) was determined more by the presence of prey pro- tective cover than by prey density. Therefore, hawks were present in habitat, such as harvested agriculture, where prey was more vulnerable. How- ever, Preston (1990) and Bildstein (1987) found Red-tailed Hawks and Northern Harriers tended to avoid harvested agriculture and Preston (1990) noted this might be due to lower prey densities in these patches. Because our findings that raptors avoided harvested agriculture generally support Preston (1990) and Bildstein (1987), we question whether this hypothesis could explain higher den- sities on CSA. Alternatively, Newton (1979) suggested the shortage of perching sites influence winter raptor density. Relative abundance of perching trees next to open hunting areas have been found to be an important regulating factor for both Red-tailed Hawks and Northern Harriers (Preston and Beane 1993, MacWhirter and Bildstein 1996). Research in Kansas by Cox (1976) and by us indicated the use of woody cover is important habitat for Red-tailed Hawks and Northern Harriers. We believe it is pos- sible that a larger availability of potential hunting areas, associated with woody cover, could have pro- moted higher densities on CSA. The abundance of prey and the availability of suitable habitat for roosting and perching affect raptor populations. Consequently, landuse practic- es can have an impact on raptors. Our results only indicate relationships on our study areas. However, we encourage managers to consider these relation- ships and address whether they could apply to oth- er agricultural and rangeland systems. Acknowledgments We thank G. Horak, J. Stephen, R. Powers, M. Paradise, K. Church, C. Roy, and A. Schleicher for assisting with counts; and J.R. Cary and M.L. Williams who provided data analysis advice. The Kansas Department of Wildlife and Parks, Federal Aid Project No. W-39-R, Wisconsin Co- operative Wildlife Research Unit, the University of Wis- consin, Emporia Area Chapter of Quail Unlimited, and the Max McGraw Foundation helped fund this research. Literature Cited Aebischer, N.J., P.A. Robertson and R.E. Kenward. 1993. Compositional analysis of habitat use from ani- mal radio-tracking data. Ecology 74:1313-1325. American Ornithologists’ Union. 1998. Check-list of North American birds, 7th ed. Am. Orinthol. Union, Washington, DC U.S.A. Andersen, D.E., O.J. Rongstad, and W.R. Mytton. 1985. September 2000 Kansas Raptor Ecology 209 Line transect analysis of raptor abundance along roads. Wildl. Soc. Bull. 13:533-539. Ardia, D.R. and K.L. Bildstein. 1997. Sex-related differ- ences in habitat selection in wintering American kes- trels, Falco sparverius. Anim. Behav. 53:1305-1311. Bechard, M.J. 1982. Effect of vegetative cover on forag- ing site selection by Swainson’s Hawk. Conrfor 84: 153- 159. Bildstein, K.L. 1987. Behavioral ecology of Red-tailed Hawks (Buteo jamaicensis) , Rough-legged Hawks (Buteo lagopus). Northern Harriers {Circus cyaneus), and American Kestrels {Falco sparverius) in south central Ohio. Ohio Biol. Surv. Biol. Notes 18. Bohall, RG. and M.W. Collopy. 1984. Seasonal abun- dance, habitat use, and perch sites of four raptor spe- cies in north-central Florida. I. Field. Ornithol. 55:181- 189. Buckland, S.T., D.R. Anderson, K.R Burnham, and J.L. Laake. 1993. Distance sampling: estimating abun- dance of biological populations. Chapman and Hall, London, U.K. Byram, T.S. 1996. Kansas farm facts. Kansas Dep. Agric. Topeka, KS U.S.A. Collopy, M.W. 1973. Predatory efficiency of American Kestrels wintering in northwestern California. Raptor Res. 7:25-31. AND K.L. Bildstein. 1987. Foraging behavior of Northern Harriers wintering in southeastern salt and freshwater marshes. Auk 104:11-16. Cox, J.A. 1976. Winter ecology of hawks in eastern Kan- sas. M.S. thesis, Univ. Kansas, Lawrence, KS U.S.A. Craighead, JJ- and F.C. Craighead, Jr. 1956. Hawks, owls, and wildlife. Stackpole, New York, NY U.S.A. Errington, RL. and WJ. Breckinridge. 1938. Food hab- its of buteo hawks in north-central United States. Wil- son Bull. 50:113-121. Fitch, H.S., H.A. Stephans, and R.O. Bare. 1973. Road counts of hawks in Kansas. Bull. Kans. Ornithol. Soc. 24:33-35. Fuller, M.R., CJ. Henny, and RB. Wood. 1995. Raptors. In E.T. LaRoe, G.S. Farris, C.E. Puckett, P.D. Doran, and M.J. Mac [Eds.], Our living resources: a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. U.S. Dep. In- ter., Natl. Biol. Serv., Washington, DC U.S.A. Grant, C.V., B.B. Steele, and R.L. Bayn, Jr. 1991. Raptor population dynamics in Utah’s Uinta Basin: the im- portance of food resource. Southwest. Nat. 36:265—280. Johnsgard, RA. 1990. Hawks, eagles, and falcons of North America. Smithsonian Institution Press, Wash- ington, DC U.S.A. Kollmorgan, W.M. and D.S. Simonett. 1965. Grazing operations in the Flint Hills — bluestem pastures of Chase County, Kansas. Ann. Assoc. Am. Geog. 55:260— 290. Laake, J.L., S.T. Buckland, D.R. Anderson, and KP Burnham. 1993. DISTANCE user’s guide V2.0. Colo- rado Coop. Fish Wildl. Res. Unit, Colorado State Univ., Fort Collins, CO U.S.A. Launchbaugh, J.L. and C.E. Owensby. 1978. Kansas rangelands — their management based on a half cen- tury of research. Kansas Agric. Exp. Station Bull. 622. Manhattan, KS U.S.A. MacWhirter, R.B. and K.L. Bildstein. 1996. Northern Harrier {Circus cyaneus). In A. Poole and F. Gill [Eds ] , The birds of North America, No. 210. The Academy of Natural Sciences, Philadelphia, PA, and The Amer- ican Ornithologists’ Union, Washington, DC U.S.A. Newton, I. 1979. Population ecology of raptors. Buteo Books, Vermillion, SD U.S.A. Owensby, C.E., R. Cochran, and E.F. Smith. 1988. Stock- ing rate effects on intensive-early stocked Flint Hills bluestem range, y. Range Manage. 41:483—487. Preston, C.R. 1990. Distribution of raptor foraging in relation to prey biomass and habitat structure. Condor 92:107-112. AND R.D. Beane. 1993. Red-tailed Hawk {Buteo ja- maicensis). In A. Poole and F. Gill [Eds.], The birds of North America, No. 52. The Academy of Natural Sci- ences, Philadelphia, PA and The American Ornithol- ogists’ Union, Washington, DC U.S.A. Sauer, J.R., S. Schwartz, and B. Hoover. 1996. The Christmas Bird Count home page. Version 95.1. Pa- tuxent Wildlife Research Center, Laurel, MD U.S.A. Selleck, D.M. and B. Glading. 1943. Food habits of nest- ing Barn Owls and marsh hawks at Dune Lakes, Cal- ifornia, as determined by the “cage nest’’ method Calif. Fish Game 20:122-131. Temeles, E.J. and T.I, Wellicome. 1992. Weather-depen- dent kleptoparasitism and aggression in a raptor guild. Auk 109:920-923. Village, A. 1989. Factors limiting European kestrel Falco tinnunculus numbers in different habitats. In B.-U. Meyburg and R.D. Chancellor [Eds.], Raptors in the modern world. World Working Group of Birds of Prey and Owls, Berlin, Germany. Wakeley, J.S. 1978. Factors affecting the use of hunting sites by Ferruginous Hawks. Condor 80:327-333. Williams, C.K. 1996. Winter ecology of the northern bobwhite in Kansas cropland and rangeland ecosys- tems. M.S. thesis, Univ. Wisconsin, Madison, WI U.S.A. Zar, J.H. 1984. Biostatistical analysis. Prentice Hall. En- glewood Cliffs, NJ U.S. A. Received 30 October 1999; accepted 22 May 2000 J. Raptor Res. 34(3):210-231 © 2000 The Raptor Research Foundation, Inc. A REVIEW AND CHECKLIST OF THE PARASITIC MITES (ACARINA) OF THE FALCONIFORMES AND STRIGIFORMES James R. Philips Math/ Science Division, Babson College, Babson Park, MA 02457-0310 U.S.A. Abstract. — Referenced checklists are provided of the 86 species of parasitic feather, quill, respiratory, skin, and nest mites (Acarina) that are known from 116 species of hawks, eagles, falcons, and vultures, and the 91 species of parasitic mites known from 51 species of owls. Key Words: Falconiformey, Strigiformes', falconsr, hawks-, eagles-, vultures-, owls; parasites-, mites-, Acarina. Un resumen y listado de piojos (Acarina) en Falconiformes y Strigiformes Resumen. — Se provee un listado referenciado de 86 especies de piojos (Acarina) en plumas, quilla, aparato respiratorio, piel y nidos conocidos a partir de 116 especies de gavilanes, aguilas, halcones, y buitres y de 91 especies de piojos conocidos a partir de 51 especies de buhos. [Traduccion de Cesar Marquez] This review summarizes our current knowledge of the host-parasite relationships between parasitic mites and members of the Falconiformes and Stri- giformes (Appendices 1 and 2). Over the years, there have been many taxonomic name changes within birds and especially mites, so my review up- dates old host records to current nomenclature, as well as indicating accidental or misidentified re- cords that should not be regarded as very signifi- cant. Nonparasitic nest mites and parasitic mites from prey occur accidentally on raptors, and birds in captivity or specimen bags may pick up mites from other species as well. My review also includes records of some new species, as yet undescribed, which I have found through necropsies of raptors. There are 21 families of mites that are associated with falconiforms and 17 families associated with owls. Mites inhabit birds’ feathers, quills, skin and subcutaneous tissues, respiratory tracts, and nests, and feed on blood, tissue fluid, skin and feather lipids and debris, keratin, fungi, algae, and other mites (Philips 1990, 1993). The mite fauna of most falconiform and strigiform species is completely unknown, but these raptors can host a diverse mite community with as many as eight mite species known from the Black Kite {Milvus migrans) and 18 species known from the Long-eared Owl {Asio otus). Since mites are so small (0.3-1. 5 mm long), they are often overlooked, but raptors that appear parasite-free to the eye can support populations of 15 000 feather mites and 4000 quill mites. Fortu- nately, most mites on raptors are not very patho- genic and feather mites in particular are usually more commensal, rarely causing harm unless they become extremely abundant. Feather Mites. There are seven families of fal- coniform feather mites: Analgidae (Ancyralges) , Av- enzoariidae (Bonnetella) , Cheylabididae (Cheylabis, Hemicheylabis) , Gabuciniidae {Aetacarus, Aposoleni- dia, Hieracolichus, Ramogabucinia) , Kramerellidae {Pseudogahucinia) , Pterolichidae (Pseudalloptinus ) , and Xolalgidae {Analloptes, DuHninia). Ancyralges occurs only on vultures and Bonnetella occurs only on Ospreys {Pandion haliaetus) . Only a few individ- uals of Ancyralges have been collected, but over 300 Bonnetella have been found on an Osprey (Miller et al. 1997). The cheylabidid, gabuciniid, and pter- olichid genera which occur on raptors do not oc- cur on other orders of birds, except for Aetacarus which includes two species associated with the Oti- didae. In these genera, species range from monox- enous to polyxenous. Pseudogahucinia, Analloptes, and Dubininia are found on several orders of birds but their falconiform species are restricted to this order. Aetacarus, Hieracolichus, Pseudalloptinus, and Pseudogahucinia live on the wings, especially the pri- maries and upper primary wing coverts. Over 15 000 Pseudalloptinus have been found on a single Bald Eagle {Haliaeetus leucocephalus) . Feather mites feed on feather fragments, lipids secretions, skin debris, and feather fungi, bacteria, and algae. The diet of Aetacarus and Pseudalloptinus includes fresh- 210 September 2000 Parasitic Mites oe Raptors 211 water diatoms which stick to feathers when birds are in water (Dubinin 1956). In great numbers, feather mites irritate the host with damage result- ing from the bird’s stress and feather pulling. Vas- yukova and Labutin (1990) found that feather mites occurred on 22% of falconiform birds and 77% of owls in Yakutia. There are three families of owl feather mites: Kramerellidae {Dermonoton, Kramerella, and Petito- ta), Psoroptoididae (Pandalura), and Xolalgidae ( Glaucalges) . These genera only occur on owls with the exception of one species of Glaucalges which occurs on Musophagidae. Kramerella species are very host specific, occupy primarily wing feathers, and are often very numerous (thousands) on an individual. Philips (1993) photographed Great Horned Owl {Bubo virginianus) alula feathers with Kramerella infestations. Kramerella is very common on owls and was found on 86% of Eurasian Pygmy- Owls (Glauddium passerinum) in Thuringia (Cerny and Wiesner 1992). Petitota, Pandalura, and Glau- calges species are more polyxenous and typically oc- cur in smaller numbers on a host (Atyeo and Phil- ips 1984) . Dermonoton also is more polyxenous but population data are lacking. QuiU Mites. There are two families of falconi- form quill mites: Ascouracaridae (Pyonacarus) and Syringophilidae {Peristerophila, undescribed gen- era) . Ascouracarid mites occur on seven orders of birds but Pyonacarus is known only from the Black Rite (Milvus migrans) . These mites eat the medulla of quills. Syringophilid mites use their mouthparts to pierce the quill wall and feed on tissue fluid from the feather follicle. Feather loss and second- ary bacterial infection can result. Each genus of Syringophilidae is primarily or exclusively associ- ated with a particular order of birds. Peristerophila is a columbiform mite and P. columbae is known from pigeons ( Columba livid) and its occurrence on a Red-tailed Hawk {Buteo jamaicensis) (Casto 1976) is unusual and may be accidental. I have found a new genus of syringophilid mite that occurs on five North American accipitrid birds. Trunk and scap- ular feathers are preferred by falconiform syrin- gophilid mites. There are three families of owl quill mites: Der- moglyphidae (Paralges) , Oconnoriidae ( Oconnoria ) , and Syringophilidae (Bubophilus) . Dermoglyphid mites can cause extensive mange because owls use their beaks to dig them out. Paralges occurs on several orders of birds, but the undescribed species from owls (Philips 1993) have not been found on other orders. In owls, Paralges colonizes the upper and un- der trunk feathers but populations over 10 have not yet been found on an individual owl. The family Oconnoriidae is known only firom the Philippine Boobook Owl {Ninox philippensis) and probably eats the medulla of quills (Gaud et al. 1989). The syrin- gophilid genus Bubophilus is known only from the Great Horned Owl (Philips and Norton 1978). Two thousand Bubophilus have been found on one bird, inhabiting mainly axillary and nearby wing feathers. Infestations of Great Horned Owl quills with Paralges and Bubophilus were photographically documented by Philips (1993). Skin Mites. Skin mites of falconiform birds which live on the skin surface or burrow into the skin include the families Cheyletiellidae, Epider- moptidae {Microlichus and Myialges), Harpyrhynchi- dae (Harpyrhynchus) , and Knemidocoptidae {Knem- idocoptes). Cheyletiellid mites feed on blood and tissue fluid, and most species are associated with a particular family of birds. Microlichus and Myialges are also associated with louseflies (Hippoboscidae) and are more fly specific. Their bird host range tends to correspond to that of their fly host. Fer- tilized Myialges females parasitize louseflies and lay their eggs on them, but the other stages of the life cycle are bird parasites. Microlichus is phoretic on louseflies and uses them only for a ride to another bird host. Microlichus lives in feather bulbs, pro- ducing congestion and swelling. These skin mites feed on surface skin debris, keratin, and tissue fluid. Skin mites of owls which live on the skin surface or burrow into the skin include the families Anal- gidae (Strelkoviacarus) , Epidermoptidae {Microli- chus, Myialges, Passeroptes) , Harpyrhynchidae {Har- pyrhynchus), and Knemidocoptidae {Knemidocoptes) . Strelkoviacarus, like Microlichus, is phoretic on louse- flies with a broad avian host range. Passeroptes oc- curs on Passeriformes and Columbiformes as well as owls, but individual species are restricted to one order of bird host. Harpyrhynchid and knemidocoptid mites bur- row into the skin, causing itching and mange. Har- pyrhynchid mite species usually have only one avi- an host species and occur on the calamus at the skin surface and in subcutaneous cysts. Schulz (1990) photographically documented feather loss on the head and neck of a Golden Eagle {Aquila chrysaetos) caused by harpyrhynchid mites. This pa- thology has not been observed in owls. Philips (1993) photographed a harpyrhynchid embedded 212 Philips VoL. 34, No. 3 in the skin of a Boreal Owl (Aegolius funereus) . Most knemidocoptid mite species are polyxenous within an order of birds, but those found on owls also occur on other bird orders. Knemidocoptid mites live in the stratum corneum of the skin, causing hyperplasia, hyperkeratosis, and inflammation. They cause «scaly encrustations on the beak and claws, known as scaly face and scaly leg disease. This condition in a Great Horned Owl {Bubo vir- ginianus) was documented photographically by Schulz et al. (1989) and is common in cage birds, but there is only one record of these mites on fal- coniform birds (Cooper 1978, 1985). Transient skin mites of both bird orders include the blood-feeding Dermanyssidae (Dermanyssus) , Macronyssidae (Ornithonyssus) , and Laelapidae {Androlaelaps) , and tissue-fluid feeding Trombi- culidae (chiggers). Falconiform chiggers include Blankaartia, Eutrombicula, Leptotrombidium, Neos- choengastia, Odontacarus, and Ornithogastia, while strigiform chiggers include Blankaartia, Euschoen- gastia, Eutrombicula, Hyponeocula, Leptotrombidium, Miyatrombicula, Neoschoengastia, Odontacarus, Or- nithogastia, and Toritrombicula, Dermanyssid and macronyssid bird parasites lay eggs on the host or in its nest and chiggers are the parasitic larval stage of a predatory soil mite. All four families usually have relatively low host specificity and can cause dermatitis. Too much blood loss results in energy and weight loss, anemia, and potentially death. Ornithonyssus often prefers to feed at the vent. Dermanyssus feeds at night. Dermanyssus on a Sharp-shinned Hawk {Accipiter striatus) was pho- tographed by Philips (1993). Avian Androlaelaps species are facultative blood suckers which also prey on other invertebrates and their eggs, on birds, and in their nests. Bird chiggers usually re- main attached for three to four days at the thighs, anus, or under the wings. Subcutaneous Mites. The Hypoderatidae ( Gypsodec- tes, Neottialges, and Tytodectes on hawks, kestrels, and vultures; Hypodectes, Neottialges, Neotytodectes, and Tyto- dectes on owls) are subcutaneous bird mites as nymphs. Nonfeeding adults lay eggs in birds’ nests. Nymphs colonize nesdings and adults and live on the surface of breast and abdominal muscles, in fat tissue and, occasionally, in respiratory and circulatory tracts. Lacking a mouth, nutrients are absorbed through the skin. Significant pathological effects from these mites remain unproven, however. Most species of hypoderatid mites have limited host rang- es, but a significant number of unusual one-time host records suggests temporarily successful colonization of other bird hosts in nesting proximity is not un- common (Pence et al. 1997) . This appears to be the case with the record of Hypodectes propus from the Burrowing Owl {Speotyto cunicularia) and Neottialges evansi from the Barn Owl (Tyto alba). H. propus is associated with pigeons, herons, and egrets and N. evansi is a cormorant mite. Gypsodectes is known only from vultures; Neotytodectes is known only from owls. Neottialges is known from four orders of birds, but the species on falconiform birds are monoxenous. Tyto- dectes occurs on owls, falcons, and kingfishers and each species occurs on only one host genus. Several infestations in the Barn Owl were photographically documented by Wurst and Havelka (1997). Respiratory Mites. Respiratory mites of falconi- form birds include the families Ereynetidae {Boy- daia, Speleognathopsis) , Rhinonyssidae (Falconyssus, Ptilonyssus, Tinaminyssus) , and Turbinoptidae {Schoutedenocoptes) . Ereynetid mites feed on mu- cous deep in the nasal cavity and nonpasserine er- eynetid mites are monoxenous or parasitize very few host species. Molted ereynetid mite skins can partially block the nasal cavity. Rhinonyssid mites feed on blood and occupy the anterior portion of the nasal cavity, usually in very small numbers. Each species of these rhinonyssid genera usually has only one or several host species. The genus Falconyssus occurs on falconiform and alcedinid birds, while Ptilonyssus and Tinaminyssus occur on many types of birds. Turbinoptid mites live in the external part of the nares and feed on the corne- ous skin there. Most turbinoptid species are mo- noxenous or restricted to one family of birds. Respiratory mites of owls include the families Cloacaridae {Pneumophagus) , Ereynetidae {Astrida, Aureliania, Neoboydaia) , and Rhinonyssidae {Rhin- oecius, Sternostoma) . The Cloacaridae is primarily a family of turtle cloaca mites. One genus is a sub- cutaneous small mammal parasite and one genus is an owl parasite. Pneumophagus is known only from two dozen individuals from the trachea and bronchi of a Great Horned Owl in Michigan (Fain and Smiley 1989). Among the ereynetid mites, Au- reliania is known only from Barn Owls ( Tyto alba ) , Astrida is known from owls and Caprimulgiformes, and Neoboydaia is known from several orders of birds. Rhinoecius is restricted to owls, each species parasitizing one or several owl species. Philips (1993) photographed Rhinoecius in the nasal cavity of a Boreal Owl. The genus Sternostoma parasitizes many bird orders but most species are restricted to September 2000 Parasitic Mites of Raptors 213 one or several host species. Sternostoma tracheacol- um, the canary lung mite, parasitizes passerines and parrots, infiltrating the lung sacs and causing mortality, but the other species remain in the nares and seem to do minimal damage to their hosts. Fleay (1968) suggested that ILytodites nudus (the air sac mite, Kytoditidae) may occur in Ninox strenua, based on a report by a veterinarian who suspected its presence, but did not find it. This mite feeds on serous secretions in the air sacs of chickens and turkeys and has not been found in owls. Acknowledgments Funding for this project was provided in part by the Babson College Board of Research. Most of the new host records resulted from my research while Visiting Scientist at The Raptor Center of the University of Minnesota, and I am extremely grateful to G. Duke, R Redig, M. Martell, D. Rose, W. Crawford, and all the other individuals who assisted me while I was there. David Ellis contributed some valuable literature. Literature Cited Amaral, V, 1962. Sternostoma augei n, sp. (Acarina: Rhi- nonyssidae Vitz., 1935) and the identification of the species Rhinoecius bisetosus Strandtmann, 1952 and Rkinoecius grandis Strandtmann, 1952. Arq. Inst. Biol. 29:69-81. Anonymous. 1963. 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Some problems of evolution of the rhinonyssid mites. First International Congress of Parasitology. Nauka: 1—7. (In Russian). . 1965. A new species of parasitic mite of the genus Rhinoecius Cooreman (Mesostigmata: Rhinonyssidae) . Entomol. Rev. 44:116-117. Brennan, J.M. and E.K. Jones. 1960. Chiggers of Trini- dad, B.W.I. (Acarina: Trombiculidae) . Acarologia 2: 493-540. AND C.E. Yunker. 1966. The chiggers of Panama. Pages 221-226 in R.L. Wenzel and V.J. Tipton. [Eds.], Ectoparasites of Panama. Field Mus. Nat. Hist., Chi- cago, IL U.S.A. Buchholz, R. 1869. Bermerkungen uber die Arten der Gattung Dermaleichus Koch. Dresden, Germany. Bunn, D.S., R.B. Warburton, and R.D.S. Wilson. 1982. The Barn Owl. Buteo Books, Vermillion, SD U.S.A Butenko, O.M. 1971. A summary of the knowledge of the nasal mites of birds of the Okskii Reserve Area Okskii Gosud. Zapov. Tr. 8:204—223. (In Russian). . 1976. New species of rhinonyssid mites (Gama- soidea, Rhinonyssidae), parasitic in owls. Parazitologiya 10:303-309. (In Russian). , K.T. Yurlov and N.M. Stolbov. 1972. Distribu- tion of avian mites of the Family Rhinonyssidae Ga- masoidea on hosts. Pages 370-372 m A.I. Cherepanov [Ed.], Trans-continental connections of migratory birds and their role in the distribution of arboviruses. Publ. House “Nauka,” Novosibirsk, U.S.S.R. Buttiker, W. and V. Cerny. 1974. Phoresie bei Hippo- bosciden (Diptera) von Saugetieren und Vogeln in der Schweiz. Bull. Soc. Entomol. 47:319-326. Canestrini, G. and P. Kramer. 1899. Demodicidae und Sarcoptidae. Das Tierreich 7:1-193. Casto, S.D. 1976. Host records and observations of quill mites (Acarina: Syringophilidae) from Texas birds. Southwest. Entomol. 1:155-160. Cerny, V. 1967. Catalogo de la fauna Cubana — XX — Lista de los Acaros parasites de Aves reportadas de Cuba. Museo “Felipe Poey” de la Academia de Ciencias de Cuba, Trabajos de Divulgacion No. 45. . 1969. The hypopi of hypoderidae (Sarcoptiformes) parasitizing Cuban birds. 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The genus Neoschoen- gastia (Acarinidae: Trombiculidae) in the western Pa- cific area. J. Parasitol. 32:286-322. Wilson, N. 1964. New records and descriptions of Rhi- nonyssidae, mostly from New Guinea (Acarina:Mesos- tigmata). Pac. Insects. 6:357-388. . 1965. New records and descriptions of Rallinyssus from Pacific birds (Acarina: Mesostigmata). Pac. In- sects. 7:623-639. . 1968. Rhinoecius cavannus, a new species of nasal mite from a Thailand owl (Mesostigmata; Rhinonys- sidae). Proc. Entomol. Soc. Wash. 70:143-147. Wink, M., D. Ristow and C. Wink. 1979. Biologie des Eleonorenfalken {Falco eleonorae). 3. Parasitenbefall wahrend der Brutzeit und Jugendentwicklung. J. Or- nithol. 120:94—97. Wrenn, W.J. and R.B. Loomis. 1974. The Euschoengastia radfordi species complex (Acarina: Trombiculidae) from western North America, with descriptions of five new species. Ann. Entomol. Soc. Am. 67:241-256. WURST, E. AND P. Havelka. 1997. Redescription and life history of Tytodectes strigis (Acari: Hypoderatidae), a parasite of the barn owl Tyto alba (Aves; Strigidae). Stuttg. Beitr. Natkd. Ser. A (Biol.) 554:1-39. 218 Philips VoL. 34, No. 3 Zeman, P. and M. Jurik. 1981. A contribution to the knowledge of fauna and ecology of gamasoid mites in cavity nests of birds in Czechoslovakia. Folia Parasitol. 28:265-271. ZuMPT, F. AND P.M. Patterson. 1951. Further notes on laelaptid mites parasitic on vertebrates. A preliminary study to the Ethiopian fauna./. Entomol. Soc, S. Afr. 14: 63-93. AND W.M. Till. 1956. Notes on Haemolaelaps glas- goxvi (Ewing) and related forms in the Ethiopian re- gion with descriptions of nine new species. Acarina: Laelaptidae). Zeit. Parasit. 17:282-291. AND . 1961. Suborder: Mesostigmata. Pages 17-91 in F. Zumpt [Ed.], The arthropod parasites of vertebrates in Africa south of the Sahara (Ethiopian Region). Publ S. Afr. Inst. Medical Res. 9:1-457. Received 30 September 1999; accepted 11 March 2000 Appendix 1. A list of the parasitic mites of the Falconiformes. Raptor Mite Habitat References Family Accipitridae Epidermoptidae® skin Herman 1945 Knemidocoptes sp. skin Cooper 1978, 1985 Shikra {Accipiter badius) Coraciacarus sp.*^ feathers McClure and Ratanaworabhan 1971 Hieracolichus nisi feathers Dubinin 1956 Schoutedenocoptes aquilae nasal cavity Fain 1977 Bicolored Hawk {Accipiter bicol- or) Chestnut-Flanked Sparrowhawk mites^ skin Bequaert 1953, Maa 1969 Aetacarus andrei feathers Gaud 1983b {Accipiter castanilius) Cooper’s Hawk {Accipiter coop- Neonyssus sp.*’ nasal cavity Peters 1936 erii) Syringophilidae n.g. quills Philips, present work Brown Goshawk {Accipiter fascia- Speleognathopsis accipitris nasal cavity Domrow 1969, Domrow 1991 tus) Northern Goshawk {Accipiter mites^ skin Walter 1989 gentilis) Pseudalloptinus aquilinuf’^ feathers Nordberg 1936, Niethammer 1938, Dubinin 1956 Hieracolichus nisi feathers Niethammer 1938, Dubinin 1956 Hieracolichus n. sp. feathers Philips, present work Neottialges vitzthumi subcutaneous Vitzthum 1934, Fain 1967 Ornithonyssus sylviarum skin/ nest Cooper 1978, 1985 Slaty-man tied Sparrowhawk {Ac- mites^ skin Maa 1966 cipiter luteoschistaceus) Black Goshawk {Accipiter melan- Schoutedenocoptes aquilae nasal cavity Fain 1956c, 1957 oleucus) Little Sparrowhawk {Accipiter Aetaecarus andrei feathers Gaud 1983b minullus) Schoutedenocoptes aquilae nasal cavity Fain 1956c, 1957 Eurasian Sparrowhawk {Accipi- mites^ skin Newton 1979, Walter 1989 ter nisus) Cnemidocoptes spp. skin Malley and Whitbread 1996 Dermoglyphus elongatu^ quills Dubinin 1956 Dubinin accipitrina feathers Niethammer 1938 Hieracolichus nisi feathers Canestrini and Kramer 1899, Nie- thammer 1938, Radford 1953, Dubinin 1956, Vasilev 1961, 1962, Shumilo et al. 1973, Mi- ronov 1997 Megninia sp.*" Niethammer 1938 Microlichus avu^ skin Walter 1989 Microlichus sp.^ *’ skin Ash and Hughes 1952 Myialges? sp.'’ skin Ash and Hughes 1952 Myialges uncu^ skin Walter 1989 Ornithonyssus bursa skin/ nest Anon. 1963 Grey Goshawk {Accipiter novae- mites'’ skin Maa 1966, 1969 hollandiae) September 2000 Parasitic Mites of Raptors 219 Appendix 1 . Continued. Raptor Mite Habitat References Ovampo Sparrowhawk (Accipiter Aposolenidia anomogonima feathers Gaud and Atyeo 1974 ovampensis) Schoutedenocoptes aquilae nasal cavity Fain 1956c, 1957 Sharp-shinned Hawk {Accipiter mites^ skin Bequaert 1953, Fain 1965, Maa striatus) Dermanyssus americanus skin/ nest 1969 Philips 1993 Ornithonyssus iheringi skin/ nest Dusbabek and Cerny 1971 Syringophiliae n.g. quills Philips, present work African Goshawk {Accipiter tachi- Aetacarus andrei feathers Gaud 1983b ro) Myialges asturi skin Fain 1965 Myialges falconis skin Fain 1965 Crested Goshawk {Accipiter tri- feather mites feathers Maa and Kuo 1965 virgatus) mites® skin Maa 1966 Besra {Accipiter virgatus) feather mites feathers Maa and Kuo 1965 mites® skin Maa 1966 Hieracolichus nisi feathers Dubinin 1956 Ornithonyssus bursa skin/nest McClure and Ratanaworabhan Golden Eagle {Aquila chrysae- Harpyrhynchus sp. skin 1971 Schulz 1990 tos) Pseudalloptinus aquilinus feathers Trouessart 1884, Lonnfors 1930, Sar copies rupicaprad^ mammals Radford 1953, 1958, Dubinin 1956 Valentin cic and Kusej 1989 Greater Spotted Eagle {Aquila Pseudalloptinus aquilinus feathers Dubinin 1956 clanga) Imperial Eagle {Aquila heliaca) Pseudalloptinus aquilinus feathers Dubinin 1956 Lesser Spotted Eagle {Aquila Pseudalloptinus aquilinus feathers Radford 1953, 1958, Dubinin pomarina) African Tawny-Eagle {Aquila ra- Pseudalloptinus aquilinus feathers 1956 Dubinin 1956 pax) Pyonacarus sp. quills Atyeo pers. comm. Schoutedenocoptes aquilae nasal cavity Fain 1956c, 1957, Gaud and Till Verreaux’s Eagle {Aquila ver- Hieracolichus dobyi feathers 1961 Gaud 1983b reauxii) Wahlberg’s Eagle {Aquila wahl- Hieracolichus dobyi feathers Gaud 1983b bergi) Grey-lined Hawk {Asturina niti- Hemicheylabis praecox feathers Trouessart 1885, Gaud and Atyeo da) African Baza {Aviceda cuculo- Aetacarus avicedae feathers 1984 Gaud 1983b ides) Hieracolichus ostodus feathers Gaud 1983b Pacific Baza {Aviceda subcristata) Tinaminyssus epileus nasal cavity Wilson 1964, 1965 Grasshopper Buzzard {Butastur Schoutedenocoptes aquilae nasal cavity Fain 1956b, 1957 rufipennis) Buteo sp. Blankaartia allei skin/nest Wharton and Fuller 1952 Zone-tailed Hawk {Buteo albono- Eutrombicula alfreddugesf skin/nest Philips 1978 tatus) Augur Buzzard {Buteo augur) Falconyssus buteonis nasal cavity Fain 1956b Common Buzzard {Buteo buteo) Pseudalloptinus aquilinud’’^^ feathers Nordberg 1936, Niethammer Harpyrhynchus tracheatus skin 1938 Fritsch 1954 Hieracolichus nisi feathers Canestrini and Kramer 1899, Rad- Myialges parr^ skin ford 1953, 1958 Biittiker and Cerny 1974 Prostigmata larva® Pseudogabucinia intermedia feathers Biittiker and Cerny 1974 Gaud 1988 220 Philips VoL. 34, No. 3 Appendix 1. Continued. Raptor Mite Habitat References Galapagos Hawk {Buteo galapa- mites^ skin Maa 1969 goensis) Myialges caulotoon^ skin Harmon et al. 1990, Madden and Red- tailed Hawk {Buteo jamai- mites^ skin Harmon 1998 Bequaert 1953, Maa 1969 censis) Aetacarus n. sp. feathers Philips, present work Eutrombicula alfreddugesi skin/ nest Loomis 1956 Harpyrhynchus sp. skin Philips, present work Myialges falconi^ skin Philips and Fain 1991 Peristerophila columbae quills Casto 1976 Schoutedenocoptes aquilae nasal cavity Fain 1956b, 1957 Syringophilidae n.g. quills Philips, present work Red-shouldered Hawk {Buteo li- Haemogamasus reidiiP mammals Redington 1970 neatus) Hieracolichus n. sp. feathers Kurey 1976 Pseudalloptinus sp. feathers Kurey 1976 Roadside Hawk {Buteo magniros- mites^ skin Maa 1969 tris) Myialges bombycillaP skin Philips and Fain 1991 Ptilonyssus souzai nasal cavity Pereira and Castro 1949 Broad-winged Hawk {Buteo pla- Hieracolichus n. sp. feathers Philips, present work typterus) Syringophilidae n.g. quills Philips, present work Ferruginous Hawk {Buteo regal- is) Swainson’s Hawk {Buteo swain- mites Bechard and Schmutz 1995 Hieracolichus sp. feathers Kurey 1976 soni) Great Black-Hawk {Buteogallus mites“ skin Maa 1969 urubitinga) Eutrombicula batatas skin/nest Brennan and Yunker 1966 Short-toed Snake Eagle {Circae- Hieracolichus nisi feathers Canestrini and Kramer 1899, Rad- tus gallicus) Western Marsh-Harrier {Circus Pseudalloptes bisubulatu^ feathers ford 1953, 1958, Dubinin 1956 Dubinin 1956 aeruginosus) Pseudogabucinia intermedia feathers Dubinin 1956 Cinereous Harrier {Circus ciner- Ingrassiinae sp.“ feathers Philips and Fain 1991 eus) Northern Harrier {Circus cy- Pseudogabucinia intermedia feathers Dubinin 1956, Cerny 1967, Kurey aneus) Pallid Harrier {Circus macrou- mites^ skin 1976 Maa 1966 rus) Aetacarus leptotrichus feathers Gaud 1983b Myialges macdonaldf' skin Philips and Fain 1991 Montagu’s Harrier {Circus py- Hieracolichus nisi feathers Canestrini and Kramer 1899, Nie- gargus) Pseudogabucinia intermedia feathers thammer 1938, Radford 1953 Dubinin 1956 Swallow-tailed Kite {Elanoides Aetacarus sp. feathers Meyer 1995 forficatus) Macrocheles sp.’’ litter/ nest Meyer 1995 Ornithonyssus bursa skin/ nest Meyer 1995 Black-winged Kite {Elanus ca- Cheylabis latus feathers Gaud and Atyeo 1984 eruleus) Falconyssus elani nasal cavity Fain 1966a Neottialges elani subcutaneous Fain 1969 Australian Black-shouldered Cheylabis latus feathers Gaud 1983a Kite {Elanus notatus) Odontacarus australiensis skin/ nest Domrow 1966, 1991 Ornithonyssus bursa skin/ nest Domrow 1966 Palm-nut Vulture ( Gypohierax mites^ skin Maa 1966 angolensis) Aetacarus hyalothrix feathers Gaud and Mouchet 1959b, Gaud Hieracolichus orthochaetus feathers and Till 1961, Gaud 1983b Gaud and Mouchet 1959b, Gaud Myialges n. sp.® skin 1983b Philips and Fain 1991 Pseudalloptinus afncanus feathers Gaud 1988 Pseudalloptinus odontopus feathers Gaud and Till 1961, Gaud 1988 September 2000 Parasitic Mites of Raptors 221 Appendix 1. Condnued. Raptor Mite Habitat References White-backed Vulture ( Oyps af- Ancyralges cometus feathers Gaud 1966, 1988 ricanus) Hemicheylabis sikyonemus feathers Gaud 1988 Hieracolichus africanus feathers Guad and Mouchet 1959b, Gaud Cape Griffon {Gyps coprotheres) Gypsodectes verrucosus subcutaneous and Till 1961, Gaud 1983b Fain 1984 Androlaelaps patersoni skin/ nest Zumpt and Till 1956, Till 1963 Ramogabucinia doleosikya feathers Gaud and Atyeo 1974, Gaud Eurasian Griffon {Gyps fulvus) Gypsodectes vulturis subcutaneous 1983b Dubinin 1953, 1956, Fain 1967 Haliaeetus sp. Pseudalloptinus aquilinus feathers Radford 1953, 1958 White-tailed Eagle {Haliaeetus Aetacarus phylloproctus feathers Dubinin 1956 albidlla) Megninia picimajorif’ Niethammer 1938 Pseudalloptinus aquilinus feathers Dubinin 1956, Vasilev 1961 Pterolichus obtusuS feathers Niethammer 1938 Bald Eagle {Haliaeetus leucoce- Analgesidae*’ Spencer 1941 phalus) Pseudalloptinus aquilinus feathers Dubinin 1956, Vasilev 1961 Syringophilidae n.g. quills Philips, present work White-bellied Fish-Eagle {Hal- Aetacarus phylloproctus feathers Canestrini and Kramer 1899, ioeetus leucogaster) Pseudalloptinus odontopus feathers Gaud and Petitot 1948b, Rad- ford 1953, 1958, Gaud and Atyeo 1974 Gaud and Till 1961, Gaud 1988 Pallas’s Sea-Eagle {Haliaeetus Aetacarus phylloproctus feathers Dubinin 1956 leucoryphus) Pseudalloptinus aquilinus feathers Dubinin 1956, Vasilev 1961 Pseudalloptinus odontopus feathers Gaud and Till 1961, Gaud 1988 Steller’s Sea-Eagle {Haliaeetus Aetacarus phylloproctus feathers Dubinin 1956 pelagicus) Pseudalloptinus aquilinus feathers Dubinin 1956, Vasilev 1961 Solomon Fish-Eagle {Haliaeetus Ornithogastia riversi skin/ nest Wharton and Hardcastle 1946, sanfordi) Pseudalloptinus odontopus feathers Goff 1979 Gaud and Till 1961, Gaud 1988 African Fish-Eagle {Haliaeetus Aetacarus puylaerti feathers Gaud 1983b vocifer) Hemifreyana marginatcP feathers Gaud and Till 1961 Hieracolichus dobyi feathers Gaud and Mouchet 1959b Pseudalloptinus aquilinus feathers Gaud 1988 Madagascar Fish-Eagle {Haliaee- Aetacarus sp. feathers Atyeo pers. comm. tus vociferoides) Brahminy Kite {Haliastur indus) Aetacarus haliasturi feathers Megnin and Trouessart 1884d, mites^ skin Radford 1953, 1958, Dubinin 1956 Maa 1969 Pseudalloptinus milvulinus feathers Radford 1953, 1958, Dubinin Harpy Eagle {Harpia harpyja) Hieracolichus hirundo feathers 1956 Radford 1953, 1958 Solitary Eagle {Harpyhaliaetus Temnalges sp.^-'’ feathers Philips and Fain 1991 solitarius) Ayres’s Hawk-Eagle {Hieraaetus Aetacarus eurychaetus feathers Gaud and Mouchet 1959b, Gaud ayresii) Hieracolichus orthochaetus feathers and Till 1961, Gaud 1983b Gaud and Till 1961 Bonelli’s Eagle {Hieraaetus fas- Pseudalloptinus aquilinus feathers Gaud 1983b ciatus) Booted Eagle {Hieraaetus penna- hypopus mites skin Hamer ton 1941 tus) Pseudalloptinus aquilinus feathers Dubinin 1956 Grey-headed Fish-Eagle {Ichthy- Aetacarus phylloproctus feathers Radford 1958 ophaga ichthyaetus) Mississippi Ktie {Ictinia mississip- Aetacarus sp. feathers Kurey 1976 piensis) 222 Philips VoL. 34, No. 3 Appendix 1 . Continued. Raptor Mite Habitat References Lizard Buzzard (Kaupifalco mon- Aetacarus andrei feathers Gaud 1983b ogrammicus) Myialges anchored skin Fain 1965 Schoutedenocoptes aquilae nasal cavity Fain 1959a White Hawk (Leucopternis albi- Temnalges sp.^’^ feathers Philips and Fain 1991 collis) Long-crested Eagle (Lophaetus Falconyssus buteonis nasal cavity Fain 1956b occipitalis) Pseudalloptinus milvulinus feathers Gaud and Till 1961, Gaud 1988 Pseudogabudnia intermedia feathers Gaud 1988 Bat Hawk {Macheiramphus aid- mites^ skin Maa 1966 nus) Myialges macdonald^ skin Philips and Fain 1991 Gabar Goshawk {Melierax gabar) Schoutedenocoptes aquilae nasal cavity Fain 1956b, 1957 Dark Chanting-Goshawk (Meli- Aposolenidia anomogonima feathers Gaud and Atyeo 1974 erax metabates) Black Kite (Milvus migrans) Hemicheylabis sp. feathers Atyeo pers. comm. Aetacarus hyalothrix feathers Gaud and Mouchet 1959b, Gaud and Till 1961 Aetacarus milvi feathers Gaud 1983b, D’ Souza et al. 1986 Hieracolichus nisi feathers Dubinin 1956 Pseudalloptinus milvulinus feathers Dubinin 1956 Pyonacarus polysarcus feathers Gaud and Atyeo 1976, Gaud 1988 Schoutedenocoptes aquilae feathers Fain 1956b, 1957 Tinaminyssus columbae feathers Fain 1957 Red Kite {Milvus milvus) Pseudalloptinus milvulinus feathers Trouessart 1884, Radford 1953, 1958, Dubinin 1956 Hooded Vulture {Necrosyrtes Hemicheylabis sikyonemus feathers Gaud 1988 monachus) Hieracolichus monachi feathers Gaud and Mouchet 1959b, Gaud and Till 1961, Gaud 1983b Pseudalloptinus glossocercus feathers Gaud 1988 Ramogabudnia furdseta feathers Gaud 1983b Osprey {Pandion haliaetus) mites skin Bequaert 1953 Analloptes buettikeri feathers Mironov 1997 Analloptes sp. feathers Gaud and Atyeo 1979, Gaud 1983a, Miller et al. 1997 Bonnetella fusca feathers Buchholz 1869, Canestrini and Kramer 1899, Lonnfors 1930, Niethammer 1938, Spencer 1941, Mrciak and Brander 1967, McClure and Ratanawor- abhari 1971, Kurey 1976, Gaud 1983a, Mironov 1991, 1997, Miller et al. 1997 Myialges caulotoon^ skin Philips and Fain 1991 Harris’ Hawk {Parabuteo uni- Neoschoengastia americana skin/nest Loomis and Crossley 1963 cinctus) Pseudalloptinus sp. feathers Atyeo pers. comm. European Honey-Buzzard {Per- feather mites feathers Maa and Kuo 1965 nis apivorus) Hieracolichus nisi feathers Canestrini and Kramer 1899, Nie- thammer 1938, Radford 1953 Hieracolichus ramosus feathers Gaud and Mouchet 1959b, Gaud and Till 1961, Gaud 1983b African Harrier-Hawk {Polyboro- tdes typus) Hieracolichus similis feathers Gaud and Mouchet 1959b, Gaud and Till 1961, Gaud 1983b Martial Eagle {Polemaetus bellico- Hieracolichus dobyi feathers Gaud 1983b sus) Pseudalloptinus aquilinus feathers White-backed Vulture {Pseudo- Dermanyssus gallinae skin/nest gyps africanus) September 2000 Parasitic Mites oe Raptors 223 Appendix 1. Continued. Raptor Mite Habitat References Snail Kite {Rostrhamus sociabilis) Ornithonyssus bursa skin/ nest Philips et al. 1976, Sykes and For- Crested Serpent-Eagle {Spilornis Comciacarus cucul^ feathers rester 1983, Sykes et al. 1995 Radford 1958 cheela) Changeable Hawk-Eagle {Spi- Coraciacarus sp.’’ feathers McClure and Ratanaworabhan zaetus cirrhatus) Crowned Hawk-Eagle {Stephan- Aetacarus hyalothrix feathers 1971 Gaud and Mouchet 1959b, Gaud oaetus coronatus) Hieracolichus dobyi feathers and Till 1961 Gaud and Mouchet 1959b, Gaud Pseudalloptinus odontopus feathers and Till 1961, Gaud 1983b Gaud and Till 1961, Gaud 1988 Bateleur ( Terathopius ecaudatus) Hieracolichus dobyi feathers Gaud 1983b White-headed Vulture ( Trigono- Hieracolichus monachi feathers Gaud 1983b ceps occipitalis) Long-tailed Hawk ( Urotriorchis Myialges caulotoon^ skin Philips and Fain 1991 macrourus) Pseudogabucinia sp.^* feathers Philips and Fain 1991 Family Cathartidae Turkey Vulture ( Cathartes aura) mites^ skin Bequaert 1953, Maa 1969 Ancyralges sp. feathers Kurey 1976 Hieracolichus sp. feathers Peters 1936, Kurey 1976 Ornithonyssus bursa skin/nest Peters 1936 Ptilonyssus ohioensis nasal cavity Fain and Johnston 1966 Lesser Yellow-headed Vulture Hieracolichus sp. feathers Atyeo pers. comm. {Cathartes burrovianus) Black Vulture ( Coragyps atratus) mites'^ skin Bequaert 1953 Eutromhicula alfreddugesi skin/ nest Wharton and Fuller 1952 Hieracolichus sp. feathers Kurey 1976 HistiogasteA’^ trees Philips and Fain 1991 Ptilonyssus donatoi nasal cavity Pereira and Castro 1949 Sancassania sp.^ ’’ litter/ nest Philips and Fain 1991 Andean Condor ( Vultur gry- Hieracolichus spp. feathers Atyeo pers. comm. phus) Family Falconidae Falco sp. mites^ skin Bequaert 1953, Fain 1965 Ptilonyssus cerchneis nasal cavity Bregetova 1964 Saker/Peregrine hybrids Dermanyssus gallinae skin/nest Malley and Whitbread 1996 Grey Kestrel {Falco ardosiaceus) Pseudalloptes falconis feathers Gaud 1983a Brown Falcon {Falco berigora) Boydaia falconis nasal cavity Domrow 1991 Leptotrombidium nissani skin/nest Domrow and Lester 1985 Ptilonyssus cerchneis nasal cavity Domrow 1965, 1967, 1969 Odontacarus nadchatrami skin/ nest Goff 1979 Lanner Falcon {Falco biarmicus) Pseudalloptes falconis feathers Gaud 1983a Pseudogabucinia microdisccA feathers Gaud 1983a Australian Kestrel {Falco cenchro- Leptotrombidium nissani skin/ nest Domrow 1974, Domrow and Les- ides) Odontacarus australiensis skin/nest ter 1985 Domrow 1966, 1991 Ornithonyssus bursa skin/ nest Domrow 1977 Ornithonyssus sylviarum skin/ nest Domrow 1987 Ptilonyssus cerchneis nasal cavity Domrow 1965, 1967, 1969 Red-necked Falcon {Falco chic- Pseudalloptes falconis feathers Gaud 1983a quera) 224 Philips VoL. 34, No. 3 Appendix 1. Continued. Raptor Mite Habitat References Saker Falcon (Falco chermg) Dermanyssus sp. skin/nest Wheeldon pers. comm. Merlin {Falco columbarius) Dubininia acdpitrina feathers Vasilev 1958, Cerny 1967, Gaud 1980, 1983a Gabuciniidae feathers Kurey 1976 Hieracolichus sp. feathers Gaud 1983a Microlichus avuf^ skin Hill et al. 1967 African Hobby {Falco cuvieri) Boydaia falconis nasal cavity Fain 1956a Eleonora’s Falcon {Falco eleono- Acarina sp. Wink et al. 1979 rae) Kramerella major^ feathers Megnin and Trouessart 1884a Pseudogabucinia intermedia feathers Dubinin 1953, 1956, Radford 1958, Gaud 1983a Lesser Kestrel {Falco naumanni) Dubininia acdpitrina feathers Gaud and Petitot 1948a, Gaud 1958, 1983a Peregrine Falcon {Falco peregri- Aetacarus} sp. feathers Kurey 1976 nus) Glaucalges attenuatu^ Niethammer 1938 Hieracolichus nisi Pandalura stri^sotH^ feathers Dubinin 1956, Cerny 1967, Gaud 1983a Niethammer 1938 Pseudalloptinus sp. feathers Kurey 1976, Gaud 1983a Pseudogabucinia intermedicf feathers Nordberg 1936, Niethammer 1938, Dubinin 1953, Radford 1958, Gaud 1983a Oriental Hobby {Falco severus) Ornithogastia riversi skin/ nest Wharton and Hardcastle 1946, Goff 1980 American Kestrel {Falco sparver- Dubininia sp.*^ feathers Philips 1990 tus) Tytodectes cerchndF subcutaneous Philips and Dindal 1979, Philips 1990 Blankaartia velascoi skin/ nest Wharton and Fuller 1952 Boydaia falconis nasal cavity Pence and Casto 1976 Ptilonyssus cerchnds nasal cavity Strandtmann 1962 Eurasian Hobby {Falco subbuteo) Microlichus falco skin Fain and Gaud 1972, Fain et al. 1987, Fain and Grootaert 1996 Neottialges heteropus subcutaneous Giebel 1861, 1871, Fain 1967 Pseudalloptinus minor feathers Megnin and Trouessart 1884b, Canestrini and Kramer 1899, Dubinin 1956, Gaud 1983a Pseudogabucinia intermedia skin Niethammer 1938, Radford 1953, 1958, Vasilev 1961, Gaud 1983a Common Kestrel {Falco tinnun- Boydaia falconis nasal cavity Fain 1963a cuius) Cheyletiella sp.'^ Niethammer 1938 Dubininia acdpitrina Megninia sp.*’ feathers Trouessart 1885, Canestrini and Kramer 1899, Niethammer 1938, Radford 1953, 1958, Gaud 1958, 1983a Neithammer 1938 Myialges sp. nr. par^ skin Philips and Fain 1991 Protolichus lunulcP feathers Vasilev 1961 Pseudalloptes falconis nasal cavity Gaud 1983a Ptilonyssus cerchnds nasal cavity Fain 1957 Tytodectes cerchnds subcutaneous Fain 1966b Tytodectes falconis subcutaneous Fain 1969 Red-footed Falcon {Falco vesper- tinus) Hieracolichus nisi feathers Shumilo et al. 1973, Gaud 1983a September 2000 Parasitic Mites of Raptors 225 Appendix 1. Continued. Raptor Mite Habitat References Barred Kestrel (Falco zoniven- Aetacarus sp. feathers Gaud 1983a tris) Barred Forest-Falcon {Micrastur Ingrassiinae sp.^ feathers Philips and Fain 1991 ruficollis) Collared Falconet {Microhierax caerulescens) Coraciacarus sp."^ feathers McClure and Ratanaworabhan 1971 Philippine Falconet {Microhier- mites^ skin Maa 1969 ax erythrogenys) Yellow-headed Caracara (Milva- mites® skin Bequaert 1953 go chimachima) Ptilonyssus souzai nasal cavity Pereira and Castro 1949 Crested Caracara {Polyborus Eutrombicula batatas skin/ nest Brennan and Yunker 1966 plancus) Hieracolichus sp. feathers Kurey 1976 Family Sagittariidae Secretary-bird {Sagittarius ser- Aetacarus laurencei feathers Gaud 1983b pentarius) ® These mites were found on louseflies (Hippoboscidae) on the bird. These are incorrectly identified or accidental records. Nest record. Cheyktiella is now restricted to mammal parasites; there are four other genera of bird parasites in the Family Cheyletiellidae. Appendix 2. A list of the parasitic mites of the Strigiformes. Owl Mite Habitat References Strigiformes Dermanyssus gallinae skin/ nest Pfister 1991 Rhinonyssidae nasal cavity Butenko et al. 1972 Family Strigidae Glaucalges attenuatus feathers Radford 1953, 1958 Kramerella lunulata feathers Radford 1953, 1958 Kramerella lyra feathers Radford 1953, 1958 Kramerella major feathers Radford 1953, 1958 Northern Saw-whet Owl {Aego- Dermanyssus americanus skin/ nest Philips 1990 lius acadicus) Petitota sp. feathers Philips, present work Boreal Owl {Aegolius funereus) Glaucalges attenuatus feathers Niethammer 1938 Harpyrhynchus n, sp. skin Philips 1993 Kramerella lunulatcA feathers Niethammer 1938, Dubinin 1953, Radford 1958 Kramerella majof^’'° feathers Megnin and Trouessart 1884a, Nordberg 1936, Dubinin 1953, Radford 1958 Kramerella mrciaki feathers Cerny 1973, Mironov 1997 Kramerella n. sp. feathers Philips, present work Mesalgoides picimajori^ feathers Lonnfors 1937 Paralges sp.® quills Philips 1993 Passeroptes n. sp. skin Philips 1990 Petitota aluconis feathers Lonnfors 1937 Petitota haengii feathers Mironov 1997 Rhinoecius aegolii nasal cavity Butenko 1971, Philips 1993 226 Philips VoL. 34, No. 3 Appendix 2. Continued. Owl Mite Habitat References Marsh Owl {Asia capensis) Dermonoton parallelus feathers Gaud and Mouchet 1959b, Gaud and Till 1961, Gaud 1980 Kramerella oti feathers Gaud 1980 Pandalura strigisoti feathers Gaud 1980 Rhinoedus africanus nasal cavity Zumpt and Patterson 1951, Zumpt and Till 1961 Short-eared Owl (Asia flam- mites*^ skin Maa 1966 meus) Dermonoton sp. feathers Dubinin 1956 Glaucalges attenuatus feathers Buchholz 1869 Kramerella flammei feathers Lonnfors 1937 Kramerella lyra feathers Megnin and Trouessart 1884a, Rad- ford 1958 Kramerella major feathers Megnin and Trouessart 1884a, Rad- ford 1958 Kramerella oti feathers Vasyukova et al. 1996 Kramerella sp. feathers Kurey 1976 Leptotrombidium akamushi skin/ nest Wharton and Fuller 1952 Microlichus trudicolcf skin Fain et al. 1987 Pandalura strigisoti feathers Rothschild and Clay 1952 Petitota aluconis feathers Gaud 1980 Proctophyllodes polyxenu^ feathers Atyeo and Braasch 1966 Rhinoedus alifanovi nasal cavity Butenko 1976 Long-eared Owl {Asio otus) chiggers (Trombiculidae) skin/ nest Maa and Kuo 1965 mites'^ skin Walter 1989 Dermanyssus americanus skin/nest Moss 1978 Dermanyssus hirundinis skin/nest Kutzer et al. 1982 Dermonoton parallelus feathers Gaud 1980 Eulaelaps stabulari^ mammals Kutzer et al. 1982 Glaucalges attenuatus feathers Buchholz 1869, Canestrini and Kra- mer 1899, Radford 1953, 1958 Glycyphagus domesticu^'^ nest Biittiker and Cerny 1974 Harpyrhynchus asio skin Fain 1972 Kramerella lyra feathers Megnin and Trouessart 1884a, Rad- ford 1958 Kramerella oti feathers Lonnfors 1937, Radford 1958, Vasi- lev 1959, Cerny 1977, Gaud 1980 Kramerella sp. feathers Kurey 1976 Microlichus avuf^ skin Ash and Hughes 1952 Microlichus charadricolcf skin Biittiker and Cerny 1974 Myialges macdonaldi^ skin Hill et al. 1967 Myialges nudus skin Fain 1965, Fain and Grootaert 1996 Neotrombicula lipovskyi skin/ nest Loomis 1956 Pandalura strigisoti feathers Buchholz 1869, Canestrini and Kra- mer 1899, Radford 1953, 1958, Kurey 1976, Cerny 1977 Myialges uncu^ skin Ash and Hughes 1952, Fain 1965 Rhinoedus brikinboricus nasal cavity Butenko 1976 Rhinoedus oti nasal cavity Cooreman 1946 Strelkoviacarus critesiP skin Hill et al. 1967 Sternostoma strigitis nasal cavity Butenko 1976 September 2000 Parasitic Mites of Raptors 227 Appendix 2. Continued. Owl Mite Habitat References Little Owl {Athene noctua) Neotrombicula autumnalis skin /nest Koptzev et al. 1961 Glaucalges attenuatus feathers Gaud 1958, 1980 Kramerella lunulata feathers Haller 1878, Niethammer 1938, Du- Ornithogastia ariadnae skin/ nest binin 1953, Radford 1958, Gaud 1980 Hushcha 1982 Pandalura strigisoti feathers Gaud 1958, 1980 Rhinoedus subbisetosus nasal cavity Bregetova 1965 Bubo sp. Dermanyssus gallinae skin/ nest Strand tmann and Wharton 1958 Dermonoton bubonisA feathers Gaud 1980 Spotted Eagle-Owl {Bubo afri- Astrida caprimulgi nasal cavity Fain 1956a, Zumpt and Till 1961 canus) Dermonoton parallelus feathers Gaud 1980 Glaucalges attenuatus feathers Gaud 1980 Kramerella maculata feathers Gaud 1980 Pandalura strigisoti feathers Gaud 1980 Rhinoedus buboensis nasal cavity Fain 1958, 1959b, 1960, Zumpt and Eurasian Eagle-Owl {Bubo mites'^ skin Till 1961, Domrow 1969 Walter 1989 bubo) Dermonoton longiventer feathers Sohn and Noh 1994 Galucalges attenuatus feathers Lonnfors 1937, Mumcuoglu and Kramerella bubonis feathers Muller 1974 Lonnfors 1937, Dubinin 1953, Rad- Kramerella major feathers ford 1958, Mrciak and Brander 1967 Megnin and Trouessart 1884a, Dubi- Pandalura strigisoti feathers nin 1953, Radford 1958 Lonnfors 1937, Mumcuoglu and Petitota bubonis feathers Muller 1974 Atyeo and Philips 1984, Sohn and Verreaux’s Eagle-Owl {Bubo Dermonoton apoplax feathers Noh 1994 Gaud 1980 lacteus) Dermonoton parallelus feathers Gaud 1980 Glaucalges attenuatus feathers Gaud 1980 Kramerella lobata feathers Gaud 1980 Kramerella lunulatcP feathers Radford 1958 Pandalura strigisoti feathers Gaud 1980 Akun Eagle-Owl {Bubo leucos- Dermonoton apoplax feathers Gaud 1980 tictus) Glaucalges attenuatus feathers Gaud 1980 Pandalura strigisoti feathers Gaud 1980 Eraser’s Eagle-Owl {Bubo poen- Dermonoton apoplax feathers Gaud and Mouchet 1959b, Gaud sis) Glaucalges attenuatus feathers and Till 1961, Gaud 1980 Gaud and Mouchet 1959b, Gaud Pandalura strigisoti feathers and Till 1961, Gaud 1980 Gaud 1980 Shelley’s Eagle-Owl {Bubo shel- Glaucalges attenuatus feathers Gaud 1980 kyi Kramerella lobata feathers Gaud 1980 Pandalura strigisoti feathers Gaud 1980 228 Philips VoL. 34, No. 3 Appendix 2. Continued. Owl Mite Habitat References Great Horned Owl {Bubo virgi- mites'^ skin Bequaert 1953, Maa 1969 nianus) Blattisodus keegan^’^ trees Philips and Fain 1991 Bubophilus ascalaphus quills Philips and Norton 1978 Dermonoton sp.*^ feathers Kurey 1976 Epidermoptidae*^ skin Herman 1945 Euschoengastia numerosa skin/nest Wrenn and Loomis 1974 Glaucalges attenuatus feathers Atyeo and Philips 1984 Harpyrhynchus sp. skin Philips, present work Knemidocoptes mutans skin Schulz et al. 1989, Schulz 1990, Mai- Kramerella n. sp. feathers ley and Whitbread 1996, Houston et al. 1998 Philips and Norton 1978, Atyeo and Myialges anchorcf skin Philips 1984, Philips 1993 Furman and Tarshis 1953, Bequaert Pandalura strigisoti feathers 1953, Fain 1965 Atyeo and Philips 1984 Paralges n. sp. quills Philips 1993 Petitota bubonis feathers Atyeo and Philips 1984 Pneumophagus bubonis lungs Fain and Smiley 1989 Proctophyllodes polyxenu^ feathers Atyeo and Braasch 1966 Rhinoedus grandis nasal cavity Strandtmann 1952 Glaucidium sp. Neotytodectes mexicanu^ subcutaneous O’Connor 1981 Ferruginous Pygmy-Owl {Glau- Eutrombicula alfreddugesi skin/ nest Brennan and Jones 1960, Loomis cidium brasilianum) Asian Barred Owlet {Glaud- Rhinoedus bisetosus nasal cavity 1969 Strandtmann 1960, Wilson 1968 dium cuculoides) Mountain Pygmy-Owl {Glaud- Kramerella sp. feathers Kurey 1976 dium gnoma) Eurasian Pygmy-Owl {Glaud- Dermonoton eventratus feathers Canestrini and Kramer 1899, Dubi- dium passerinum) Kramerella glauddii feathers nin 1956, Radford 1953, 1958 Mrciak and Brander 1967, Cerny Pearl-spotted Owlet {Glaud- Astrida caprimulgi nasal cavity and Wiesner 1992 Fain 1956a, Zumpt and Till 1961 dium perlatum) Cuban Pygmy-Owl {Glauddium Tytodectes glauddii subcutaneous Fain 1967, Cerny 1969 siju) Barking Owl {Ninox connivens) Leptotrombidium nissani skin/nest Domrow 1974, Domrow and Lester Neoschoengastia americana skin/nest 1985 Domrow and Lester 1985 Rhinoedus cooremani nasal cavity Domrow 1969, 1987 Solomon Hawk-Owl {Ninox Odontacarus trisetosus skin/nest Goff 1979 jacquinoti) Morepork {Ninox novaeseelan- Leptotrombidium nissani skin/ nest Domrow 1974, Domrow and Lester diae) Neoschoengastia americana skin/nest 1985 Domrow and Lester 1985 Rhinoedus cooremani nasal cavity Domrow 1967, 1987 New Britain Hawk-Owl {Ninox mites^^ skin Maa 1966 odiosa) Analgidae*^ skin Philips and Fain 1991 Philippine Hawk-Owl {Ninox Oconnoria inexpectata quills Gaud et al. 1989 philippensis) Snowy Owl {Nyctea scandiaca) Knemidocoptes sp. skin Cooper 1978, 1985 Rhinoedus nycteae nasal cavity Butenko 1976 September 2000 Parasitic Mites of Raptors 229 Appendix 2. Continued. Owl Mite Habitat References Otus sp. Myialges bombycilla^ skin Philips and Fain 1991 Eastern Screech-Owl {Otus mites'^ skin Bequaert 1953, Fain 1965, Maa 1969 asio) Dermanyssus americanus skin/ nest Ewing 1925, 1936, Radford 1950, Evans and Till 1962, Moss 1978 Dermonoton sp. feathers Kurey 1976 Harpyrhynchus sp. skin Philips 1993 Miyatrombicula cyno^ skin/ nest Philips 1978, Philips and Din dal 1990 Neoschoengastia americana skin/nest Everett et al. 1972 Syringophilidae quills Johnston and Kethley 1973 Variable Screech-Owl {Otus Blankaartia sinnamaryi skin/nest Brennan and Yunker 1966 atricapillus) Indian Scops-Owl {Otus bakka- chiggers (Trombiculidae) skin/ nest Maa and Kuo 1965 moena) feather mites feathers Maa and Kuo 1965 Dermonoton sp. feathers McClure and Ratanaworabhan 1971 Leptotrombidium deliense nest/ skin McClure and Ratanaworabhan 1971 Ornithonyssus bursa skin/ nest McClure and Ratanaworabhan 1971 Rhinoecius cavannus nasal cavity Wilson 1968, McClure and Ratana- worabhan 1971 Toritrombicula densipiliata skin/nest Nadchatram 1967, Vercammen- Grandjean and Langston 1976 Toritrombicula vorca skin/nest Vercammen-Grandjean and Lang- ston 1976 White-faced Scops-Owl {Otus Pandalura strigisoti feathers Gaud 1980 leucotis) Reddish Scops-Owl ( Otus rufes- Leptotrombidium deliense skin/ nest McClure and Ratanaworabhan 1971 cens) Toritrombicula densipiliata skin/ nest McClure and Ratanaworabhan 1971 Eurasian Scops-Owl {Otus chiggers (Trombiculidae) skin/nest Maa and Kuo 1965 scops) feather mites feathers Maa and Kuo 1965 mites'^ skin Maa 1969 Dermonoton parallelilobu^ feathers Radford 1953, 1958 Dermonoton parallelus feathers Megnin and Trouessart 1884c, Ca- nestrini and Kramer 1899, Dubi- nin 1956, Gaud and Till 1961 Dermonoton sp. feathers McClure and Ratanaworabhan 1971 Kramerella lunulata feathers Dubinin 1953 Kramerella lyra feathers Dubinin 1953 Kramerella major feathers Shumilo et al. 1973 Leptotrombidium deliense skin/nest McClure and Ratanaworabhan 1971 Neoschoengastia longipes skin/ nest McClure and Ratanaworabhan 1971 African Scops-Owl ( Otus sene- Astrida caprimulgi nasal cavity Fain 1956a, Zumpt and Till 1961 galensis) Mountain Scops-Owl {Otus Astrida caprimulgi nasal cavity Fain 1963a spilocephalus) Dermonoton sp. feathers McClure and Ratanaworabhan 1971 Leptotrombidium scutellare skin/ nest McClure and Ratanaworabhan 1971 Neoschoengastia sp. skin/ nest McClure and Ratanaworabhan 1971 Whiskered Screech-Owl {Otus Dermonoton sp. feathers Kurey 1976 trichopsis) Band-bellied Owl {Pulsatrix me- Rhinoecius nycteae nasal cavity Amaral 1962 lunota) Vermiculated Fishing-Owl ( Sco- Dermonoton parallelihbus feathers Gaud 1980 topelia bouvieri) 230 Philips VoL. 34, No. 3 Appendix 2. Continued. Owl Mite Habitat References Pel’s Fishing-Owl (Scotopelia pell) Dermonoton parallelilobus feathers Gaud and Mouchet 1959b, Gaud and Till 1961, Gaud 1980 Glaucalges attenuatus feathers Gaud and Till 1961, Gaud 1980 Pandalura strigisoti feathers Gaud 1980 Burrowing Owl (Speotyto cuni- Dermonoton sp. feathers Kurey 1976 cularia) Euschoengastoides gurneyi skin/nest Loomis 1956 Hypodectes propu^ subcutaneous Pence and Bergan 1996 Hyponeocula montanensis skin/ nest Loomis 1956 Kramerella major feathers Megnin and Trouessart 1884a, Dubi- nin 1953, Radford 1958 Neoschoengastia americana skin /nest Loomis 1956, Everett et al. 1972 Proctophyllodes polyxenu^^ feathers Atyeo and Braasch 1966 Rhinoedus bisetosus nasal cavity Strandtmann 1952, Amaral 1962 Sternostoma augei nasal cavity Amaral 1962 Tytodectes speotyto subcutaneous Pence and Bergan 1996 Tawny Owl {Strix aluco) Dermanyssus hirundini^ skin/ nest Zeman and Jurik 1981 Glaucalges attenuatus feathers Atyeo pers. comm. Kramerella aluconis feathers Lonnfors 1937, Dubinin 1953, Rad- ford 1958, Shumilo et al. 1973 Kramerella major feathers Dubinin 1953, Radford 1958 Pandalura strigsoti feathers Gaud 1958, 1980 Petitota aluconis feathers Buchholz 1869, Radford 1953, 1958 Brown Wood-Owl {Strix lepto- feather mites feathers Maa and Kuo 1965 grammica) Great Grey Owl {Strix nebulo- sa) Dermonoton parallelilobus feathers Megnin and Trouessart 1884c, Ca- nestrini and Kramer 1899, Rad- ford 1953, 1958, Dubinin 1956, Gaud and Till 1961, Gaud 1980 Kramerella aprotuberantia feathers Philips, present work Pandalura strigisoti feathers Philips, present work Passeroptes n. sp. skin Philips, present work Petitota sp. feathers Philips, present work Spotted Owl {Strix occidentalis) Euschoengastia sp. (probably numerosa) skin/nest Hunter et al. 1994, Gutierrez et al. 1995 Mottled Wood-Owl {Strix ocel- Myialges bombydllad skin Philips and Fain 1991 lata) Ural Owl {Strix uralensis) Kramerella aprotuberantia feathers Dubinin 1953, Radford 1958 Petitota aluconis feathers Niethammer 1938 Barred Owl {Strix varia) Dermonoton sp. feathers Kurey 1976 Dermonoton parallelilobus feathers Banks 1915 Kramerella sp. feathers Kurey 1976 Omithonyssus sp. feathers Peters 1936 Pandalura strigisoti feathers Atyeo pers. comm. Paralges n. sp. quills Philips, present work Passeroptes n. sp. skin Philips, present work Rhinoedus cooremani nasal cavity Strandtmann 1952, Pence 1973 Mottled Owl {Strix virgata) Blankaartia sinnamaryi skin/nest Brennan and Yunker 1966 Eutrombicula alfreddugesi skin/nest Brennan and Jones 1960, Loomis 1969 African Wood-Owl {Strix wood- Dermonoton spp. feathers Cheke 1972, 1978 fordii) Glaucalges attenuatus feathers Gaud 1980 Northern Hawk Owl {Surnia ulula) Kramerella major feathers Megnin and Trouessart 1884a, Dubi- nin 1953, Radford 1958 September 2000 Parasitic Mites of Raptors 231 Appendix 2. Continued. Owl Mite Habitat References Kramerella sp. feathers Vasyukova et al. 1996 Family Tytonidae Congo Bay-Owl {Phodilus prigo- Dermonoton parallelus feathers Gaud 1980 ginei) Barn Owl {Tyto alba) mites^^ skin Maa 1969 Aureliania aureliani nasal cavity Fain 1956b, 1963b, Zumpt and Till 1961, Domrow 1969, 1991 Dermonoton sclerourus feathers Gaud 1980, D’Souza et al. 1986 Dermonoton sp. feathers McClure and Ratanaworabhan 1971 Glaucalges attenuatus feathers Rothschild and Clay 1952, Radford 1958, Gaud 1958, 1980, Gaud and Till 1961, Cerny 1967, D’Souza et al. 1986 Glaucalges sp. feathers McClure and Ratanaworabhan 1971, Kurey 1976 Harpyrhynchus tyto skin Fain 1972 Kramerella lunulata feathers Niethammer 1938, Gaud and Petitot 1948a, Cerny 1967, Bunn et al. 1982 Kramerella lyra feathers Radford 1958 Kramerella quadrata feathers Gaud 1980 Kramerella sp. feathers Kurey 1976 Leptotrombidium nissani skin/nest Domrow 1974, Domrow and Lester 1985 Neoboydaia sp. nasal cavity Dusbabek and Cerny 1970 Neottialges evansf' subcutaneous Pence and Bergan 1996 Ornithonyssus bursa skin/nest Domrow 1977 Ornithonyssus sylviarum skin/nest Cooper 1978 Ornithonyssus sp. skin/nest Keymer 1972 Pandalura strigisoti feathers Niethammer 1938, Radford 1958, Gaud 1958, Gaud and Mouchet 1959a, Gaud and Till 1961, Gaud 1980 Rhinoecius tytonis nasal cavity Fain 1956c, 1959a, Zumpt and Till 1961, Domrow 1969 Tytodectes strigis subcutaneous Gene 1848, Fain 1967, Wurst and Havelka 1997 Tytodectes tyto subcutaneous Fain 1966b, 1967, Pence and Ber- gan 1996 African Grass-Owl {Tyto capen- Dermonoton sclerourus feathers Gaud 1980 sis) Kramerella quadrata feathers Gaud 1980 Australian Masked-Owl {Tyto mites'^ skin Maa 1966 novaehollandiae) Tytodectes tyto subcutaneous Domrow 1992 ^ These are incorrectly identified or accidental records. Nest record. These mites were found on louseflies (Hippoboscidae) on the bird. Dermonoton bubonis from Bubo sp. (Gaud 1980) is actually an invalid nomen nudum for an undescribed species of Dermonoton from Bubo virginianus (Gaud pers. comm.) . Short Communications J Raptor Res. 34(3):232-235 © 2000 The Raptor Research Foundation, Inc. Diurnal Vocal Activity of Young Eagle Owi.s and its Implications in Detecting Occupied Nests Vincenzo Penteriani Estacion Biologica de Donana, Avda. de Maria Luisa s/n Pabellon del Peru, Apartado de Correos 1036, 41013 Sevilla, Spain Max Gallardo Parc Naturel Regional du Luberon, 60 place Jean Jaures, BP 122, 84404 Apt, France Helene Cazassus Centre d’Etude Ornithologique de Bourgogne, Dijon, France Key Words: Eagk Owl, Bubo bubo; diurnal calling activ- ity, food- and contact-call, call practice, occupied nest census-, productivity evaluation. Vocal surveys are used extensively to locate nests and estimate numbers of birds (Ralph and Scott 1981, Fuller and Mosher 1987, Ralph et al. 1995, Stewart et al. 1996). They are particularly useful for nocturnal birds that can- not be easily located during the day (Reid et al. 1999). Due to the crepuscular and nocturnal habits of owls, nu- merous census techniques have been developed (Fuller and Mosher 1981, Smith 1987). They include visual searches, passive auditory surveys (Reid et al. 1999), lo- cation of roosts and nests, and use of tape-recorded calls to elicit responses (acoustic-lure survey, Reid et al. 1999). When a species is being censused, it is essential to have a good knowledge of its behavior and breeding cycle to ensure accuracy of the results (e.g., broadcasting of tape- recorded vocalizations when the probability that birds are near the nest is high). For this reason, it is essential to study the behavior of species to be censused. Mysterud and Dunker (1982) and Penteriani and Pinchera (1991) concluded that passive auditory surveys of adult Eagle Owls {Bubo bubo) were most reliable for locating nests because the owls did not consistently respond to playback of their vocalizations, especially when they had nestlings or fledglings. Although playback and passive auditory surveys of adult Eagle Owls have been used extensively to locate territories (e.g., Bergerhausen and Willems 1988, Penteriani 1996), no one has investigated the pos- sibility that passive auditory surveys of juveniles might also be useful for surveying Eagle Owls. Data on the vocal activity pattern and distribution of young Eagle Owls are scarce, although their call rates are very high (Kranz 1971, Mikkola 1983). To investigate the possibility of using passive auditory surveys of juvenile Eagle Owls to locate nests and fledged young during the day, we studied diurnal patterns of vo- calizations of nestling and fledgling Eagle Owls in south- ern Erance. The study was prompted by field observa- tions that indicated that young Eagle Owls were particularly vociferous during the day (V. Penteriani and M. Gallardo unpubl. data). Methods The study was conducted during 1999 on Luberon Mountain in southern Erance (43°53'N, 5°24'E). Eleva- tion ranged from 160 m in the Durance River valley to 1125 m on Grand Luberon ridge. The study area was characterized by a mosaic of rock cliffs, shrub vegetation ( Quercus coccifera. Thymus vulgaris, and Rosmarinus officin- alis) , Mediterranean forest ( Quercus ilex, Q. pubescens, and Pinus halepensis) , croplands, pastures, and fallow fields. We systematically listened to young Eagle Owls from the age of about 3 wk (nestlings), when their calls are easily distinguishable, to about 8 wk (fledglings), when their calls begin to resemble those of adults (Glutz Von Blotzheim and Bauer 1980) and their diurnal vocal activ- ity near the nest seems to decrease (V. Penteriani unpubl. data) . During this period (May to July in our study area) , we recorded both frequency and distribution of the main call type of young owls, the dry rasping chwdtch, consid- ered as a food-call (Cramp and Simmons 1980). For pas- sive auditory surveys, we divided each day into 14 1-hr intervals, from sunrise to sunset, and evenly distributed surveys (on a rotation basis) among nine owlets (two young in a nest in four cases, one young alone in one case), randomly selected inside the study area. We dis- tributed the surveys over the May-July period to obtain data on the vocal activity of each individual for the entire length of each solar day at the end of the eighth week of life. In each observation period, we collected the time of start of a vocal event, duration of the vocal event, and 232 September 2000 Short Communications 233 (sunrise) (sunset) HOURLY BLOCKS Figure 1. Diurnal vocal activity of nine young Eagle Owls in southern France: mean duration of vocalizations (sec; grey bars) and mean number of calls (solid line) by time of day. Hourly blocks represent the intervals of the day, from sunrise to sunset. the number of vocal events. We used a stopwatch to de- termine the duration of a given vocal event and we iden- tified the end of a vocal event as the last call heard more than 60 sec before the next call (i.e., 1 min of silence between calls or between sequences was regarded as a dividing unit of time) . Isolated calls were arbitrarily as- signed a duration of 1 sec. We did not conduct observa- tions on windy or rainy days and always recorded vocali- zations from the same location and from the same distance (<500 m from the nesting cliff). We always re- mained out of sight of the owls because the presence of humans alters the behavior of the young. We used a Repeated Measures ANOVA (Sokal and Rohlf 1995) to compare the duration of vocalizations and the number of calls throughout the day. We used the Spearman rank correlation coefficient to determine a possible common pattern between the duration of the vocal events and the call number characterizing them (Sokal and Rohlf 1995). Results The duration of vocalizations (Fig. 1; Fg is = 47.36, P < 0.001) and the number of calls (Fig. 1; Fg 13 = 38.73, P < 0.001) were significantly different in the various hourly blocks, with peaks occurring during 3 hrs after sunrise and 3 hrs before sunset (Fig. 1). A common pos- itive pattern between the duration of the vocal events and the number of calls was observed (r^ = 0.85, P < 0.001, Spearman rank). The mean number of calls per series was 65.6 ± 127.1 (±SD, range = 1-259) (Fig. 1). Dura- tion of vocalizations in a single series ranged from 1—1130 sec (x = 808.4 ± 891.4 sec). The maximum time interval between two neighboring series was 40 min, during the hourly block corresponding to 5 hr after sunrise. The mean interval between calls was 10.5 ± 6.02 sec (range = 2-28.7). During the passive auditory periods, all nine juveniles were heard, always in the immediate vicinity of the nest hole, even after they left the nest. In four cases where we observed adults near juveniles that were calling, the adults appeared to ignore the juveniles. Discussion Our findings that vocalizations peaked 3 hr before sun- set and 3 hr after sunrise highlighted the diurnal activity of this dominantly crepuscular and nocturnal species The typical chwdtch call of nestling and fledgling Eagle Owls has been described as a food call (Cramp and Sim- mons 1980), but its high diurnal frequency, use during the period of the day coinciding with low adult activity (although young are regularly fed during the day by fe- males, L. Dalbeck pers. comm.), and observed indiffer- ence of adults to this type of behavior make it difficult to explain how this call is used for feeding alone. It may, in fact, be a method of communicating within family 234 Short Communications VoL. 34, No. 3 groups (e.g., contact call). Fledglings of some suboscine species use their song as a contact call in their early stages of life (Rroodsma 1984) when they are just beginning to learn sounds in their environment and recognizable pro- duction of those sounds occurs a month or more later, and only after extensive practice, or subsong (Kroodsma 1981). The high rates of diurnal vocalizations in Eagle Owls may simply result from young owls practicing their voices, just as high rates of diurnal activity may represent muscular exercise (e.g., flight training). Our results suggest that passive auditory surveys of young Eagle Owls are effective when owlets are 5-8-wk old, and are most effective during the 3-hr period after sunrise and preceding sunset. Listening sessions must be 40 min in duration. Although, in these hourly blocks, we always heard young Eagle Owl calls, we suggest two lis- tening sessions as a precaution before considering a site as not occupied by a successfully breeding pair. Since we did not conduct surveys in the hours before sunrise and after sunset, we cannot address survey effectiveness dur- ing those periods. We recommend that listening points be selected such that they are hidden from the owls’ view and at a maximum distance of 500 m from potential nest- ing sites, especially in noisy areas. Although the calls of young can be heard on silent nights as far as 500 m away, the background noise during diurnal hours makes listen- ing sessions problematic. Days with wind (>15 km/hr) and intense precipitation are unsuitable for conducting surveys with this technique. Our results suggest that passive auditory surveys during the day are useful for surveying Eagle Owls because young are normally very vocal during the day, surveys can be conducted at a time of day and year when adults are relatively secretive, and they allow estimation of the min- imum number of young produced. It would be interesting to determine if diurnal calls are typical of Eagle Owls in other European countries and of congeners. For example, it seems that there are obvious differences in diurnal call behavior between our study area and western Germany, where the calls of young are irregular during the day (W. Bergerhausen and L. Dal- beck pers. comm.). The Great Horned Owl {Bubo virgi- manus) is the geographical and ecological counterpart of the Eurasian Eagle Owl. The reasons for treating this as a distinct species have rarely been made clear (Voous 1988). It would be interesting to investigate whether the vocal behavior of young Great Horned Owls has patterns similar to those of the Eagle Owl. The Great Horned Owl seems to be relatively silent during the day, probably be- cause diurnal begging juveniles could be subject to high- er rates of predation by Northern Goshawks {Accipiter gen- tihs) and Red-tailed Hawks {Buteo jamaicensis) , or “mobbing” by jays and crows (E. Forsman unpubl. data). However, passive surveys are useful for locating young Great Horned Owls at night or just before sunrise or after sunset, when they are quite vocal (E. Forsman un- publ. data). Resumen. — ^A1 censar aves, es esencial saber su compor- tamiento y ciclo reproductivo para asegurar la veracidad de los resultados. En el caso de Bubo bubo, un metodo efectivo de investigacion es el de utilizar un metodo pa- sivo de audicion de vocalizaciones espontaneas de adul- tos. Sin embargo, se conoce poco acerca de los patrones y distribucion de la actividad vocal de juveniles, los cuales vociferan bastante durante el dia. Observamos el com- portamiento de vocalizacion de juveniles de buhos en el sur de Francia para determinar si pueden ser localizados consistentemente durante el dia utilizando un metodo pasivo de audicion. La duracion de las vocalizaciones (^8,13 = 47.36, P < 0.001) y el numero de vocalizaciones (^ 8,13 = 38.73, P < 0.001) fue significativamente difer- ente en distintos momentos del dia, la duracion de las vocalizaciones diurnas fueron mayores en las primeras 3 horas del amanecer y en las 3 horas antes del atardecer Escuchar las vocalizaciones espontaneas de juveniles puede ser considerado como un metodo util para el monitoreo de buhos debido a que estos vociferan bastan- te durante el dia. Las investigaciones deben llevarse a cabo para estimar un numero minimo de juveniles prod- ucidos. Nuestros resultados indican que la alta actividad diurna de juveniles puede estar relacionada con la ne- cesidad de comunicarse entre el grupo familiar (i.e., vo- calizaciones de contacto) para estimular la alimentacion por parte de los adultos o practicar sus vocalizaciones. [Traduccion de Cesar Marquez] Acknowledgments W. Bergerhausen, L. Dalbeck, E. Forsman, F. Libera- tori, S. Saraceni, D. Smith, and F. Sergio provided useful comments on an earlier version of the paper. We thank H. Magnin for logistic support. The Regional Park of Lu- beron provided hnancial support for this work. Literature Cited Bergerhausen, W. and H. Willems. 1988. Methodik und effizienz der bestandkontrolle einer population des uhus (Bubo bubo'L.). Charad. 24:171-187. Cramp, S. and K.E.L. Simmons. [Eds.]. 1980. Handbook of the birds of Europe, the Middle East and North Africa. Vol. 2. Oxford Univ. Press, Oxford, U.K. Fuller, M.R. and J.A. Mosher. 1981. Methods of detect- ing and counting raptors. Pages 235-246 in C.J. Ralph and J.M. Scott [Eds.], Estimating the number of ter- restrial birds. Stud. Avian Biol. No. 6. and . 1987. Raptor survey techniques. Pag- es 37-65 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline, and D.M. Bird [Eds.], Raptor management techniques manual. Natl. Wildl. Fed., Washington DC U.S.A. Glutz Von Blotzheim, U.N. and K.M. Bauer. 1980. Handbuch der vogel Mitteleuropas. Wiesbaden, Ger- many. Kranz, P. 1971. Nagot om berguvens aktivitat och foda Faglar i Sormland 4:13-23. September 2000 Short Communications 235 Kroodsma, D.E. 1981. Ontogeny of bird song. Pages 518- 532 in K. Immelmann, G. Barlow, L. Petrinovich, and M. Main [Eds.], Early development in man and ani- mals. The Bielefeldt project. Cambridge Univ. Press, Cambridge, U.K. . 1984. Songs of the Alder Flycatcher (Empidonax alnorum) and Willow Flycatcher {Empidonax traillii) are innate. Auk 101:13-24. Mikkola, H. 1983. Owls of Europe. T. & A.D. Poyser, Cal- ton, U.K. Mysterud, I. AND H. Bunker. 1982. Food and nesting ecology of the Eagle Owl, Bubo bubo L., in four neigh- bouring territories in southern Norway. Swedish Wild- life Research, Viltrevy 12:3. Penteriani, V. 1996. The Eagle Owl. Calderini Ed., Bo- logna, Italy. and F. Pinchera. 1991. Comparison of the play- back and the listening methods in the census of Eagle Owl (in Italian). Pages 385-388 in M. Fasola [Ed.], Atti II Seminario Italiano Censimenti Faunistici dei Vertebrati. Suppl. Ric. Biol. Selv. Vol. XVI, Bologna, Italy. Ralph, C.J. and J.M. Scott. [Eds.]. 1981. Estimating the number of terrestrial birds. Stud. Avian Biol. No. 6. , J.R. Sauer and S. Droege. [Eds.]. 1995. Moni- toring bird populations by point counts. Gen. Tech. Rep. PSW-GTR-149. Albany, CA, U.S.A. Reid, J.R., R.B. Horn, and E.D. Forsman. 1999. Detec- tion rates of Spotted Owls based on acousticdure and livedure surveys. Wildl. Soc. Bull. 27:986-990. Smith, D.G. 1987. Owl census techniques. Pages 304-309 in R.W. Nero, R.J. Clark, R.J. Knapton, and R.H. Ham- re [Eds.] , Biology and conservation of northern forest owls: symposium proceedings. Gen. Tech. Rep. RM- 142, Fort Collins, CO U.S.A. Sokal, R.R. and FJ. Rohlf. 1995. Biometry. The princi- ples and practice of statistics in biological research, 3rd ed. W.H. Freeman and Company, New York, NY U.S.A. Stewart, A.C., R.W. Campbell, and S. Dickin. 1996. Use of dawn vocalizations for detecting breeding Cooper’s Hawks in an urban environment. Wildl. Soc. Bull. 24- 291-293. Voous, K.H. 1988. Owls of the Northern Hemisphere. William Collins Sons & Co., London, U.K. Received 2 December 1999; accepted 20 March 2000 J. Raptor Res. 34(3):235-237 © 2000 The Raptor Research Foundation, Inc. Food Habits of the Striped Owl {Asio clamator) in Buenos Aires Province, Argentina Juan P. Isacch,^ Maria S. Bo, and Mariano M. Martinez^ Laboratorio de Vertebrados, Departamento Biologia, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3250, (7600) Mar del Plata, Argentina Key Words: Striped Owl, Asio clamator; food habits-, Argen- tina. The Striped Owl {Asio clamator) is a widespread species from Mexico through tropical and subtropical South Amer- ica to Argentina (Grossman and Hamlet 1964, Canevari et al. 1991, Holt et al. 1999). It inhabits deciduous seasonal forests, lowland seasonal forests, gallery forests, lowland sa- vannas, desert forests, and grasslands (Grossman and Ham- let 1964, Canevari et al. 1991, Holt et al. 1999). Despite its widespread distribution, the status of the Striped Owl is poorly known (Burton 1973, Holt et al. 1999) and it is con- * Present address: Comisidn de Investigaciones Cientifi- cas de la Provincia de Buenos Aires, Buenos Aires, Ar- gentina. 2 Deceased. sidered to be a rare species in Buenos Aires Province in Argentina (Narosky and Di Giacomo 1993). Studies of the Striped Owl in Argentina have focused mainly on anecdotal aspects of its biology and breeding ecology (e.g., Bledinger et al. 1987, Martinez et al. 1996). Its diet is poorly studied but the limited information that is available indicates that it preys mainly on small mam- mals (Grossman and Hamlet 1964, Burton 1973, Phelps and Meyer de Schauensee 1994) followed by birds, rep- tiles, and insects (Holt et al. 1999). Here, we report on the diet of Striped Owls in the southernmost extreme of its distribution in the southeastern portion of Buenos Ai- res Province, Argentina. Methods Our study was carried out in Mar Chiquito Biosphera Reserve (37°40'S, 57°23'W), Buenos Aires Province, Ar- gentina. The reserve covers 30 000 ha and supports a di- verse array of habitats including ponds, salt marshes. 236 Short Communications VoL. 34, No. 3 grasslands, woodlands, exotic tree plantations, and agri- cultural fields. We found a pair of Striped Owls in an area of tala {Celtis tala) forest at Nahuel Ruca Ranch. The tala forest is derived from thorn forests (Espinal) and this relict patch represents the southernmost extreme of Espinal forest in Argentina. The patch covered a 6 ha area and was surrounded by a pond and grazed native grassland. There were a few houses and a plantation of eucalyptus {Eucaliptus spp.) trees nearby. From August to November 1997, pellets and prey re- mains were collected in different plucking stations and roosting sites of the owls. Bird, mammal, and insect re- mains were identified based on bones, feathers, bills, hair, dentaries, and exoskeletons, and compared with the collections of Laboratorio de Vertebrados, Facultad de Ciencias Exactas y Naturales-Universidad Nacional de Mar del Plata and Museo Municipal de Ciencias Natura- les “Lorenzo Scaglia” de Mar del Plata. The majority of prey were identified to species level. Bird and mammal weights were obtained from the literature (Salvador 1988, Camperi 1992, Redford and Eisenberg 1992) and unpub- lished data (M. Kittlein pers. comm.). A weight of 1 g was assigned to each insect prey species (Jimenez 1993). Results and Discussion A total of 56 prey items was identified from 34 pellets and 3 prey remains (pile of feathers) . Rodents were the main prey (55.4%) followed by birds (42.9%) and insects (1 8%, Table 1). Rattus spp. was the most common prey Item (43%). Among birds, Rufous-collared Sparrows {Zonotrichia capensis, 23.2%) and Eared Doves (Zenaida auriculata, 17.9%) were most frequently taken. Other items comprised only a small fraction of the diet (16.2%). Prey weights ranged from a low of 1 g in the case of insects to a high 630 g in the case of Cavia aperea (Table 1). Rodents comprised up to 81.5% of prey by weight and Rattus spp. contributed with the highest value (66.9%) followed by Cavia aperea (14%). The occurrence of adult C. aperea in the diet was surprising, since they weigh more than one and a half times as much as Striped Owls (maximal weight recorded of Striped Owl is 485 gr, Salvador 1988). We were not certain if C. aperea were eat- en as carrion or actually hunted but Striped Owls are highly adapted to hunt live prey (Holt et al. 1999) . The biomass contribution of birds was minor (20.1%) with Eared Doves contributing the largest amount (12%, Ta- ble 1). Other studies have confirmed that birds are com- mon in the diets of Striped Owls (Grossman and Hamlet 1964, Burton 1973, Phelps and Meyer de Schauensee 1994, Holt et al. 1999). Our results agree with those of Martinez et al. (1996) who studied the diet of Striped Owls in an area of shrub and exotic trees in Laguna de Los Padres Reserve, locat- ed 35 km north of Nahuel Ruca in Buenos Aires Prov- ince. They recorded seven bird and mammal species in the diet; three of which {Reithrodon auritus, Holochilus bras- iliensis, and Carduelis magellanica) were absent in the diet of the Striped Owls we studied. Table 1. Frequency of prey items, weight of individual prey and total percent biomass of prey in the diet of Striped Owl {Asia damator) in Mar Chiquito Biosphera Reserve, Buenos Aires Province, Argentina. Ere- Individual Total QUENCY Weight Biomass Prey (%) (g) (%) Aves Columbiformes Columbidae Zenaida auriculata Passeriformes Emberizidae 17.9 134.6 15.0 Sicalis luteola 1.8 16 1.8 Zonotrichia capensis Mammalia Rodentia Caviidae 23.2 22.5 3.3 Cavia aperea (adult) 3.6 630 7.0 Cavia aperea (young) Muridae 1.8 315 7.0 Akodon azarae 1.8 21 0.2 Calomys musculinus 3.6 10 0.2 Oryzomys flavescens 1.8 17 0.2 Rattus spp. Insecta 43.0 250 66.9 Coleoptera Scarabaeidae Sulcophanaeus menelas 1.8 1 0.0 The Striped Owl is typically found in woodlands, for- ests, and savannas of tropical and subtropical zones (Grossman and Hamlet 1964). Our data show that it also occurs in the temperate-warm zone that corresponds to the Pampean Fitogeographic (Chaqueno Dominion, Ca- brera 1976). In the past, this zone was dominated by tall grasslands without trees. Perhaps Striped Owls occur here because there is a natural corridor of tala forest which extends from the Entre Rios Province to Mar Chi- quita Lagoon (Vervoorst 1967). Resumen. — Se presenta informacion sobre la dieta del Le- chuzon Orejudo (Asia damator) en base al an^isis de pellets (N = 34) y restos presa {N = 3), en el extremo Sur de su distribucion Provincia de Buenos Aires, Argentina. Se iden- tificaron 56 items presa, correspondiendo el 55.4% a los mamiferos, el 42.9% a las aves y el 1.8% a los insectos. El rango de pesos presa consumidos por esta lechuza fue de Ig a 630 g. El item mejor represen tado tanto en numero (43%) como en biomasa (66.9%) fue Rattus spp. seguido en importancia numerica por el Chingolo Comun {Zonotn- chia capensis, 23.2%) ylaTorcaza {Zenaida auriculata, 17.9%). A nivel de las aves el mayor aporte de biomasa fue dado por Z. auriculata (15%). [Traduccion de Autores] September 2000 Short Communications 237 Acknowledgments We thank R. Caceres, M. Favero, S. and L. Bachmann, and students for field assistance, and A. Malizia for as- sisting in mammal identification. F. Jaksic and two anon- ymous referees made important contributions to improve this paper. Finally, we would like to express our especial gratitude to Mariano Manuel Martinez, and this paper is dedicated to his memory. Literature Cited Bledinger, R, E. De Luca, and M. Saggese. 1987. Nidi- ficacion otono-invernal del Lechuzon Orejudo. Nues- tras Aves 5:19. Burton, J. [Ed,], 1973. Owls of the world. Their evolu- tion, structure and ecology. E.P. Dutton and Co., Inc., New York, NYU.S.A. Cabrera, A. 1976. Regiones Fitogeograficas Argentinas. Enciclopedia Argentina de Agricultura y Jardineria. Tomo 11, fasciculo 1. Ed. Acme, Buenos Aires, Argen- tina. Camperi, A.R. 1992. Estudio sobre aves colectadas en el extremo sudoeste de la Provincia de Buenos Aires. Neotropica 38:127-140. Canevari, M., P. Canevari, G.R. Carrizo, G. Harris, J. Rodriguez Mata, and R. Straneck. 1991. Nueva guia de las aves argentinas. Tomos I y II. Fundacion Acin- dar, Buenos Aires, Argentina. Grossman, M.L. and J. Hamlet. 1964. Birds of prey of the world. Bonanza Books, New York, NY U.S.A. Holt, D.W., R. Berkley, C. Deppe, P.L. Enriquez Rocha, P.D. Olsen, J.L. Petersen, J.L. Rangel Salazar, K P Segars, and K.L. Wood. 1999. Family Strigidae (Typ- ical Owls). Pages 152-242 mj. del Hoyo, A. Elliot, and J. Sargatal [Eds.], Handbook of the birds of the world. Vol. 5. Barn Owls to hummingbirds. Lynx Edicions, Barcelona, Spain. Jimenez, J.E. 1993. Notes on the diet of the Aplomado Falcon {Falco femoralis) in northcentral Chile./. Raptor Res. 27:161-163. MartInez, M.M., J.P. ISACCH AND F. Donatti. 1996. As- pectos de la distribucion y biologia reproductiva de Asio clamator en la Provincia de Buenos Aires, Argen- tina. Ornitologia Neotropical 7:157-161. Narosky, T. and a. Di Giacomo. 1993. Las aves de la provincia de Buenos Aires: distribucion y estatus. Asoc. Ornitologica del Plata, Vazquez Mazzini Ed y L.O.L.A., Buenos Aires, Argentina. Phelps, Jr., W.H. and R. Meyer De Schauensee. 1994. Una guia de las aves de Venezuela. Graficas Armitano, Caracas, Venezuela. Redford, K.H. AND J.F. Eisenberg. 1992. Mammals of the neotropics. The Southern Cone. Vol. 2. Univ. Chicago Press, Chicago, IL U.S.A. Salvador, S.A. 1988. Datos de peso de aves argentinas. Hornero 13:78-83. Vervoorst, F. 1967. Las comunidades vege tales de la de- presion del Salado (Prov. de Buenos Aires) . INTA. La vegetacion de la Republica Argentina 7:1-262. Received 1 May 1999; accepted 20 March 2000 J. Raptor Res. 34(3) :237-241 © 2000 The Raptor Research Foundation, Inc. Diet of Breeding Cinereous Harriers ( Circus cinereus) in Southeastern Buenos Aires Province, Argentina Maria S. Bo, Sandra M. Cicchino, and Mariano M. Martinez^ Departamento de Biologia, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350, (7600) Mar del Plata, Argentina Key Words: Cinereous Harrier, Circus cinereus; breeding diet, trophic niche breadth', Argentina. The Cinereous Harrier (Circus cinereus), one of two South American harriers, is widespread and distributed from Colombia and Ecuador, through Peru, Bolivia and Paraguay, southwestern Brazil to Tierra del Fuego and Islas Malvinas (Grossman and Hamlet 1964, Canevari et al. 1991, del Hoyo et al. 1994). In Argentina, it is most ^ Deceased. common in Patagonia and Islas Malvinas (Narosky and Yzurieta 1987) but it has also been recorded throughout northwestern, central and, occasionally, the northeastern parts of the country (Canevari et al. 1991). The Cinere- ous Harrier inhabits savannas, grasslands, wetlands, marshes, lagoons, shrubsteppes, and shrublands 0-4500 m elevation (Jimenez and Jaksic 1988, Canevari et al. 1991, Narosky and Di Giacomo 1993, del Hoyo et al. 1994). Little has been reported about the Cinereous Harrier The few previous studies of this species have focused on aspects of ecology and behavior (Jimenez and Jaksic 238 Short Communications VoL. 34, No. 3 1988) and breeding biology (Narosky and Yzurieta 1973, Saggese and De Lucca 1995). General information about Its feeding habits suggests that it eats birds, small mam- mals, and reptiles (Humphrey et al. 1970, De La Pena 1985, Canevari et al. 1991, del Hoyo et al. 1994). Its diet has only been analyzed in detail in southernmost Chile (Jimenez and Jaksic 1988), where it preys on insects, birds, mammals, reptiles, and arachnids. In this paper, we report on the breeding season diet and trophic niche breadth of the Cinereous Harrier in the Pampas Zone of Argentina. Methods The study was carried out in Laguna de los Padres In- tegral Reserve (37°56'S, 57°44'W), located 16 km west of Mar del Plata City, in southeastern Buenos Aires Prov- ince. The reserve is 680 ha in size, with a gentle relief composed of low hills and plains. The climate is subhu- mid to humid with a mean annual temperature of 13.8°C and a mean annual precipitation of about 844 mm (J. Cionchi unpubl. data). The breeding area studied was located in the “El Cur- ral” Intangible Reserve Zone, an area 87 ha in size, where Cinereous Harriers nested in sympatry with Long- winged Harriers {Circus buffoni). The area is character- ized by a mosaic of shrublands consisting of the native “Curro” {Colletia paradoxa) , the exotic blackberry {Rubus ulmifolius) and modified pampean grassland genera such as Stipa, Bothriochloa, Conium, and Carduus (Cabrera and Zardini 1978). Cultivated fields, pastures, tree plantations (mainly Eucalyptus spp.), and suburban zones surround the core study area, which is located 400 m from the closest water (Laguna de Los Padres) . Harrier pellets and prey remains were collected every 5-6 d from nesting sites, plucking stations, and roosts from September to March of 1992-93 and 1993-94. Iden- tification of remains of birds, mammals, and amphibians found in pellets and other prey remains was based on bones, feathers, beaks, hair, and dentition. We compared these items to collections in Museo de Ciencias Naturales de La Plata, Museo de Ciencias Naturales “Lorenzo Scag- lia” de Mar del Plata along with the collections of the Laboratorio de Vertebrados, Facultad de Ciencias Exactas y Naturales-Universidad Nacional de Mar del Plata. Most prey items were identified to species. During identifica- tion, pellets and prey remains in a day’s collection from each breeding pair were lumped and reconstructed by matching the remiges, rectrices, beaks, and bones of birds and the fur, skull parts, and feet of mammals. This procedure minimized the possibility of overcounting the number of individuals of each species (Marti 1987). Weights of adult birds were obtained from the litera- ture (Fiora 1933, Contreras 1979, Salvador and Salvador 1986, Salvador 1988, 1990, Camperi 1992) and from un- published data of the Museo de Ciencias Naturales “Lor- enzo Scaglia” (Mar del Plata City). Weights of mammals were provided by M. Kittlein (unpubl. data) and V. Com- paratore and A. Barbini (unpubl. data). The weight of the common toad {Bufo arenarum) was taken from Lan- gone (1994). When the sex of prey could not be deter- mined, the mean weight of males and females for that species was used. Geometric mean weights for total prey were calculated as x ± SE (Marti 1987). Levins’ index of trophic niche breadth (Marti 1987) was calculated as fol- lows: B = 1/XjLi where pi is the proportion of prey in different categories (mainly species) . B varies from 1 to n, maximum number of prey categories. If prey are equally common in all categories, then B = n. If all prey belong to only one category, B = 1. Results We collected 63 pellets and 45 prey remains from five Cinereous Harrier pairs breeding in 1992-93 and five pairs breeding in 1993-94. The pellets had a mean length of 35.9 ± 8.0 mm (±SD) and a mean width of 17.7 ± 2.9 mm {N = 53). A total of 104 prey items was identified from three taxonomic classes that included 20 vertebrate species and unidentified items (Table 1). Lev- ins’ index was 7.1 {N = 20). Birds accounted for 94% of the total prey items, followed by mammals (5%). Only one amphibian was identified (Table 1). Avian prey included 14 species, with passerines being the most common of all prey (88%) (Table 1). Among passerines, House Sparrows {Passer domesticus) (21%), Ru- fous-collared Sparrows {Zonotrichia capensis) (19%), and Grassland Yellow-finches {Sicalis luteola) (19%) were the most abundant species in the diet. Doves (15%), the Eared Dove {Zinaida auriculata), and the Picui Ground- Dove ( Columbina picui) , were the second most numerous taxa consumed (Table 1). Among mammal prey, rodents were the most common (3%), followed by lagomorphs (2%) (Table 1). Prey weights of animals consumed ranged from 1.5 g (bird egg in one pellet) to 300 g (ju- venile European hare, Lepus capensis) (Table 1). The geo- metric mean weight of prey was 31.2 g ± 5.5 (±SE). Most prey (84%) weighed <60 g, and the most abundant prey were Grassland Yellow-finches, House Sparrows, and Ru- fous-collared Sparrows. Birds contributed most to the total prey biomass (81%), with Eared Doves (28.2%) being the main con- tributor. House Sparrows (14.3%), Rufous-collared Spar- rows (9.2%), and Grassland Yellow-finches (6.7%) were also important in the biomass. Biomass contributed by mammals was 15%, with juvenile European hares con- tributing the highest value (12.5%). Amphibian biomass was low (3.8%) in the diet of this harrier (Table 1). Discussion Birds were the most common prey in the diet of the Cinereous Harrier, both numerically and in terms of bio- mass. Birds are the most common prey of many other species of Circus (Schipper 1973, Baker-Gabh 1981, Bar- nard et al. 1987, Witkowski 1989, Gonzalez Lopez 1991, del Hoyo et al. 1994, Bo et al. 1996). Cinereous Harriers preyed primarily upon passerine birds such as House Sparrows, Rufous-collared Sparrows, and Grassland Yel- low-finches. The food hahits we recorded differed from those re- September 2000 Short Communications 239 Table 1. Percent total frequency of prey items, mean individual weight, and percent total biomass in the diet of Cinereous Harriers during the breeding season in southeastern Buenos Aires Province, Argentina. Prey % Total Frequency Mean Individual Weight (g) % Total Biomass Amphibia ( 1 . 0 )- Bufonidae Bufo arenarum 1 . 0 *^ 180 3.8 Birds ( 94 . 0 ) Nonpasserine Columbidae Columbina picui 5.5 55 6.9 Zenaida auriculata 9.5 135 28.2 Picidae Colaptes campestris 1.0 200 4.2 Passerine Tyrannidae Tyrannus melancholicus 1.0 45 0.9 Troglodytidae Troglodytes aedon 1.0 10 0.2 Emberizidae Sicalis luteola 19.0 16 6.7 Sicalis luteola (egg) 1.0 1.6 < 0.1 Sicalis spp. 2.0 16 0.7 Zonotrichia capensis 19.0 22 9.2 Sporophila caerukscens 1.0 11 0.2 Molothrus bonariensis 2.0 62 2.6 Molothrus badius 2.0 53 2.2 Carduelis magellanica 3.0 15 0.9 Carduelis chloris 3.0 25 1.6 Ploceidae Passer domesticus 21.0 31 14.3 Unidentified Passeriformes 2.0 23 " 1.0 Unidentified birds 1.0 46 ‘i 0.9 Mammals ( 5 . 0 ) Leporidae Lepus capensis (juveniles) 2.0 300 12.5 Muridae Oxymycterus rufus 1.0 70 1.5 Akodon azarae 1.0 21 0.4 Unidentified murids 1.0 45 " 0.9 Total Number of Prey Items 104 * Total by prey class. Total by prey species. Average of the three most common passerine birds in the sample. Average of all the birds in the sample. ^ Average of the two murids in the sample. ported previously. In southernmost Chile, Jimenez and Jaksic ( 1988 ) identified a total of 1259 prey items of which 33 . 6 % were insects, followed by birds ( 2 V . 2 %), mammals ( 19 . 1 %), reptiles ( 19 . 1 %), and arachnids ( 1 . 0 %). House (in Jimenez and Jaksic 1988 ) also indicat- ed that Cinereous Harriers in Chile preyed predomi- nantly upon rats and field mice (species names not pro- vided by these authors), and that they also ate birds, insects, and reptiles. In Tierra del Fuego, the Cinereous Harrier did not prey on birds, taking only lizards and rodents (Humphrey et al. 1970). The absence of reptiles in the diet of birds from our study area in part might 240 Short Communications VoL. 34, No. 3 have been due to their lower availability in comparison to Chile and Patagonia. In terms of biomass, birds were the most important group in the diet, a finding that was similar to that of Jimenez and Jaksic (1988) in southernmost Chile. Three species, Eared Dove, House Sparrow, and Rufous-collared Sparrow, made up over 52% of the biomass in our study. When compared with the diet of Long-winged Harrier (Bo et al. 1996), which nests sympatrically with the Ci- nereous Harrier, we found that the values of trophic niche breadth were similar for the Long-winged Harrier (standarized Levins’ index — B' = 0. 21) and the Cine- reous Harrier (B' = 0.19; N = 34). There was both over- lap and divergence in the prey of these sympatric species (Pianka’s overlap index = 0.67; this value calculated from data of this study and data of B6 et al. 1996) . For both species, birds were the most abundant prey. For the Cinereous Harrier, birds comprised 94.2% of the diet whereas for the Long-winged Harrier, birds comprised 80%. Both harriers preyed principally upon passerines (Cinereous Harrier = 81.2%, Long-winged Harrier = 61.2%), with Rufous-collared Sparrows being most com- mon in both diets (Cinereous Harrier = 19%, Long- winged Harrier = 27.5%). The Long-winged Harrier preyed upon aquatic birds (7.2%) which did not occur in the diet of the Cinereous Harrier. Mammals were the second most common taxa consumed by the two harriers, although the percentage varied (Cinereous Harrier = 5%, Long-winged Harrier = 17.5%). Utilization of ter- restrial prey was comparable with observations of Narosky and Yzurieta (1973) who found that Cinereous Harriers were more terrestrial hunters than Long-winged Harri- ers. Minimum prey weight did not vary between Cinereous Harriers (1.5 g: Grassland Yellow-finch egg) and Long- winged Harriers (1 g: insects) but the maximum weight was greater in Long-winged Harriers than that in Cine- reous Harriers (Long-winged Harrier = 450 g White- faced Ibis, Pkgadis chihv, Cinereous Harrier = 300 g ju- venile European hare). However, the geometric mean weight was similar (Cinereous Harrier = 31.2 ± 5.5 g; Long-winged harrier = 32.4 ± 11.2 g). Birds contributed most of the biomass in the diet of both species, with a higher percentage for Cinereous Harriers (81%) than for Long-winged Harriers (68%). However, the species contributing most of the biomass were not the same. Cinerous Harriers ate mainly Eared Doves and Long-winged Harriers ate mainly White-faced Ibis. ResumeN. — Se estudio la dieta del Gavilan Ceniciento {Circus cinereus) durante dos periodos reproductivos en la Reserva Integral Laguna de Los Padres, Provincia de Buenos Aires. El area de nidificacion se encuentra en un ambiente arbustivo circundado por campos cultivados, pasturas, montes, lagunas y areas suburbanas. Se recolec- taron 63 egagropilas y 45 restos presa, provenientes de 10 parejas nidificantes. Se identificaron 104 items presa, corespondiendo el 94% a las aves, el 5% a los mamiferos y un solo anfibio. La amplitud de nicho trofico (B) fue de 7.1 (N = 20). Los paseriformes fueron las presas mas comunes (88%) del total de items presa, dentro de las cuales el Gorrion {Passer domesticus) , el Chingolo ( Zono- trichia capensis) y el Misto {Sicalis luteola) fueron las prin- cipales especies capturadas. La media geometrica del peso de presas consumidas fue de 31.2 g ± 5.5 {x ± SE) (rango = 1.5-300 g). En cuanto a la biomasa aportada las aves contribuyeron en un 81%. La dieta del Gavilan Ceniciento en la provincia de Buenos Aires difirio con otras areas de estudio (Chile y zona Patagonica) pero presento similitud con su congenere el Gavilan Planea- dor {Circus buffoni) nidificando en simpatria. [Traduccion de Autores] Acknowledgments We thank R. Simmons for his very helpful suggestions, E. Madrid and R. Caceres for their valuable help in the field and A. Vassallo for assistance in mammal identifi- cation. We also thank N. Bo and C. Darrieu, curators of the Museo de Ciencias Naturales de La Plata, and S. Cas- ertano and D. Romero of the Museo de Ciencias Natur- ales “Lorenzo Scaglia,” who allowed access to collections under their care. The continued support of J. Bo is great- ly appreciated. We are grateful for the review and com- ments provided by D. Smith, D. Varland, and two anon- ymous reviewers. Finally we would like to express our special gratitude to Mariano Manuel Martinez. This pa- per is dedicated to his memory. Literature Cited Baker-Gabb, D.J. 1981. Breeding behaviour and ecology of the Australasian Harrier ( Circus approximans) in the Manawatu-Rangitikei Sand-Country, New Zealand. No- torwA 28:103-119. Barnard, P.E., B. MacWhirter, R. Simmons, G.L. Han- sen, AND PC. Smith. 1987. Timing of breeding and the seasonal importance of passerine prey to North- ern Harriers {Circus cyaneus). Can. J. Zool. 65:1942- 1946. B6, M.S., S.M. CiccHiNO, and M.M. Martinez. 1996. Diet of Long-winged Harrier {Circus buffoni) in southeast- ern Buenos Aires Province, Argentina. J. Raptor Res. 30:237-239. Cabrera, A.L. and E.M. Zardini. 1978. Manual de la flora de los alrededores de Buenos Aires. Editorial ACME S.A.C.I., Buenos Aires, Argentina. Camperi, A.R. 1992. Estudio sobre aves colectadas en el extremo sudoeste de la Provincia de Buenos Aires Neotropica 38:127-140. Canevari, M., P. Canevari, G.R. Carrizo, G. Harris, J. Rodriguez Mata, and RJ. Straneck. 1991. Nueva guia de las Aves Argentinas. Fundacion Acindar, Buenos Aires, Argentina. Contreras, J.R. 1979. Birds weights from northeastern Argentina. Bull. Br. Ornithol. Club 99:21-24. September 2000 Short Communications 241 De La Pena, M.R. 1985. Gma de Aves Argentinas, Falcon- iformes. Edicion del autor, Santa Fe, Argentina. DEL Hoyo, J., A. Elliott, and J. Sargatal. [Eds.]. 1994. Handbook of the birds of the world. Vol. 2. New World vultures to guineafowl. Lynx Edicions, Barce- lona, Spain. Fiora, a. 1933. El peso de las aves. Hornero 5:174-188. Gonzalez Lopez, J.L. 1991. El Aguilucho Lagunero Cir- cus aeru^nosus (L., 1748) en Espana. Situacion, Biol- ogia de la Reproduccion, Alimentacion y Conserva- cion. ICONA — C.S.I.C, Madrid, Espana. Grossman, M.L. and J. Hamlet. 1964. Birds of prey of the world. Bonanza Books, New York, NY U.S.A. Humphrey, P.S., D. Bridge, P.W. Reynolds, and R.T. Pe- terson. 1970. Birds of Isla Grande (Tierra del Fue- go). Preliminary Smithsonian Manual. Smithsonian Inst., Washington, DC U.S.A. Jimenez, J.E. and F. Jaksic. 1988. Ecology and behavior of southern South American Cinereous Harriers, Circus cinereus. Rev. Chil. Hist. Nat. 61:199-208. Langone, J.A. 1994. Ranas y sapos del Uruguay. Recon- ocimiento y aspectos biologicos. Museo Damaso An- tonio Larrahaga, No. 5-Serie de Divulgacion. Monte- video, Uruguay. Marti, C.D. 1987. Raptor food habits studies. Pages 67- 80 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline, and D.M. Bird [EdS.], Raptor management tech- niques manual. Nat. Wildl. Fed., Washington, DC U.S.A. Narosky, T. and A.G. Di Giacomo. 1993. Las Aves de la Provincia de Buenos Aires: distribucion y estatus. Aso- ciacion Ornitologica del Plata, Vazquez Mazzini Ed y L.O.L.A., Buenos Aires, Argentina. and D. Yzurieta. 1973. Nidificacion de dos circi- dos en la zona de San Vicente (Pcia. de Buenos Ai- res). Hornero 11:172-176. AND . 1987. Guia para la identificacion de las Aves de Argentina y Uruguay. Asoc. Ornitologica del Plata, Buenos Aires, Argentina. Saggese, M.D. AND E.R. De Lucca. 1995. Reproduccion del Gavilan Ceniciento Circus cinereus en la patagonia argentina. Hornero 14: 21-26. Salvador, S.A. 1988. Datos de peso de aves Argentinas. Hornero 13:78-83. . 1990. Datos de pesos de aves Argentinas 2. Hor- nero 13:169-171. AND L.A. Salvador. 1986. Nota sobre la reprod- uccion del misto {Sicalis luteola) en Cordoba, Argen- tina. Hornero 12:274—280. Schipper, W.J.A. 1973. A comparasion of prey selection in sympatric harriers (Circus) in western Europe. Ger- faut 63:17-120. WiTKOWSKi, J. 1989. Breeding biology and ecology of the Marsh Harrier Circus aeruginosus in the Barycz Valley, Poland. Acta Ornithol. 25:223-320. Received 6 June 1999; 21 March 2000 J Raptor Res. 34(3) :241-243 © 2000 The Raptor Research Foundation, Inc. Abundance of the Ogasawara Buzzard on Chichijima, The Pacific Ocean Tadashi Suzuki and Yuka Kato Department of Biological Science, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachi-ohji, Tokyo 192-0397, Japan Key Words: Ogasawara buzzard', Buteo buteo toyoshimai; Bonin', endemic, density. The Ogasawara buzzard (Buteo buteo toyoshimai) is an insular subspecies of the Common Buzzard (B. buteo, Or- nithological Society of Japan 1974, Brazil 1991, Monroe and Sibley 1993). It is endemic to the Ogasawara (Bonin) Islands, which lie about 1000 km south of Tokyo in the Pacific Ocean. It usually nests on rocky cliffs (Funatsu and Chiba 1991), although tree nesting has been recently reported (Takagi and Ueda 1998, Kato and Suzuki 1999). It differs from a nearest subspecies, B. buteo japonicus, be- cause of its drab plumage with less brown on the uppers and its longer beak and shorter wings and tarsi (Momi- yama 1927). The Ogasawara buzzard is listed as an endangered spe- cies in Japan (Japan Environmental Agency 1998) be- cause the population is so small. It is known to inhabit the two island groups of the Ogasawaras, Chichijima-ret- to, and Hahajima-retto (Brazil 1991), with total areas of 38.2 km^ and 27.0 km^, respectively (Ogasawara Natural Environmental Group 1992). Among the islands, Chich- ijima is the largest and probably supports the largest pop- ulation of buzzards. It is also the most developed of the Ogasawara Islands with a human population of about 1900 in 1998. In the early 1990s, the number of pairs of Ogasawara buzzards on Chichijima was estimated to be 242 Short Communications VoL. 34, No. 3 about 15 (Higuchi et al. 1988, Funatsu and Chiba 1991) but no recent estimates of the present population have been made. Here, we present the results of a study we undertook to estimate the number of pairs currently on Chichijima. Study Area Chichijima is situated at 27°04'N and 142°13'E and is approximately 24 km^ in area. Terrain on the island is steep with many mountain areas of volcanic origin but elevations do not exceed 326 m. There are many rocky coastal and mountain cliffs that provide potential nest sites for Ogasawara buzzards. Chichijima is generally cov- ered with low vegetation and canopy trees consisting of native and introduced species do not exceed 15 m in height (Shimizu and Tabata 1991). About 73% of Chich- ijima is covered with regenerated native forests and scrubs, and the remaining 27% includes coastal forests, exotic low shrubs {Leucaena leucocephala) and grasses {Stachytarpheta jamaicensis) , cultivated fields, crags, and vil- lage areas. Methods We systematically searched Chichijima for Ogasawara buzzards in March, April, May, June, August, and Decem- ber 1998 and February, March, April, and May 1999 (1- 2 wk per mo) during which time at least one of us stayed on Chichijima. When buzzards were found, we recorded their numbers, spatial position, flight path, any social in- teractions, and other patterns of behavior. Whenever pos- sible, buzzards were individually identified using plumage characteristics, plumage deficits or differing stages of plumage development. When necessary, we searched pre- sumed territories to determine occupancy. In so doing, we considered two nonantagonistic adults inhabiting a putative territory to be a pair. Results and Discussion We found a total of 28 territorial pairs and one un- mated, territorial individual by March 1999 and recon- firmed their occupancy of territories in May 1999. The pairs were dispersed rather evenly in both native and in- troduced habitats. For 16 of the 28 pairs, breeding activ- ity was confirmed either by observing deliveries of nest- ing materials to nests, adults attending nests, incubating adults, nestlings in nests, or fledglings in their territories. For the remaining eight pairs, neither attended nests nor fledglings were found; nevertheless, we suspected that they bred because we observed them either delivering prey to presumed nests, repeatedly visiting and leaving the same locations (probably nesting sites) on cliffs, or they showed aggressive or alert behavior when we en- tered their territories during the breeding season. Our estimate of 28 pairs of Ogasawara buzzards on Chichijima was nearly twice that previously reported for the island (Suzuki 1982, Higuchi et al. 1988, Funatsu and Chiba 1991). However, a comparison of our data with previous reports indicated that the increase was mainly due to the fact that we surveyed the island more thor- oughly. Therefore, it is unlikely that the population of buzzards on the island has increased in recent decades. We estimated the density of the buzzard population on Chichijima to be approximately 1.2 pairs per km^. Our density estimate was rather high compared to densities of other breeding populations of Common Buzzards. Densities up to 0.78 pairs per km^ have been reported in wooded areas of middle Europe (Newton et al. 1982) but normally densities are <0.5 pairs per km^ (Newton 1979, Newton et al. 1982, Dare and Barry 1990, Davis and Davis 1992, Halley 1993, Jedrejewski et al. 1994, Penteriani and Faivre 1997). Factors limiting raptor population are food supply, nest-site availability, and human intrusion (New- ton 1991). No other raptors, excluding occasional visi- tors, inhabit Chichijima; therefore, the high density of Ogasawara buzzards on Chichijima may be due to the abundance of nest sites and the lack of competition from other raptors for food. It may also be due to the overall absence of human persecution. The density of buzzards also appears to be high on other islands in Chichijima-retto and Hahajima-retto, al- though recent survey data are not available (Higuchi et al. 1988, Funatsu and Chiba 1991, Suzuki 1991). We es- timated the total population of Ogasawara buzzards on the Ogasawara Islands to be only about 85 pairs using our density estimate of 1.2 pairs per km‘^ on Ogasawara and a total area of potential habitat of 70.7 km^ including Mukojima-retto, the third island group of the Ogasawar- as. Further study is needed to better document the total population of Ogasawara buzzards, including nonterri- torial individuals, and to determine its nesting ecology to insure the future conservation of the subspecies. Resumen. — Buteo buteo toyoshimai es endemico a las Islas Ogasawara (Bonin), a 1000 km al sur de Japon. Investi- gamos el numero de parejas de Buteo buteo toyoshimai en Chichijima (ca. 24 km^), la isla mas grande de las Oga- sawara, en 1998-99. Veintiocho parejas fueron encontra- das. Este estimativo fue el doble que el previamente re- portado, probablemente debido a la busqueda minuciosa hecha en la isla. La densidad de parejas (1.2 parejas por km‘^) fue mas alta en comparacion con los valores de Buteo buteo reportados en otras partes del mundo. [Traduccion de Cesar Marquez] Acknowledgments We thank T. Yasui, F. Nobushima, and H. Chiba for helpful information and field support, and S. Katada, N. Hasebe, T. Kubota, and Y. Kamimura for field assistance. We are grateful to S. Nohara and N. Kachi for providing us with the opportunity to conduct this study, and also to reviewers of JRR for improving the manuscript. This study was partially supported by the Research Project on Conservation Methods of Subtropical Island Ecosystems coordinated by S. Nohara and funded by Japan Environ- ment Agency. September 2000 Short Communications 243 Literature Cited Brazil, M.A. 1991. The birds of Japan. Christopher Helm, London, U.K. Dare, P.J. and J.T. Barry. 1990. Population size, density, and regularity in nest spacing of buzzards Buteo buteo in two upland regions of North Wales. Bird Study 37: 23-29. Davis, P.E. and J.E. Davis. 1992. Dispersal and age of first breeding of buzzards in central Wales. Br. Birds 83: 578-587. Funatsu, T. and H. Chiba. 1991. Status of the Common Buzzard on Chichijima. Pages 159-163 m M. Ono, M. Kimura, K. Miyashita, and M. Nogami [Eds.], Reports of the second general survey of natural environment of the Ogasawara (Bonin) Islands. Tokyo Metropoli- tan University, Tokyo, Japan. (In Japanese). Halley, D.J. 1993. Population changes and territorial dis- tribution of Common Buzzards Buteo buteo in the Cen- tral Highlands, Scotland. Bird Study 40:24-30. Higuchi, Y., S. Hanawa, K. Ueda, and H. Koyama. 1988. Status of the Ogasawara buzzard on Chichijima and Hah^ima. Pages 45-66 in Wild Bird Society of Japan [Ed.], Survey on special birds requiring protection. Wild Bird Society of Japan, Tokyo, Japan. (In Japa- nese). Japan Environmental Agency. 1998. Red list, birds, http: //www.eic.or.Jp/kisha/ attach. (In Japanese) . Jedrejewski, W., a. Szymura, and B. Jedrejewski. 1994. Reproduction and food of the buzzard Buteo buteo in relation to the abundance of rodents and birds in Bi- alowieza National Park, Poland. Ethol. Ecol. & Evol. 6: 179-190. Kato, Y. and T. Suzuki. 1999. Tree nesting by the Oga- sawara buzzard. Ann. Rep. Ogasawara Res. 22:57-60. (In Japanese). Momiyama, T.T. 1927. Twenty-five new birds from Japa- nese territories. Annot. Ornithol. Orient. 1:81-101. Monroe, B.L. and C.G. Sibley. 1993. A world checklist of birds. Yale Univ. Press, New Haven, CT U.S.A. Newton, I. 1979. Population ecology of raptors. T. & A.D. Poyser, Berkhamsted, U.K. . 1991. Population limitation in birds of prey: a comparative approach. Pages 3-21 in C.M. Pernns, J-D. Lebreton, and G.J.M. Hirons [Eds.], Bird popu- lation studies. Oxford Univ., Oxford, U.K. , P.E. Davis and J.E. Davis. 1982. Ravens and buz- zards in relation to sheep-farming and forestry m Wales. J. Appl. Ecol. 19:681-706. Ogasawara Natural Environmental Group. 1992. The nature of the Ogasawara Islands. Kokin-shoin, Tokyo, Japan. (In Japanese). Ornithological Society of Japan. 1974. Check-list of Japanese birds, 5th ed. Gakken, Tokyo, Japan. Penteriani, V. AND B. Faivre. 1997. Breeding density and landscape-level habitat selection of Common Buz- zards {Buteo buteo) in a mountain area (Abruzzo Ap- ennines, Italy)./. Raptor Res. 31:208-212. Shimizu, Y and H. Tabata. 1991. Forest structures, com- position, and distribution on a Pacific island, with ref- erence to ecological release and speciation. Pac. Sa. 45:28-49. Suzuki, T. 1982. Status of the Ogasawara buzzard on Chichijima “Estimation of distribution and abun- dance.” Ann. Rep. Ogasawara Res. 6:23-34. (In Japa- nese). . 1991. Status of the landbirds on the satellite is- lands of Hahajima, the Ogasawara Islands, with spe- cial reference to Common Buzzards, Oriental Green- hnches and Bonin Islands Honeyeaters. Pages 148- 157 in M. Ono, M. Kimura, K. Miyashita, and M. Nogami [Eds.], Reports of the second general survey of natural environment of the Ogasawara (Bonin) Is- lands. Tokyo Metropolitan University, Tokyo, Japan. (In Japanese). Takagi, M. and M. Ueda. 1998. Tree nesting by the Oga- sawara buzzard on Chichijima, in the Bonin Islands. Jpn. J. Ornithol. 46:175-176. Received 2 December 1999; accepted 25 May 2000 Letters J Raptor Res. 34(3): 244-245 © 2000 The Raptor Research Foundation, Inc. Golden Eagle Attacks and Kills Adult Male Coyote Golden Eagles (Aquila chrysaetos) attack and kill a wide range of small mammals, birds, and reptiles (e.g., Olendorff 1976, Am. Midi. Nat. 95:231-236; Johns 1977, Blue Jay 35:92-93; Servheen 1978, Murrelet 59:77; O’Gara 1994, Pages E41-E48 in S.E. Hygnstrom, R.M. Timm, and G.E. Larson (Eds.), Prevention and Control of Wildlife Damage. USDA, Animal and Plant Health Inspection Service, Animal Damage Control, Washington, DC U.S.A.). When the abundance of preferred prey declines (Steenhof and Kochert 1988,/. Anim. Ecol. 57:37-48), Golden Eagles will attack larger animals, including sheep and cattle (Arnold, 1954, USFWS Cir. 27; Lock and Stephen 1959,/ Anim. Ecol. 28:43-50; Bergo 1987, Fauna Norv. Ser. C. Cinculus 10:95-102; Phillips et al. 1996, Wildl. Soc. Bull. 24:468-470), reindeer {Rangifer tarandus; Nybakk et al. 2000, Wildl. Soc. Bull. 27:1038-1042), ibex {Capra ibex, Nievergelt 1966, Der alpensteinbock Capra ibex L. in seinem Levensraum Verlag Paul Parey, Hamburg, Germany), red deer {Cervus elaphus; Northeast 1978, Br Birds 71:36-37; Rebecca 1986, Scott. Birds 14:86), pronghorn {Antilocapra americana; Deblinger and Alldredge 1996, /. Raptor Res. 30:157-159), and roe deer {Capreolus capreolus; von Raesfeld 1965, Das rehwild, Verlag Paul Parey, Hamburg, Germany) . Apparently, such depredation on large mammals is neither unusual nor site specific (Nybakk et al. 2000) . Golden Eagles also will attack other predators, including Peregrine Falcons {Falco peregrinus; VanZandt 1982, Colo. Field Ornithol. 16:20-21) and red fox {Vulpes vulpes; Hatch 1968, Blue Jay 26:78-80). Eagles have been seen feeding on coyote {Canis latrans; e.g., Woelfl and Woelfl 1994, Can. Field-Nat. 108:494—495) carcasses, but no incidents of actual killing of coyotes have been reported. On 23 December 1998 at 1600 H, I observed a coyote running along the crest of a hill in sagebrush-grass steppe 20 km northeast of Preston, ID U.S.A. A Golden Eagle circling perhaps 20 m above the hill stooped on the coyote and struck it just behind the shoulders knocking it to the ground. Almost immediately (within 10 sec), the eagle released the coyote and the coyote stood and ran over the crest of the hill. After a few moments (perhaps 30 sec) , the eagle flew off in the direction the coyote disappeared. I arrived at the attack site about 20 min. later and followed the coyote’s tracks and a blood trail in fresh snow. I flushed the eagle from a coulee about 50 m from the top of the hill and found the coyote where the eagle was. The coyote was dead and the body cavity had been opened just below the ribs. The heart and portions of the liver were missing. The stomach and intestines remained intact, although they had been pulled from the carcass. The coyote was an adult male and the carcass (minus the portion consumed by the eagle) weighed 13.5 kg. There were two sets of puncture wounds just anterior to the shoulders. Each set consisted of two punctures about 4 cm apart with a third wound about 10 cm behind. This pattern is typical of an eagle attack (Wade and Browns 1984, Texas Agric. Ext. Serv. Publ. No. B-1429). I skinned the coyote and found that the talons had punctured the lungs and aorta. There were no other obvious wounds. Others have reported eagle attacks on coyotes and eagles feeding on coyote carcasses. Woelfl and Woelfl (1994) reported four Golden Eagles feeding on a freshly killed coyote pup in southeastern Alberta, Canada. They surmised that the coyote was surprised and killed while foraging about 300 m from cover. Ford and Alcorn (1964, Condor 66: 76-77) and Dekker (1985, Can. Field-Nat. 99:383-385) described several unsuccessful Golden Eagle attacks on coyotes Bowen (1980,/ Mammal. 61:376-377) and Wells and Bekoff (1978,/. Mammal. 59:886-887) reported apparent com- petition among Bald Eagles (Haliaeetus leucocephalus) , Golden Eagles, and coyotes for carrion. All reports of eagle predation on coyotes describe attacks during winter and early spring (Woelfl and Woelfl 1994). Golden Eagles will attack a variety of large mammals, most frequently during winter and early spring, times of the year when food is scarce or nutritional requirements may be high (e.g., Deblinger and Alldredge 1996; Seguin and Thibault 1996, Rev. Ecol. Terre Vie 51:329-339). The available evidence suggests that these attacks are generally suc- cessful, provided that the quarry can be individually isolated (Nybakk et al. 2000) , and that it can be ridden until it collapses from exhaustion, shock, or internal injuries (Watson 1997, The Golden Eagle, T. 8c A.D. Poyser, London, U.K.). While limited, there is literature suggesting that mammalian predators are more likely to attack large prey when provisioning offspring (Till and Knowlton 1983,/. Wildl. Manage. 47:1018-1025; Knowlton etal. 1999,/. Range Manage., 52 398-412). I speculate that the same motivation could, in part, explain predation by Golden Eagles on relatively large animals. During the nesting season, Golden Eagles will kill 230 kg domestic calves (O’Gara 1978, Proc. Vertebr 244 September 2000 Letters 245 Pest Conf. 8:206-213; Grahm 1986, Scott. Birds 14:86; Phillips and Blom 1988, Proc, Vertebr. Pest Conf. 13:241-244; Phillips et al. 1996), adult domestic sheep and lambs (Svendson 1980 Var Fuglefauna 3:20-26 Hewson 1984,/. Appl. Ecol. 21: 843-868; Scrivner et al. 1990, Univ. Calif. Hopland Field Stn. Publ. No. 101:10-13) and adult reindeer (Nybakk et al. 2000). Although large prey are most often selected in inverse relationship to the availability of smaller prey (e.g., Steenhof and Kochert 1988), killing of livestock can occur even when small otherwise preferred prey such as jack- rabbits {Lepus spp.) and ground squirrels {Spermophilus spp.) are readily available (Phillips et al. 1996). Likewise, Nybakk et al. (2000) documented winter and early spring predation on semidomesticated reindeer calves and does. Halda (1983, Fauna 36:101) reported late winter and early spring Golden Eagle predation on mature roe deer. Tigner (1973, Southwest. Nat. 18:346-348), Goodwin (1977, 94:789-790) and Deblinger and Alldredge (1996) all reported eagle attacks on adult and fawn pronghorns in spring. Northeast (1978) and Rebecca (1986) reported winter and spring attacks on red deer; Lawson and Johnson (1982, Pages 1037-1055 mJ.A. Chapman and J.A. Feldhammer [Eds.], Wild mammals in North America: biology, management and conservation, Johns Hopkins Univ. Press, Balti- more, MD U.S.A.) reported predation on bighorn sheep lambs {Ovis canadensis) and Wigal and Coggins (1982, Pages 1008-1020 mJ.A. Chapman and J.A. Eeldhammer [Eds.], Wild mammals in North America: biology, management and conservation, Johns Hopkins Univ. Press, Baltimore, MD U.S.A.) reported killing of mountain goat {Oreamnos americanus) kids. Seasonal differences in prey selection by eagles, especially as they might reflect changes in nutritional requirements, have not been well investigated (Seguin and Thibault 1996) and the available evidence is somewhat contradictory Some studies, for example, suggest that large prey are favored early in nesting (Fernandez and Ceballos 1990, Orms Scand. 21:236-238). Others suggest that such prey are unimportant for nesting birds but instead are favored by overwintering eagles (Mollhagen et. al. 1976,/. Wildl Manage. 36:784-792). Because there are data consistent with the possibility that prey-size selection by mammalian predators may be influenced by the number of offspring being fed (Till and Knowlton 1983), it might be worthwhile to investigate whether there is evidence of a similar facultative response expressed by raptors. I thank M. Fall, A. Harmata, and C. McIntyre for comments on the manuscript. — J.R. Mason, USDA, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, Utah State University, Logan, Utah 84322-5295 U.SA. /. Raptor Res. 34(3):245-246 © 2000 The Raptor Research Foundation, Inc. Golden Eagle Pair Kills Ferruginous Hawk in Wyoming We saw a pair of Golden Eagles {Aquila chrysaetos) kill a lone adult Ferruginous Hawk {Buteo regalis) in Thunder Basin National Grassland (TBNG) in East Central Wyoming on 20 June 1999. The attack took place around 1100 H m the Rochelle Hills area (43°52T8"N, 105°01'42"W). We were sitting in a stopped vehicle and watched the attack from 0.8 km away. The eagles alternatively dove upon the hawk as it flew less than 7 m from the ground. The attack lasted about 25 min from the time we first observed it and consisted of five dives by each eagle. The attack sequence entailed one eagle diving on the hawk followed within 30 sec by the second when the hawk was occupied with the first eagle. The Ferruginous Hawk either rolled onto its back exposing its talons to the diving eagles or turned sharply to avoid contact. On the fifth attempt, the second eagle hit the hawk in the air. The eagle continued to hold onto the dead hawk as they fell to the ground where the eagle mantled the hawk. Previous literature indicated this tandem hunting strategy used by eagles taking black-tailed jackrabbits {Lepus californicus) and a red fox {Vulpes fulva) in which one eagle either flushed the prey or diverted its attention while the second eagle attacked (Hatch 1968, Blue Jay 26: 78-80, Collopy 1983, Auk 100:747-749). We did not determine the sex of the eagle that made the kill. The second eagle landed 2 m away and both eagles remained on the ground for 5 min. Neither eagle consumed any of the carcass and the pair flew off together. We watched the event from a distance and did not harass the eagles forcing them to abandon the kill. Neither eagle appeared disturbed for any reason but remained calm during the time spent on the ground and as it flew away. Golden Eagles prey upon a variety of species ranging in size from small rodents to ungulates such as antelope {Antilocapra americana) and mule deer {Odocoileus hemionus) (Hogstrom and Wiss 1992, Ornis Fenn. 69:39-44, Watson et al. 1993, Ibis 135:387-393, Deblinger and Alldredge 1996,/ Raptor Res. 30:157-159). Golden Eagles have attacked 246 Letters VoL. 34, No. 3 other birds of prey for a variety of reasons including food robbing, predation, and nest defense (Hays 1987,/. Raptor Res. 21:87-5, Ferrer 1990,/. Raptor Res. 24:210-218; Clouet et al. 1999,/. Raptor Res. 33:102-109). In TBNG, Golden Eagles and Ferruginous Hawks often pursue similar prey species, primarily the black-tailed prairie dog {Cynomys ludovicianus) and several lagomorphs. We wondered if the eagles might be defending a food source from a potential competing species but it did not seem likely. Nest defense was examined as a possible explanation for the attack. A search of the area did not reveal any nest but it may have been overlooked due to irregular terrain. Even though a nest was not located, nest defense seemed be the logical explanation for this attack. Protection of nestlings may have been the reason for the attack even though Ferruginous Hawks have not been known to take Golden Eagle nestlings. Golden Eagles do aggressively defend their nesting territory from other raptor species (Watson 1997, The Golden Eagle, T. 8c A.D. Poyser, London, U.K.). The Golden Eagle pair may have been protecting its nest from a perceived threat. — Matt L. Buhler, Jake H. Powell, and Stanley H. Anderson, Wyoming Cooperative Fish and Wildlife Research Unit, P.O. Box 3166, University of Wyoming, Laramie, WY 82071 U.SA. BOOK REVIEW Edited by Jeffrey S. Marks J Raptor Res. 34(3):247-248 © 2000 The Raptor Research Foundation, Inc. Handbook of the Birds of the World, Volume 5. Barn-owls to Hummingbirds. Edited byjosep del Hoyo, Andrew Elliott, and Jordi Sargatal. 1999. Lynx Edicions, Barcelona, Spain. 759 pp., 76 color plates, 406 color photographs, 758 distribution maps, 3 figures, and 1 table. ISBN 84-87334^25-3. Cloth, $185.00. — The Handbook of the Birds of the World (HBW) will be the first series to illustrate all of the species of birds on earth and to provide ac- cess to all of the essential information about each one of them. In fact, the editors claim that it will be the first work to deal with each member of an entire class of the animal kingdom. HBW is not yet half completed — it will consist of 12 volumes in all — and yet it already totals 3519 pages in volumes 1 to 5. The rate of production has been impressive considering the immense volume of material con- tained and that the first volume appeared in 1992. Volume 5, reviewed here, completes coverage of the raptors begun with the falconiforms in Volume 2. In addition to the Strigiformes, Volume 5 covers Caprimulgiformes and Apodiformes, but the ma- jority of this review will be concerned with the owl sections considering the primary interests of the readership of the Journal of Raptor Research. The owl portion of Volume 5 was written by 13 authors, including some well-recognized owl ex- perts and some individuals who will not be familiar even to those who follow the owl literature closely. More surprising than the use of litde-known au- thors is that many living owl experts are not among the authors of this work. A Forward discusses factors concerning risks to survival of bird populations in general and is fol- lowed by a very brief Introduction that notes three new developments for Volume 5: more plates and photographs, the longest single-species account to date (the Barn Owl {Tyto alba]), and the inclusion of details on restricted-range species. Illustration of the species covered in this volume could only be described as lavish: the photographs and paintings are excellent. Nineteen artists con- tributed the 76 color plates, seven of whom pro- duced the owl plates. My only complaint regarding the color plates is that the heads of the tytonids are uniformly too large in proportion to their bod- ies. Outstanding photographs show species in nat- ural habits illustrating a variety of behaviors. The bulk of the book is taken up with family and species accounts: two families for the strigiforms (242 pages), five for the caprimulgiforms (144 pag- es), and three for the apodiforms (294 pages). Each family account begins with a map of the group’s worldwide distribution, the general distin- guishing characteristics, size range, habitat require- ments, the number of genera and species, the number of species considered to be threatened, and the number that are extinct. Family accounts range from 6 to 77 pages in length and are fol- lowed by accounts for each species. Species ac- counts range in length considerably, reflecting the extent of knowledge on the various species. Tytonidae, containing only 16 species, is the third longest family account in the book, mirroring the wide geographic range and quantity of infor- mation available on the group. M.D. Bruce com- piled a huge quantity of knowledge about the bi- ology of tytonids, but I noted a few discrepancies between what Bruce presented and the original sources. For example, in the second paragraph on page 57, P.A. Stewart used 30°N latitude in the United States to delimit northern and southern populations of Barn Owls for the purpose of study- ing dispersal. Bruce, however, gives 3°N as the lat- itudinal demarcation. In the first paragraph on page 54, Bruce’s summary of the results of my study on lifetime reproductive success in Barn Owls incorrectly states that in one year, 1 1 % of owl pairs produced second broods. This should have read that over the 19-year study, 11% of pairs pro- duced double broods. The latitudinal error may be typographical, and the second-brood error may be the result of a too-hasty reading of only the paper’s abstract. They render some doubt, however, about the accuracy of other information in the account. 247 248 Book Review VoL. 34, No. 3 The family account of Strigidae is about twice as long as that of Tytonidae for a family with 12 times the number of species. A good discussion of recent DNA-DNA hybridization and mitochondrial DNA data reaffirms that strigiforms and falconiforms are not closely related despite their host of shared ad- aptations for prey capture. DNA also clearly con- firms that the caprimulgiforms are the closest rel- atives of strigiforms. Just like the account of Tytonidae, this account presents a huge quantity of information on the biology of the typical owls. One of the most serious criticisms of previous volumes of HBW (Gill, Condor 96:566-567, 1994; Jehl, Condor 100:405-409, 1998; Bates, Condor 100: 769-775, 1998; Brightsmith, Auk 116:1158-1159, 1999) was that literature citations are not given in the text, making it difficult or impossible to ascer- tain the source of a particular bit of information. I, too, found this omission to be a frustration, mak- ing the large body of references included less use- ful than it could have been. The entire HBW series with its extensive access to the literature and wonderful illustrations is a must for every library, but the cost and sheer bulk may deter individual ornithologists from obtaining the entire set. Raptor biologists, though, will want to add volumes 2 and 5 to their libraries. — Carl D. Marti, Raptor Research Center, Boise State Uni- versity, Boise, ID 83725 U.S.A. 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Other Features Inciude: • Factory tuned to any 4MHz wide segment in the 148-174HHz Band * Very high serrsitivity of •143dBm to •ISOdBm • Illuminated display and keypad for use in low light or darkness • User selectable scan rates from 1«30 seconds in 1 second steps • Rechargeable batteries operate the receiver for 12 hours and can be replaced with standard AA Alkaline batteries in the held. Both 12vdc and llOvac chargers are included. • 6.1" (15.5cm) high, 2.6‘ (6.6cm) wide. 1.5“ (3.8cm) deep. • 3 year warranty • 1 day delivery $ 695.00 Please specify desired 4HHz wide segment in the 148174MHz band Visit our website for complete specihcations. operating manual and information on the R-1000 or c “ toll-free number to order your receiver now. Try the New R-1000 and You'll Be Impressed! COMMUNICATIONS SPECIALISTS, INC. 426 West Taft Avenue • Orange. CA 92865-4296 • 1-714-998-3021 • Fax 1-714-974-3420 Entire U.S.A. (800) 854-0547 • Fax (800) 850-0547 • http://www.com-spec.com BUTEO BOOKS The following Birds of North America Species Accounts are available through Buteo Books, 3130 Laurel Road, Shipman, VA 22971. TOLL-FREE ORDERING; 1-800-722-2460; EAX: (804) 263-4842. E-mail; alien® buteobooks.com Barn Owl (1). Carl D. Marti. 1992. 16 pp. Boreal Owl (63). G.D. Hayward and RH. Hayward. 1993. 20 pp. Broad-winged Hawk. (218). L.J. Goodrich, S.C. Crocoll and S.E. Senner. 1996. 28 pp. Burrowing Owl (61). E.A. Haug, B.A. Millsap and M.S. Martell. 1993. 20 pp. Common Black-Hawk (122). Jay H. Schnell. 1994. 20 pp. Cooper’s Hawk (75). R.N. Rosenfield and J. Bielefeldt. 1993. 24 pp. Crested Caracara (249). Joan L. Morrison. 1996. 28 pp. Eastern Screech-owl (165). Erederick R. Gehlbach. 1995. 24 pp. Ferruginous Hawk (172). MarcJ. Bechard and Josef K. Schmutz. 1995. 20 pp. Flammulated Owl (93). D. Archibald McCallum. 1994. 24 pp. Great Gray Owl (41). Evelyn L. Bull and James R. Duncan. 1993. 16 pp. Great Horned Owl (372). C. Stuart Houston, Dwight G. Smith, and Christoph Rohner. 1998. 28 pp. Gyrfalcon (114). Nancy J. Clum and Tom J. Cade. 1994. 28 pp. Harris’ Hawk (146). James C. Bednarz. 1995. 24 pp. Long-eared Owl (133). J.S. Marks, D.L. Evans and D.W. Holt. 1994. 24 pp. Merlin (44). N.S. Sodhi, L. Oliphant, R James and 1. Warkentin. 1993. 20 pp. Mississippi Kite (402). James W. Parker. 1999. 28 pp. Northern Saw-whet Owl (42). Richard J. Cannings. 1993. 20 pp. Northern Goshawk (298) . John R. Squires and Richard T. Reynolds. 1997. 32 pp. Northern Harrier (210). R. Bruce MacWhirter and Keith L. Bildstein. 1996. 32 pp. Northern Hawk Owl (356). James R. Duncan and Patricia A. Duncan. 1998. 28 pp. Red-shouldered Hawk (107). Scott T. Crocoll. 1994. 20 pp. Red-tailed Hawk (52). C.R. Preston and R.D. Beane. 1993. 24 pp. Short-eared Owl (62). D.W. Holt and S.M. Leasure. 1993. 24 pp. Snail Kite (171). RW. Sykes, Jr., J. A. Rodgers, Jr. and R.E. Bennetts. 1995. 32 pp. Snowy Owl (10). David F. Parmelee. 1992. 20 pp. Spotted Owl (179). R.J. Gutierrez, A.B. Franklin and W.S. Lahaye. 1995. 28 pp. Swainson’s Hawk (265). A. Sidney England, MarcJ. Bechard and C. Stuart Houston. 1997. 28 pp. Swallow-tailed Kite (138). Kenneth D. Meyer. 1995. 24 pp. Turkey Vulture (339). David A. Kirk and Michael J. Mossman. 1998. 32 pp. White-tailed Hawk (30). C. Craig Farquhar. 1992. 20 pp. White-tailed Kite (178). Jeffrey R. Dunk. 1995. 16 pp. Buteo Books stocks all published species accounts, not only those covering raptors. The current list in taxo- nomic order may be viewed at: http://www.buteobooks.com Buteo Books stocks the Handbook of the Birds of the World. The first five volumes of this projected 12-volume work have been published including: Volume 2: New World Vultures to Guineafowl (1994) covering the diurnal raptors and Volume 5: Barn Owls to Hummingbirds (1999) covering owls. These volumes are priced at $185 each plus shipping and handling. Usually available from Buteo Books, the classic reference on diurnal birds of prey: Brown, Leslie and Dean Amadon. Eagles, Hawks and Falcons of the World. Country Life Books, 1968. Two volumes. First English edition in brown cloth. Fine in slipcase. $300.00 and other editions at lesser prices. 2000 ANNUAL MEETING The Raptor Research Foundation, Inc. 2000 annual meeting will be held on 8-11 November in Jonesboro, Arkansas, U.S.A. For information about the meeting contact James C. Bednarz, Depart- ment of Biological Sciences, Arkansas State University, P.O. Box 599, State University, AR 72467 U.S.A. Telephone 501-972-3082, E-mailjbednarz@navajo.astate.edu. Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Send requests for information concerning membership, subscriptions, special publications, or change of address to OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A. The Journal of Raptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $33.00 per year and to libraries and institutions for $50.00 per year from The Raptor Research Foundation, Inc., 14377 117th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental United States.) Periodicals postage paid at Hastings, Minnesota, and additional mailing offices. POSTMASTER: Send address changes to The Journal of Raptor Research, OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A. Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A. Copyright 2000 by The Raptor Research Foundation, Inc. Printed in U.S.A. 0 This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). Raptor Research Foundation, Inc., Awards Recognition for Significant Contributions^ The Dean Amadon Award recognizes an individual who has made significant contributions in the field of systematics or distribution of raptors. Contact: Dr. Clayton White, 161 WIDE, Department of Zoology, Brigham Yoimg University, Provo, UT 84602 U.S.A. Deadline August 15. The Tom Cade Award recognizes an individual who has made significant advances in the area of captive propagation and reintroduction of raptors. Contact: Dr. Brian Walton, Predatory Bird Research Group, Lower Quarry, University of California, Santa Cruz, CA 95064 U.S.A. Deadline: August 15. The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significantly to the understanding of raptor ecology and natural history. Contact: Dr. David E. Andersen, Department of Fisheries and Wildlife, 200 Hodson Hall, 1980 Folwell Avenue, University of Minnesota, St. Paul, MN 55108 U.S.A. Deadline: August 15. Recognition and Travel Assistance The James R. Kophn Travel Award is given to a student who is the senior author of the paper to be presented at the meeting for which travel funds are requested. Contact: Patricia A. Hall, 5937 E. Abbey Road, Flagstaff, AZ 86004 U.S A. The William C. Andersen Memorial Award is given to the student who presents the best paper at the annual Raptor Research Foundation Meeting. Contact: Ms. Laurie Goodrich, Hawk Mountain Sanctuary, Rural Route 2, Box 191, Kempton, PA 19529-9449 U.S.A. Deadline: Deadline established for meeting paper abstracts. Grants^ The Stephen R. TuUy Memorial Grant for $500 is given to support research, management and conservation of raptors, especially to students and amateurs with limited access to alternative funding. Contact: Dr. Kimberly Titus, Alaska Division of Wildlife Conservation, P.O. Box 20, Douglas, AK 99824 U.S.A. Dead- line: September 10. The Leshe Brown Memorial Grant for $500-$1,000 is given to support research and/or the dissemination of information on raptors, especially to individuals carrying out work in Africa. Contact: Dr. Jeffrey L. Lincer, 1220 Rosecrans St. #315, San Diego, CA 92106 U.SA. Deadline: September 15. ^Nominations should include: (1) the name, title and address of both nominee and nominator, (2) the names of three persons qualified to evaluate the nominee’s scientific contribution, (3) a brief (one page) summary of the scientific contribution of the nominee. ^Send 5 copies of a proposal (^5 pages) describing the applicant’s background, study goals and methods, anticipated budget, and other funding.