([SSN 0»92-]OL61 The Journal OF Raptor Research Volume 27 June 1993 Number 2 Contents Nesting Ecolcx;v of Ferruginolis Hawk in Northwestern New Mexico, M. Ramakkd and Rjobrrt T. Woycwodmc. 97 Nest-Site Habitat Selected sy Common Buzzard (Bvteo huteo) in Southwestern France. Chriaiinc Hubert , . 102 Roadside Rap'Ior Surveys in the Argentinean Patagonia. a. Dona^ar, li- Oigs OebatluK, Aiejsindm Trav^aini xnA Fernando ILiialdo . ^ ^ ^ ^ , , _ , ^ ^ ^ ^ ^ , 1 (^6 Short Communications I^AOiaR Owl pRHiATiON ON Eqyftiaw Vulture awo Northern Gosiivlwk: Possmle Effect Ol' A DECREA.'tR IK EUROPEAN Rahbit AVAILABILITY. 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THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. VoL. 27 June 1993 No. 2 J Raptor Res. 27(2);97-101 © 1993 The Raptor Research Foundation, Inc. NESTING ECOLOGY OF FERRUGINOUS HAWK IN NORTHWESTERN NEW MEXICO James M. Ramakka^ U.S. Bureau of Land Management, 1235 La Plata Highway, Farmington, NM 87401 U.S.A. Robert T. Woyewodzig^ U.S. Bureau of Indian Affairs, Shiprock, NM 87420 U.S.A. Abstract. — Ferruginous Hawk (Buteo regalis) nesting biology and habitats were studied in northwestern New Mexico from 1981-88. A total of 72 nest sites were located. The maximum number of breeding pairs recorded in any 1 year was 26. Clay or rock pinnacles were the most commonly used nest substrate. Nests were most frequently (56.9%) located in steeply eroded “badland” habitat even though this habitat type comprised only 3.9% of the total area studied. Nest building began in early March and fledging peaked during the last week in June. Mean number of young fledged per successful nest was 2.4. Mean number fledged per breeding pair was 1.8. The primary threat to Ferruginous Hawk in the study area was human disturbance caused by increased human settlement and recreational use of the badlands. Ecologia de la nidificacion de Buteo regalis en el noroeste de Nuevo Mexico Resumen. — Desde 1981-88 se estudio la biologia de nidificacion y habitats de Buteo regalis en el noroeste de Nuevo Mexico. Se ubico un total de 72 sitios de nidificacion. El mayor mimero de parejas reproductivas registradas en un aho fue de 26. Cimas rocosas o arcillosas fueron las mas usadas como sustrato de nidificacibn. Los nidos estuvieron frecuentemente (56.9%) localizados en pendientes fuertemente erosionadas de barrancos, aun cuando este tipo de habitat comprendia solamente el 3.9% del area total estudiada. La construccion del nido comenzo a principios de marzo y el mimero maximo de volantones se obtuvo durante la ultima semana de junio. El mimero promedio de jovenes volantones por nido exitoso fue 2.4. El mimero promedio de volantones por par reproductive fur 1.8. La amenaza principal para esta especie en el area de estudio fue la perturbacion humana. Causada por el aumento de establecimientos humanos y uso recreascional de estos sitios. [Traduccion de Ivan Lazo] The purpose of our study was to determine the number of Ferruginous Hawks nesting in areas of potential mineral and gas development and to identify faetors affeeting the use of nesting habitats. The orig- inal focus, starting in 1981, was on BLM administered lands in potential coal lease areas. As inventory and monitoring continued the study became more intensive. In 1986, the Bureau of Indian Affairs and the Navajo Game and Fish Department joined the study and be- gan examining Ferruginous Hawk habitat on Navajo Indian lands. Study Area The study area began as a 1619 km x 16 km belt starting 48 km south of Farmington, New Mexico and extending southeast to Cuba, New Mexico. In 1986, about 400 km^ of Little is known concerning the biology of the Fer- ruginous Hawk {Buteo regalis) in the southwestern United States (Hall et al. 1988). The species has been reported as a rare to uncommon nesting resident of New Mexico (Ligon 1961, Hubbard 1978). Tolle (1977) located an occupied nest in a coal lease area near Farmington but no large scale surveys for this species have been reported for this area. ' Present address: U.S. Bureau of Land Management, La- hontan Resource Area, 1535 Hot Springs Rd. Suite 300, Carson City, NV 89706 U.S.A. ^ Present address: U.S. Bureau of Land Management, Far- mington Resource Area, 1235 La Plata Highway, Farming- ton, NM 87401 U.S.A. 97 98 James M. Ramakka and Robert T. Woyewodzic Navajo Reservation land was added to the study area and searched for nests during the breeding season. In 1987, the study area was expanded to its final size of 5504 km^, in- cluding 4289 km^ of public land in the BLM Farmington Resource Area and 1215 km^ of Indian land in the northeast comer of the reservation. Elevations in the study area ranged from 1524-2134 m. Annual precipitation averaged 25-36 cm. Vegetation in the study area was characterized by gently rolling sandy grasslands dominated by Indian ricegrass (Ory- zopsis hymenoides) , sandhill muhly {Muhlenbergia pungens), and snakeweed {Xanthocephalum sarothrae). On mixed shmb/ grass uplands the dominant species were fourwing saltbush {Atriplex canescens), green rabbitbrush {Chrysothamnus visci- diflorus), snakeweed, gall eta grass {Hilaria jamesii) , and blue gramma {Bouteloua gracilis). Interspersed between these areas were broad, low flatlands bearing alkali sacaton (Sporobolus airoides), and areas of unvegetated exposed clay soil and rock outcrop classified as “badlands” or badland complex (Keetch 1980). Badland areas ranged from a few to many thousand ha in size. In the northern portion of the study area, grasslands and mixed shrub/grass uplands were replaced by big sage- brush {Artemisia tridentata) / gra.ss uplands. There were nu- merous ephemeral drainages bordered by narrow (2-40 m wide) bands of black greasewood {Sarcobatus vermiculatus) and rubber rabbitbrush {Chrysothamnus nauseosus). Utah ju- niper (Juniperus utahensis) and pinyon {Pinus edulis) occurred at higher elevations and, occasionally, in areas of rock outcrops in the grasslands. Fremont cottonwood trees {Populus fre- montii) occurred infrequently along drainages and edges of stock ponds. All of the study area was grazed by either cattle, sheep, goats, or horses. Human habitation was sparse and limited to widely scattered houses or small clusters of houses occupied by Navajo ranchers or herders. In the northwest corner of the study area, native grasslands were being converted into cultivated fields as part of the Navajo Indian Irrigation Proj- ect. In 1988 approximately 21 400 ha were under cultivation for production of alfalfa {Medicago sativa), corn {Zea mays), beans {Phaseolus vulgaris), potatoes {Solanum tuberosum), and onions {Allium cepa). Three small (<300 ha) and two large (>1000 ha) coal mines were active in the study area. Methods Nests were located by both ground and aerial searches. Approximately 100 hr of helicopter and 16 hr of fixed-wing flight time were used. Nests were recorded on parallel tran- sects, flying at altitudes of 30-200 m between late March and mid-May in 1981 and 1984-87. Ground searches were conducted on foot and with the use of 4-wheel drive vehicles. They were usually concentrated in areas where adult Fer- ruginous Hawks were observed but no nest had been pre- viously located. Stereographic aerial photographs and orthophotographs were used to plot the exact location of each nest on topographic maps (scale 1 :24 000). Height of the nest above the surround- ing terrain and description of the nest substrate were also recorded. Detailed vegetation measurements were not part of our study. However, some habitat information was gathered for nests located on public land. The vegetation within a radius of 100 m of the nest site was visually classified into one of five general habitat types based on an ocular estimation VoL. 27, No. 2 of the dominant plant community. These habitat types were: grassland, rabbitbrush/greasewood, big sagebrush, pinyon/ juniper woodland, and badlands. Grassland was composed of communities in which Indian rice grass, alkali sacaton, blue gramma, or galleta grass dominated. Rabbitbrush/ greasewood consisted primarily of shrub communities along drainages and flat areas that were seasonally flooded. Big sagebrush habitat was dominated by sage plants but often had a grass understory. Areas were classified as pinyon/ juniper habitat if they contained >4 trees/ha and trees were in a stand > 5 ha. Badlands were unvegetated areas of actively eroding clay soil and rock outcrop. The percent of each type present on public land in the study area was obtained by planimetering existing vegetation communities delineated on broad scale (1:126720) rangeland survey maps prepared for BLM land use plans. Equivalent mapping was not available for the reservation portion of the study area. Surrounding habitat type was not recorded for nests on the reservation. Nests with evidence of eggs or young were considered active. Productivity data were gathered from all active nests Occupied nests (incubating adult present) were observed from at least 300 m with a 20-60 x spotting scope to avoid disturbance. All occupied nests were revisited at least once late in the nesting season to count the number of young. Ages of young were estimated using the pictorial guide developed by Moritsch (1985). Unless field evidence indicated other- wise, nests containing young 30 d or older were considered successful. Results and Discussion Nests. A total of 72 Ferruginous Hawk nests (51 on public land, 21 on reservation land) was located between 1981-88. Based on observations of nest use in successive seasons, we believe this represented a minimum of 35 different territories used over the years. As many as five nests were contained in a single ter- ritory. The maximum number of breeding pairs we recorded in a single breeding season was 26. Nest height and substrate type were recorded for all 72 nests. Height of nests above the surrounding terrain averaged 7.7 m (range 0.0-24.6 m, SD = 6.1 m). Nest size and construction were typical of that de- scribed in other areas (Weston 1969, Olendorff 1973, Woffinden and Murphy 1982). On two oceasions ex- isting old nests virtually disappeared as new nests were constructed nearby suggesting that sticks from the old nests were used to construct new ones. Of the 72 total nests, 86% were situated on the tops of clay or rock pinnacles, 6% on cliffs and 4% were on the ground. Only 3% of the nests in our study area were in trees. Trees are a preferred nest substrate in some locations (Howard and Wolfe 1976, Smith and Murphy 1978, Gilmer and Stewart 1983, Perkins and Lindsey 1983, Woffinden and Murphy 1983, Schmutz 1984). Cliffs and trees were preferred nest substrates in Washington (Bechard et al. 1990). June 1993 Ferruginous Hawk in New Mexico 99 Table 1. Occurrence by habitat type of 51 Ferruginous Hawk nest sites on 4289 km^ of public land in northwestern New Mexico between 1981-88. Data from the Navajo Indian Reservation are not included. Confidence intervals are calculated according to Neu et al. (1974) and are based on a 90 % family confidence coefficient. Habitat Type Number of Nests Observed Proportion of Area in Each Habitat Type Proportion of Nests Observed IN Each Type (P i) Confidence Interval on Proportion of Occurrence Badlands 29 0.039 0.569 0.388 < Pi < 0.746 Rabbitbrush/greasewood 9 0.069 0.176 0.039 < P2 ^ 0.313 Grasslands 12 0.334 0.235 0.082 < p3 < 0.388 Big sagebrush 1 0.190 0.020 -0.031 < P4 < 0.071 Pinyon/juniper 0 0.368 0.0 — Habitat data were gathered from the 51 nests on public land (Table 1). A goodness-of-fit comparison indicated the expected number of nests in each habitat type differed significantly from the occurrence of gen- eral habitat types (x^ = 405.1, df = 4, P < 0.001). Calculation of confidence intervals by habitat type (Neu et al. 1974) revealed that badland sites were used sig- nificantly more than expected, while big sagebrush and pinyon/juniper were used significantly less often (a = 0.10). The proportion of nests located in grassland and rabbi tbrush/greasewood habitat were within the con- fidence intervals for expected values. Frequently, small badland areas surrounded by grassland were selected for nest sites. Such sites ap- parently serve as a special habitat feature by providing abundant erosional remnants and rocky pinnacles which are preferred as nest substrates (Evans 1983). Blair and Schitoskey (1982) also found Ferruginous Hawk nests in South Dakota in ungrazed or lightly grazed prairie or badlands surrounded by prairie. Nests in rabbitbrush/greasewood habitat were usu- ally placed on eroded pinnacles adjacent to a wash or drainage channel. Nests in grassland were usually lo- cated on small buttes or similar erosional remnants, while the one nest in big sagebrush habitat was located on a low cliff face. Further work is needed to define more narrowly the habitat factors which may influence nest site selection in our study area. Nesting Chronology. Adult Ferruginous Hawks were observed in courtship or nest building activity as early as the first week in March. A similar date was reported for Utah and southern Idaho (Howard 1975, Smith and Murphy 1978). Although downy young were seen in nests as early as the first week in May, most nests contained eggs at that time. Fledging dates were estimated for 67 successful nests. The majority (82.1%) fledged young between 19 June and 6 July with the peak (35.8%) occurring between 25 and 30 June. Nest Productivity, Nest productivity (Table 2) was similar to that reported for Ferruginous Hawks in South Dakota (Lokemoen and Duebbert 1976), Utah (Howard and Wolfe 1976, Woffinden and Murphy 1977, Smith and Murphy 1978) and Colorado (Olen- dorff 1973) but less than that recorded in Alberta (Schmutz et al. 1980) and Nevada (Perkins and Lind- sey 1983). Woffinden and Murphy (1989) state a productivity of 1.5 young/pair/yr is needed to maintain a stable Table 2. Productivity of Ferruginous Hawks monitored in northwestern New Mexico from 1981-88. Successful pairs were defined as those raising young to an age of at least 30 d. Increases in number of breeding pairs during periods 1983-84 and 1985-87 were due to increases in size of study area. Year Breeding Pairs Success- ful Pairs (% OF Total) Mean Brood Size Mean No Yng./ Pair 1981 4 3(75) 2.0 1.5 1982 4 4 (100) 2.5 2.5 1983 3 2(67) 2.5 1.7 1984 7 6 (86) 2.5 2.1 1985 7 6 (86) 1.7 1.4 1986 12 8(67) 2.0 1.3 1987 26 19 (73) 2.6 1.9 1988 26 19 (73) 2.7 2.0 All years combined 89 67 (75) 2.4 1.8 100 James M. Ramakka and Robert T. Woyewodzic VoL. 27, No. 2 population of Ferruginous Hawks, assuming a 657o juvenile mortality and 25% adult mortality. The pro- ductivity for the last 2 yr of our study, the period in which study area size was constant, appeared to exceed that needed for stability. WofRnden and Murphy (1989) also found a reduction in productivity in response to decreased prey availability indicating that our short term productivity estimate may not be an accurate assessment of Ferruginous Hawk productivity in this study area. An assessment of prey relationships and continued long-term monitoring of productivity is needed before any conclusions can be made concerning the stability of this population. Potential Impacts on the Population. The Fer- ruginous Hawk is prone to nest desertion and reduced productivity if disturbed prior to or during incubation (Fyfe and Olendorff 1976, White and Thurow 1985). Homestead development on Indian lands and recre- ational use of the badlands were the most common sources of disturbance in this area. New homes were being built by Navajo settlers in previously unoccupied areas and we documented two cases of nest failure due to apparent disturbance caused by nearby residents. Agricultural development can adversely affect nest density (Schmutz 1984). Since completion of our study, Ferruginous Hawks have constructed nests and suc- cessfully raised young in badlands adjacent to the ir- rigated croplands of the Navajo Irrigation Project (K. McCoy pers. comm.) indicating that cultivation has not yet adversely impacted Ferruginous Hawks in this area. No nests were located in the developed areas prior to cultivation nor do we have data to indicate that these areas provided important foraging sites for Ferruginous Hawks before being developed. Likewise existing coal, oil, and gas development have not ad- versely impacted this population. Acknowledgments BHP Utah International funded inventory flights on the Navajo Indian Reservation. Additional field assistance and logistical support were provided by the U.S. Fish and Wildlife Service and Navajo Game and Fish Department. We es- pecially thank O. Estrada, C. Gorman, S. Grogan, K. Mc- Coy, J. Medlin, and P. Ryan who spent many hours assisting in field work. S.O. Williams III reviewed an early draft. Many valuable suggestions for improvement of the manu- script were made by R. Olendorff, M. Restani, and N. Wof- finden. Literature Cited Bechard, M.J., R.L. Knight, D.G. Smith and R.E. Fitzner. 1990. Nest sites and habitats of sympatric hawks {Buteo spp.) in Washington. J. Field Ornithol. 61: 159-170. Blair, C.L. and F. Schitoskey, Jr- 1982. Breeding bi- ology and diet of the Ferruginous Hawk in South Dakota. Wilson Bull. 94:46-54. Evans, D.L. 1983. Ferruginous Hawk (ffwteo re^a&). Pages 109-123 in J.S. Armbruster [Ed.], Impacts of coal surface mining on 25 migratory bird species of high federal in- terest. Fish and Wildlife Service, U.S. Dept. Interior, Ft. Collins, CO U.S.A. Fyfe, R.W. and R.R. Olendorff. 1976. Minimizing the dangers of nesting studies to raptors and other sensitive species. Occas. Paper 23, Canadian Wildlife Service, En- vironment Canada, Ottawa, ON, Canada. Gilmer, D.S. AND R.E. Stewart. 1983. Ferruginous Hawk populations and habitat use in North Dakota. /. Wildl. Manage. 47:146-157. Hall, R.S., R.L. Glinski, D.H. Ellis, J.M. Ramakka and D.L. Base. 1988. Ferruginous Hawk. Pages 111-118 in R.L. Glinski, B.G. Pendleton, M.B. Moss, M N LeFranc, Jr., B.A. Millsap and S.W. Hoffman [Eds ], Proceedings of the Southwest Raptor Management Sym- posium and Workshop. National Wildlife Federation, Washington, DC U.S.A. Howard, R.P. 1975. Breeding ecology of the Ferruginous Hawk in northern Utah and southern Idaho. M.S. thesis, Utah State Univ., Logan, UT U.S.A. AND M.L. Wolfe. 1976. Range improvement practices and Ferruginous Hawks. J. Range Manage. 29. 33-37. Hubbard, J.P. 1978. Revised checklist of the birds of New Mexico. Publ. No. 6, New Mexico Ornithological Society, Albuquerque, NM U.S.A, Keetch, C.W. 1980. Soil survey of San Juan County, New Mexico, eastern part. Soil Conservation Service, U.S. Dept. Agric., Aztec, NM U.S.A. Eicon, J.S. 1961. New Mexico birds and where to find them. University of New Mexico Press, Albuquerque, NM U.S.A. Lokemoen, J.T. and H.F. Duebbert. 1976. Ferruginous Hawk nesting ecology and raptor populations in northern South Dakota. Condor 78:464-470. Moritsch, M.O. 1985. Photographic guide for aging nest- ling Ferruginous Hawks. Bureau of Land Management, U.S. Dept. Interior, Boise, ID U.S.A. Neu, C.W., C.R. Byers and J.M. Peek. 1974. A tech- nique for analysis of utilization-availability data. J. Wildl. Manage. 38:541-545. Olendorff, R.R. 1973. The ecology of the nesting birds of prey of northeastern Colorado. Tech. Rep. No. 211, U.S. International Biological Program, Grassland Biome, Colorado State Univ., Fort Collins, CO U.S.A. Perkins, M.W. AND W.J. Lindsey. 1983. Nesting studies of Ferruginous Hawks in the Ely BLM District, Nevada N. Am. Bird Bander 8:106-107. Schmutz, J.K. 1984. Ferruginous and Swainson’s Hawk abundance and distribution in relation to land use in southeastern Alberta. J. Wildl. Manage. 48:1180-1187. June 1993 Ferruginous Hawk in New Mexico 101 , S.M. ScHMUTZ AND D.A. BoAG. 1980. Coexis- tence of three species of hawks {Buteo spp.) in the prairie- parkland ecotone. Can. J. Zool. 58:1075-1089. Smith, D.G. and J.R. Murphy. 1978. Biology of the Ferruginous Hawk in central Utah. Sociobiology 3:79-95. Tolle, D.A. 1977. A survey of breeding and migratory birds southwest of Farmington, New Mexico. Great Basin Nat. 34:489-500. Weston, J.B. 1969. Nesting ecology of the Ferruginous Hawk {Buteo regalis). Sci. Bull. Biol. Ser. 10, Brigham Young University, Provo, UT U.S.A. White, C.M. and T.L. Thurow. 1985. Reproduction of Ferruginous Hawks exposed to controlled disturbance. Condor 87:14-22. WoFFiNDEN, N.D. AND J.R. MuRPHY. 1977. Population dynamics of the Ferruginous Hawk during a prey decline. Great Basin Nat. 37:411-425. AND . 1982. Analysis of nesting materials from a Great Basin Ferruginous Hawk nest. Raptor Res. 16:1-4. AND . 1983. Ferruginous Hawk nest site selection. /. Wildl. Manage. 47:216-219. AND . 1 989. Decline of a Ferruginous Hawk population: a 20-year summary. /. Wildl. Manage. 53: 1127-1132. Received 10 July 1992; accepted 22 January 1993 J. Raptor Res. 27(2):102-105 © 1993 The Raptor Research Foundation, Inc. NEST-SITE HABITAT SELECTED BY COMMON BUZZARD (Buteo buteo) IN SOUTHWESTERN FRANCE Christine Hubert Centre de Recherche en Biologie du Comportement, U.A. C.N.R.S. 664, Universite Paul Sabatier, 118, route de Narbonne, 31062 Toulouse, France Abstract. — I studied the habitat characteristics associated with nest sites of Common Buzzards {Buteo buteo) in southwestern France during three years. Nineteen nest sites were compared to 60 random points in buzzard nesting habitat using 21 quantitative habitat variables. Most nests were in large pines or oaks and in the upper ys of the tree at a mean height of 13.4 m. It appeared that buzzards selected nest sites in mature wooded areas with easy access, rather high in the tree, and close to woodland edges. Seleccion de sitios de nidificacion por Buteo buteo en el suroeste de Francia Resumen. — Estudie las caracteristicas del habitat asociado a los sitios de nidificacion de Buteo buteo en el suroeste de Francia durante tres anos. Se compararon 19 sitios de nidificacion con 60 puntos escogidos al azar en el habitat de esta especie; se usaron 21 variables cuantificables del habitat. La mayoria de los nidos se encontraron en grandes pinos o robles y sobre el tercio superior del arbol, a una altura media de 13.4 m. Al parecer esta especie selecciona sitios de nidificacion en areas de arboles maduros, de facil acceso a la cima del arbol y cercanos a areas abiertas. [Traduccidn de Ivan Lazo] Although many nest-site preferences have been described for the Common Buzzard, few studies have attempted to determine the decisive factors involved in its nest-site selection. These studies have con- cluded that tree nests simply need to be adequate in size and shape. No previous studies attempted to describe nest-site habitat of the buzzard quantita- tively. Materials and Methods Study Area. I conducted my study in the forest of Bou- conne (2300 ha) located near Toulouse (southwestern France) which is surrounded by cultivation and villages, and lies between 200 and 300 m elevation. Dominant overstory trees are oaks, including Quercus pedonculata, but also Q. sessilifiora and Q. lanuginosa, and introduced pines {Pinus sylvestris and P. pinaster). The understory is mixed with hornbeam {Carpinus betulus), chestnut {Cas- tanea sativa), ash {Fraxinus excelsior), maple {Acer cam- pestre), lime {Tilia platyphyllos) and wild service tree {Sor- bus aria). Undergrowth is composed of hawthorn {Crataegus spp.), blackthorn {Prunus Spinoza), broom {Sarothamnus scoparius), heath {Erica spp.), holly {Ilex aquilifolium) and bramble {Rubus Jruticosus). The forest is subject to logging; oaks are cut when 160 years old and pines when 80 years old. Because of logging, the forest is divided into numbered sections delimited by large pathways. Nesting Habitat Description. Buzzard nests were lo- cated in the winters of 1989, 1990, and 1991 through systematic foot searches of Vs of the forest. Frequent visits were made to each nest to see if buzzards were attending or defending nest sites, and later in the spring in order to see if there were brooding buzzards or nestlings. All nest sites were plotted on a 1:25 000 topographic map. A nest site was defined as the nest tree plus a 0.04- ha circular plot (11.3 m radius) centered on the nest tree (Titus and Mosher 1981). Within the nest site, all woody plants over 1.65 m were tallied according to species, di- ameter at breast height (dbh) and whether the predomi- nant foliage was part of the overstory or understory. Sep- arate size categories were created for understory plants and overstory trees. In such a way, 21 quantitative habitat variables (Table 1) were either measured directly or cre- ated by aggregation. Height measurements were made using a clinometer. Distances were measured directly on the field when short (<50 m), or measured from the map. Percentage of vegetation cover was simply visually esti- mated. If the plot fell at the edge of a field or other forest opening, no corrections were made, this opening being considered as part of the plot. Altitude was not considered here because of the flatness of the forest, nor was the exposure. Available Nesting Habitat. Random sampling was used to estimate available nesting habitat. A numbered grid (grid squares of 250 x 250 m) of 226 points was overlaid on the forest. Sixty points were drawn at random (Titus and Mosher 1981). Each random point was plotted on the map. Once the approximate site was located in the woods, the nearest tree was made the center of the random plot A tree was used to remain consistent with a nest-site sam- ple plot. Except for the nest-tree specific variables, the 102 June 1993 Common Buzzard Nesting Habitat 103 Table 1. Sample means and standard deviation of nest site and random plots and significant differences between random and nest-site plots (ANOVA (F) and Mann-Whitney (U, z) values are given). Variables Nest Site (V = 19) (Ranges) Random (V = 57) (Ranges) Test P Values Canopy height (m) 20.6 ± 0.83 16.98 ± 0.6**“ P = 0.002 (12.5-23.4) (10-25.4) F(l,75) = 9.95 Distance to nearest open water (m) 901 ± 162 805 ± 46.2 P = 0.43 (20-2425) (20-1750) F(l,75) -0.61 Distance to nearest woodland edge (m) 211 ± 46.1 480 ± 40.8** P = 0.0007 (14-887) (0-1000) F(l,75) = 12.6 Distance to pathways (m) 67.4 ± 7.5 54.2 ± 5.8 P = 0.13 (16-137) (0-162) t/=418, z= -1.5 % of canopy cover 35.3 ± 3.4 37.37 ± 2.1 P = 0.617 (15-60) (10-75) F(l,75) = 0.25 % of understory cover 34.5 ± 3.6 32.8 ± 1.7 P- 0.94 (20-60) (20-60) U= 536, z= -0.06 % of ground cover 54.7 ± 6.2 40.79 ± 3.3 P = 0.059 (10-95) (10-100) U=385,z= -1.88 Number of species of overstory 1.42 ± 0.12 1.56 ± 0.07 P = 0.27 (1-2) (1-2) U=46\,z= -0.96 Number of species of understory cover 2.68 ± 0.32 3.05 ± 0.14 P - 0.22 (1-5) (2-6) P(l,75) = 1.54 Number of ground species 4.58 ± 0.40 4.61 ± 0.24 P = 0.94 (2-8) (2-8) P(l,75) = 0.005 Number of overstory trees 17.2 ± 2.01 27.47 ± 1.90** P = 0,004 (1-35) (1-68) U= 308, z= -2.80 Number of overstory trees <25 cm dbh 10.7 ± 2.36 23.63 ± 2.21* P = 0.002 (1-35) (1-68) C/=288, z- -3.03 Number of overstory trees 26-50 cm dbh 5.42 + 1.02 3.54 ± 0.52 P- 0.035 (1-18) (1-11) t/= 367, z= -2.09 Number of over story trees >50 cm dbh 1.05 ± 0.24 0.3 ± 0.07*** P = 0.0003 (1-3) (1-3) U = 288, z — —3.6 Number of understory stems 1-4 cm dbh 18.21 ± 6.33 40 + 13.9* P = 0.01 (0-124) (1-800) U= 338, z= -2.4 Number of understory trees 5-8 cm dbh 16.05 ± 2.32 14.65 ± 1.75 P = 0.36 (4-39) (1-72) U- 465, z= -0.91 Number of understory trees >9 cm dbh 15.74 ± 1.95 11.25 ± 7.71 P = 0.04 DBH of the nest tree Height of the nest tree (m) Height of the nest (m) (5-32) 52.85 ± 2.76 (33-73) 20.6 ± 0.83 (12-23.4) 13.39 ± 1.02 (4.1 ± 23.2) (1-38) U= 2>73,z= -2.0 a * = p < 0.01; ** = p < 0.001; *** = P < 0.005. sampling variables were the same as that of the nest site. The criterion for accepting a random plot was that the plot must be within a forested area with a canopy height greater than or equal to 1 0 m. This excluded some habitats in which buzzards do not nest (young plantation areas) but included some areas where nesting was unlikely (copsewoods, partly cut areas of timber woods). This scheme generally allowed the sampling of the total forest area without preselecting “representative” or “typical” areas (Green 1979 in Titus and Mosher 1981). Statistical Methods. Parametric and nonparametric statistics were used where appropriate. Univariate ANO- VA was conducted on the two groups (buzzard nest site and random samples) for 6 of the 17 variables which had 104 Christine Hubert VoL. 27, No. 2 Table 2. Proportion of oaks and pines in the forest of Bouconne (from 57 random plots). % Overstory % Overstory % Total Tree Trees <25 Trees >26 Overstory Species cm dbh cm dbh Trees Pine 2 56 9 Oak 98 44 91 a distribution close to the Gauss curve. For the 10 other variables (showing nonnormal distributions), Mann- Whitney tests were conducted. Results and Discussion I found a total of 33 nests of which 23 nests were occupied at least once by a buzzard pair during the three years. One nest was occupied twice by a pair of European Sparrowhawk {Accipiter nisus), one nest by a pair of Booted Eagle {Hieraaetus pennatus) , and one nest by a pair of Goshawks {Accipiter gentilis). The other nests showed no evidence of occupation or defence by any species. Four actively defended buzzard nest trees were cut down by foresters. Hence only 19 buzzard nest sites were characterized quan- titatively. No nests were found in areas with canopy heights below 14 m (Table 1). The mean height of nests was 13.4 m. Most nests (52%) were in the upper % of the tree, with 80% in the upper half. Buzzards nested in mature trees more than expected, based on the fact that most nests (89%) were in trees over 40 cm dbh (Table 1). The marked preference to nest in mature plots could be due to the fact that mature trees allowed high nest placement, shelter from pred- ators, and also gave a safe base to the nest (Solonen 1982). Most of the nests were at the same height as understory trees which gave additional protection after the appearance of the foliage (Morris et al. 1982). Moreover, a low density of overstory trees around the nest site facilitated accessibility and vig- ilance. All species of overstory trees were used as nest trees, but nests occurred slightly more often in pines (11) than in oaks (8). This trend depended on the proportion of pines and oaks counted in the random plots (Table 2). Whatever the diameter, pines rep- resented only 10% of the total overstory trees of the random plots. A chi-square test showed no differ- ences between the proportion of large oaks and large pines (over 26 cm dbh) as determined from the ran- dom sampling versus the proportion of nest trees used {N = 57, Z = 1.318, P = 0.19). Numerous studies on buzzards show a preference for a tree species. Oak is generally selected in France (Roche 1977, Nore 1979). In Finland, 66% of buzzard nests are in spruce Picea sp. (Solonen 1982). In Germany, 70% of the nests are in beech Fagus sp. (Rockenbauch 1975 in Bayle and de Ruffray 1980). In the United Kingdom, pines are sometimes used (Dare 1961, Picozzi and Weir 1974) but rock sites are also se- lected (Brown 1976, Dare 1989). In this study, the selection of nest-tree species simply reflected the availability of large specimens of available species. Buzzards also nested significantly nearer to edges of woodlands than expected (Table 1). Although one nest was 800 m away from an edge, 50% of the nests were less than 200 m from an edge. The importance of woodland edges has already been mentioned for buzzards (Joenson 1968, Nore 1979, Kostrzewa 1987), and is explained by the fact that buzzards hunt mainly at the woodland edge or on the sur- rounding land (Joenson 1968). Thiollay (1972) em- phasized that buzzard density is correlated with the length of contact between woods and open land: 600- 900 m of edge per pair. The association between buzzards and forest openings could be even stronger when buzzards nest on hedgerows (Roche 1977) or on pylons (Melde 1983). Moreover, closeness to woodland edges facilitates nest accessibility (Roche 1977). Buzzards did not select nest sites in relation to open water; the distance to pathways did not influ- ence the buzzard in its nest-site selection. Neither percentage cover (whatever the story) nor the num- ber of species (whatever the story) influenced selec- tion of the nest-site (Table 1). Based on these results, I concluded that Common Buzzard selected mature wooded areas with an easy access, rather high in the tree itself, and close to the woodland edge. It could be interesting to compare nest-site habitat of the Common Buzzard with the ecologically similar Red-tailed Hawk {Buteo jamai- censis; Cramp and Simmons 1977): nest-site re- quirements of both species appear to be rather sim- ilar (Orians and Kuhlman 1956, Titus and Mosher 1981, Bechard et al. 1990). Acknowledgments P. Winterton kindly improved the English. I acknowl- edge with gratitude V. Bretagnolle, A. Gallo, J. Lauga and M.J. Bechard for their comments on earlier drafts. June 1993 Common Buzzard Nesting Habitat 105 Literature Cited Bayle, P. and P. de Ruffray. 1980. Analyse biblio- graphique de la Buse variable Buteo buteo. Bull. Nat. O.N.C. 40:11-15. Bechard, M.J., R.L. Knight, D.G. Smith and R.E. Fitzner. 1990. Nest-sites and habitats of sympatric hawks {Buteo spp.) in Washington. /. Field Ornithol. 61:159-170. Brown, L. 1976. British birds of prey. Collins, London, U.K. Cramp, S. and K.E.L. Simmons. 1977. The birds of the western palearctic. Univ. Press, Oxford, U.K. Dare, P.J. 1961. Ecological observations on a breeding population of the Common Buzzard Buteo buteo with particular reference to the diet and feeding habits. Ph.D. Dissertation, Univ. of Exeter, U.K. . 1989. Aspects of the breeding biology of the Buzzard Buteo buteo in north Wales. Naturalist 114: 23-32. JOENSON, A. H. 1968. An investigation on the breeding population of the Buzzard {Buteo buteo) on the island Als in 1962 and 1963. Dan. Ornithol. Foren. Tidsskr. 62:17-31. Kostrzewa, a. 1987. Quantitative analyses of nest- habitat separation in the Common Buzzard {Buteo bu- teo), Goshawk {Accipiter gentilis) and Honey Buzzard {Pernis apivorus). J. Ornithol. 128:209-229. Melde, M. 1983. Der Maiisebussard Die Neue Brehm Biicherei, Wittenburg Lutherstadt, Ger- many. Morris, M.M.J., B.L. Penak, R.E. Lemmon and D.M Bird. 1982. Characteristics of Red-shouldered Hawk {Buteo lineatus) nest sites in southwestern Quebec. Can Field-Nat. 96:139-142. Nore, T. 1979. Rapaces diurnes communs en Limousin pendant la periode de nidification, Buse, Bondree, Mi- lan noir, Busard St. Martin et cendre. Alauda 47:183- 194. Orians, G. and F. Kuhlman. 1956. Red-tailed Hawk and Great Horned Owl populations in Wisconsin. Con- dor 58:371-385. Picozzi, N. and D. Weir. 1974. Breeding biology of the Buzzard in Speyside. Br. Birds 67:199-210. Roche, J. 1977. Un recencement de Buses en plaine de Saone; quelques donnees concernant la nidification. Jean-le-Blanc 16:48-63. SOLONEN, T. 1982. Nest-sites of the Common Buzzard {Buteo buteo) in Finland. Ornis Fenn. 59:191-192. Thiollay, J.M. 1972. Ecologie d’une population de rapaces diurnes en Lorraine. La Terre et la Vie 2:116- 176. Titus, K. and J.A. Mosher. 1981. Nest-site habitat selected by woodland Hawks in the central Appala- chians. Auk 98:270-281. Received 8 December 1992; accepted 1 March 1993 J. Raptor Res. 27(2):106-110 © 1993 The Raptor Research Foundation, Inc. ROADSIDE RAPTOR SURVEYS IN THE ARGENTINEAN PATAGONIA Jose A. Donazar Estacion Biologica de Donana, CSIC, Apdo 7056, 47080 Sevilla, Spain Olga Ceballos Grupo de Estudios Biologicos Ugarra, Carlos III 79, 37002 Pamplona, Spain Alejandro Travaini and Fernando Hiraldo Estacion Biologica de Donana, CSIC, Apdo 7056, 47080 Sevilla, Spain Abstract. — Roadside raptor surveys were conducted in November 1991 along 1224 km in the northern Argentinean Patagonia. Twelve species and 477 individuals were observed. The most common species were Chimango Caracaras (Milvago chimango) (N = 243) and Black Vultures (Coragyps atratus) {N = 72). Raptor abundance and diversity index were highest in lowland valleys and in grassy hills near the Andean cordillera. Shrubsteppe zones near other habitats had higher raptor abundance and lower diversity than inner steppe areas. The Andean woodlands had the lowest raptor abundance. We suggest that deforestation of Andean woodlands and other human-induced alterations may have had positive effects on raptor open land abundance. Conteos de aves rapaces por carretera en la Patagonia argentina Resumen. — En noviembre de 1991 se recorrieron 1224 km en el norte de la Patagonia argentina y se registraron 12 especies de aves rapaces diurnas y un total de 477 individuos. Las especies mas comunes fueron el Chimango {Milvago chimango) (N — 243) y el Jote de Cabeza Negra {Coragyps atratus) {N = 72). Los indices de diversidad y abundancia de rapaces fueron maximos en las zonas de mallines (fondos hiimedos de valle) y en las colinas herbosas del piedemonte andino. En las estepas arbustivas, la abundancia de rapaces fue maxima en las zonas de borde cercanas a otros habitats. Los bosques presentaron las menores abundancias. Se sugiere que la abundancia de aves rapaces se ha visto incrementada por la deforestacion en la cordillera andina y por el incremento de las actividades humanas. Roadside surveys have been widely employed to determine relative abundances of raptors in many regions of the world (see review in Ellis et al. 1990). In some cases, surveys have been used to compare relative abundances and diversities between broad regions and/or biomes (Meyburg 1973, Reichfold 1974, Ellis et al. 1990), and to assess the impact of human-induced habitat transformations on raptor species richness (Ellis et al. 1990). Here, we report the results obtained in three rap- tor roadside surveys carried out in the northern Ar- gentinean Patagonia. Previous raptor roadside sur- veys in this region were made by Olrog (1979) and by Ellis et al. (1990). Olrog (1979) did not provide any reference about the habitats surveyed, but Ellis et al. (1990) considered a single habitat — the desert scrub. Northern Patagonia, however, is crossed by extensive valleys where rivers and streams favor the occurrence of a very different kind of landscape dom- inated by wet grasslands (“mallines”), small wood- lots, and some agriculture. In other arid regions of the world the existence of isolated humid zones pro- motes changes in the avian community composition and richness (Valverde 1957, Newton 1979). We hypothesized, therefore, that raptor diversity and abundance indices in the northern Patagonia are not uniform, being influenced by local habitat differ- ences within the biome. Additionally, we recorded data on raptor relative abundance in other marginal habitats in northwestern Patagonia: Andean wood- lands, Andean grassy hills, and villages. Study Area and Methods The weather in northern Argentinean Patagonia (prov- inces of Ghubut, Rio Negro and Neuquen) is dry and cold, with frost almost throughout the year and frequent snow- fall in winter. Topographically, the area consists of great plains at 800-900 m above sea level, dissected by steep rugged areas and valleys with large rivers. Mountains 106 June 1993 Raptor Surveys in Patagonia 107 occupy the west part of the study area. Physiographically, from west to east, this area can be subdivided into the main Andean cordillera, the precordilleran foothills, and the Patagonian plains. Within this area, we recognized the following habitats: Shrubsteppe (Desert) of the Patagonian Plains. The vegetation was characterized by a mixed steppe of bunch- grasses (Stipa spp. and Festuca spp.) and spiny shrubs. Trees were absent. Valleys with Wet Zones. These were flat areas situated at the bottom of the valleys and in lowlands (river, mal- lines). The vegetation was primarily herbaceous with a high productivity. Trees were concentrated along rivers and in plantations around ranches. Andean Woodlands. This area was characterized by temperate rainforests dominated by 50 m tall Nothofagus spp. with a dense bamboo understory of Chusquea culeou. This woodland occupies rugged areas on the foothills and the Andean cordillera. In some parts logging and fire have degraded the forest opening clearings and reduced the age of the stands. Andean Grassy Hills. Grassland areas are situated in rugged terrains of the foothills of the Andean cordillera. Trees are scarce because of soil characteristics and/or human pressure tending to expand areas suitable for live- stock raising. Villages. Urban areas, including the cities of Trelew, Esquel, San Carlos de Bariloche and Junin de los Andes, made up this category. The surveys (Fig. 1) were conducted in 1991 on the following dates and localities: 15 November (0625-1930 H) at Trelew-San Carlos de Bariloche (920 km), 16 No- vember (0825-1148 H) at San Carlos de Bariloche-Junin de Los Andes (221 km), and 25 November (1416-1726 H) at Junin de los Andes-Estancia Quemquemtreu (83 km). Roadside counts were conducted by two experienced observers: the driver and another person sitting on the front seat of a car. A third person recorded information. The surveys were carried out in fine weather, without clouds and with a wind velocity lower than 20 km/hr. The average driving speed was 60-70 km/hr. We recorded every raptor seen. In a few cases it was necessary to stop the vehicle to identify the birds. In this case, we did not take records on the new birds discovered during the stop. Relative abundance of raptors was esti- mated as the number of kilometers traveled per individual observed. The Shannon index was used to calculate di- versity (Herrera 1974). To determine whether raptor abundance and diversity indices varied within the main habitat (shrubsteppe) due to the vicinity of other habitats, we established two cate- gories: “outer steppe” (the first or last 20 km after or before entering a different habitat) and “inner steppe” (the rest of the surveys). Additionally, between 15 and 30 September 1991, one observer equipped with 10 x 40 binoculars conducted 15 point counts in the Nothofagus woodland of the Lanin National Park. The points had reduced visibility (ap- proximately 50-150 m) but the radius of detection of rap- tor calls was greater. The weather conditions were ap- propriate (calm air and no rain). Figure 1. Location of roadside raptors surveys. 1. Tre- lew, 2. San Carlos de Bariloche, 3. Junin de los Andes, 4. Estancia Quemquemtreu. Results Chimango Caracaras Milvago chimango {N = 243) and Black Vultures Coragyps atratus (N =72) were the most common species, followed by American Kestrels Falco sparverius (N = 45), Grey Eagle-Buz- zards Geranoaetus melanoleucus {N = 26), Turkey Vultures Cathartes aura (N = 24), Crested Caracaras Polyborus plancus {N = 23), and Red-backed Hawks Buteo polyosoma {N = 20; Table 1). Turkey Vultures, Black Vultures and Crested Caracaras reached their highest abundances in val- leys and Andean grassy hills. The Chimango Cara- cara abundance was maximum in villages, followed by shrubsteppes and valleys. American Kestrels and Cinereous Harriers {Circus cinereus) occurred most- ly in valleys. The Grey Eagle-Buzzard was detected mainly in Andean grassy hills whereas Buteo species were observed more frequently in shrubsteppes. Most individuals were seen alone or in pairs (Table 2). Three species were clearly gregarious: Turkey Vul- 108 Jose A. Donazar et al. VoL. 27, No. 2 Table 1. Results of roadside raptor counts (S = shrubsteppe, V = valley, W = Andean woodland, H = Andean grassy hill, VI = village). Species Total 1234 km S V H W Vl Cathartes aura 91.4 30.0 19.0 0.00 0.0 Coragyps atratus — 4.5 — 28.6 0.0 Vultur gryphus 640.0 300.0 — — — Circus drier eus 640.0 60.0 133.0 143.0 — Geranoaetus melanoleucus 80.0 60.0 12.1 71.5 — Buteo albicaudatus 640.0 — — — — Buteo polyosoma 40.0 75.0 — — — Buteo sp. 106.7 — 133.0 — — Polyborus plancus 71.1 42.9 19.0 — — Milvago chimango 4.2 5.2 8.3 11.9 1.3 Falco sparverius 58.2 10.7 33.2 71.5 — Falco femoralis 640.0 — — 71.5 — Falco peregrinus — 100.0 — — — Total species 10 10 7 6 1 Total Individuals 212 188 47 24 6 Diversity 0.461 0.722 0.716 0.620 0.000 km/individual 3.0 1.6 2.8 6.0 1.3 ture (maximum group size of 5 birds), Black Vulture and Chimango Caracara. Raptor diversity was highest in valleys and An- dean grassy hills (Table 1). These two habitats were also those having the highest raptor abundances. The abundance index was least in Andean woodlands. The habitats lowest in raptor diversity were shrub- steppes and villages. There were important variations in raptor abun- dance in counts carried out in similar habitats but in different places. The values obtained in the three surveys made in shrubsteppes were uneven (Table 1). In contrast, the diversity values were very similar. When we compared the results obtained in inner shrubsteppe surveys with those obtained in outer shrubsteppe (Table 3), the latter had higher raptor abundances. On the other hand, diversity was higher in inner steppes. Surveys carried out in different zones of valleys also demonstrated important differences (Table 1). All the valley zones were of small size. As a con- sequence, an analysis similar to that made for the shrubsteppe habitat was not possible. The main dif- ferences between surveys seem to be determined by the presence of scavenger species. When Turkey Vultures, Black Vultures and Andean Condors were excluded from the counts, the abundance indices for the three valleys became more similar, changing from 3.6, 0.6, and 1.2 to 3.7, 2.0, and 1.6, respectively. We conducted 15 point counts in the Nothofagus woodland of the Lanin National Park totaling 13 hours of observation. Eight individuals were detect- ed: one Buteo sp., one Crested Caracara, five Chi- mango Caracaras, and one American Kestrel. These raptors were seen in small clearings within the forest, none inside the woodland. Discussion Our results showed that high abundances and diversities of raptor species occur in valleys and An- dean grassy hills. These two habitats also had low raptor richness. This may have been influenced by the variety of potential nest-sites: sparse trees, wood- lots, flooded and dry prairies, rivers, cliffs, and by the primary productivity which determines a high density of wild and domestic herbivores whose car- casses are exploited by vultures and facultative scav- engers. The villages had the greatest abundance in- dex and the lowest diversity due to the important number of Chimango Caracaras that visit urban areas for foraging and nesting. This species has been observed breeding in San Carlos de Bariloche, Junin de los Andes, and San Martin de los Andes (author’s unpubl. data). Finally, the low abundance obtained June 1993 Raptor Surveys in Patagonia 109 Table 2. Group sizes of the species observed throughout the surveys. No. Individuals Species 1 2 3-10 >10 Cathartes aura 7 4 2 _ Coragyps atratus 2 1 2 1 Vultur gryphus 2 — - - Circus cinereus 6 1 - - Geranoaetus melanoleucus 14 4 1 - Buteo albicaudatus 1 — - - Buteo polyosoma 18 1 - - Buteo sp. 5 1 Polyborus plancus 19 2 - - Milvago chimango 113 10 8 3 Falco sparverius 39 3 - - Falco femoralis 1 1 - - Falco peregrinus 1 1 - - in the Andean woodlands could be partly due to the lower probability of detecting raptors in forested areas (Fuller and Mosher 1987). We think, however, that this apparent low abundance was real. The roads normally cross the mountain slopes, so the detection band was broad enough. In addition, the point counts made in the Nothofagus woodland of the Lanin National Park yielded only eight obser- vations in 13 hours. The impoverished avifauna of the Nothofagus woodlands was also noted by Darwin (1839). The heterogeneity of results obtained in surveys carried out in similar habitats may be due to different factors. In the shrubsteppe, raptor abundance seems reinforced by the proximity to other habitats. This proximity could stimulate raptors breeding in deserts to utilize other habitats for foraging and vice versa. In other arid zones, raptor richness increases when areas are irrigated (Newton 1979). In our study area, only the Buteo species maintain similar abun- dances in inner and outer steppes. This may be due to the high density of small mammals living in this habitat (up to 200/ha during summer; A. jTravaini et al. unpubl.). A similar trend cotild be expected for the American Kestrel, because the most abundant rodents inhabiting the steppe have small body sizes (Pearson 1986): Eligmodontia typus (6-12 g) and Akodon spp. (10-15 g). American Kestrels, however, seem to be scarcer in the steppe zones than in the valleys. The differences observed between valley surveys may be due to local fluctuations in food availability, especially of carrion: raptor abundance indices in- creased when vultures were excluded from the counts. Table 3. Number of contacts (times each species was detected) and number of individuals observed at outer (<20 km from other habitats) and inner (>20 km) shrubsteppes. Outer Steppe 237 km Inner Steppe 414 km Contacts N Contacts N Cathartes aura 3 7 — Coragyps atratus — — — — Vultur gryphus 1 1 — — Circus cinereus 1 1 — — Geranoaetus melanoleucus 4 7 1 1 Buteo albicaudatus — — 1 1 Buteo polyosoma 7 8 8 8 Buteo sp. 2 3 3 3 Polyborus plancus 6 6 2 3 Milvago chimango 40 138 12 13 Falco sparverius 8 8 2 3 Falco femoralis 1 1 — — Falco peregrinus — — — — Total species 9 6 Total individuals 180 32 Diversity 0.405 0.596 km/individual 1.3 12.9 110 Jose A. Donazar et al. VoL. 27, No. 2 It is known that vultures concentrate near predict- able feeding places (Brown and Amadon 1968), and 60 of the 72 observed Black Vultures were detected near a communal roost located in a zone with a high food availability. Additionally, scavenger species showed the largest group sizes. The global abundance index found in our Pata- gonian surveys (1 individual/0.39 km) is half that found in March 1979 by Ellis et al. (1990; 1/0.69 km) but five times higher than that found by Olrog (1979) in January 1976 (1/10 km). It is difficult to make comparisons among these results because the three surveys were carried out at different stages of the breeding season and we do not know the habitat proportions in the surveys made by the other authors. Olrog (1979) argued that the numbers he found were low due to raptor extirpation through human persecution and pesticide treatments. Per- haps our higher abundance indices may result from the progressive respect shown to raptors by human populations (raptors have been legally protected in Argentina since 1975). In any case, certain groups of raptors seem to have benefited from human-in- duced alterations in the Patagonian habitats. Before European colonization, the Patagonian drylands and woodlands were very poor in raptors; Darwin (1839) observed only three species, all of them vultures in the steppe and two in the forest. With European settlements, the Andean woodlands were largely de- stroyed to expand the area of grassland suitable for livestock (Veblen et al. 1992). As has occurred in other American regions (Reichfold 1974, Wilbur 1983), the shift from wild herbivores (guanaco) to domestic livestock herds (sheep and cattle) undoubt- edly favored vultures and other scavengers. Later, around 1950-60, the European hare {Lepus euro- paeus) was introduced and seems to have benefited large eagles that maintain very dense populations with high reproductive success (Travaini et al. un- publ.), and also small and medium-sized scavengers that exploit the carcasses of road-killed hares. These scavenging species have also benefited from the growth of human settlements and the ensuring in- crease in number and size of refuse dumps (Donazar et al. unpubl.). Acknowledgments E.R. Justo, D.G. Smith and an anonymous referee im- proved the manuscript. This research was funded by the Ministry of Science and Education of Spain through a cooperative program between the Estacidn Bioldgica de Donana, CSIC (Spain) and the Centro de Ecologia Apli- cada del Neuquen (Argentina). Logistic support was pro- vided by the CEAN, and the assistance of Martin Funes was especially valuable. I. Bustamante helped with the English translation. Literature Cited Brown, L. and D. Amadon. 1968. Eagles, hawks and falcons of the world. Country Life Books, London, U.K. Darwin, C. 1839. Narrative of the surveying voyages of His Majesty’s ships Adventurer and Beagle, between the years 1826 and 1836. Corlbun, London, U.K. Ellis, D.H., R.L. Glinski and D.G. Smith. 1990. Raptor road surveys in South America. J. Raptor Res 24:98-106. Fuller, M.R. and J.A. Mosher. 1987. Raptor surveys techniques. Pages 37-65 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline and D.M. Bird [Eds.], Raptor techniques manual. Sci. Tech. Ser. No. 10. National Wildlife Federation, Washington, DC U.S.A. Herrera, C.M. 1974. Trophic diversity of the Barn Owl Tyto alba in continental western Europe. Ornts Scand. 7:29-41. Meyburg, B.-U. 1973. Observations sur I’abondance relative des rapaces (Falconiformes) dans le nord et I’ouest de I’Espagne. Ardeola 19:129-150. Newton, I. 1979. Population ecology of raptors. T. and A.D. Poyser, Berkhamsted, U.K. Olrog, C.C. 1979. Alarmante escasez de rapaces en el sur argentino. Hornero 12:82-84. Pearson, O.P. 1986. Annotated keys for identifying small mammals living in or near Nahuel Huapi National Park and Lanin National Park, Southern Argentina. Museum of Vertebrate Zoology, Univ. of California, Berkeley, CA U.S.A. Reichfold, J. 1974. Artenreichtum, Haufigkeit und Diversitat der Greifvdgel in einigen Gebieten von Siid- amerika. /. Ornithol. 115:381-397. Val VERDE, J.A. 1957. Aves del Sahara espanol. Instituto de Estudios Africanos, Madrid, Spain, Veblen, T.T., M. Mermoz, C. Martin and T. Kitzberger. 1992. Ecological impacts of introduced animals in Nahuel Huapi National Park, Argentina. Conserv. Biol. 6:71-83. Wilbur, S.R. 1 983. The status of vultures in the western hemisphere. Pages 54-67 in S.R. Wilbur and J.A. Jackson [Eds.], Vulture biology and management. Univ. of California Press, Berkeley, CA U.S.A. Received 15 October 1992; accepted 25 February 1993 Short Communications /. Raptor Res. 27(2):1 1 1 -1 12 © 1993 The Raptor Research Foundation, Inc. Eagle Owl Predation on Egyptian Vulture and Northern Goshawk: Possible Effect of a Decrease in European Rabbit Availability Josfe L. Tella' and Santi MaNosa^ Departamento de Biologta Animal, Faculdad de Biologia, Universidad de Barcelona, Avda. Diagonal, 645, 08028, Barcelona, Catalonia, Spain Eagle Owls {Bubo bubo) occasionally prey upon small and medium-sized birds of prey (Mikkola 1983). Here we report observations of Eagle Owl nest predation on Egyp- tian Vulture {Neophron percnopterus) and Northern Gos- hawk {Accipiter gentilis) made during two intensive studies of these diurnal raptors in the Ebro basin, northeastern Spain. We monitored 178 breeding attempts of 58 pairs of Egyptian Vultures from 1980-91 and 101 breeding attempts from 26 pairs of goshawks from 1987-90. Eagle Owl predation affected seven nests of Egyptian Vultures. On two occasions, nestlings older than 35-40 d were beheaded, which is a characteristic behavior of Eagle Owls (Cramp 1985, J.A. Donazar pers. comm.). Only their heads and some wing feathers were found in the nest. The remains of a decapitated adult bird, probably killed while incubating or brooding very small chicks, were found 50 m from another nest. Nestlings in the other four nests were very young and disappeared without leaving any trace. The nests were inaccessible to mammalian predators that can kill nestlings (e.g., the red fox Vulpes vulpes; Donazar and Ceballos 1989, Tella and Torre 1990), and Eagle Owl nests or roosting sites were detected nearby. Eagle Owl predation was the most plausible explanation for these losses. Four goshawk nests with young between 13-38 d were depredated by Eagle Owls. In one case, a nestling aged 38 d was taken from a nest which contained three young. The remains and leg band of that bird were found in an Eagle Owl nest 3 km away. On another occasion, the remains of a 17-18 d old goshawk chick were found in the same Eagle Owl nest, 2 km away from a goshawk nest that had lost its 15-20 d old chicks on the same day. ’ Present address: Estacion Biologica de Donana (CSIG), Avda. M* Luisa s/n, Pabellon de Peru, 41013 Sevilla, Spain. ^ Present address: The Game Conservancy, Fording- bridge, Hampshire, SP6 lEF, United Kingdom. Although this chick was not marked, no other goshawk nest in the area lost nestlings of that particular age at the same time. The other two nests were found empty, except for a few feathers left in one of them. In nests where nestlings starved or were killed by humans, we never de- tected the action of scavengers or the parents removing the carcasses. Moreover, no signs of human robbery or mam- malian predation were found, leaving Eagle Owl predation as the most plausible explanation for these losses. In one of these two nests, which contained three young, the pre- dation of two chicks was detected 4 d after the first one had been taken. This is a common behavior of Eagle Owls, who can take several consecutive nights to kill and remove nestlings of a whole brood (Olsson 1979 in Cramp 1985). No case of Eagle Owl predation on the Egyptian Vul- ture has been reported until now, and only a few cases on the goshawk (Mikkola 1983). In the study area, 31% of Egyptian Vulture nests were <200 m from Eagle Owl nests or roosts which may have increased the risk of pre- dation (Real and Manosa 1990). Nevertheless, no dep- redations were reported before 1989 {N = 52), while 7.1% {N = 99) of the nests with young were depredated after that year (Fisher’s exact test, upper tail = 0.0478, lower tail = 0.0483), accounting for 50% of brood losses (Telia 1991). For goshawks, 6.1% {N = 33) of nests containing nestlings were affected by Eagle Owl predation in 1987- 88, and this percentage increased to 18.2% {N = 11) in 1989 (Fisher’s exact test, upper tail = 0.0000, lower tail = 0.2565). In the Ebro Valley, the European rabbit {Oryctolagus cuniculus) is the main prey of the Eagle Owl (Donazar 1989), as it is in other Mediterranean areas (Donazar et al. 1989). Yearly peak abundances of European rabbits in the area were determined by following a 19.7 km tran- sect at dusk 1-5 times each month in a vehicle at a max- imum speed of 40 km/hr. All the rabbits seen on the transect were recorded and the monthly average number of rabbits per km was calculated. Peak rabbit abundances were 2.1 rabbits/km in 1987 and 2.9 in 1988, but numbers 111 112 Short Communications VoL. 27, No. 2 decreased to 0.7 in 1989 and 1990, and to 0.4 in 1991, probably due to the viral haemorrhagic disease (Telia 1991, Mahosa 1992). During this period, the diet of an Eagle Owl pair was determined by collecting prey remains at their nest during and after the nestling period. We detected an increase in the percentage of diurnal raptors consumed from 3.5% (N =144 prey) in 1986-87 to 9.3% {N = 43 prey) in 1989 (Fisher’s exact test, upper tail = 0.0897, lower tail = 0.1250). Although our results do not provide conclusive evidence, we suggest that a diet shift of the Eagle Owl in response to the scarcity of its main prey may be responsible for the increased predation on nests of other species of raptors after 1989. A similar effect has been reported by Mc- Invaille and Keith (1974) for the Great Grey Owl (Strix nebulosa) and Red-tailed Hawk {Buteo jamaicensis). This may be an important factor in the management of some endangered species of birds of prey, as well as for the dynamics of the predator-prey communities involved (Rohner and Doyle 1992, Polls and Myers 1989). Resumen. — Se describen diversos casos de predacion de nidos de alimoche {Neophron percnopterus) y azor {Accip- iter gentilis) por parte del buho real {Bubo bubo) en el noreste de la Peninsula Iberica. Estas predaciones han aumentado a partir de 1989 coincidiendo con un impor- tante descenso en las poblaciones de su presa principal, el conejo {Oryctolagus cuniculus), por lo que se sugiere un importante papel del buho real en la dinamica de las poblaciones de rapaces en periodos de escasez del lago- morfo. Acknowledgments We are grateful to J.A. Donazar for his advice when writing the paper, and to J.L. Lagares for helping in the field. C. Rohner, S. De Stefano, J. Reynolds, N. Aebischer, and F. Hiraldo made very useful comments of an early version of the manuscript and R. Sage improved the En- glish of the draft. A F.P.I. grant from the Ministerio de Educacion y Ciencia financed the work on goshawk, and field work on Egyptian Vulture was partially financed by Diputacion General de Aragon, Seccion de Conservacion del Medio Natural, Plan 533-1 de Proteccion y Conser- vacion de la Fauna Silvestre, project R-297-91, adminis- trative director M. Cabrera. Literature Cited Cramp, S. [Ed.]. 1985. The birds of the western pa- learctic. Vol. 4. Oxford Univ. Press, Oxford, U.K. Donazar, J.A. 1989. Variaciones geograficas y esta- cionales en la dieta del Buho Real {Bubo bubo) en Navarra. Ardeola 36:25-39. and O. Ceballos. 1988. Red fox predation on fledgling Egyptian Vultures. /. Raptor Res. 22(3):88. , F. Hiraldo, M. Delibes and R.R. Estrella. 1989. Comparative food habits of the Eagle Owl Bubo bubo and the Great Horned Owl Bubo virginianus in six Palearctic and Nearctic biomes. Ornis Scand. 20: 298-306. MAf^oSA, S. 1992. Incidencia de la pneumonia virica del conill sobre la comunitat de rapinyaires segarrencs. El Medi Natural del Valles 3:141-149. McInvaille, W.B. and L.B. Keith. 1974. Predator- prey relations and breeding biology of the Great Horned Owl and Red-tailed Hawk in Central Alberta. Can Field-Nat. 88:1-20. Mikkola, H. 1983. Owls of Europe. T. and A.D. Poy- ser, Calton, U.K. PoLis, G. A. AND C. A. Myers. 1989. The ecology and evolution of intraguild predation: potential competitors that eat each other. Annu. Rev. Ecol. Syst. 20:297-330. Real, J. AND S. Ma5Josa. 1990. Eagle Owl {Bubo bubo) predation on juvenile Bonelli’s Eagles {Hieraaetus fas- ciatus). J. Raptor Res. 24:69-71. Rohner, C. and F.I. Doyle. 1992. Food-stressed Great Horned Owl kills adult Goshawk: exceptional obser- vation or community process? J. Raptor Res. 26:261- 263. Tella, J.L. 1991. Dinamica poblacional del alimoche {Neophron percnopterus) en el valle medio del Ebro. Valoracion de la NHV del conejo sobre las poblaciones de alimoche. Unpubl. report Direccion General de Ar- agon, Seccion de Conservacion del Medio Natural, Za- ragoza, Spain. AND I. Torre. 1990. Observaciones sobre re- laciones cleptoparasitarias interespedficas en el ali- moche Neophron percnopterus. Butll. G.C.A. 7:33-35. Received 14 September 1992; accepted 14 March 1993 /. Raptor Res. 27(2):113-116 © 1993 The Raptor Research Foundation, Inc. A Threat Display of the Northern Saw-Whet Owl {Aegolius acadicus) Charles T. Collins Department of Biology, California State University, Long Beach, CA 90840 U.S.A. Despite a voluminous literature on owls of the world (Burton 1973, Clark et al. 1979, Mikkola 1983, Johnsgard 1988, Voous 1988) much remains to be learned about the display behaviors of many strigids (Holt et al. 1990), par- ticularly those inhabiting remote areas. I describe herein a threat behavior sequence of the Northern Saw-whet Owl (Aegolius acadicus) not previously reported in recent field studies of this species (Hayward and Garton 1984, Can- nings 1987). Observations The observations were made on three captive adult owls (Collins 1961, 1963) captured in southern Michigan dur- ing the winters of 1960-61 and 1962-63. One female owl was maintained indoors in an area of high human activity and the other two (1 male, 1 unsexed) in an enclosed porch with little human contact. All were tethered on block perches by jesses and a short leash and fed laboratory mice (Mus musculus). When approached within 2 m the owls often became excited and exhibited the preflight fright reaction de- scribed by Catling (1972) for untethered birds. This in- cluded head bobbing, head turning, foot shifting and even- tual escape flight. Only once, stimulated by the calling of a captive kestrel (Falco sparverius), was the extreme sleeked- feather concealing pose (Catling 1972:Fig. 1, Holt et al. 1990) observed. On at least 15 occasions, however, each of the three owls exhibited a distinct fluff up, bow, buzz (FUBB) display sequence in reaction to similar such hu- man approach. The FUBB display was not observed in newly captured individuals but only after the owls had been in captivity for a minimum of one week. The sequence (Fig. 1) began with a general fluffing up of the body plumage and exaggerated upright stance. It was followed by a forward bow of the body and head. It ended with the raising of the head and a brief insect-like buzz vocalization. In the first stage, the feathers of the upper belly and breast were fluffed up and spread laterally (Fig. 2a) increasing the apparent size of the bird. This was quickly followed by the extension of the legs to raise the upright body (Fig. 2b). The wings and tail did not appear to be extended during this sequence, nor was there any apparent ptiloerection of the dorsal body feathers, head, or face. In the second stage, the body was bent forward until the head was facing downward and the bill was nearly at the level of the perch substrate (Fig. 2c, d). At this point, with the body still in the near horizontal position, the head was raised so that it again faced forward toward the intruder (Fig. 1) and the buzz vocalization was emitted. Following this the owl returned to the normal upright stance and sometimes began the fright reaction and attempted flight. In no case was the FUBB display immediately repeated although it could be again elicited by the observer moving away for a couple of minutes and then approaching the owl again. Discussion Some components of the FUBB display sequence re- semble behaviors noted in other owl species under various conditions. The extreme upright stance (Fig. 2b), not ac- companied by plumage fluffing, was noted many times in a hand-reared captive juvenile Eastern Screech-Owl (Otus asio) when inquisitive and exploring its environment (Fig. 3). A similar upright defense posture with feather erection occurs in the Barking Owl (Ninox connivens; Fleay 1968) but that species also includes wing spreading not noted in Aegolius. Similarly, fluffing of the body plumage accom- panied by sideways swaying and a raising and lowering of the body is part of a threat display of the Tropical Screech-Owl (Otus choliba-, Thomas 1977). A more gen- eralized fluffing of the plumage at the approach of a person or foreign object has been noted in several species of strigids in captivity (pers. observation). Threat displays of the Barn Owl (Tyto alba; Walker 1974:2, Bunn et al. 1982, pers. observation). Sooty Owl (Tyto tenebricosa; Fleay 1968), Masked Owl (Tyto novae- hollandiae; Fleay 1968) and Asian Bay Owl (Phodilus bad- ius; Wells 1986) include an arching of the head forward until the bill faces the ground or almost backward between the legs. In these species, this display is accompanied by arching the spread wings and usually a side-to-side rocking of the body with a shifting from one foot to the other. In Barn Owls, a high intensity expression of this display is accompanied by a rapidly repeated keck-keck-keck vo- calization or bill snapping (pers. observation). In the Saw- whet Owl, there is: 1) no spreading or arching of the wings, 2) a pronounced forward bending of the body (Fig. 1, 2d) and not just an arching forward and lowering of the head, and 3) no lateral movement of the body or feet. In the Bay Owl, the performance is terminated by the head being flung up and forward emphasizing the pale facial disk, large dark eyes and open bill (Wells 1986). In the Saw- whet Owl, the raising of the head is deliberate rather than rapid and the buzz vocalization accompanies this head movement. Although FUBB display components are sim- ilar to parts of displays of other tytonid and strigid owls, the total sequence seems unique to Saw- whet Owls. No similar display has been recorded to date in field studies of the congeneric Boreal Owl (Aegolius funereus , Mikkola 1983, Hayward et al. 1987). The function of this display and the context in which it would be utilized in wild owls is unclear. It is likely to be a form of threat display and the buzz component com- parable to the hissing sounds reported for a number of species including some owls (Bent 1938, Sibley 1955, Fleay 1968, Mikkola 1983, Johnsgard 1988). The previously described concealing (Catling 1972) or freezing (Taylor 113 114 Short Communications VoL. 27, No. 2 Figure 1. The complete fluff up, bow, buzz (FUBB) display sequence of the Saw-whet Owl. From left to right, resting pose, feather fluff and upright stance, bow, and bow with raised head when buzz is emitted. Figure 2. Fluff up, bow, buzz (FUBB) display components, a) Initial fluffing of breast feathers, b) full feather fluff and upright stance, c) start of bow, d) full bow with bill facing down. Not shown is raised head position which is accompanied by buzz vocalization. June 1993 Short Communications 115 Figure 3. Upright inquisitive stance of juvenile Eastern Screech-Owl. 1962) posture and fright reaction (Catling 1972) in Ae- golius are more frequently observed in approach situations. However, there are also numerous reports of wild Saw- whet Owls allowing very close approach by humans with the owls showing no signs of either defense or escape (Wilson 1931, Bent 1938). The FUBB display may be utilized in situations when easy escape is not an option. This would account for the FUBB display not being seen in newly captured birds but only in ones that had adjusted to captivity and their inability to escape. In support of this, a female Saw-whet Owl cornered in a nest box (Santee and Granfield 1939) showed the fluffed out breast feathers typical of the first stage of the FUBB display; the bird subsequently left the box without any other FUBB com- ponents being noticed. Michael and Michael (1928) re- ported a Saw-whet Owl perched just inside the opening of a nest cavity to emit a buzzing vocalization which re- sembled “the sizzling of water on a hot stove” when star- tled. However, this was certainly the begging vocalization of a nestling (R.J. Cannings, pers. comm.) rather than an adult vocalization as suggested by Michael and Michael (1928). No FUBB components were noticed in other cap- tive Saw-whet Owls even when stimulated to the point of attack (SchaeflFer 1973). Further field studies of wild owls may help verify the exact function and context of this display. ResuMEN. — Una conducata de amenaza es descrita para el buho Aegolius acadicus. La conducta incluye una postura erguida con un aumento de volumen del cuerpo por ex- pansion de las plumas, seguido por una inclinacion hacia adelante y una vocalizacion parecida a un zumbido. [Traduccjon de Ivan Lazo] Acknowledgments I am grateful to Ann Wurdeman for her drawing (Fig. 1) and to P.H. Collins, R.J. Cannings, D.W. Holt and K. McKeever for helpful comments on the manuscript. Literature Cited Bent, A.C. 1938. Life histories of North American birds of prey. Part 2. Bull. No. 170, U.S. National Museum, Washington, DC U.S. A. Bunn, D.S., A.B. Warburton and R.D.S. Wilson. 1982. The Barn Owl. Buteo Books, Vermillion, SD U.S.A. Burton, J. A. 1973. Owls of the world, their evolution, structure and ecology. E.P. Dutton & Co. Ltd., Lon- don, U.K. Cannings, R.J. 1987. The breeding ecology of Northern Saw-whet Owls in southern British Columbia. Pages 193-198 in R.W. Nero, R.J. Clark, R.J. Knapton and R.H. Hamre [Eds.], Biology and conservation of north- ern forest owls: symposium proceedings. Gen. Tech. Rep. RM-142, U.S. Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO U.S.A. Catling, P.M. 1972. A behavioral attitude of Saw-whet and Boreal Owls. Auk 89:194-196. Clark, R.J., D.G. Smith and L.H. Kelso. 1979 Working bibliography of owls of the world. Sci. Tech. Ser. 1, National Wildlife Federation, Washington, DC U.S.A. Collins, C.T. 1961. Tail molt of the Saw-whet Owl Auk 78:634. . 1963. Notes on the feeding behavior, metabo- lism, and weight of the Saw-whet Owl. Condor 65' 528-530. Fleay, D. 1968. Nightwatchmen of bush and plain. Jacaranda Press, Brisbane, Australia. Hayward, G.D. and E.O. Garton. 1 984. Roost habitat selection by three small forest owls. Wilson Bull. 96: 690-692. , P.H. Hayward and E.O. Garton. 1987. Movement and home range use by Boreal Owls in Central Idaho. Pages 175-184 in R.W. Nero, R.J. Clark, R.J. Knapton and R.H. Hamre [Eds.], Biology and conservation of northern forest owls: symposium proceedings. Gen. Tech. Rep. RM-142, U.S. Forest Service, Rocky Mountain Forest and Range Experi- ment Station, Fort Collins, CO U.S.A. Holt, D.W., R. Kline and L. Sullivan-Holt. 1990. A description of “tufts” and concealing posture in Northern Pygmy Owls. J. Raptor Res. 24:59-63. Johnsgard, P.A. 1988. North American owls. Smith- sonian Institution Press, Washington, DC U.S.A. Michael, C.W. and E. Michael, 1928. Behavior of Saw- whet Owls in Yosemite Park. Condor 30:323-324. Mikkola, H. 1983. Owls of Europe. T. and A.D. Poy- ser, Calton, U.K. Santee, R. and W. Granfield. 1939. Behavior of the Saw-whet Owl on its nesting grounds. Condor 41:3-9. Schaeffer, F.S. 1973. Tactile bristles of Saw-whet Owls are sensitive to touch. Bird-Banding 44:125. Sibley, G.G. 1955. Behavioral mimicry in the titmouse 116 Short Communications VoL. 27, No. 2 (Paridae) and certain other birds. Wilson Bull. 67:128- 132. Taylor, R.R. 1962. Fall Saw-whet Owl concentrations in Ontario. Blue Jay 20:118-119. Thomas, B.T. 1977. Tropical Screech Owl nest defense behavior and nestling growth rate. Wilson Bull. 89:609- 612. Voous, K.H. 1988. Owls of the northern hemisphere. Massachusetts Institute of Technology Press, Cam- bridge, MA U.S.A. Walker, L.W. 1974. The book of owls. A. A. Knopf, New York, NY U.S.A. Wells, D.R. 1986. Further parallels between the Asian Bay Owl Phodilus badius and Tyto species. Bull. Br. Ornithol. Club 106:12-15. Wilson, E.S. 1931. Tameness of Saw-whet Owl (C77/)- toglaux acadica acadica). Auk 48:266-267. Received 1 September 1992; accepted 22 January 1993 J Raptor Res. © 1993 The Raptor Research Foundation, Inc. Natal Origins and Winter Site Fidelity of Rough-legged Hawks Wintering in California Barrett A. Garrison Wildlife Management Division, California Department of Fish and Game, 1416 Ninth Street, Sacramento, CA 95814 U.S.A. Peter H. Bloom Western Foundation of Vertebrate Zoology, 439 Calle San Pablo, Camarillo, CA 93010 U.S.A. Rough-legged Hawks (Buteo lagopus) are a relatively common winter resident in California (Small 1974), but to date there has been no information published on the breeding areas and movements of California’s wintering population. Therefore, we analyzed encounters of banded birds to document natal origins, site fidelity, and migratory movements of Rough-legged Hawks wintering in Cali- fornia. All currently known banding encounters (N =16) in- volving Rough-legged Hawks in California were analyzed for this study. The Bird Banding Laboratory, U.S. Fish and Wildlife Service, provided 13 banding encounters of Rough-legged Hawks recovered in California or banded in California and recovered elsewhere between 1966 and 1991. In addition, three recaptures of banded birds were used in this study. P.H. Bloom captured and/or recaptured six birds using bal-chatris (Berger and Mueller 1959) baited with two domestic House Mice (Mus musculus) or one House Mouse in combination with other domestic rodents or House Sparrows (Passer domesticus; Bloom 1987). Four encounters (Nos. 1-3 and 5) were of nestling Rough-legged Hawks banded on their natal areas and recovered during the winter period in California (Table 1). Three nestlings were banded in July at three different locations on the Colville River, Alaska, and the fourth nestling was banded in August at Franklin, Banks Island, Northwest Territories. A fifth banding encounter from a natal area was an immature (HY) bird (No. 4) that was banded September 1988 near Delta, Alaska and found dead August 1990 near Santa Cruz, California. The sum- mer recovery date for bird No. 4 is atypical because it was found dead, and it is not known when the bird died. The four Alaska birds were recovered at different locations in California (Table 1). Ten birds were banded in California and one bird was banded in Nevada during the winter period between No- vember and February; all were recovered between De- cember and April (Table 1). Of these 11 birds, 4 (36%, Nos. 9, 10, 15 and 16) were banded in California and recovered or recaptured in the same Lat-Long block where banded. Bird No. 15, banded by P.H. Bloom as an HY in December 1977, was recaptured in December 1978 in the same field where initially banded, while No. 16 was re- captured in January 1988 within 1.6 km of the banding location of February 1987 (L. Spiegel and P. Detrich pers. comm.). Three birds (27%, Nos. 6, 12 and 14) were re- covered one Lat-Long block from the initial banding block, and four birds (36%, Nos. 7, 8, 11 and 13) were banded at different locations in California and Nevada and re- covered at different locations in California, Oregon, and Nevada. The length of time between banding and recovery for the 16 encounters averaged 540 ± 697 SD d. Young of the year (L and HY) (N = 7) birds averaged 413 ± 304 SD d between banding and recovery, while older birds (AHY, SY, ASY, U) banded on the wintering grounds averaged 640 ± 903 SD (N = 9) d. The difference between recovery periods for young of the year and older birds was June 1993 Short Communications 117 Table 1 . Banding encounters of 1 6 Rough-legged Hawks recovered in California or banded in California and recovered elsewhere (L = Local, HY = Hatch Year, AHY = After Hatch Year, SY = Second Year, ASY = After Second Year, U = Unknown). The Lat-Long number represents the southeast corner of the 10-min block of latitude and longitude within which the encounter occurred. Banded Recovered Location Date Age Lat-Long Location Date Lat-Long 1. Umiat, AK 23/07/71 L 690-1541 Newell, CA 03/12/71 415-1212 2. Ocean Point, AK 09/07/85 L 700-1513 McArthur, CA 21/11/85 412-1203 3. Ocean Point, AK 21/07/88 L 700-1513 Klamath, CA 19/01/89 414-1241 4. Delta, AK 11/09/88 HY 634-1443 Santa Cruz, CA 15/08/90 370-1220 5. Banks Is., NW Terr. 06/08/75 L 715-1244 Sacramento, CA 15/02/78 383-1213 6. Rosamond Lake, CA 09/12/72 HY 344-1181 Rosamond Lake, CA -/02/74 345-1180 7. Bishop Creek, CA 29/11/74 Unk 372-1183 Winnemucca, NV 22/12/82 405-1174 8. McKessick Peak, CA 03/01/76 AHY 401-1202 Malheur Lake, OR 01 /04/76 432-1185 9. Pit River, CA 19/01/78 ASY 410-1210 Pit River, CA 26/04/78 410-1210 10. Fieldbrook, CA 22/01/85 SY 405-1240 Fieldbrook, CA 04/03/85 405-1240 11. Petrolia, CA 25/02/85 ASY 402-1242 Newell, CA 17/04/87 415-1212 12. Lancaster, CA 05/12/87 AHY 344-1181 Lancaster, CA 18/01/89 344-1180 13. Washoe Lake, NV 06/02/66 AHY 391-1193 Burns Reservoir, CA 22/12/66 373-1202 14. Bishop, CA 06/12/89 ASY 372-1183 Crowley Lake, CA 27/12/91 373-1184 15. Rosamond Lake, CA 03/12/77 HY 344-1181 Rosamond Lake, CA 10/12/78 344-1181 16. Dayton, CA 07/02/87 AHY 393-1215 Dayton, CA 31/01/88 393-1215 not significantly different (Mann-Whitney 7/-test, U = 29.0, P < 0.780). The shortest period was 41 d (No. 10), and the longest period was 8 years and 24 d (No. 7). Mortality causes were known for eight birds. One bird was shot (No. 6), and five birds were hit by automobiles (Nos. 3, 7, 10, 12 and 14). The remaining two birds died by hitting wires or towers (Nos. 9 and 11). A ninth bird (No. 8) was found dead on a road, indicating it may have been hit by a car. In North America, Rough-legged Hawks breed across western and northern Alaska and northern Canada. Their winter range extends from southern Alaska south to south- ern California across Arizona, New Mexico, Texas, Mis- souri, Tennessee, and Virginia (American Ornithologists’ Union 1983). Our results showed that Rough-legged Hawks wintering in California breed in several locations including the Colville and Tanana rivers, Alaska, and Banks Island, Northwest Territories, Canada. The five recoveries in California of birds banded at natal areas suggest that Rough-legged Hawks from the western part of their breeding range migrate to the western part of their wintering range. Therefore, there may be a lon- gitudinal migration corridor for Rough-legged Hawks west of the Rocky Mountains (Table 1). In addition, three birds from the Colville River were recovered at different loca- tions indicating that birds from the same natal area may not necessarily winter in the same area. Several authors have reported that Rough-legged Hawks maintain winter territories (Brown and Amadon 1968, Craighead and Craighead 1969, Newton 1979, Watson 1986a). Our data suggest that some Rough-legged Hawks maintain winter territories because two birds (Nos. 9 and 10) were recovered in the same Lat-Long block during the same winter. In addition, some Rough-legged Hawks showed a strong affinity for returning to the same area in subsequent win- ters. Four encounters occurred in the same Lat-Long block where the birds were banded, and three encounters oc- curred in adjacent Lat-Long blocks. It should be noted, however, that distances between banding and recovery for encounters from adjacent Lat-Long blocks may be as close as encounters within the same Lat-Long block. The four birds recovered at locations different than where banded indicated that Rough-legged Hawks may use different wintering areas in subsequent winters, or these hawks were in transition between their breeding and wintering areas. Wintering populations of Rough-legged Hawks fluc- tuate due to local prey conditions (Brown and Amadon 1968, Baker and Brooks 1981, Watson 1986b). Therefore, Rough-legged Hawks should be expected to move about during the same and subsequent winters in response to changes in prey populations, and birds would remain on their wintering territories when prey populations are ad- equate. In addition, weather conditions, particularly snow depths and ambient temperature, are known to influence Rough-legged Hawk populations by influencing avail- ability of prey (Thiel 1985, Watson 1986b). Also, Watson 118 Short Communications VoL. 27, No. 2 (1986a) found that Rough-legged Hawks shifted winter territories in response to inclement weather. Most hawks in our sample were trapped or recovered in agricultural valleys. The observation that a substan- tial proportion of recoveries of Rough-legged Hawks showed strong winter site fidelity in subsequent years has important conservation implications since many of these agricultural areas in California are being lost to devel- opment (Garrison and Bloom pers. observation). There- fore, the link between natal and wintering areas suggests that the continued stability of Alaskan and Canadian breeding populations is predicated, in part, upon conser- vation of wintering areas, as noted by Bosakowski and Smith (1992) in southern New Jersey. This linkage has also been described by Terborgh (1989) for neotropical migrant birds breeding in North America where popu- lation stability is tied to habitat fragmentation on their wintering grounds in Central and South America. Resumen. — Un total de 16 Buteo lagopus marcados fueron avistados en California y analizados para determinar sus areas de nacimiento y fidelidad al sitio de invernada en California. Cinco aves, cuatro polluelos y un inmaduro, que fueron marcadas durante la estacion reproductiva en tres diferentes localidades de Alaska y una en Canada, fueron recuperadas en California durante el invierno. La localizacion occidental de las areas natales indican la po- sibilidad de un corredor de migracion longitudinal, donde B. lagopus puede migrar desde la parte oeste de su rango reproductive hasta la parte oeste de su rango de invernada. Siete de los 1 1 (64%) encuentros de aves marcadas en las zonas de invernada ocurrieron en el mismo o en las in- mediaciones de un cuadrante de 10 minutos de latitud- longitud, indicando que la mayoria de los B. lagopus presentaban fidelidad al sitio de invernada. No obstante, cuatro de los once (36%) encuentros tuvieron una difer- encia sustancial entre su localizacidn de marcaje y de re- cuperacion, indicando que B. lagopus tambien puede pre- sentar un movimiento considerable entre sitios de invernada. [Traduccidn de Ivan Lazo] Acknowledgments We thank Skip Ambrose, Tom Cade, Susan Dahl, Phil Detrich, Ray Evans, Richard Fyfe, Carol McIntyre, Lin- da Spiegel, Ted Swem, and Brian Woodbridge for per- mission to use their banding results, and the staff at the Bird Banding Laboratory for providing the data. We also thank Jim Watson, Thomas Bosakowski, and an anony- mous reviewer for their helpful reviews of the manuscript. Literature Cited American Ornithologists’ Union. 1983. Check-list of North American birds, 6th edition. Allen Press, Lawrence, KS U.S.A. Baker, J.A. and R.J. Brooks. 1981. Distribution pat- terns of raptors in relation to density of meadow voles. Condor 83:42-47. Berger, D.D. and H.C. Mueller. 1959. The bal- chatri: a trap for the birds of prey. Bird-Banding 20. 18-26. Bloom, P.H. 1987, Capturing and handling raptors Pages 99-123 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline and D.M. Bird [Eds.], Raptor manage- ment techniques manual. Sci. Tech. Ser. No. 10, Na- tional Wildlife Federation, Washington, DC U.S.A. Bosakowski, T. and D.S. Smith. 1992. Demography of wintering Rough-legged Hawks in New Jersey. J. Raptor Res. 26:61-65. Brown, L. and D. Amadon. 1968. Eagles, hawks and falcons of the world. Country Life Books, London, U.K. Craighead, J.J. and F.C. Craighead, Jr. 1969. Hawks, owls and wildlife. Dover Publications, Inc., New York, NY U.S.A. Newton, I. 1979. Population ecology of raptors. Buteo Books, Vermillion, SD U.S.A. Small, A. 1974. The birds of California. Collier Books, Macmillan Publishing Co., Inc., New York, NY U.S.A. Terborgh, J. 1989. Where have all the birds gone? Princeton Univ. Press, Princeton, NJ U.S.A. Thiel, R.P. 1985. Snow depth affects local abundance of wintering Rough-legged Hawks. Passenger Pigeon 47:129-130. Watson, J.W. 1986a. Range use by wintering Rough- legged Hawks in southeastern Idaho. Condor 88:256- 258. . 1986b. Temporal fluctuations of Rough-legged Hawks during carrion abundance. Raptor Res. 20:42- 43. Received 25 July 1992; accepted 22 January 1993 / Raptor Res. 27(2):119-120 © 1993 The Raptor Research Foundation, Inc. POLYANDROUS TRIOS IN A POPULATION OF EGYPTIAN VULTURES {Neophron percnopterus) Jose Luis Tella Departamento de Biologia Animal (Vertebrados) , Faculdad de Biologia, Universidad de Barcelona, Avda. Diagonal 645, 08028 Barcelona, Spain Polyandry is a breeding strategy adopted by few birds. Among raptors, the only species to show it with some frequency are the Galapagos Hawk {Buteo galapagoensis) and the Harris’ Hawk {Parabuteo unicinctus; Oring 1986). The Egyptian Vulture {Neophron percnopterus) is a mo- nogamous bird (Cramp and Simmons 1980) that occa- sionally forms polyandrous trios (Perennou et al. 1987), though the frequency with which this happens remains unknown. In a recent review of the Spanish breeding population (1324-1373 breeding pairs; Perea et al. 1990), no documented case of polyandry was included and only two trios have been recorded in Bardenas Reales (northern Spain, J.A. Donazar and O. Ceballos pers. comm.). In the Ebro Valley of Spain, I monitored 58 pairs of Egyptian Vultures between 1980 and 1991 (Tella 1991a). During this study I documented the presence of two re- productive trios made up of two male birds and one female. Sex of the members of the first trio was determined by the observation of consecutive copulations by each male with the same female when all three birds were present. This trio was discovered in 1982 and persisted until 1990 when the first unsuccessful reproductive attempt by the group was recorded. After that, no more than two of the members of the original group were seen together. In 1991 the trio’s definite dissolution was established after 32 visits to the breeding territory. The second trio was found in 1991 in a territory that had previously been occupied by a pair since 1989. In this case it was impossible to observe any copulation, but we assumed from other behavior that they were a polyandrous trio. I observed the participation of all three individuals in reproductive tasks (courtship flights, access to the nest, and standing with the nestlings and fledglings) giving be- havioral evidence of cooperative polyandry. No genetic measures of paternity were made. Taking into account only territories where I could de- termine the mating system after at least 10 visits of 1-3 hr spaced throughout the breeding cycle {N = 37), the two recorded polyandrous trios amounted to 5.4% of breeding females. This incidence is similar to that verified in Bar- denas Reales (O. Ceballos and J.A. Donazar pers. comm.), but much lower than that shown by B. galapagoensis (39- 68%, Oring 1986), P. unicinctus (46%, Mader 1975; al- though J.C. Bednarz [pers. comm.] believed the frequency was closer to 20% in Arizona), and the Bearded Vulture {Gypaetus barbatus) in the Pyrenees (14.3%), a species in which polyandry is also an exceptional phenomenon (Don- azar 1991). No difference was detected between the pro- duction of young/pair/yr between trios (x = 1, iV = 5) and neighboring pairs (x = 0.97, N = 144) of Egyptian Vultures in similar territories. Several reasons for the formation of trios have been proposed (Oring 1986). In this case, the explanation does not seem to be an imbalanced sex ratio caused by a higher death rate of females (Newton 1979). The data available are scarce — only two of the 38 birds found dead in the study area (Telia and Torre 1990, Tella 1991a, Tella and Manosa in prep.) were identifiable to sex (one male and one female). However, the presence of a large nonbreed- ing population fluctuating between 30% and 50% of the total population (Tella 1991a, 1991b), seemed enough to replace the low numbers of breeding birds. On three oc- casions the reconstitution of pairs after one of the birds died was observed. According to Newton (1979), polyandry may be the result of food shortage which may favor the cooperation of males to permit a higher probability of successful re- production (Perennou et al. 1987, Bednarz and Ligon 1988). Nests in the study area were placed in two main habitat types: the ribera (riparian areas and irrigated plains of the Ebro river) and the secano (dry areas; Tella 1991c) The availability and diversity of food resources (cattle, fish, birds, and rabbits) were significantly higher in the first habitat than in the latter because of the proximity to rivers {t = —7.88, df = 35, P < 0.0001) and rubbish dumps {t = —3.12, df = 35, P < 0.01). Both trios were located in the area with greatest resources, the ribera. Thus, this evidence does not support the food-shortage hypoth- esis. Alternatively, trios may be favored because of available space. This proposal is probably most appropriate for the Bearded Vulture (Donazar 1991), and for the population of the Egyptian Vultures of Badenas Reales, where this species is known to have its greatest density (Ceballos and Donazar 1990). The population of Egyptian Vulture that I monitored in this study appears to be going through a regression. Numbers have decreased 257o in the last de- cade, leaving several empty territories which were seldom occupied again (3.6-8.5%/yr; Tella 1991a). This could suggest ecological saturation caused by important changes in the environment during the last 40 yr (decrease of European rabbit supply caused by myxomatosis, major 119 120 Short Communications VoL. 21, No. 2 agriculture and cattle range decreases, and increasing hu- man population pressure in the area), after which many territories became unsuitable for the species. In this sit- uation, polyandry could be an advantage for male birds who would otherwise not be successful in reproduction and may assure the occupation of favorable territories after the death of one male cooperator. It may also improve survivorship and long-term reproductive success (Faaborg et al. 1980, Faaborg 1986, Donazar 1991). If this as- sumption is valid, and if the present population decline and saturation of resource continues, the frequency of polyandrous females may increase much like the pyrenaic population of Bearded Vulture did under similar circum- stances (Heredia and Donazar 1990). Resumen. — El seguimiento de una poblacion de alimo- ches, caracterizada por encontrarse en regresion y por presentar una importante fraccion no reproductora, ha permitido constatar la existencia de dos trios poliandricos. La proporcion de trios (5.4%) es inferior a la hallada en otras rapaces poliandricas. La aparicion de los mismos no parece responder a la escasez de alimento ni se ve traducida en un aumento del exito reproductor. Tampoco se cree debida a un desequilibrio en la razon de sexos ni a la saturacion del espacio. Se propone como explicacion mas probable una disminucion de la capacidad de carga del medio, situacion ante la cual la formacion de trios puede resultar una estrategia ventajosa a largo plazo. Acknowledgments I am grateful to Alfredo Legaz and Daniel Oro for their assistance in the field work. J.C. Bednarz, J.A. Donazar, J, Faaborg, S. Manosa and J.K. Schmutz made many constructive comments on the previous manuscript. This research was partially financed by Diputacion General de Aragon, Servicio de Conservacion de la Fauna, Plan 533-1 de Proteccion y Conservacion de la Fauna Silvestre, project R-297-91, dir. adn. M. Cabrera. Literature Cited Bednarz, J.C. and J.D. Ligon. 1988. A study of the ecological bases of cooperative breeding in the Harris’ Hawk. Ecology 69:1176-1187. Ceballos, O. and J.A. DonAzar. 1990. Parent-off- spring conflict during the post- fledging period in the Egyptian Vulture Neophron percnopterus (Aves, Acci- pitridae). Ethology 85:225-235. Cramp, S.C. and K.E.C. Simmons (Eds.), 1980. The birds of the western Palearctic. Vol. 2. Oxford Univ. Press, Oxford, U.K. Donazar, J.A. 1991. Unidades reproductoras inu- suales: trios poliandricos. Pages 39-45 in R. Heredia and B. Heredia [Eds.], El quebrantahuesos {Gypaetus barbatus) en Los Pirineos. Caracteristicas ecologicas y biologia de la conservacidn. ICON A. Coleccion Tecnica Madrid, Spain. Faaborg, J. 1986. Reproductive success and survivor- ship of the Galapagos hawk Buteo galapagoensis: po- tential costs and benefits of cooperative polyandry. Ibis 128:337-347. , T. de Vries, C.B. Patterson and C.R. Griffin. 1980. Preliminary observations on the occurrence and evolution of polyandry in the Galapagos hawk {Buteo galapagoensis). Auk 97:581-590. Heredia, R. and J.A. Donazar. 1990. High frequency of polyandrous trios in an endangered population of Lammergeiers Gypaetus barbatus in Northern Spain. Biol. Conserv. 53:163-171. Mader, W.J. 1975. Biology of the Harris’ Hawk in southern Arizona. Living Bird 14:59-85. Newton,!. 1979. Population ecology of raptors. T. and A.D. Poyser, Calton, U.K. Oring, L.W. 1986. Avian polyandry. Pages 309-351 in R.F. Johnston [Ed.], Current ornithology. Vol. 3. Ple- num Press, New York, NY U.S.A. Perea, J.L., M. Morales and J, Velasco. 1990. El alimoche {Neophron percnopterus) en Espana. Pobla- cion, distribucion, problematica y conservacion. ICONA Coleccion Tecnica. Madrid, Spain. Perennou, C., M. Fily and D. Cantournet. 1987 Note sur un cas de polyandrie chez le Vautour perc- noptere Neophron percnopterus. Alauda 55:73-75. Tella, J.L. and I. Torre. 1990. Observaciones sobre relaciones cleptoparasitarias interespecificas en el Al- imoche Neophron percnopterus. Butll. GCA 7:33-35. . 1991a. Dinamica poblacional del alimoche {Neophron percnopterus) en el Valle Medio del Ebro. Valoracion de la incidencia de la NHV del conejo sobre las poblaciones de alimoche. Unpubl. report D.G.A., Sec. Conservacion del Medio Natural, Zaragoza, Spain. . 1991b, Dormideros de alimoches en el Valle Medio del Ebro. 7 Congreso Internacional sobre Aves Carroneras (ed. ICONA):69-75. . 1991c. Estudio preliminar de la alimentacion del alimoche {Neophron percnopterus) en el Valle Me- dio del Ebro. 7 Congreso Internacional sobre Aves Car- roneras (ed. ICONA);53-68. Received 10 August 1992; accepted 25 February 1993 / Raptor Res. 27(2):121 -122 © 1993 The Raptor Research Foundation, Inc. Nest Record and Dietary Items for the Black Hawk- eagle {Spizaetus tyrannus) from the Yucatan Peninsula J. Luis Rangel- Salazar Departamento de Ecologia Terrestre, Centro de Investigaciones de Quintana Roo, Apdo Postal 424, 77000 Chetumal, Quintana Roo, Mexico Paula L. Enriquez-Rocha Apdo Postal 4-071 , 06400 Mexico, D.F., Mexico Most large tropical raptors are poorly known, partic- ularly those species that inhabit New World tropical for- ests. We believe that the continuing decline of raptor pop- ulations in tropical forests is due to habitat loss, shooting, trade, pesticide use, and exotic competitors (Ramos 1985, Thiollay 1985). However, little is known regarding the life history and ecology of large raptors that inhabit those forests. The Black Hawk-eagle {Spizaetus tyrannus) is a large Neotropical species inhabiting lowland forests, forest edg- es, and partially cleared woods. The species is resident from central Mexico to Bolivia, Paraguay, and north- eastern Argentina and southeastern Brazil (Blake 1977, Amadon and Bull 1988). Black Hawk-eagles are uncom- mon to common in Belize (Clinton-Eitniear 1986) and Guatemala (Vannini 1989). Their populations are de- creasing in Mexico due to habitat loss (Ramos 1986), but It is not considered to be a vanishing species (Burton 1987) nor is it listed as threatened in Mexico (SEDUE 1991). It has, however, been reported less frequently on the Yu- catan Peninsula than the endangered Ornate Hawk-eagle {S. ornatus; Paynter 1955, L6pez-Ornat et al. 1989). Al- most no information is available on breeding biology or food habits and only one nest site has been described in Panama (Smith 1970). In this paper we describe a Black Hawk-eagle nest and document some dietary items for the species. Site Location and Methods The nest was in a tropical deciduous forest in the central part of Quintana Roo on the Yucatan Peninsula (19°40'N 88“05'W), Terrain there is flat and less than 40 m above sea level. The mean annual temperature is 27°C and mean annual precipitation is 1 200 mm falling mainly from May- October. We measured the nest and collected food remains in and below the nest. Prey were identified using bird and mammal reference collections of the Instituto Nacional de Investigaciones Forestales y Agropecuarias in Bacalar. Nest construction materials were also collected and identified in the Centro de Investigaciones de Quintana Roo her- barium in Chetumal City. Results The nest was found on 7 March 1991 in a 23 m tall mahogany tree (Swietenia macrophylla) with a diameter at breast high of 1.94 m and foliage beginning at 9.2 m. The nest was 17.2 m above the ground and had the following dimensions: outer diameter = 0.70 m, outer depth = 0.66 m, bowl diameter = 0.4 m, and bowl depth ranged from 5. 1-7.6 cm. An immature bird was seen on 8 March close to the nest. On 7 April we measured the nest and collected prey items. Adult birds were heard but not seen near the nest on that date. Nest materials were identified as zapote {Minilkara za- pote), txalam (Lysiloma latisiliquia) , and a vine {Styzo- phyllum riparium). Sticks ranged from 20-45 cm in length and from 0.5 -1.5 cm in diameter. Keel-billed Toucans {Ramphastos sulfuratus) were the most abundant prey species (Table 1). Mammals rep- resented 17.67o of the total prey remains. Discussion The eagle nest we report was in a fork of one of the tallest trees in the area. A nest of the Black Hawk-eagle found in Panama was in the crown of a royal palm {Roys- tonea sp.) 13.5 m above the ground (Smith 1970), and was double the outer diameter but considerably shallower than our nest. The nest we describe was similar to those re- ported for the Ornate Hawk-eagle in Tikal (Flatten et al. 1989), but only about half as large. In contrast to our dietary results, Clinton-Eitniear (1986) reported small mammals as the most common food for the Black Hawk-eagle. Although the Ornate Hawk-eagle eats primarily small mammals, toucans also represent an im- portant resource in the breeding season (Madrid et al 1991). Both eagles commonly eat several bird and mammal species, and reptiles have been identified in their diet a few times (Smith 1970, Clinton-Eitniear et al. 1991). The nest we describe was also occupied in the 1990 breeding season (M. Cab pers. comm.); a juvenile and adults were seen on four occasions near the nest. It is possible that the Black Hawk-eagle breeds only every third year in Yucatan as it does in Panama (Smith 1970). The Ornate Hawk-eagle also nests every third year in Tikal (Madrid et al. 1991). Tourism and deforestation for cattle ranching and the timber industry are reducing habitat for large eagles such as the Black Hawk-eagle in the Yucatan Peninsula. Future studies should be focused on the ecology of this species so that conservation efforts may follow. Particularly needed is information on breeding biology, diet, and home range size. Resumen. — Un nido del Aguila Tirana Spizaetus tyrannus 121 122 Short Communications VOL. 27, No. 2 Table 1. Prey remains of Black Hawk-eagle (77 = 17) collected on 7 April 1991, in Central Quintana Roo, Mex- ico. Prey Number of Items Percent Mammals Yucatan Squirrel 1 5.9 {Sciurus yucatanensis) Squirrel 1 5.9 {Sciurus sp.) Raccoon 1 5.9 {Procyon lotor) Total mammals 3 17.7 Birds Keel-billed Toucan 7 41.2 {Ramphastos sulfuratus) Collared Aracari 2 11.7 {Pteroglossus torquatus) Unidentified 5 29.4 Total birds 14 82.3 Total prey 17 100.0 se encontro cerca de la Reserva de la Biosfera de Sian ka’an, Quintana Roo, Mexico. El nido se localize a una altura de 17.18 m sobre un arbol de Caoba de 23 m de alto. El nido presento 0.70 m de diametro externo, 0.66 m de profundidad externa, 0.43 m de diametro interne y 0 05 a 0.075 m de profundidad interna. Los restos ali- menticios encontrados fueron principalmente del Tucan Piquiverde y del Tucancillo Collarejo. Tambien se en- contraron restos de mamiferos y otras aves. El Aguila Tirana no se ha considerado como una especie que este amenazada y tampoco se encuentra en la lista mexicana de aves a proteger. Acknowledgments We would like to thank M. Cab, C. Gonzalez, H. Bahena and E. Escobedo for field assistance. Thanks es- pecially to J. Espinoza for comments and English trans- lation, to J. Nava for identification of mammal remains, and to E. Cabrera for identification of plants. J. Clinton- Eitniear and P.H. Bloom provided helpful comments on the manuscript. Literature Cited Amadon, D., and j. Bull. 1988. Hawks and owls of the world: a distributional and taxonomic list. Pro- ceedings of the Western Foundation of Vertebrate Zoology. Los Angeles, CA U.S.A. Blake, E. 1977. Manual of Neotropical birds. Vol. I. Univ. of Chicago Press, Chicago, IL U.S.A. Burton, P. 1987. Vanishing eagles. Chartwell Books Inc., Secaucus, NJ U.S.A. Clinton-Eitniear, j. 1986. Status of the large forest eagles of Belice. Birds Prey Bull. 3:107-110. , M.R. Gartside AND M.A. Kainer. 1991. Or- nate Hawk- Eagle feeding on green iguana. /. Raptor Res. 25:19-20. Flatten, C., J. Madrid, A. Hernandez and R. Ger- HARDT. 1989. Observaciones del nido de un Aguilu- cho de Penacho {Spizaetus ornatus). Reporte de Pro- greso II. Proyecto Maya. The Peregrine Fund, Inc., Boise, ID U.S.A. Lopez-Ornat, a., j. Lynch and B. Mackinnon. 1989. New and noteworthy records of birds from the eastern Yucatan peninsula. Wilson Bull. 101:309-409. Madrid, J., H. Madrid, S. Funes, J. LOpez, R. Botzoc AND A. Ramos. 1991. Biologia de la reproduccion y comportamiento del Aguila Elegante {Spizaetus orna- tus), en el Parque Nacional de Tikal. Reporte de Pro- greso IV. Proyecto Maya. The Peregrine Fund, Inc., Boise, ID U.S.A. Paynter, R. 1955. The ornithogeography of the Yu- catan peninsula. Bull. No. 9. Peabody Museum of Natural History, Yale Univ., New Haven, CT U.S.A. Ramos, M. 1985. Endangered tropical birds in Mexico and northern Central America. Pages 305-318 in I. Newton and R. Chancellor [Eds.], Conservation stud- ies on raptors. Vol. 5. ICBP Technical Publication, Cambridge, U.K. . 1986. Birds in peril in Mexico: the diurnal raptors. Birds Prey Bull. 3:26-42. SEDUE. 1991. Diario Oficial de la Federacion. Tomo CDLII (12):17-36. Smith, N.G, 1970. Nesting of King Vulture and Black Hawk-Eagle in Panama. Condor 72:247-248. Thiollay, J.M. 1985. Falconiforms of tropical rain forest: a review. Pages 155-165 in I. Newton and R. Chancellor [Eds.], Conservation studies on raptors. Vol. 5. ICBP Technical Publication, Cambridge, U.K. Vannini, j. 1989. Neotropical raptors and deforestation: notes on diurnal raptors at Finca El Faro, Quetzal- tenango, Guatemala. /. Raptor Res. 23:27-38. Received 29 September 1992; accepted 25 February 1993 J Raptor Res. 27(2): 123 © 1993 The Raptor Research Foundation, Inc. Letters Predation Upon Nestling Egyptian Vultures {Neophron percnopterus) IN THE Vratsa Mountains of Bulgaria J.A. DonAzar and O. Ceballos (1988, Ardeola 35:3-13) indicated that, except for their observations, very little has been published about predation upon nestlings of the Egyptian Vulture {Neophron percnopterus-, L. Brown and D Amadon 1968, Eagles, hawks, and falcons of the world. Country Life Books, London, U.K., P.J. Mundy 1982, The comparative biology of southern African vultures. Vulture Study Group, Johannesburg, South Africa). We report here ten observations of predation by mammals and birds upon nestling Egyptian Vultures occurring from 1987-1992. We observed two cases of predation by Golden Eagle {Aquila chrysaetos). On 2 June 1987 we saw an eagle capture, kill, and eat a nestling as it sunbathed near its nest. In a similar incident on 24 August 1991, we saw an eagle catch and carry away a nestling sunbathing on a rock near its nest. On 29 June 1989, a nestling vulture disappeared from its nest. We found the remains of what was probably the same nestling about 900 m away among the prey remains of a pair of Eagle Owls {Bubo bubo). Jackals {Canis aureus) apparently killed two nestlings that had fallen from their nests and could not fly well. One was on 15 August 1988 and the other on 15 August 1990. Another nestling fell from a nest on 13 June 1990 and was killed and eaten by a red fox {Vulpes vulpes). A group of Egyptian Vultures were observed feeding on a carcass on 20 August 1989. Among them was an 86 d old fledgling. When the group was approached by two wolves {Canis lupus), the adult vultures escaped, but the fledgling could not and was killed and eaten by the wolves. In addition to the incidents noted above, we know of three more nestlings killed by red foxes. Thus, of 61 nestling vultures that hatched in the interval of our observations, 10 (16.4%) were killed by predators (two by Golden Eagles, two by Eagle Owls, two by jackals, four by red foxes, and one by wolves). In addition, we observed 12 unsuccessful predation attempts by Golden Eagles and six by Common Ravens {Corvus corax). Most of the vultures we documented died between 65-70 d of age. After fledging, the vultures rarely returned to their nests and were vulnerable to mammalian predators while roosting in exposed sites where the adults carried food to them. We are very thankful to L. Andreev for help in field work, P. Jankov for helpful criticism on an earlier draft, R. Stoyanov for the loan of infrared binoculars, and J.A. Donazar for drawing our attention to his paper “Red Fox Predation on Fledgling Egyptian Vultures” that stimulated our paper. — Y. Stoyanova and N. Stefanov, Blvd. “Nikola Viovodov” 19, Apartment 79, Vratsa 3000, Bulgaria. J Raptor Res. 27(2):123-125 © 1993 The Raptor Research Foundation, Inc. Northward Migration of Peregrine Falcons Along the Caribbean Coast of Costa Rica Several migrant raptor species form immense concentrations during their annual northward and southward move- ments through the Central American isthmus (N.G. Smith 1980, Hawk and vulture migrations in the Neotropics, Pages 51-65 in A. Keast and E.S. Morton [Eds.], Migrant birds in the Neotropics: ecology, behavior, distribution, and conservation, Smithsonian Institution Press, Washington, DC U.S.A; A. Wetmore 1981, The birds of the Republic of Panama, Part 1, Smithsonian Institution Press, Washington, DC U.S.A). The Peregrine Falcon {Falco peregrinus) occurs in Central America principally as a migrant (P. Slud 1964, The birds of Costa Rica, distribution and ecology, Volume 128, Bull. Am. Mus. Nat. Hist., New York, NY U.S.A.; F.G Stiles and A. Skutch 1989, A guide to the birds of Costa Rica, Cornell Univ. Press, Ithaca, NY U.S.A.). However, there are no reports of this species passing anywhere in Central America in large numbers. We present here observations of a concentrated spring flight of peregrines along Costa Rica’s Caribbean coast. Observations were made during 1-3 May 1992 between the port city of Moin and the Tortuguero area of Limon Province (Fig. 1). A fixed point of observation was established at the Cano Palma Biological Research Station of the Canadian Organization for Tropical Education and Rainforest Conservation. The area consists of tropical wet forest 123 124 Letters VoL. 27, No. 2 Figure 1. Locations where Peregrine Falcons were observed on migration on the Atlantic coast of Costa Rica, on 1- 3 May 1992. (L R. Holdridge et al. 1971, Forest environments in tropical life zones: a pilot study, Pergamon Press, Oxford, U.K.) with various agricultural and rural developments interlaced by a system of man-made and natural waterways parallel- ing the coast. This expansive costal plane (average elevation 5 m) is broken only by the isolated Cerro Tortuguero (119 m). During the 3 d observation period we saw 83 Peregrine Falcons. About half the birds were identifiable to age and these were all adults. R.K. Murphy and M.T. Green (1992,/. Raptor Res. 26(2):101-102) reported seeing only adults migrating through North Dakota between 7-26 May. The dates of our observations fall within dates reported for other spring migrations north of Costa Rica (W.G. Hunt and F.P. Ward 1988, Habitat selection by spring migrant peregrines at Padre Island, Texas, pages 527-535 in T.J. Cade, J.H. Enderson, C.G. Thelender and G.M. White [Eds.], Peregrine Falcon populations: their management and recovery. Peregrine Fund, Inc, Boise, ID U.S.A.). On 1 May, during the 79 km trip by boat between Moin and Cano Palma (1000-1300 H) two peregrines were perched in trees along the canals. On 2 May at the Cano Palma Station, 2 flew over in the morning (0800-1100 H), and then 59 passed over in the afternoon (1400-1750 H). On 3 May, again at the station, another 14 flew by in the morning (0700-1 115 H). During the return trip to Moin in the afternoon (1300-1600 H) five were seen flying and one perched. Seven Merlins (F. columbarius) were also seen migrating during the 3 d. Thousands of swallows (mostly Hirundo rustica), Chimney Swifts {Chaetura pelagica) and nighthawks (Chordeiles minor and C. acutipennis) passed overhead as well, on a concurrent coastal migration. During periods of low clouds or drizzle (as on the afternoon of 2 May) the falcons flew in direct flapping or gliding flight at altitudes of 30-100 m, the majority passing at less than 60 m. However, when it was sunny, the falcons tended to soar higher, over 100 m, especially around Cerro Tortuguero, and took longer to pass. There was a steady but light wind from the northeast for the entire period. The flight line followed the coast with roughly equal numbers passing over forest, canal and beach. The falcons came by individually or in pairs, although on several occasions up to five birds were in view at one time. These observations were incidental to our main purpose, which was to band migratory passerines. No one was June 1993 Letters 125 observing full time at Cano Palma until we realized the extent of peregrine migration. From 1400 H on 2 May to 1115 H on 3 May one person was assigned to count peregrines; during both boat trips, three observers ran a census of all birds. From our point of observation we had only a partial view of the sky. Several persons dedicated to looking for peregrines from a vantage point such as Cerro Tortuguero would certainly have obtained a better picture of the migration. Whether or not the flight occurs there annually on this scale remains to be determined. For those interested in establishing monitoring sites for this alluring raptor, it is a question worth investigating. We thank W. Grainger Hunt and two anonymous referees for their suggestions on the manuscript. The Museo Nacional de Costa Rica, Canadian Organization for Tropical Education and Rainforest Conservation and Junta Administracion Portuaria y Desarrollo de la Vertiente Atlantica (JAPDEVA) kindly provided logistical support Thanks goes also to Rafael Chacon and Felicia Espinoza for their help. — Daniel A. Hernandez, Museo Nacional de Costa Rico, Departamento de Historia Natural, Seccion de Ornitologia, Apdo. 749-1000, San Jose, Costa Rica; James R. Zook, Selva Mar S,A., Apdo. 215-8000, San Isidro de El General, Costa Rica. J Raptor Res. 27 (2): 125 © 1993 The Raptor Research Foundation, Inc. First Record of the Eurasian Kestrel {Falco tinnunculus) in French Guiana A subadult male Eurasian Kestrel {Falco tinnunculus) remained from 12-21 March 1991 in a semihumid lowland savanna along the Kourou River, mainly perching on and hunting from an electric power transmission line near the city of Kourou, French Guiana (52°39'W 5°09'N). The falcon was observed on six days by A. Brosset, Jean-Luc Dujardin, and both authors. We could not approach within 100 m of the bird, but observations were made with a 15 X 20 spotting scope. On 13 March the bird was observed continually for 4 hr during which time it made several prey captures (insects and lizards). The apparent proficiency in hunting and shyness toward humans made it very unlikely that the bird had escaped from captivity. The head was gray with a well-marked mustache. Back and upperwing coverts were light rufous with contrasting dark flight feathers. The beige underparts were spotted on the belly. The tail was long and light gray in color with small dark spots underneath and a wide black subterminal band. Cere, eye-rings, and legs were bright yellow and the tip of the beak and the claws were black. Extensive observations one year later at the same location failed to detect an Eurasian Kestrel. We found only one other record in the literature of an Eurasian Kestrel in Martinique (French West Indies; R.S. Palmer 1988, Handbook of North American birds, vol. 5, Yale Univ. Press, New Haven, CT U.S.A.). — Alain LeDrefF and Pierre A. Raynaud, Centre ORSTOM de Cayenne, BP 165, 97323 Cayenne, Cedex, France. / Raptor Res. 27(2):125-126 © 1993 The Raptor Research Foundation, Inc. Live Passerine Nestling Found in Ferruginous Hawk Nest On 11 June 1991, we climbed to a Ferruginous Hawk {Buteo regalis) nest, located about 30 km south of Hanna, Alberta, Canada. Our purpose was to check the status of the nestlings prior to trapping the adult birds for a morphometric study. The nest was an artificial structure, approximately 4.5 m high on a steel powerline tower. J.D. Smith initially climbed to the nest and discovered a live passerine nestling along with the three nestling hawks. The passerine nestling was partially feathered and appeared uninjured upon examination. The hawk nestlings were approximately 3 wks old (two were later banded prior to fledging, and aged by backdating to be 17- and 24-days-old on 11 June) (J.K. Schmutz pers. comm.). We left the passerine in the nest and set up for trapping. We stopped trapping due to an approaching storm and returned on 12 June. While rechecking the nest, only the three hawk nestlings were present, but we collected one partially grown passerine feather, presumed to belong to the previously found nestling. 126 Letters VoL. 27, No. 2 We surmised that the passerine nestling was a kingbird (Tyrannidae), sparrow (Emberizidae), or a Horned Lark (Eremophila alpestris), presumably brought to the nest by one of the adult hawks as a prey item. The nestling was not feathered enough to have flown to the nest; there were no other nest structures on the power tower, and no nearby trees. This nest was occupied by a six-year-old color-banded male for at least three years and an unbanded female (J.K. Schmutz pers. comm.). An experienced hunter may have easily captured the nestling from a tree or ground nest. We hypothesize that the nestling’s small size, or the lack of a struggle, may have inhibited the adult hawk from tightly grasping and engaging the digital tendon locking mechanism during capture and transport. Nonlethal predation appears to be the best explanation for our observation. Other nonlethal predation by raptors has been reported recently in the literature (P.R. Stefanek et al. 1992, J. Raptor Res. 26:40-41), and we feel that these events may occur more frequently than the literature suggests. We consider brood parasitism unlikely, due to the disparity between the age of the nestling hawks and the passerine. We wish to thank J.K. Schmutz for encouraging us to report this observation. — Daniel N. Gossett, Raptor Research and Technical Assistance Center, Department of Biology, Boise State University, 1910 University Drive, Boise, ID 83725 U.S.A.; Jeffrey D. Smith, Department of Biology, University of Saskatchewan, Saskatoon, SK S7N OWO Canada. J. Raptor Res. 27(2): 126-1 27 © 1993 The Raptor Research Foundation, Inc. Bald Eagles Rear Red-tailed Hawks Recently, Stefanek et al. (1992,/, Raptor Res. 26:40-41) reported an unusual incident of a nestling Red-tailed hawk (Buteo jamaicensis) and two nestling Bald Eagles {Haliaeetus leucocephalus) in an eagle’s nest in Michigan. We report here on similar incidents of Bald Eagles rearing mixed-broods of eaglets and Red-tailed Hawks in northern Puget Sound of Washington state. We first suspected mixed-broods in June during helicopter surveys when we counted young at eagle nests. Three mixed broods were confirmed in photographs taken from helicopters. Two instances of mixed-broods occurred on the same territory but at different nests in 1987 and 1990 when one hawk and one eaglet, and one hawk and two eaglets fledged, respectively. We did not determine whether adult eagles continued to feed the hawks after fledging. These eagle nests were about 300 m from a Red-tailed Hawk nest where two young fledged in 1989, and occasional heckling of adult eagles by adult hawks was observed (L. Gunther pers. comm.). A mixed-brood of these two species was observed on another territory in 1988 (one hawk and one eaglet with fledging success unknown). Our interpretation of the photos taken, specifically the degree of feathering of nestlings’ crowns and body contours, indicated that hawks were 29-35 d old (M.G. Moritsch 1983, Photographic guide for aging nestling Red-tailed Hawks, Bureau Land Manage., U.S. Dept. Interior, Boise, ID U.S.A.), while the eaglets were at least 56 d old (M.V. Stalmaster 1987, The Bald Eagle, Universe Books, New York, NY U.S.A.). The 4 wk age difference was similar to that noted by Stefanek et al. (1992) for a mixed-brood of these species. The reported range in duration of incubation for Red- tailed Hawks (28-34 d; P.A. Johnsgard 1990, Hawks, eagles, and falcons of North America, Smithsonian Institution Press, Washington, DC U.S. A.) is the same or less than that of Bald Eagles (34-38 d; J.S. Gerrard, 1988, pages 214- 215 in R.S. Palmer [Ed.], Handbook of North American birds, Vol. 4, Yale Univ. Press, New Haven, CT U S.A.). The observed age difference, therefore, would require that adult hawks displaced eagles from nests late in incubation, and layed their own eggs. We concur with Stafanek et al. (1992) that this was unlikely. Aggression of territorial Red-tailed Hawks against Bald Eagles is not uncommon (P.V. LeDuc 1970, Auk 87:586), but Bald Eagles also have killed and/or permanently displaced Red-tailed Hawks and Osprey (Pandion haliaetus) from at least four territories in Puget Sound (J.W. Watson unpubl.). We discounted other explanations for mixed broods, including the placement of nestling hawks in the eagle nests by humans. This was unlikely due to the difficulties in climbing the trees (old-growth firs) and without the knowledge of landowners that live nearby and monitor the nests. It was also unlikely that the hawks flew to the eagle nests; the hawks were unable to fly when first observed. Nonlethal predation of downy hawks by eagles and their subsequent adoption by eagles is the explanation proposed by Stefanek et al. (1992). This also seems to be the most likely explanation for the mixed broods we observed. We suspect that mixed broods of hawks and eagles are unusual (e.g., 0.5% of 662 broods we observed from 1987-91), and June 1993 Letters 127 when they occur, hawk nestlings may die from fratricide and/or starvation before fledging because of their smaller size. We are unaware of other accounts of mixed broods of raptors being fledged under natural conditions. However, in a similar instance where nonlethal predation and adoption was suspected. Black-breasted Buzzards {Hamirostra melanosternon) reared seven Australian Kestrels {Falco cenchroides) that varied in age by 6 wks, feeding them other kestrels they had captured (J. Cupper and L. Cupper 1981, Hawks in focus, Jaclin Enterprises, Mildura, Australia). — James W. Watson, Michael Davison and Lora L. Leschner, Washington Department of Wildlife, 16018 Mill Creek Boulevard, Mill Creek, WA 98012 U.S.A. J. Raptor Res. 27(2):127 © 1993 The Raptor Research Foundation, Inc. Behavior of a Group of Zone-tailed Hawks The Zone-tailed Hawk (Buteo albonotatus) is a neotropical raptor that breeds north to the southwestern United States. In Texas the Zone-tailed Hawk breeds from late March to July (H. Oberholser and E. Kincaid 1974, The bird life of Texas, Univ. of Texas Press, Austin, TX U.S.A.), with most nests found in tall trees in narrow, steep- sided canyons (H.A. Snyder and R.L. Glinski 1988, pages 105-110 in R.L. Glinski, B.G. Pendleton, M.B. Moss, M.N. LeFranc, B.A. Millsap and S.W. Hoffman [Eds.], Proceedings of Southwest Raptor Management Symposium and Workshop, National Wildlife Federation, Washington, DC U.S.A.). The young remain near the nest for several weeks after fledging as the adults continue to feed them (Snyder and Glinski 1988). Here we report on the behavior of a group of Zone-tailed Hawks observed by us at Madrid Falls, Big Bend Ranch State Natural Area, in Texas. The area is a steep canyon with abundant water running from natural springs and supports large cottonwood (Populus sp.), ash (Fraxinus sp.), and oak {Quercus sp.) trees. On 21 June 1991 three Zone- tailed Hawks dove (to within 10 m) and screamed at us and then at a mountain lion (Felis concolor) as we observed them between 1230-1430 H. Two of the hawks were adults and the third had the spotted breast of a juvenile (W.S. Clark and B.K. Wheeler 1987, Hawks, Houghton Mifflin Co., Boston, MA U.S.A.). We observed the hawks again on 8 August 1991 from 1000-1430 H. Of three birds seen on this occasion one was a juvenile with heavy spotting on the breast, one had few spots, and the third had no spots. Again the birds were quite aggressive, diving to within 1 m of us. The loudest and most aggressive hawk had the most spotting. A fourth hawk, an adult, flew into view carrying prey, and transferred it to another individual in the air. We observed two more prey transfers in the air, a third while the birds roosted in a Yucca, and a fourth on the ground. Three of the hawks, including one adult, were fed by the fourth hawk. We did not, however, observe the bird capturing prey as it would leave the area and come back with the prey. This observation supports F.M. Hiraldo, M. Delibes, and R. Rodriguez Estrella’s (1989, /. Raptor Res. 23:103- 106) assertion that one adult does most of the hunting while the other adult defends the brood. Our observations raised several questions. The juvenile observed on 21 June could represent a record egg-laying date for Texas. With an incubation period of 35 days (I. Newton 1979, Population ecology of raptors, Buteo Books, Vermillion, SD U.S.A.) and 6-7 wk to fledging (Snyder and Glinski 1988) the latest possible egg date for the juvenile seen in June would be 5 April. However, the aggressive behavior and flying ability of the juvenile suggests that it was much further advanced. An egg date earlier than the record 29 March given by Oberholser and Kincaid (1974), perhaps early March, is very likely. The second juvenile could have been a clutch mate of the first observed on 21 June, or the pair may have produced two clutches for the year. Renesting, however, has not been documented for Zone-tailed Hawks. The observed behavior differs somewhat from the only published information on postfledgling behavior. Hiraldo et al. (1989) reported a decrease in the time adults spent near the nest as the postfledgling period progressed, with a low of 0.2% by the fourth week. They also reported an increase in aggression between parents and young. Another possibility is the presence of a helper in the observed group. We were unable to determine age of the juveniles by their plumage since no data are available on molting pattern of juveniles (R.S. Palmer 1988, Handbook of North American birds, Vol. 5, Yale Univ. Press, New Haven, CT U.S.A.). The juvenile observed on 21 June may have been raised the previous year. Although helpers have not been documented for Zone-tailed Hawks, they have been for other raptors (P.C. James and L.W. Oliphant 1986, Condor 88:533-534). The aggression first directed toward us and then at the mountain lion may have been due to the presence of eggs in a nearby nest. These observations were made during a project funded by the Expanded Research Area of the Texas Agricultural Experiment Station. — Beth E. Wilson, Cade Coldren, Mary Coldren, Felipe Chavez-Ramirez and Tim Archer, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843 U.S.A. J. Raptor Res. 27(2):128 © 1993 The Raptor Research Foundation, Inc. “Tool” Use by the Red-tailed Hawk {Buteo jamaicensis) Perhaps the best documented example of regular tool use for a falconiform is the Egyptian Vulture {Neophron percnopterus) striking an Ostrich {Struthio camelus) egg with a stone (J. van Lawick-Goodall and H. van Lawick- Goodall 1966, Nature 212:1468-1469; R.K. Brooke 1979, Ostrich 50:257-258). Another species, the Lammergeier {Gypaetus barbatus), routinely drops bones on stone slabs to gain access to the marrow within (L. Brown and D Amadon 1968, Eagles, hawks and falcons of the world, McGraw-Hill, New York, NY U.S.A.). Some, however, would argue that, because the stone is not manipulated, the bone-dropping Lammergeier is not actually using a tool. Another reported example of tool use is the Ferruginous Hawk {Buteo regalis) that allegedly cast a stone at a human intruder near its nest (C.L. Blair 1981, Raptor Research 15:120). The following may be yet another example of tool use by a raptor. On 5 June 1985, we observed an adult Red-tailed Hawk {Buteo jamaicensis) soaring low (ca 15 m) over the grass-covered slopes of the Galiuro Mountains in southern Arizona. The bird had, probably just moments before, captured a ca 1 m snake (probably a glossy snake, Arizona elegans, judging by size, shape and color). When the hawk passed near us, it was holding the snake by both feet near the snake’s midpoint. With head elevated and mouth open, the snake appeared intent upon biting the hawk. When the hawk was ca 100 m distant from us, it made several shallow stoops over a scattered group of large boulders. On some (and perhaps all) passes, the bird swept sharply upward as it passed over and nearly collided with a boulder. The centrifugal force associated with this change in direction caused the snake to pendulate below the hawk’s talons and strike the boulder. During one pass, we observed the snake’s head and tail flipping up behind the hawk after slapping the boulder. Not all swoops were over the same boulder, but one particularly obtrusive (ca 1 m tall) boulder was used at least twice. On the last two swoops, the snake hung limp and apparently lifeless from the hawk’s talons After the last swoop, the hawk dropped out of sight into tall grass ca 200 m from our position and presumably ate the snake because we could observe no prey in the hawk’s talons when it soared up 13 min later. If the anvil (not held in the hand) is a tool as well as the hammer (held in the hand), then the Red-tailed Hawk may be added to the short list of raptors that have been known to use tools. — David H. Ellis and Shawn Brunson, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, MD 20708 U.S.A. 128 J Raptor Res. 27(2):129-131 © 1993 The Raptor Research Foundation, Inc. News and Reviews 1992 Stephen R. Tully Memorial Grant Recipient Martha J, Desmond Martha J. Desmond received a B.A. degree in environmental studies from Wells College, Aurora, New York, and an M.S. degree in wildlife ecology from the University of Nebraska where she studied ecological aspects of Bur- rowing Owl nesting strategies. Currently, she is a Ph.D. candidate at the University of Nebraska continuing to study Burrowing Owls. She is concen- trating on their population reductions, movements, and genetic diversity. Before returning to graduate studies, she had a diversity of experience including evaluating potential areas for black-footed ferret reintroductions in Nebraska, wading bird studies in Florida, raptor nesting surveys in Alaska, raptor migration studies at Hawk Mountain and in Israel, and recovery pro- grams for Bald Eagles and Peregrines in Maine. 1992 Leslie Brown Memorial Grant Recipient G.E.A. Banfield G.E.A. Banfield was born in London in 1918 and studied mining at the Royal School of Mines at London University. After serving with the British military in World War II, he moved to Africa where he was employed for 24 years by mining companies in South Africa and Zimbabwe. He also served 18 years on the faculty and as department head at Zimbabwe’s School of Mines. Now retired, he continues to lecture part-time. Having a long-term interest in birds, Banfield has been a member of the Ornithological Association of Zimbabwe. He joined the Black Eagle Survey Team in 1980 and has been the head organizer of the survey for the past nine years. 129 130 News and Reviews VoL. 27, No. 2 Birds of the night: owls, frogmouths and nightjars of Australia by David Hollands. Reed Books Pty Ltd, Balgowlah NSW, 1991. 224 pp. ISBN 0-7301-0325-0. Cost is S49.95 plus shipping, available from the author at Box 125, Orbost, Victoria, 3888 Australia. Many animals of Australia are unique and the nocturnal birds of that continent are no exception. David Fleay “whetted our appetite” on these birds with his Nightwatchman of Bush and Plains (1968) and David Hollands serves us the “main course” for those hungering to know about these fascinating birds. This book on the natural history of the Australian night birds is based on many years of traveling across much of Australia, untold nights in hides at nests, careful record-keeping, and the taking of many photographs (often triggered by infrared devices) with 124 colored photographs included in the book. The photographs were all taken in native habitats; hence, they reveal much about the biology of the birds but many are aesthetic as well. The text is loaded with biological information but is written in fine natural history style, e.g., “In north Queensland, Rufous Owl country lies between the foothills of the Dividing Range and the sea. Here the tumbling creeks from the mountains slow their rush to the sea and wind slowly across the plain; green ribbons of tropical luxuriance in a sea of dry savannah woodland. Often only a stone’s throw in width, these narrow strips are rainforests in miniature, dark and lush, with a flora and fauna quite different from the woodland that lies beside them.” Or, “Nightfall comes in layers in the rainforest. The sun had not quite set and, above the canopy, there was still light across the tops of the trees. On the forest floor, beneath the shrubs and tangled vines, it was already almost night. Most of the daytime birds had already fallen silent with only the squawk and cackle of a Jungle Fowl from the depths of the brush and the raucous shrieks of the last White Cockatoos heading home to roost. Then they too paused and, in the ensuing stillness, the male Lesser Sooty called from his roost along the creek. Above the canopy the cry carried with icy sharpness, a piercing, chilling scream, descending the scale and lasting a full two seconds. Often this call has been know as the ‘falling bomb whistle’ and, when heard from a distance, this is certainly an apt description but, heard at close quarters, the cry came with such icy intensity that I instinctively felt a thrill of fear, even though the cause was known.” In addition to the 16 chapters that cover the night birds of Australia, there are chapters on pellets, eyes, ears and hunting, trees, hides and cameras, and a unique chapter (for this type of book) called a field guide. There is considerable information in this field guide on vocalizations, other names, field characters (including size — note the nature of dimorphism in some of the Ninox owls is reversed from the usual, i.e., female smaller than the male), food and hunting, breeding (including season, display, nest, eggs, incubation, young, fledging and postfledging), habitat, distribution (including maps) and distribution abroad. While the author-photographer is a medical doctor, the text reveals considerable understanding of natural history. It also reveals a sincere caring, by the author, for the safety of his photographic subjects and he addresses the danger of using call-back techniques in locating owls and points out the possibility of severely disrupting breeding cycles. While the stunning photography would suit this book as a coffee-table book the biology within the text will ensure Its use by serious researchers and birders as well. The author shows some owl species at their nests for the first time and there are photos of owls, frogmouths and nightjars in flight. — Richard J. Clark June 1993 News and Reviews 131 The U.S. Bureau of Reclamation, in fulfillment of the Endangered Species Act Section 7 commitments for Central Arizona Project storage features, contracted with BioSystems Analysis, Inc. to conduct a baseline study of the ecology of the Arizona Bald Eagle breeding population. This major research project is now complete and the Bureau anticipates the release of the 3-volume final report in early 1993. Bureau of Reclamation, Lower Colorado Regional Office, P.O. Box 61470, Boulder City, Nevada 89006-1470. Nikolai Stefanov THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966) OFFICERS PRESIDENT: Richard J. Clark SECRETARY: Betsy Hancock VICE-PRESIDENT: David M. Bird TREASURER: Jim Fitzpatrick BOARD OF DIRECTORS EASTERN DIRECTOR: Keith L. Bildstein CENTRAL DIRECTOR: Thomas Nicholls MOUNTAIN & PACIFIC DIRECTOR: Karen Steenhof CANADIAN DIRECTOR: Paul C. James INTERNATIONAL DIRECTOR #1: Fabian M. Jaksi6 INTERNATIONAL DIRECTOR #2: M. Isabel Bellocq DIRECTOR AT LARGE #1: Michael W. Collopy DIRECTOR AT LARGE #2: Robert E. Kenward DIRECTOR AT LARGE #3; Jeffrey L. Linger DIRECTOR AT LARGE #4: Josef K. Schmutz DIRECTOR AT LARGE #5: Paul F. Steblein DIRECTOR AT LARGE #6: Gary E. Duke EDITORIAL STAFF JOURNAL EDITOR: Carl D. Marti, Department of Zoology, Weber State University, Ogden, UT 84408-2505 U.S.A. ASSOCIATE EDITORS Keith L. Bildstein Fabian JaksiC Gary R. Bortolotti Patricia L. Kennedy Charles J. Henny Erkki Korpimaki EDITOR OF RRF KETTLE: Paul F. Steblein 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 215 by 280 mm (8Vi x 11 in.) or standard international, white, bond paper, with 25 mm (1 in.) margins. The cover page should contain a title, 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. Submit the current address on a separate page placed after the literature cited section. 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 numerals. 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 (6th ed., 1983) 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,” J. Raptor Res., Vol. 24(1-2), which is available from the editor. 1993 ANNUAL MEETING The Raptor Research Foundation, Inc. 1993 annual meeting will be held on 3-7 November at the Marriott City Center Hotel in Charlotte, North Carolina. Details about the meeting and a call for papers will be mailed to Foundation members in the summer, and can be obtained from Keith Bildstein or Laurie Goodrich, Scientific Program Chairpersons, Hawk Mountain Sanctuary, Rural Route 2, Box 191, Kempton, PA 19529-9449 U.S.A. Telephone (215) 756-6961, FAX (215) 756-4468. For futher information about the meeting or the associated art show, contact Robert Gefaell, Local Chairperson, P.O. Box 16443, Charlotte, NC 28297 U.S.A. Telephone (704) 334-8078 or (704) 875- 6521 (Carolina Raptor Center). For information about the associated symposium “Raptors Adapting to Human Environment,” contact David Bird, Raptor Research Centre, McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec, Canada H9X ICO. Telephone (514) 398-7760, FAX (514) 398-7983. RAPTOR RESEARCH REPORTS #1, R.R. Olendorff. 1971. Falconiform Reproduction: A Review Part 1. The Pre-nesting Period. $10.00 members, $12.50 non-members. #2, F.N. Hamerstrom, B.E. Harrell and R.R. Olendorff [Editors]. 1974. Management of Raptors. Pro- ceedings of the Conference on Raptor Conservation Techniques, Fort Collins, CO, 22-24 March 1973. $10.00 members, $12.50 non-members. #3, J.R. Murphy, C.M. White and B.E. Harrell [Editors]. 1975. Population Status of Raptors. Proceedings of the Conference on Raptor Conservation Techniques, Fort Collins, CO, 22-24 March 1973. (Part 6). $10.00 members, $12.50 non-members. #4, R.R. Olendorff, A. Miller and R. Lehman [Editors]. 1981. Suggested Practices for Raptor Protection on Powerlines: State of the Art in 1981. $5.00 members, $20.00 non-members. #5, S.E. Senner, C.M. White and J.R. Parrish [Editors]. 1986. Raptor Research Conservation in the Next Fifty Years. Procedings of a Conference held at Hawk Mountain Sanctuary, Kempton, PA, 14 October 1984. $3.50 members, $4.50 non-members. #6, D.M. Bird and R. Bowman [Editors]. 1987. The Ancestral Kestrel. Proceedings of a Symposium on Kestrel Species, St. Louis, MO, 1 December 1983. $10.00 members, $12.50 non-members. #7, R.R. Olendorff [Editor]. 1989. The Raptor Research Foundation, Inc. Bibliographic Index (1967-1986) . $2.50 members, $5.00 non-members. #8, R.R. Olendorff, D.D. Bibles, M.T. Dean, J.R. Haugh and M.N. Kochert. 1989. Raptor Habitat Management under the U.S. Bureau of Land Management Multiple-Use Mandate. $5.00 members, $6.50 non-members. Add $2.50 for postage and handling, and $1.00 each for additional reports. BOOKS Biology and Management of Bald Eagles and Ospreys. Proceedings of the First International Symposium, Montreal, Canada. D.M. Bird [Editor]. 1983. $15.00 members, $18.00 non-members plus $5.00 shipping. JOURNAL BACK ISSUES Journal Back Issues are available. For details write: Jim Fitzpatrick, Treasurer, Raptor Research Foundation, Inc., Carpenter St. Croix Valley Nature Center, 12805 St. Croix Trail, Hastings, MN 55033. The fournal of Raptor Research has been selected for abstracting/indexing by several organizations. Articles appearing in the Journal are covered in Biological Abstracts, Current Contents/ Agriculture, Biology and Envi- ronmental Sciences, Ecological Review, Science Citation Index, Wildlife Review and Zoological Record.