fissN ngss-ioiG) The Journal of Raptor Research Volume 24 Autumn 1990 Number 3 Contents Diets of Sympatric Raptors in Southern Chile, j. Agustin iriarte, william l. Franklin and Warren E. Johnson 41 Density and Habitat Use of Raptors along the Rio Bavispe and Rio YaQUI, SONORA, Mexico. Ricardo Rodriguez- Estrella and Bryan T. Brown 47 Nesting Habitat of Flammulated Owls in Oregon. Evelyn L. Bull, Anthony L. Wright and Mark G. Henjum 52 POST-FLEDGING BEHAVIOR OF AMERICAN KESTRELS IN CENTRAL KENTUCKY. Christopher Kellner 56 A Description of “Tufts” and Concealing Posture in Northern PYGMY-OWLS. Denver W. Holt, Rick Kline and Lynn Sullivan-Holt 59 Environmental Influences on Osprey Foraging in Northeastern NOVA Scotia. Stephen P. Flemming and Peter C. Smith 64 Short Communications Northern Harrier Casts Pellet While in Flight. Mark. A. Manske 68 Above-ground Nesting by Burrowing Owls. Paul M. Cavanagh 68 Eagle Owl (Bubo bubo) Predation on Juvenile Bonelli’s Eagles (Hieraaetus fasciatus). Joan Real and Santi Manosa 69 Osprey Nestlings Fostered by Hacked Adults Two Weeks After Predation of Their Young. Larry M. Rymon 71 Daytime Activity of Little Owls (Athene noctua) in Southwestern Spain. J.J. Negro, M.J. de la Riva and F. Hiraldo 72 News and Reviews 75 3|s9fe4e9fe9fe3fc9fe»fea|e9|e9te9fea|ei|e9|e^e9{e9fe»ita|e Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Send requests for information concerning membership, subscriptions, special publications, or change of address to Jim Fitzpatrick, Treasurer, 12805 St. Croix Trail, Hastings, Minnesota 55033, U.S.A. The Journal of Raptor Research (ISSN 0892-1016) is published quarterly for $18.00 per year by The Raptor Research Foundation, Inc., 12805 St. Croix Trail, Hastings, Minnesota 55033, U.S.A. Second class postage paid at Hastings, Minnesota, and additional mailing offices. Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A. Copyright 1990 by The Raptor Research Foundation, Inc. Printed in U.S.A. THIS PUBLICATION IS PRINTED ON ACID-FREE PAPER. THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. Vol. 24 Autumn 1990 No. 3 J Raptor Res. 24(3):41-46 © 1990 The Raptor Research Foundation, Inc. DIETS OF SYMPATRIG RAPTORS IN SOUTHERN CHILE J. Agustin Iriarte 1 Center for Latin American Studies, University of Florida, Gainesville, FL 32611 William L. Franklin Department of Animal Ecology, Iowa State University, Ames, I A 50011 Warren E. Johnson 1 Patagonia Wildlife Research Center, Torres del Paine National Park, Chile Abstract. — We report on the diets of four sympatric raptor species in Torres del Paine National Park, Magallanes region, Chile. This assemblage includes some of the least-known raptors in southern South America. Two strigids, Great Horned Owl ( Bubo virgimanus) and Barn Owl ( Tyto alba), had the most generalized diets. The Cinereous Harrier ( Circus cinereus) preyed primarily on birds and lizards, and the Black-chested Buzzard Eagle ( Geranoaetus melanoleucus) on the introduced European Hare ( Lepus capensis). The Barn Owl and the Great Horned Owl, both nocturnal predators, preyed mainly on rodents and showed the largest dietary overlap. Raptor weight was positively correlated with mean weight of vertebrate prey but not with food-niche breadth. Las dietas de aves rapaces simpatricas en el sur de Chile Extracto. — Se presentan las dietas de cuatro especies de aves rapaces en el Parque Nacional Torres del Paine, en la region de Magallanes, Chile. Este grupo incluye algunas de las especies de rapaces menos conocidas en el cono sur sudamericano. Dos estrigiformes, el Tucuquere ( Bubo virginianus) y la Lechuza ( Tyto alba), mostraron los habitos alimenticios mas generalizadas. El Vari ( Circus cinereus) consumio principalmente aves y lagartijas, y el aguila ( Geranoaetus melanoleucus) predo principalmente sobre la liebre introducida ( Lepus capensis). La Lechuza y el Tucuquere, ambos predadores nocturnos, consu- mieron principalmente roedores y mostraron los mayores indices de sobreposicion de dieta. El peso de las aves estuvo positivamente correlacionado con el peso promedio de la presas vertebradas, y no corre- lacionado con el ancho del nicho dietetico de las especies estudiadas. The South American Patagonia steppe covers 565 000 km 2 , with 465 000 km 2 in Argentina and the remainder in the southern portion of Chile. The Chilean Patagonia contains a highly diverse fauna (Miller and Rottmann 1976, Caviedes and Iriarte 1 Present address: Department of Animal Ecology, Iowa State University, Ames, IA 50011. 1989), the result of a blend of faunas from the Chil- ean and Argentinean sides of the Andes. Eight fal- coniform and four strigiform species occur in the northern portion of the Chilean Patagonia (Johnson 1965, Venegas and Jory 1979, Araya and Millie 1986). Except for a brief report on Great Horned Owls {Bubo virginianus) (Jaksic et al. 1978) and Cinereous Harriers {Circus cinereus) (Jimenez and Jaksic 1988), no dietary information was previously 41 42 Iriarte et al. Vol. 24, No. 3 available for raptorial birds from the Chilean Pat- agonia. Here, we analyze the diets of an assemblage of four common raptor species in Torres del Paine National Park as they relate to prey availability. Specifically our objectives were to 1) determine the diets of two strigiforms, the Great Horned Owl and Barn Owl ( Tyto alba), and one falconiform, the Black- chested Buzzard Eagle or Chilean Eagle ( Gera - noaetus melanoleucus ), 2) compare our results with similar data on the Cinereous Harrier (Jimenez and Jaksic 1988), and 3) discuss these results in con- nection with prey distribution and current quanti- tative estimators of trophic structures (Jaksic 1985). Study Area and Methods Field studies were conducted in Torres del Paine Na- tional Park (51°3'S, 72°55'W) in the Magallanes region of Chile, on the eastern foothills of the Andes and on the western edge of Patagonia. Created in 1959, the 240 000- ha park provides relatively undisturbed habitat for wild- life. The topography of the study area ranges from foothills to plains with elevation ranging from 100-700 m. Ap- proximately 80% of the park consists of steppe biome, classified as “pre-Andean, dry shrub association” and characterized by the pampa grassland common in both southern Chile and Argentina at elevations below 500 m (Pisano 1973, 1974), The remainder is a rich mosaic of lakes, shrub, and dense Nothofagus deciduous forest. To analyze habitat use by prey species, we classified habitat as either grassland, shrubland, or Nothofagus forest. The most common grassland species in order of decreasing cover were Festuca gracillina, Anarthrophyllum patagoni- cum, and F. palhscens (Texera 1973, Pisano 1973, 1974, Ortega and Franklin 1988). The locally dominant shrub- land species was “Mata Barrosa” ( Mulinum spinosum), a spiny, dome-shaped shrub, common in thin, rocky upland and rapidly draining soils, and “Mata Negra” ( Verbena tridens). Other important species were “Senecio” ( Senecio patagonicus ), “Calafate” ( Berberis buxifolia), and “Para- mela” {Adesmia boronoides). The Nothofagus forest habitats were dominated by two medium-size tree species, “Nirre” (N. antarctica) and “Lenga” (N. purrulio). Great Horned Owl pellets were collected beneath perch- es and nest sites of two pairs at the edge between open patches of grassland and Nothofagus forest near the park’s administration office from January through March 1987 and from April through June 1988. Barn Owl pellets were collected at cliff nests of at least two pairs near Laguna Amarga, in the east part of the park from April through June 1988. Black-chested Buzzard Eagle pellets were col- lected beneath nine perches and five nests in Nothofagus forests in the northern portion of the park from April through June 1988. We identified prey remains in pellets by comparing hair, feathers, and bones with our reference collection and with the key of Reise (1976). Mammalian prey was classified to the species level, with the exception of rodents of the genus Akodon, which we were unable to distinguish from prey remains. Avian prey were categorized to the family level. We estimated habitat use and relative abundance of rodent species by trapping in the grassland, shrubland, and forest habitats from May 1987 through May 1988. Within each selected area we placed 49 (8 by 10 by 23 cm) Sherman aluminum live-traps in a 70 x 70 m grid with each trap 10 m apart. Traps were set each month for 4 days and 4 nights, baited with rolled oats, and checked daily in the morning. Additional trapping was conducted in areas not covered by the grids to determine the presence of species using more restricted habitats. Although we probably did not adequately sample certain trap-shy species and had to assume species had equal capture probabilities in each area, this index provided an initial measure of relative habitat use. We obtained raptors’ weights from Jaksic et al. (1981), Jaksic and Delibes (1987), and Ji- menez and Jaksic (1988). Food-niche breadth was deter- mined using Levins’ (1968) formula. This index ranges from 1 up to the number of prey categories recognized (n). We calculated food-niche breadth at the highest possible level of taxonomic resolution of prey categories, species level for mammals and family level for birds and insects. To make comparisons among species that used different numbers of prey categories, we calculated a standardized food-niche breadth proposed by Colwell and Futuyma (1971:569). B sta ranges between 0 and 1, or from minimum to maximum food-niche breadth. Food-niche overlap, a measure of diet similarity, was calculated with the formula described by Pianka (1973). This index ranges from 0 (signifying no overlap) to 1 (signifying complete overlap). Geometric mean weight of vertebrate prey in the diet was calculated by summing the products of the numbers of individual prey items with their natural-log weight and dividing by the total number of prey items used in the calculation. With the exception of species of the genus Akodon which we analyzed together, only prey items iden- tified to species were included in this calculation. Average weights of prey were determined from adults of each species captured throughout the year. All prey were assumed to be adult-sized because we were unable to determine the frequency of occurrence of different prey sizes. This pro- cedure overestimates the mean weight of prey for each raptor species, especially for the Black-chested Buzzard Eagle, which ate primarily European Hares, but the prob- lem is partially alleviated by the use of natural-log-trans- formed weights to compute mean weight of vertebrate prey (see Jaksic and Braker 1983). Simple linear regression was used to determine the relation between mean weight of vertebrate prey, food-niche breadth, and raptor weight. We used a chi-square analysis to compare the propor- tion of rodent species in the pellets and rodent abundance estimates to determine if the Barn Owl or Great Horned Owl preyed upon rodent species in proportions different than would be expected based upon the trapping results. Because of their low comparative abundances, Reithrodon physodes, Auliscomys micropus, Euneomys chinchilloides, Phyllotis darwini, Eligmodontia typus , and Chelemys macro- nyx were combined for statistical analysis (Sokal and Rohlf 1981). Autumn 1990 Southern Chilean Raptors 43 Table 1. Diet of four raptors in Torres del Paine National Park, Chile, based on regurgitated pellets collected from January through March 1987 and April through June 1988 (subtotals in parentheses). Data on Circus cinereus were taken from Jimenez and Jaksic (1988). Barn Owl % Great Horned Owl % Chilean Eagle % Cinereous Harrier % Mammals Akodon sp. 30.1 22.2 — — Reithrodon physodes 19.6 9.3 — — Oryzomys longicaudatus 15.3 19.8 — — Auliscomys micropus 13.7 7.4 — — Eligmodontia typus 5.1 3.7 — — Phyllotis darwini 3.2 2.5 — — Chelemys macronyx 2.4 2.5 — — Euneomys chinchilloides 1.7 8.0 — — Unidentified rodents 8.7 3.1 2.1 28.9 Total rodents (99.8) (78.5) (2.1) (28.9) Ovis aries — — — 0.1 Lepus capensis — 17.3 91.3 0.1 Dusicyon griseus — — 1.1 — Conepatus humboldti — — 1.1 — Unidentified mammals — — 1.1 — Total mammals (99.8) (95.8) (96.7) (29.1) Birds Anatidae — 1.1 — Emberizidae — — — 0.6 Fringillidae — — — 5.4 Furnariidae — — — 1.5 Hirundinidae — — — 0.1 Muscicapidae — — — 0.1 Podicipedidae — — — 0.1 Psittacidae — — 1.1 — Tyrannidae 0.2 4.2 1.1 — Unidentified birds — — — 34.0 Total birds (0.2) (4.2) (3.3) (41-8) Reptiles Iguanidae — — — 29.1 Number of vertebrate prey 531 162 93 823 a Number of pellets 302 100 91 413 Food-niche breadth b 5.5 (0.5) 6.9 (0.6) 1.2 (0.3) 3.5 (0.3) MWVP‘ (g) 29.9 80.3 2567.3 33.9 Raptor weight (g) 310 1500 2000 417 a Jimenez and Jaksic (1988) also found 436 remains of insects and arachnids in the pellets. b Standardized food-niche breadth in parentheses. c Mean weight of vertebrate prey. Results Standardized food-niche breadth was broadest for Great Horned Owl, followed by the Barn Owl, Ci- nereous Harrier, and Black-chested Buzzard Eagle (Table 1). Dietary overlap was greatest between the Great Horned Owl and Barn Owl, because these two species preyed essentially on the same rodents (Table 2). The main difference between their diets 44 Iriarte et al. Vol. 24, No. 3 Table 2. Food-niche overlap among four common raptor species in Torres del Paine National Park, Chile. Great Horned Owl Chilean Eagle Cinereous Harrier Barn Owl 0.818 0.051 0.496 Great Horned Owl — 0.505 0.520 Chilean Eagle — 0.309 was due to more European Hares in the diet of the Great Horned Owl and the comparatively larger percentage of Akodon spp., R. physodes, and A. mi- cropus taken by the Barn Owl. The Black-chested Buzzard Eagle preyed primarily on European Hares (91% of its diet), whereas the Cinereous Harrier preyed mainly on birds (42%), lizards (29%), rodents (29%) and insects. Mean weight of prey in the diet increased with predator weight (Table 1), but not significantly (r 2 = 0.60, F = 2.95, df = 1, P = 0.23). Three rodent species, Akodon xanthorhinus , A. lon- gipilis, and Oryzomys longicaudatus accounted for 88% of the total trap captures. The majority of the rodents were captured in shrub and forest habitats (Table 3). Neither owl preyed on rodent species in propor- tion to their availability (Barn Owl, x 2 = 57.0, df = 2, P < 0.001; Great Horned Owl, x 2 = 55.7, df = 2, P < 0.001), with both species selecting for the group of R. physodes, A. micropus, E. chinchilloides , P. darwini, E. typus, and C. macronyx and avoiding Akodon species. The Barn Owl took a higher percentage of its prey from forested and shrub areas. Akodon spp., O. longicaudatus, and A. micropus, which together com- prised 60% of the Barn Owl’s diet, were trapped primarily in forested areas (Table 3). Similarly, the Great Horned Owl took rodents which we trapped mostly in shrub and forest habitats. Although this owl took some European Hares, inhabitants of open- patches (Grigera and Rappoport 1983), they preyed primarily on rodents trapped in dense cover such as Akodon sp., E. chinchilloides, and 0. longicaudatus. The high proportion of European Hares in the Black- chested Buzzard Eagle diet indicated that this species hunted primarily in open habitats, which was the most extensive habitat in the park (more than 80% of the total study area). Discussion As previously reported for other areas of Chile (Johnson 1965, Jaksic and Yanez 1979, 1980), we found that the Barn Owl in Torres del Paine Na- tional Park preyed primarily on rodent species. Ac- cording to Jaksic et al. (1981), the Barn Owl in mediterranean-type habitats of central Chile preys Table 3. Mean adult body weights and number of rodents captured per 1000 trap nights in the three most common habitat types in Torres del Paine National Park, Chile from May 1987 through May 1988. Mean Body Weight g (n) Grassland Shrub Forest Average Akodon longipilis 31 (38) 0.4 100.7 130.5 77.2 Akodon olivaceus 27 (18) 1.7 58.0 31,3 30.3 Akodon sanborm 20 (4) 0.0 0.0 1.7 0.6 Akodon xanthorhinus 21 (49) 49.0 313.0 234.8 198.9 Auliscomys micropus 47 (5) 0.0 4.0 1.7 1.9 Chelemys macronyx 43 (3) 0.4 0.0 0.0 0.1 Eligmodontia typus 17(3) 1.1 0.0 0.0 0.4 Euneomys chinchilloides 54 (2) 0.0 0.9 3.3 1.4 Oryzomys longicaudatus 26 (36) 0.4 127.5 102.6 76.8 Phyllotis darwini 52 (3) 0.0 0.0 3.3 1.1 Reithrodon physodes 60 (8) 1.1 23.3 8.8 11.1 Total captures 298 1424 1243 2956 No. trap-nights 5389 2275 2398 10 062 Captures /trap-nights 0.06 0.63 0.52 0.29 Number of species 7 7 9 11 Autumn 1990 Southern Chilean Raptors 45 on almost every small mammal species present. The degree to which the Barn Owl takes particular ro- dent species depends upon several factors. Apparent selectivity may result from differing degrees of noc- turnal activity of the rodent prey, thus rendering some of them more readily available to this owl, a strictly nocturnal predator (Jaksic and Yanez 1980). Foraging behavior and habitat use may also be im- portant. The greater occurrence of R. physodes and A. micropus in the Barn Owl diet suggests they may be utilizing the shrub habitat more than the Great Horned Owl. The prevalence of European Hares in the Great Horned Owl’s diet compared to the Barn Owl par- allels findings in central Chile (Jaksic and Yanez 1979, 1980), where the latter species ate significant amounts of the European rabbit ( Oryctolagus cunic- ulus). Our data showed that Great Horned Owls consumed a greater frequency of European Hare than previously reported for this species in the park (Jaksic et al. 1978, 1986). This apparent difference in diet can perhaps be attributed to seasonal or an- nual variations in prey availability, individual hunt- ing behavior of owls, or even the use of a different habitat. According to Jaksic et al. (1986), in Chile, the geometric mean weight of prey consumed and diet breadth of the Great Horned Owl declined from north to south. Our results agreed with this general pattern as our consumed prey sizes and diet breadths are the smallest reported for Chile. The Cinereous Harrier relied primarily on avian and small reptilian prey, taking some small mam- mals as well. This was the only raptor species in the study that ate reptiles and had a significant amount of insects in its diet (Jimenez and Jaksic 1988). In our study the Black-chested Buzzard Eagle had the most restricted diet, feeding almost exclusively on European Hares. This raptor can be more of a generalist than our data suggests, however. For ex- ample, in central Chile, rodent species constituted 76% of the Black-chested Buzzard Eagles’ diet (Schlatter et al. 1980). Also, since the European Hare was introduced in southern South America 90 years ago (Miller and Rottmann 1976, Grigera and Rappoport 1983), the Black-chested Buzzard Eagle has shifted its food habit considerably. Raptors are often considered to be opportunistic predators. The Black-chested Buzzard Eagle, being the largest ae- rial predator in the park, is likely to be the raptor best able to exploit the European Hare. The presence of gray foxes ( Dusicyon griseus) and of Patagonia hog-nosed skunks ( Conepatus humbold- ti) in the diet of Black-chested Buzzard Eagles dem- onstrated their ability to take larger, and perhaps more difficult-to-catch prey, provided that they do not scavenge on carrion. The mean weight of ver- tebrate prey in the diet of Black-chested Buzzard Eagles in Torres del Paine was almost eight times that reported for central Chile (2367 vs. 308 g) (Schlatter et al. 1980). However, such large differ- ences between different areas are not unusual among raptors (Jaksic and Braker 1983, Jaksic 1988). Acknowledgments We are grateful to Fredy Barrientos, Gail Blundell, Kyle Harms, Judith Hoffman, Richard Lawrence, and Torres del Paine Park rangers Francisco Barrientos, Jovi- to Gonzalez, Guillermo Santana, and Juan Toro for their help in the fieldwork and data gathering. We appreciate the assistance and collaboration of the Chilean National Forest and Park Service (CONAF). We thank Chris Can- aday, James J. Dinsmore, Peter Feinsinger, Fabian M. Jaksic, R. Scott Lutz, Kent H. Redford, and two anon- ymous reviewers for constructive criticisms on different versions of the paper. This study was funded by grants from the National Geographic Society (Grant No. 3581- 87), Patagonia Research Expeditions, and the Program for Studies in Tropical Conservation, University of Flor- ida. This project was conducted under a research agree- ment (Proyecto Puma) between Iowa State University and CONAF. Journal paper No. J-13459 of the Iowa Agri- culture and Home Economics Experiment Station, Ames, Iowa. Project No. 2519. Literature Cited Araya, B. and G. Millie. 1986. Guia de campo de las aves de Chile. Editorial Universitaria, Santiago, Chile. Caviedes, C.N. and J.A. Iriarte. 1989. Migration and distribution of rodents in central Chile since the Pleis- tocene: the palaeogeographic evidence. J. Biogeogr. 16: 181-187. Colwell, R.R. and D.J. Futuyma. 1971. On the mea- surement of niche breadth and overlap. Ecology 52: 567-576.- Grigera, D.E. and E.H. Rappoport. 1983. Status and distribution of the European Hare in South America. J. Mammal. 64:163-166. JaksiC, F.M. 1985. Toward raptor community ecology; behavior bases of assemblage structure. Raptor Res. 19: 107-112. . 1988. Trophic structure of some nearctic, neo- tropical and palearctic owl assemblages: potential roles of diet opportunism, interspecific interference and re- source depression. J. Raptor Res. 22:44-52. and H.E. Braker. 1983. Food-niche relation- ships and guild structure of diurnal birds of prey: com- petition versus opportunism. Can. J. Zool. 61:2230- 2241. 46 Iriarte et al. Vol. 24, No. 3 and M. Delibes. 1987. A comparative analysis of food-niche relationships and trophic guild structure in two assemblages of vertebrate predators differing in species richness: causes, correlations, and conse- quences. Oecologia (Berl.) 71:461-472. , H.W. Greene and J.L. YA5?ez. 1981. The guild structure of a community of predatory vertebrates in central Chile. Oecologia (Berl.) 49:21-28. , J. Rau and J.L. YAftEZ. 1978. Oferta de presas y predacion por Bubo virginianus (Strigidae) en el Parque Nacional “Torres del Paine.” An. Inst. Patagonia (Chile) 9:199-202. AND J.L. YAftEZ. 1979. The diet of the Barn Owl in central Chile and its relation to the availability of prey. Auk 96:619-621. and . 1980. Differential utilization of prey resources by Great Horned Owls and Barn Owls in central Chile. Auk 97:895-896. , and J.R. Rau. 1986. Prey and trophic ecology of Great Horned Owls in western South Amer- ica: an indication of latitudinal trends. Raptor Res. 20: 113-116. Jimenez, J.E. and F.M. Jaksig. 1988. Ecology and behavior of southern South American Cinereous Har- riers, Circus cinereus. Rev. Chil. Hist. Nat. 61:199-208. Johnson, A.W, 1965. The birds of Chile and adjacent regions of Argentina, Bolivia and Peru. Platt Estable- cimientos Graficos, Buenos Aires. Levins, R. 1968. Evolution in changing environments: some theoretical explorations. Princeton University Press, Princeton, NJ. Miller, S.D. and J. Rottmann. 1976. Guia para el reconocimiento de los mamiferos chilenos. Editora Na- cional Gabriela Mistral, Santiago, Chile. Ortega, I.M. and W.L. Franklin. 1988. Feeding hab- itat utilization and preference by guanaco male groups in the Chilean Patagonia. Rev. Chil. Hist. Nat. 61:209- 216. PlANKA, E.R. 1973. The structure of lizard communities. Ann. Rev. Ecol. Syst. 4:53-74. Pisano, E. 1973. Plant communities on the Argentine Patagonia. An. Inst. Patagonia (Chile) 10:1-12. . 1974. Estudio ecologi co de la region continental sur del area andino patagonica. II Contribution a la fitogeografia de la zona del Parque Nacional Torres del Paine. An. Inst. Patagonia (Chile) 5:59-104. Reise, D. 1976. Clave para el reconocimiento de roe- dores chilenos. Gayana, Universidad de Concepcion , Chile 27:1-20. Schlatter, R.P., J.L. YAAez and F.M. Jaksic. 1980. Food-niche relationships between Chilean Eagles and Red-backed Buzzards in central Chile. Auk 97:897- 898. Sokal, R.R. and F.J. Rohlf. 1981. Biometry: the prin- ciples and practice of statistics in biological research Second ed. W.H. Freeman and Co., San Francisco, CA. TEXERA, W. 1973. Distribution y diversidad de mamife- ros y aves en la Provincia de Magallanes. Historia geologica de los generos de mamiferos nativos ter- restres. Annales del Institute de la Patagonia, Punta Are- nas , Chile 4:1-3. Venegas, C. and J. Jory. 1979. Guia de campo para las aves de Magallanes. Publ. Inst. Patagonia (Chile), Serie Monografias 11:1-253. Received 24 October 1989; accepted 13 June 1990 J. Raptor Res. 24(3):47-51 © 1990 The Raptor Research Foundation, Inc. DENSITY AND HABITAT USE OF RAPTORS ALONG THE RIO BAVISPE AND RIO YAQUI, SONORA, MEXICO Ricardo Rodriguez- Estrella Centro de Investigaciones Biologicas, Apdo. Postal 128, La Paz, 23000, Baja California Sur, Mexico Bryan T. Brown P.O. Box 3741, Tuscon, AZ 85722 Abstract. — Raptor populations of the Rio Yaqui and one of its principal tributaries, the Rio Bavispe, of Sonora, Mexico, were surveyed by boat in the early spring of 1987 and 1988. The purposes of this survey were to document population status, to examine patterns of habitat use, and to compare raptor abundance between rivers. Turkey Vulture ( Cathartes aura ) and Black Vulture ( Coragyps atratus ) were the two most abundant raptors in the study area, although most vultures observed during the study period appeared to be migrants. Nesting raptors included Bald Eagle ( Haliaeetus leucocephalus) , Red-tailed Hawk (Buteo jamaicensis), Common Black-Hawk ( Buteogallus anthracinus) , and Peregrine Falcon {Falco p ere - grinus ). Common Black-Hawk was the most abundant nesting raptor, exhibiting a density of 0.35 pairs/ km in riparian woodland along the Rio Bavispe, the highest reported density for this species in Mexico. Common Black-Hawks were strongly associated with riparian areas dominated by dense stands of large Honey Mesquite (Prosopis glandulosa) and Pithecellobium ( Pithecellobium mexicanum ), a habitat that has apparently increased in extent due to the operation of an upstream dam and reservoir. Bald Eagles and Peregrine Falcons nested on riverside cliffs. Densidad y uso del habitat por aves rapaces a lo largo del Rio Bavispe y del Rio Yaqui, Sonora, Mexico Extracto.— Durante el inicio de la primavera de 1987 y 1988 se censaron las poblaciones de aves rapaces del Rio Yaqui y del Rio Bavispe, en Sonora, Mexico. Los rios fueron recorridos en canoas con el proposito de registrar la abundancia de aves rapaces y determinar los patrones del uso del habitat que las diferentes especies tienen en los dos rios. El Aura Comun ( Cathartes aura ) y el Zopilote Negro ( Coragyps atratus) fueron las rapaces mas abundantes en los censos, aunque la mayoria de los individios eran problamente migratorios. Las especies que se reproducian en la zona incluyen el Aguila Calva {Haliaeetus leucocephalus), el Aguililla colirroja {Buteo jamaicensis), el Aguililla Cangrejera {Buteogallus anthracinus) y el Halcon Peregrino {Falco peregrinus). La especie que anidaba mas abundantemente fue el Aguililla Cangrejera, con una densidad de 0.35 pares/km en el bosque de galeria del Rio Bavispe. Esta es la mas alta densidad reportada para la especie en Mexico. El Aguililla Cangrejera estuvo particularmente asociada a areas densas dominadas por Mezquite {Prosopis glandulosa) y por Palo Fierro {Pithecellobium mexicanum), un habitat que se ha incrementado debido aparentemente a la operation de una presa ubicada en la parte alta del rio. El Aguila Calva y el Halcon Peregrino fueron vistos anidando sobre los riscos que bordean el rio. Few studies exist regarding raptor populations of Mexico (Wetmore 1943, Friedmann et al. 1950, Thiollay 1977, 1978, 1979, 1980). Most of these studies were conducted in eastern Mexico and few relate to raptor status and habitat use in the more arid northwestern portion of Mexico. Here we pre- sent information on the density and habitat use of raptors along the Rio Yaqui and one of its principal tributaries, the Rio Bavispe, in Sonora, Mexico. Spe- cial attention has been focused on nesting raptors associated with riparian zones, particularly Com- mon Black-Hawk {Buteogallus anthracinus). Study Area The Rio Yaqui, the largest river of Sonora (Fig. 1), is formed by the confluence of its major tributaries, the Rio Aros and Rio Bavispe. The study area consisted of the Rio Bavispe from the town of Granados downstream to its confluence with the Rio Aros (65 km) and the main- stream Rio Yaqui from the Aros/Bavispe confluence downstream to the El Raspadero Mine at the head of the 47 48 Ricardo Rodriguez-Estrella and Bryan T. Brown Vol. 24, No. 3 Figure 1, The Rio Bavispe and Rio Yaqui study area was surveyed in 1987-1988. Bold line shows the portions of each river censused. El Novillo Reservoir (80 km). Elevations along the river range from 520 m at Granados to 330 m at the El Novillo Reservoir; mountain peaks adjacent to the rivers rise to over 1800 m. The Rio Bavispe flows through relatively narrow canyons, while the Rio Yaqui flows through a broad canyon. Cliff's up to 100 m in height occur infre- quently along both rivers. Upland vegetation consists of subtropical, winter-deciduous thornscrub averaging 10 m in height dominated by Lysiloma divaricata. Acacia cochlia- cantha, Ceiba acuminata, Cercidium praecox. Mimosa dyso- carpa, and Fouquieria macdougalii (White 1948). Riparian vegetation consisted of Pithecellobium ( Pithe - cellobium mexicana), Honey Mesquite ( Prosopis glandulo- sa ), Gooding Willow (Salix gooddingii), Fig (Ficus petio- laris), Canyon Ragweed ( Ambrosia ambrosioides) , Soapberry (Sapindus saponaria ), and a few scattered cottonwoods (Populus fremontii ) and palms (Erythea roezlii). Riparian vegetation also invaded narrow floodplains in the river canyons (White 1948). Riparian vegetation of the Rio Bavispe, and to a lesser extent the Rio Yaqui, has been modified by the upstream construction and operation of the Angostura Reservoir on the Rio Bavispe since the mid 1930s. The dam eliminated the large annual floods which had formerly scoured away all vegetation below the pre-dam high water mark, allow- ing a dense new zone of woody vegetation to develop at the post-dam river’s edge. Although the extent of this increase in riparian habitat is undocumented, our quali- tative observations suggest that Mesquite- and Pithecel- lobium-dominated riparian woodland along the Rio Ba- vispe increased several hundred percent, from an estimated pre-dam 50 ha to a post-dam 200 ha. A continuous, dense band of closed-canopy, even-aged riparian woodland dom- inated by Mesquite and Pithecellobium averaging 12 m in height had formed along the Rio Bavispe by the 1980s. This is analogous to the increase in extent of riparian vegetation documented along the Colorado River in Ari- zona after the completion of Glen Canyon Dam (Turner and Karpiscak 1980). Riparian vegetation was less well- developed along the Rio Yaqui due to the recurrence of annual floods from the undammed Rio Aros. The riparian zone of the Rio Yaqui was greatly dis- turbed by human activities including agriculture, grazing, mining, roads, and the presence of several small ranches and a village. The Rio Bavispe was relatively undisturbed except for grazing and the presence of two small ranches. Methods We surveyed raptor populations in the study area from 24 March to 2 April 1987, and from 7-14 April 1988. The surveys were made from canoes as we floated down- stream, censusing a distance of 15-20 km/day. Up to eight skilled observers participated in the surveys. Each survey was designed as a continuous transect (Fuller and Mosher 1981) where the transect length was the length of the river traversed in km. All raptors observed within 0.5 km of the river were recorded between 1000 and 1800 H, the range of times when we were actively moving downstream. For each raptor we recorded species, location, indications of breeding, if any, and habitat. We classified the study area into five major habitats: Pithecellobium and Mesquite, Gooding Willow and Pithecellobium, Mes- quite, upland mountain or cliff, or disturbed areas. Habitat occurrence for raptors whose nest location was known was classified according to the nest location; habitat occurrence for raptors whose nest location was not known was clas- sified according to the initial habitat in which they were observed. Several techniques, including the continuous visual transect, nest searches, and observations of territorial be- havior, were used to determine raptor abundance. Nest sites of cliff-nesting species were located by visual inspec- tion of cliff habitat; tree nests were often visible from the river as we floated past. Observation of the territorial behavior of single or paired Common Black-Hawks was useful in determining the Autumn 1990 Rio Yaqui Raptors 49 Table 1. Raptors observed along the Rio Bavispe and the Rio Yaqui, in Sonora, Mexico, 1987-1988. Bavispe ( 65 river-km) Yaqui (80 river-km) Total (145 river-km) 1987 1988 1987 1988 1987 1988 Black Vulture ( Coragyps atratus) 77 141 54 64 131 205 Turkey Vulture ( Cathartes aura ) 122 67 179 57 301 124 Bald Eagle ( Haliaeetus leucocephalus) — — 4 4 4 4 Sharp-shinned Hawk ( Accipiter striatus ) 1 1 2 4 3 5 Cooper’s Hawk ( Accipiter cooperi ) — 2 1 1 1 3 Common Black- Hawk ( Buteo gallus anthracinus) 37 42 15 16 52 58 Gray Hawk ( Buteo nitidus ) — — 1 — 1 — Red-tailed Hawk ( Buteo jamaicensis) 11 3 13 8 24 11 American Kestrel ( Falco sparverius) 1 — 2 — 3 — Peregrine Falcon {Falco peregrinus) 2 — 2 — 4 — Prairie Falcon {Falco mexicanus) 2 — — — 2 — No. of species 8 6 10 7 11 7 Total individuals 253 256 273 154 526 410 Individuals /km 3.8 3.9 3.4 1.9 3.6 2.8 number of pairs present, particularly along the Rio Bavis- gyps atratus) were the two most abundant species pe. Single or paired adults would regularly precede or accompany us, screaming loudly, as we floated down- stream through their territory. The adult(s) would break away and fly back upstream after a certain point, which we interpreted to be the territorial boundary. Here, the raptors were often replaced by other single or paired adults which would likewise precede or accompany us through their territory. Constant observation of the activity patterns of Common Black-Hawks allowed us to estimate their population size along the river. Nests attended by single or paired adults were interpreted to indicate the center of activity of a pair. Single adults exhibiting territorial be- havior were interpreted as a pair, unless single adults were observed < 1 km from another single adult exhibiting ter- ritorial behavior. In the latter case, the two adults may have been paired but were temporarily in different areas of their territory. Pairs of Common Black-Hawks were not included in the census as long as they continued to fly downstream ahead of the advancing boats, but only when they were seen to fly back upstream or away from the river on a course that would not result in their being counted twice. Results A total of 526 individuals of 11 raptor species were observed along the two rivers in 1987; 410 individuals of seven species in 1988 (Table 1). Mean values of 3.6 and 2.8 individuals/km occurred in the study area in 1987 and 1988, respectively. Turkey Vulture ( Cathartes aura ) and Black Vulture (Cora- encountered (Table 1). The next most abundant species was the Common Black-Hawk, a common nesting species. We observed different patterns of habitat occu- pation among selected raptor species (Table 2). Black Vultures were almost entirely associated with dis- turbed areas, while Turkey Vultures were primarily associated with riparian areas dominated by Mes- quite and Pithecellobium. Common Black-Hawks were also largely found in riparian areas dominated by Mesquite and Pithecellobium. Bald Eagles ( Hal - iaeetus leucocephalus ) and Peregrine Falcons ( Falco peregrinus ) occurred at sites with suitable cliffs, while Red-tailed Hawk ( Buteo jamaicensis ) observations were at both mountain cliffs and riparian areas dom- inated by Mesquite and Pithecellobium. The abun- dance of different habitats within the study area was not examined, precluding a quantitative comparison of habitat preferences. We observed only four species nesting in the study area, although more species may nest during sum- mer. Two occupied Bald Eagle nests were attended by adults in both 1987 (Brown 1988) and 1988. An occupied Peregrine Falcon eyrie was attended by two adults in 1987, but was unoccupied in 1988. Courtship was observed at two probable Red-tailed Hawk nests in 1987 and 1988 where incubation had 50 Ricardo Rodriguez- Estrella and Bryan T. Brown Vol. 24, No. 3 Table 2. Proportions of raptors observed in five riparian habitats along the Rio Bavispe, and Rio Yaqui, Sonora, Mexico, 1987. Species Numbers of Individuals Pithe- cellobium/ Mesquite Goodding Willow/ Pithe- cellobium Mountain/ Cliffs 3 Disturbed Areas 15 Black Vulture 131 0.04 0 0 0.96 Turkey Vulture 306 0.57 0.02 0.13 0.28 Bald Eagle 4 0 0 1.0 0 Common Black-Hawk 52 0.70 0.25 0.03 0.02 Red-tailed Hawk 24 0.38 0.04 0.58 0 Peregrine Falcon 4 0 0 1.0 0 Total 521 224 20 64 213 a Mountain/cliffs were largely associated with upland vegetation. b By human influence (i.e, fields, pastures, cattle-ranches). not yet begun. The fourth nesting species was the Common Black-Hawk, which exhibited courtship behavior and strong territorial behavior during the study period. Five and seven probable Common Black-Hawk nests were located in 1987 and 1988, respectively, although incubation had evidently not yet begun for most pairs. Common Black-Hawk was the most abundant riparian-nesting raptor in the study area, where it occurred at densities of up to 0.35 pairs/km along the Rio Bavispe (Table 3). Discussion We observed a proportionately greater concentra- tion of Turkey Vultures and Black Vultures than other raptors on the Rio Yaqui. These species are clearly associated with human activities (Table 2). Table 3. Pairs of Common Black-Hawks and their den- sity/river-km on the Rio Bavispe, and Rio Ya- qui, Sonora, Mexico, as determined through downriver continuous transect surveys per- formed in late March and early April, 1987 and 1988. Single adults exhibiting territorial behavior were counted as a pair. Rio Bavispe Rio Yaqui Total Den- Den- Den- Year No. SITY a No. sity No. sity 1987 23 0.35 8 0.10 33 0.22 1988 21 0.32 8 0.10 30 0.20 a Density expressed as a number of pairs/km. The greatest concentrations (up to 50 individuals/ site) of Black Vultures were observed near small villages or ranches. The primary difference between the 1987 and 1988 abundance of vultures in the study area was apparently due to greater numbers of Black Vultures near the ranches and villages in 1988, and greater numbers of Turkey Vultures overall in 1987. These differences may have been due to the timing of vulture migration during the two study years, since most of the vultures observed were probably migrants. Lower raptor density on the Rio Yaqui may be explained by the presence of humans per se, or subtle habitat differences between the two rivers. Direct human interference of sensitive raptors is a well- documented detriment to their occurrence (Newton 1979, Thiollay 1984, 1985). The Rio Yaqui expe- riences more human disturbance than the Rio Ba- vispe. However, the Rio Bavispe has also experi- enced substantial human-related modification (i.e., increase in the extent of riparian woodland due to the Angostura Reservoir). These modifications ap- parently increased the complexity and extent of the riparian environment. The Common Black-Hawk was a specialist in the use of habitats not favored by other species (dense riparian woodland dominated by Mesquite and Pithecellobium). This habitat was most developed along the Rio Bavispe, where the highest nesting density of Common Black-Hawks occurred (Table 3). Their high density there may have been associ- ated with the increase in riparian habitat brought about by the construction and operation of the An- gostura Reservoir. Autumn 1990 Rio Yaqui Raptors 51 Little comparative information on Common Black- Hawk density exists from other portions of its range (8 pairs/3000 ha, Palma Sola, Veracruz; Thiollay 1978), but its abundance on this 65-km stretch of the Rio Bavispe represents the highest reported for this species in Mexico. Densities reported in Table 3 should be conservatively interpreted as minimum population sizes. Only one survey was made each year, when several surveys per nesting season would have provided more accurate information. Common Black-Hawks are restricted to riparian habitat in the arid Southwest (Millsap 1981), and our limited observations on the configurations of their territories in the study area suggested linear terri- tories nearly equally spaced along the Rio Bavispe. Their affinities for riparian habitat, territorial re- sponses to intruders early in the breeding season, and nature of the habitat they occupy suggest that surveys by boat, when feasible, may be an efficient method of censusing Common Black-Hawk popu- lations. The occurrence of the two rarer nesting species, Bald Eagle and Peregrine Falcon, was of special interest. The Rio Yaqui drainage is the only known locality on the mainland of Mexico (excluding Baja California) where Bald Eagles are known to nest (Brown et al. 1987, Brown 1988). Two young ap- parently fledged from one of the occupied nests in 1987, and both nests contained two young near fledg- ing in 1988, suggesting that the quality of the Rio Yaqui territories was adequate. Swenson et al. (1986) found that a stable food source appeared to be the most important factor influencing selection of nesting territories by Bald Eagles, but the presence of suit- able sites for nest-placement is also critical (Mc- Ewan and Hirth 1979). We observed many fish in the Rio Yaqui near the two Bald Eagle nests. Both nests were located on high cliffs above the river. The status and abundance of Peregrine Falcons in Sonora is poorly known (Hitchcock 1977), The single occupied eyrie we observed along the Rio Ba- vispe in 1987 suggested that this species was rare in the study area, although other pairs could have gone undetected in our survey. Acknowledgments Special thanks are due to Alfredo Ortega, M.S. Laura Arriaga, and Peter L. Warren for their comments on pre- vious drafts of this manuscript. S. Anderson, J. Arenas, W. Leibfried, R. Mesta, S. Reyes, and P. Warren gave valuable assistance in the field. The illustration is by R. Lomeli. Financial support was provided by the U.S. Bu- reau of Reclamation, the Salt River Project, and Secretaria de Programacion y Presupuesto and Centro de Investi- gaciones Biologicas of Mexico. Literature Cited Brown, B.T. 1988. Additional Bald Eagle nesting rec- ords from Sonora, Mexico. J. Raptor Res. 22:30-32. , P.L. Warren and L.S. Anderson. 1987. First Bald Eagle nesting record from Sonora, Mexico. Wilson Bull. 99:279-280. Friedmann, H., L. Griscom and R.T. Moore. 1950. Distributional checklist of birds of Mexico, Part 1 Pacific Coast Avifauna No. 29. Cooper Ornithol. Club, Berkeley, California. Fuller, M.R. and J.A. Mosher. 1981. Methods of detecting and counting raptors: a review. Studies in Avian Biol. 6:235-246. Hitchcock, M.A. 1977. A survey of the Peregrine Fal- con population in northwestern Mexico, 1976-77. Contrib. No. 40, Chihuahuan Desert Research Insti- tute, Alpine, Texas. McEwan, L.C. and D.H. Hirth. 1979. Southern Bald Eagle productivity and nest site selection. J. Wildl Manage. 43:585-594. Millsap, B.A. 1981. Distributional status of falconi- formes in west-central Arizona, with notes on ecology, reproductive success, and management. Tech. Note 355, U.S.D.I. Bureau of Land Management, Phoenix, Ar- izona. Newton, I. 1979. Population ecology of raptors. Buteo Books, Vermillion, SD. Swenson, J.E., K.L. Alt and R.L. Eng. 1986. Ecology of Bald Eagles in the greater Yellowstone ecosystem. Wildlife Monogr. 95. Thiollay, J.M. 1977. La migration d’automne sur la cote orientale du Mexique. Alauda 45:344-346. . 1978. Comparaisons entre les peuplements de falconiformes des plaines coheres du Mexique et de Cote D’Ivoire. Le Gerfaut 68:139-162. . 1979. L’importance d’un axe de migration: la cote est du Mexique. Alauda 47:235-245. . 1980. Spring hawk migration in eastern Mex- ico. Raptor Res. 14:13-20. . 1984. Raptor community structure of a primary rain forest in French Guiana and effect of human hunt- ing pressure. Raptor Res. 18:117-122. . 1985. Composition of falconiform communities along successional gradients from primary rainforest to secondary habitats. Inti. Council for Bird Preser- vation, Tech. Publ. No. 5:181-190. Turner, R.M. and M.M. Karpisgak. 1980. Recent vegetation changes along the Colorado River between Glen Canyon Dam and Lake Mead, Arizona. U.S Geological Survey Prof. Pap. 1132, U.S. Government Printing Office, Washington, D.C. Wetmgre, A. 1943. The birds of southern Veracruz, Mexico. Proc. U.S. Nat. Mus. 93:215-340. White, S. 1948. The vegetation and flora of the region of the Rio Bavispe in northeastern Sonora, Mexico. Lloydia 11:229-302. Received 19 December 1989; accepted 5 July 1990 /. Raptor Res. 24(3):52-55 © 1990 The Raptor Research Foundation, Inc. NESTING HABITAT OF FLAMMULATED OWLS IN OREGON Evelyn L. Bull and Anthony L. Wright 1 USD A Forest Service, Pacific Northwest Research Station, Forestry and Range Sciences Laboratory, La Grande, OR 97850 Mark G. Henjum Oregon Department of Fish and Wildlife, 107 20th St., La Grande, OR 97850 Abstract. — Thirty-three Flammulated Owl ( Otus flammeolus) nests were located in northeastern Oregon during 1987-1988. The average nest tree dbh and height of the cavity were 72 cm and 12 m, respectively. Important characteristics of nest habitat included: large-diameter dead trees with cavities at least as large as those made by Northern Flickers ( Colaptes auratus)-, located on ridges and upper slopes with east or south aspects; in stands of large diameter (>50 cm dbh) ponderosa pine {Pinus ponderosa) and Douglas- fir ( Pseudotsuga menziesii) or grand fir ( Abies grandis ) with ponderosa pine in the overstory. Habitat para anidar de los Otus flammeolus en Oregon Extracto. — Treintitres nidos de buhos ( Otus flammeolus) han sido localizados en el noreste de Oregon durante 1987-1988. Los promedios de profundidad y altura de la cavidad en el arbol fueron de 72 cm y 12 m respectivamente. Las caracteristicas mas notables del habitat para los nidos incluian: arboles secos de gran diametro con cavidades por lo menos tan grandes como las que hacen los Colaptes auratus-, ubicados en cumbres y altas pendientes con frentes al este o sur; en Pinos Ponderosa {Pinus ponderosa) de gran diametro (>50 cm de profundidad) Abetos Douglas {Pseudotsuga menziesii) o Abetos Grandes {Abies grandis), con Pinos Ponderosa en la parte alta. The Flammulated Owl {Otus flammeolus) is a small, migratory, insectivorous cavity-nester of co- niferous forests in western North America (Bent 1938). This species was once considered rare (Bent 1938), but recent studies have shown it to be common in some areas of Colorado (Reynolds and Linkhart 1987a), New Mexico (McCallum and Gehlbach 1988), California (Winter 1974, Marcot and Hill 1980), and Oregon (Goggans 1986). Detailed information on nesting habitat is essen- tial for effective management of habitat for this owl. Land management agencies are maintaining dead trees for cavity-nesting birds, but need more detailed information on the species and size of dead trees and sites best suited to Flammulated Owls. Our objective was to describe the nesting habitat of Flammulated Owls in northeastern Oregon. 1 Present address: Running Creek Ranch, Cascade, ID 83611. [Traduccion de Eudoxio Paredes-Ruiz] Study Area The study was conducted on a 5270-ha area on the Starkey Experimental Forest (Starkey) located 35 km southwest of La Grande in northeastern Oregon. Starkey is characterized by undulating uplands dissected by mod- erately- to steeply-walled drainages with elevations of 1070 to 1 525 m. The study area consisted of a mosaic of forests (84% of area) interspersed with shallow-soil grasslands (16%). Forest types (classified by Burr 1960) were 14% open ponderosa pine {Pinus ponderosa), 41% ponderosa pine/Douglas-fir {Pseudotsuga menziesii), and 45% grand fir {Abies grandis) with Douglas-fir /ponderosa pine/west- ern larch {Larix occidentals). Fire suppression and selective timber harvesting in the 1930s resulted in uneven-aged stand structure. Multilay- ered canopies with some much larger trees characterized most stands. As these large trees died or were cut, favorable conditions allowed new tree establishment. Over time, this created multilayered stands with numerous patches of young, even-aged trees and a few large, overmature trees. We assigned stands into 1 of 3 successional stages. Class A were stands with all trees <30 cm dbh; class B were stands with >12 trees 30-50 cm dbh/ha; class C were stands with >12 trees >50 cm dbh/ha. Ninety percent of the area had not been logged in 40 years; the remainder had a partial removal of the overstory within the last 15 52 Autumn 1990 Flammulated Owl Nesting Habitat 53 years. Large-diameter dead trees containing nest cavities were abundant (98/40 ha) and distributed throughout the study area. Methods We searched for Flammulated Owls during April- July in 1987 and 1988. In April and May of each year we walked 26 routes totaling 220 km through the study area after sunset listening for Flammulated Owl vocalizations. Routes were 0.3-0. 5 km apart and followed roads when available; the entire study area was covered in 2 months. We stopped every 0.3 km for 5 min. We first listened for vocalizations; if none were heard, we imitated the owl’s vocalization. If an owl was heard, we recorded date, time, location, and forest type. In June and July we searched for nests during the day in areas within 0.5 km of where individual owls were heard at night. We scratched the bark of all trees with a cavity large enough to accommodate a Flammulated Owl in order to get the owl to reveal itself. A Flammulated Owl in a cavity in June or July during the day was classified as a nest. We believe this was a valid assumption because radio-tagged male Flammulated Owls roosted on branches of live trees during nesting, not in cavities (Gog- gans 1986, Reynolds and Linkhart 1987b). Reynolds (pers. comm.) confirmed that cavities containing an owl during the day were always nests. At each nest we recorded: tree species, condition (live or dead), dbh, height, cavity type (Pileated Woodpecker Dryocopus pileatus, Northern Flicker Colaptes auratus, or natural), and cavity height from the ground. Pileated Woodpecker cavities were dome-shaped and approxi- mately 12 cm high and 9 cm wide; Northern Flicker cav- ities were round and approximately 6-8 cm in diameter. Habitat characteristics were measured in a 0.1 -ha circular plot centered on the nest tree: location (ridge, slope, draw), slope aspect (measured with compass) and gradient (mea- sured with clinometer), forest type and successional stage, tree density (number stems/0.1 ha), distance to opening >1 ha in size, canopy closure (measured with spherical densiometer), and number of canopy layers. To obtain a sample of available dead trees, we searched 1534 ha of the study area and measured dead trees >50 cm dbh with potential nest cavities for Flammulated Owls. We located 3706 dead trees, 342 of which contained cav- ities that had been excavated by Pileated Woodpeckers or Northern Flickers, as determined by size and shape of the cavity entrance. Cavities in live trees were not recorded due to the difficulty in finding them. We did not climb trees with potential cavities to verify that they were cav- ities, because the majority of the trees were unsafe to climb. Only dead trees >50 cm dbh were characterized because 88% of the Flammulated Owl nests occurred in dead trees this size. These data were considered representative of the entire study area because of the homogeneity in habitat type, successional stage, and snag density throughout the study area. Cost and time constraints prohibited a complete survey of all snags on the study area. At each dead tree with a potential cavity we recorded tree species, dbh, height, size of cavity, forest type, succes- sional stage class, logging activity, slope aspect, and slope position. Chi-square analyses were used to compare the number of nests observed with the number expected based on data from available dead trees with cavities: 1) by forest type, 2) by tree species, 3) by type of cavity (Pileated Woodpecker versus Northern Flicker cavities), 4) by successional stages, 5) by logging activity, 6) by slope po- sition, and 7) by slope aspect. An unpaired Z-test was used to compare dbh and height of nest trees with those of available dead trees. Significance was established when P < 0.05. Results In 1987 the first Flammulated Owl was heard on 3 May, and 24 calling sites were located in May during 19.5 hours of walking routes. In 1988 the first Flammulated Owl was heard on 10 May, and 62 calling sites were located in May during 108.5 hours of walking routes. No Flammulated Owls were heard in April either year. Galling activity was greatest within 2 hr after sunset when 77% of the owls were first heard. Only 26% of the time spent listening was within this 2-hr period. The remainder of the time was spent listen- ing 2-7 hr after sunset. The location of singing owls detected was independent of forest type (x 2 = 0.64, 2 df, P = 0.73). We located 13 nests in 1987 and 21 nests in 1988. All nests were located in June and July, and only 1 tree was used both years by nesting Flammulated Owls. Of these 33 different nest cavities, 67% had been excavated by Pileated Woodpeckers, 27% had been excavated by Northern Flickers, and 6% had been created by decay. By comparison, the available cavities large enough to accommodate these owls in- cluded 45% Pileated Woodpecker and 55% Northern Flicker cavities. Relative to availability, Flammu- lated Owls used a higher percentage of Pileated Woodpecker cavities than expected (x 2 = 8.15, P < 0.01). Ninety-one percent of nests were in dead trees and 9% in live trees. Seventy percent of the nests were in ponderosa pine, 27% in western larch and 3% in grand fir trees. There was no difference be- tween species (x 2 = 1.47, 2 df, P = 0.49) or dbh ( t — 0.37, 368 df, P = 0.71) of dead trees used as nests and those available with cavities large enough to accommodate the owls (Table 1). Height of nest trees was significantly greater than of available trees (t = 3.49, 368 df, P < 0.01). Fifty-eight percent of the nests occurred in pon- derosa pine/Douglas-fir forest types, while the re- 54 Bull et al. Vol. 24, No. 3 mainder occurred in grand fir forest. Ponderosa pine was an overstory species at 73% of the nest sites. Although there was no difference between used and available dead trees by forest type (x 2 = 3.20, 2 df, P = 0.13) or logging activity (x 2 = 1.6, 1 df, P = 0.22), there was a difference among successional stage (x 2 = 6.35, 1 df, P = 0.04), slope aspect (x 2 = 8.87, 3 df, P < 0.05), and slope position (x 2 = 9.86, 3 df, P < 0.05). Ridges and the upper third of slopes were used more and lower slopes and draws were used less often than expected if selection was random. East and south slopes were used in greater propor- tion and north and west slopes used in lesser pro- portion than if used at random based on available dead trees with cavities large enough to accommodate the owls. Stands with trees >50 cm dbh were used as nest sites in greater proportion than if selected at random; 42% of the nests occurred here, yet only 24% of available cavities were in these stands. Discussion The detection of 62 singing owls during 1 nesting season suggests that Starkey had a high density of Flammulated Owls. Only a portion of the owls were detected because the entire study area could not be covered in the 2-3 week period that the birds vo- calized intensively. Densities of singing owls have been reported as 0.72/40 ha in Oregon (Goggans 1986), and 2.1/40 ha (Winter 1974) and 0.03-1.09/ 40 ha (Marcot and Hill 1980) in California. Density of pairs has been reported as 0.47/40 ha in Oregon (Goggans 1986) and 0.03-0.5/40 ha in Colorado (Reynolds and Linkhart 1987b). Apparent preference for Pileated Woodpecker cavities as nest sites was perhaps due to the larger cavities Pileated Woodpeckers excavate or the higher placement above the ground of these nests compared to those of flickers (X = 15 m, SD = 5.6; X = 8 m, SD = 6.2, respectively; Bull et al. 1986). Nests in live trees may have been underrepresented as such cavities are more difficult to detect. Nonetheless, large snags with Pileated Woodpecker cavities are clearly an important part of Flammulated Owl nesting hab- itat. Ridges and upper slopes were perhaps preferred because they provided the gentlest slopes, which would minimize the energy expenditure of birds car- rying prey to nests or because of prey availability. Goggans (1986) suggested such preference may be related to the diversity and density of prey. Prey may also be more abundant or at least more active on Table 1. Measurements taken at 33 Flammulated Owl nest trees in Oregon, 1987-1988. Variable Mean SD Nest tree DBH (cm) 72 14.4 Height (m) 24 9.1 Cavity height (m) 12 4.7 Nest habitat Trees >10 cm/0.1 ha 33 14.6 Trees 2-10 cm/0.1 ha 48 29.6 Canopy closure (%) 55 20.1 Number of canopy layers 2.5 0.5 Slope gradient (%) 18 11.8 Distance to opening (m) 50 51.3 higher slopes because these slopes are warmer than lower ones (Reynolds, pers. comm.). The preference for east and south aspects may also be related to temperature and availability or abundance of prey. Reynolds and Linkhart (1987b) suggested that stands with trees >50 cm dbh were preferred be- cause they provided better habitat for foraging due to the open nature of the stands, allowing the birds access to the ground and tree crowns; stands of dense, young trees were avoided. Some stands of larger trees also allow more light to the ground which produces ground vegetation, serving as food for some insects preyed upon by owls. Our findings suggest that the best way to manage habitat for the Flammulated Owl is to leave dead trees (>50 cm dbh and >6 m tall) with cavities at least as large as a Northern Flicker cavity. These trees are best left on ridges or upper slopes with east or south aspects in stands of large-diameter (>50 cm dbh) ponderosa pine/Douglas-fir or grand fir forest types, with ponderosa pine in the overstory. Retaining large diameter live trees in addition to snags, will provide for future snags. Another ap- proach is to manage habitat for Pileated Wood- peckers and Northern Flickers in these same situ- ations, as they will provide nest sites for these small owls over time. Acknowledgments We thank H.D. Cooper, R.D. Dixon, and J.E. Hoh- mann for their assistance with field work. E.D. Forsman, T.R. Madden, R.T. Reynolds, and J.W. Thomas re- viewed the manuscript. Funding was provided by the Autumn 1990 Flammulated Owl Nesting Habitat 55 USDA Forest Service’s Pacific Northwest Research Sta- tion and Oregon Department of Fish and Wildlife Non- game Fund. Literature Cited Bent, A.C. 1938. Life histories of North American birds of prey (Part 2). U.S. Natl. Mus. Bull. 170. Bull, E.L., S.R. Peterson and J.W. Thomas. 1986. Resource partitioning among woodpeckers in north- eastern Oregon. USDA For. Serv. Research Note PNW 444. Burr, J.A. 1960. Soil survey, Starkey Experimental Forest and Range, Union and Umatilla Counties, Or- egon. USDA Soil Conservation Service and Forest Ser- vice. Goggans, R. 1986. Habitat use by Flammulated Owls in northeastern Oregon. M.S. thesis. Oregon State Univ., Corvallis. Marcot, B.G. and R. Hill. 1980. Flammulated Owls in northwestern California. Western Birds 11:141-149. McCallum, D.A. and F.R. Gehlbach. 1988. Nest- site preferences of Flammulated Owls in western New Mexico. Condor 90:653-661. Reynolds, R.T. and B.D. Linkhart. 1987a. Fidelity to territory and mate in Flammulated Owls. Pages 234-238 in R.W. Nero, R.J. Clark, R.J. Knapton and R.H. Hamre [Eds.], Biology and conservation of Northern Forest Owls, Symposium Proceedings. U.S. Department of Agriculture, Forest Service, Tech. Rep. RM-142, Fort Collins, CO. AND . 1987b. The nesting biology of Flammulated Owls in Colorado. Pages 239-248 in R.W. Nero, R.J. Clark, R.J. Knapton and R.H. Hamre [eds.], Biology and conservation of Northern Forest Owls, Symposium Proceedings. U.S. Department of Agriculture, Forest Service, Tech. Rep. RM-142, Fort Collins, CO. Winter, J. 1974. The distribution of the Flammulated Owl in California. Western Birds 5:25-44. Received 5 October 1989; accepted 17 July 1990 /. Raptor Res. 24(3):56-58 © 1990 The Raptor Research Foundation, Inc. POST-FLEDGING BEHAVIOR OF AMERICAN KESTRELS IN CENTRAL KENTUCKY Christopher Kellner 1 Department of Biological Sciences, Eastern Kentucky University, Richmond, KY 40475 Abstract. — Observations on the post-fledging behavior of fledglings from 2 nests of American Kestrels ( Falco sparverius ) were collected during 1983 in central Kentucky. At nest 1, fledglings remained within 100 m of the nest during the first 14 days postfledging. From the 14th to 24th day postfledging they remained within 350 m of their natal nest and after their 24th day postfledging they traveled to areas outside their parents’ hunting area. They migrated in at least 2 groups after the 27th day postfledging. At nest 2, fledglings followed their parents immediately after fledging. They spent most of their time 250 m NW and 500 m N of their natal nest. Juveniles from nest 2 were observed with their parents up to 75 days postfledging. Differences between the behavior of the fledglings from those nests may be associated with differences in prey abundance, or parental behavior (possibly associated with a second nesting attempt by the adults at nest 1). Conducta del Cernicalo Americano joven, inmediata a su primer vuelo, en Kentucky central Extracto. — Observaciones de la conducta de Cernicalos Americanos ( Falco sparverius) tiernos, recien emplumados y neofitos en el vuelo, fueron realizadas en dos nidos durante 1983 en Kentucky central. En el nido no. 1 los cernicalos tiernos permanecieron dentro de los 100 metros de distancia del nido durante los primeros 14 dias de haberlo dejado. Desde el dia 14 hasta el dia 24 de la experiencia de vuelo, estos cernicalos permanecieron dentro de 350 metros de distancia de su nido, y despues del dia 24, ellos viajaban a areas que estaban fuera de la que, para cazar, usaban sus padres. Elios migraron en por lo menos dos grupos despues del dia 27 de su primer vuelo. En el nido no. 2, los cernicalos tiernos siguieron a sus padres inmediatamente despues de haber dejado el nido. Ellos pasaron la mayor parte de su tiempo a 250 m al Noroeste y a 500 m al Norte de su nido. Estos jovenes cernicalos fueron vistos junto a sus padres hasta 75 dias despues de haber dejado el nido. Las diferencias entre la conducta de estas aves de los nidos observados, pueden estar relacionadas con las diferencias en la abundancia de posibles presas o con la conducta de los padres (probablemente relacionada con una segunda posibilidad para anidar de los adultos del nido no. 1). [Traduccion de Eudoxio Paredes-Ruiz] The American Kestrel ( Falco sparverius) is a fairly common and easily studied raptor. Yet detailed in- formation concerning its post-fledging biology is lim- ited. Sherman (1913) published some observations on post-fledging movements of individual kestrels from one nest. Balgooyen (1976) published a gen- eralized account on activities of recently fledged American Kestrels in the Sierra Nevada of Califor- nia. Lett and Bird (1987) reported observations on fledglings from three families of kestrels focusing on perch selection, flight quality and social interactions. Finally, Bird (1988) reviewed aspects of post-nesting dependency and duration of family bonds in Amer- ican Kestrels. 1 Present address: Department of Biology, Virginia Poly- technic and State University, Blacksburg, VA 24060. I report observations on movements, and behavior of recently fledged American Kestrels in central Kentucky. Observations were made on the Central Kentucky Wildlife Management Area located 17 km SSE of Richmond, in Madison Co., Kentucky. Vege- tation on the area is characterized by expansive open areas alternating with fencerows, small thickets and fields. Elevation ranges from 287 to 310 m above sea level. Nine fledglings from two nest boxes located on barns were observed during spring and summer of 1983. Five young (2 males and 3 females) fledged from nest 1 and were observed from 20 May to 23 June, and 4 young (3 males and 1 female) fledged from nest 2 and were observed from 10 June to 28 August. At nest 1, radio transmitters (MPB-LD- 1220, Wildlife Materials Inc., Carbondale, Illinois) were affixed to the backs of a male and female kestrel 56 Autumn 1990 Kestrel Post-fledging Behavior 57 five days prior to fledging, using a backpack mount (Dunstan 1972) constructed of braided nylon. The total transmitter package weighed less than 6 grams. I attempted to locate the transmitter-equipped in- dividuals (hereafter referred to as male T and female T) every day after they fledged except for their 20- 23rd d after fledging. Observations were not re- stricted to transmitter-equipped birds but included siblings whenever possible. Observations of fledg- lings from nest 2 were made every 3-5 d. Vegetation on the area occupied by juveniles from nest 2 made observation difficult. However, juveniles were often located in the vicinity of their parents who were fitted with transmitters. Most observations were made be- tween 0900 and 1700 H. All locations were plotted on a topographic map (scale 1 cm : 122 m). Distances of those locations from the nest were calculated to the nearest 1 m. During the first 14 d after fledging all 5 juveniles at nest 1 remained within 100 m of the nest and moved little. They often perched in the same tree or within a few meters of each other on telephone wires and spent up to 2 h on such perches without moving more than 3 m. After the 14th d, juveniles from nest 1 extended their area of activity by approximately 250 m. They frequented a barn in which their par- ents were renesting (353 m west of the original nest). Up to the 24th d after fledging, juveniles were usually observed within 100 m of the nest or the barn in w'hich their own parents were renesting. The one exception is as follows: on the 17th d after fledg- ing, male T traveled 1.1 km NNE from his nest. He encountered a group of 4 recently fledged kestrels (none of which were banded as were his siblings) and perched within approximately 30 m of them. When an adult female kestrel flew toward that group with a microtine rodent, male T flew towards her. He was immediately chased from the area by an unmarked adult male who stooped on him. Imme- diately after the stoop, the juvenile returned to the vicinity of his natal nest. Following their 24th d, juveniles at nest 1 became less cohesive and began traveling to areas more dis- tant from their parents’ nests. On the 25th d, the group split into at least two subgroups; male T was approximately 350 m NNE of the nest while female T was 250 m NNW of the nest. At 0810 H the next day, 5 juveniles, including male and female T, were 100 m south of the nest. They traveled 1.3 km to the southwest where they joined a group of five ju- venile kestrels at 1055 FI. They hunted together with this group for 35 min, then returned to the vicinity of nest 1. At 1141 H the next day, male T and two juvenile females returned and again joined five ju- veniles to hunt for at least 35 min. No aggression was observed between individuals of the two groups on either occasion, even though members intermixed and perched together on utility wires with an inter- kestrel distance of only 1 to 3 m. Female T was not present during the second meeting. Female T and one juvenile male were last seen at 0900 H on the 27th d after fledging. Male T and two females remained in the area for 4 more days and hunted together 850 m south of the nest, an area outside the range of both parents. I observed those juveniles last on the evening of the 31st d after fledg- ing. Two days later the adults’ second nest failed and the adult female disappeared. The adult male was observed for 4 more days. I observed what could be interpreted as play be- havior only once. On the 11th d after fledging, at 1500 H a juvenile male and female (without trans- mitters) were observed for 1 5 min alternately circling and diving at one another without contact. The first attempts at prey capture were observed on the 6th and 7th d after fledging. On the 6th d I observed a juvenile (sex unknown) dive 5 m into tall grass. On the 7th d after fledging, I witnessed an unsuccessful attack by a juvenile male toward an adult male Red- Winged Blackbird ( Agelaius phoeniceus) . The first observed prey captured were invertebrates (probably grasshoppers) on the 25th d after fledging. I located roosting sites on 4 occasions. On the fourth night after fledging, male and female T roost- ed in Eastern Red-cedar (Jumperus virgimana ) trees 60 m northwest of the nest. On the 1 5th night after fledging, female T roosted in tall deciduous trees 300 m east of the nest barn. On the 30th d after fledging, male T either used that same deciduous tree 300 m east of the barn or one very close by. Finally, on his last night in the area, male T used an Eastern Red- cedar 60 m west of his nest although he had foraged 0.8 km to the southeast during that day. Four young fledged from nest 2 but only three were observed after the 4th d. Those three followed their parents immediately after fledging. During 26 d of observation between 15 June and 28 August 1983 I always found at least one juvenile with the adults. During that period they ranged from as close as 48 m E of their natal nest (observed this close only once, 30 days after fledging) to as far as 853 m to the NE. However, most of their time was spent 58 Christopher Kellner Vol. 24, No. 3 in areas 250 m NW and 500 m N of their nest. Since those juveniles were not equipped with trans- mitters, I cannot be certain of their range. The two groups of juvenile kestrels differed strik- ingly in their movements. The first group remained close to their natal nest during the first 24 d after fledging, the second group left the vicinity of their nest and traveled over their parents’ hunting range soon after fledging. Those differences in movements may be due to variation in prey abundance for the two nesting areas, differences in parental care as- sociated with the renesting attempt of the parents at nest 1 , or a combination of both factors. Groups of foraging kestrels composed of fledglings from more than one nest were observed on two occasions. Other investigators have reported similar groups of kestrels (e.g., Berger and Mueller 1959, Lett and Bird 1987), and mixed species groups (e.g., Cade 1955). The two groups of fledglings differed with respect to onset of migration. One group left their natal area in the early summer independent of the adults while the other group remained with the adults late into the summer. Sherrod (1983) speculated that there is great variation in the tendency of Peregrine Fal- cons ( Falco peregnnus) to migrate as a family group and I suspect the same may be true for American Kestrels. Some kestrels may remain together for as little as three weeks (e.g., Smith et al. 1972), and migrate separately from adults (e.g., Balgooyen 1976). On the other hand, some evidence suggests that kestrels migrate as a family group (e.g., Cade 1955, Sherrod 1983). Juvenile kestrels alternated use of roosts on a daily basis. I also found that boxes were not used after kestrels fledged. In contrast, Balgooyen (1976) found that juveniles and adults often returned to the nest cavity after young fledged. In central Kentucky, kes- trels experience heavy predation within nest boxes (53.5% predation for nestlings overall and 12.5 and 25.0% for adults in 1985 and 1987 respectively; Kell- ner and Ritchison 1988). After young fledge, kestrels may avoid using nest boxes as roost sites in order to avoid predation. Acknowledgments G. Ritchison provided guidance throughout the study. K. Smith, H. Hunt, S. Sherrod, D. Lett and three anon- ymous reviewers provided helpful comments on an earlier draft of the manuscript. The research was supported by a Frank M. Chapman Research Grant from the American Museum of Natural History. Literature Cited Balgooyen, T.G. 1976. Behavior and ecology of the American Kestrel ( Falco sparverius L.) in the Sierra Nevada of California. Univ. Calif. Publ. Zool. 103. Berger, D.D. and H.C. Mueller. 1959. The Bal- Chatri: a trap for the birds of prey. Bird Banding 30: 18-26. Bird, D.M. 1988. Reproduction. Pages 266-279 in R.S. Palmer [Ed.], Handbook of North American birds, Vol 5. Yale University Press, New Haven. Cade, T.J. 1955. Experiments on winter territoriality of the American Kestrel {Falco sparverius). Wilson Bull 67:5-17. Dunstan, T.C. 1972. A harness for radio-tagging rap- torial birds. I.B.B. News 44:4-8. Kellner, C. and G. Ritchison. 1988. Nesting success and incubation behavior of American Kestrels in cen- tral Kentucky. Wilson Bull. 100:317-319. Lett, D.W. and D.M. Bird. 1987. Postfledging be- havior of American Kestrels in southwestern Quebec. Wilson Bull. 99:77-82. Sherman, A.R. 1913. The nest life of the Sparrow Hawk. Auk 30:406-418. Sherrod, S. 1983. Behavior of fledgling peregrines. Pi- oneer Impressions, Fort Collins, CO. Smith, D.G., C.R. Wilson and H.H. Frost. 1972 The biology of the American Kestrel in central Utah. Southwestern Natur. 17:73-83, Received 25 May 1989; accepted 10 August 1990 /. Raptor Res. 24(3):59-63 © 1990 The Raptor Research Foundation, Inc. A DESCRIPTION OF “TUFTS” AND CONCEALING POSTURE IN NORTHERN PYGMY-OWLS Denver W. Holt The Owl Research Institute, P.O. Box 8335, Missoula, MT 59807 Rick Kline 1455 Wilderness Valley Road, Poison, MT 59860 Lynn Sullivan- Holt The Owl Research Institute, P.O. Box 8335, Missoula, MT 59807 Abstract. — We describe concealing posture for the Northern Pygmy-Owl ( Glaucidium gnoma). Head tufts, previously undescribed for this species, are part of the concealing posture. The tufts are actually extensions of the eyebrows. We believe that camouflage and disruptive coloration are used synergistically. We also believe that the concealing posture described aids the owls in hiding from predators and from mobbing by potential prey species. Una description de los penachos y las facilidades mimeticas de los buhos de la especie Glaucidium gnoma Extracto. — Describimos la capacidad de mimetismo de los buhos de la especie Glaucidium gnoma. Los penachos que previamente no han sido descritos en esta especie, son una ayuda a esa capacidad mimetica. Los penachos son extensiones de las cejas. Creemos que el camuflaje y la coloration disruptiva son usados simultaneamente. Tambien creemos que la capacidad de mimetismo descrita, ayuda a estos buhos para esconderse de los predadores y para evitar la alerta de sus posibles presas. [Traduction de Eudoxio Paredes-Ruiz] The Northern Pygmy-Owl ( Glaucidium gnoma ) is widely distributed in western North America (AOU 1983). Except for a few observational reports (Hol- man 1926, Holt and Norton 1986), aspects of the biology and ecology of this species are among the least known of North American owls. Although fre- quently observed during the non-breeding season, Northern Pygmy-Owls are very difficult to locate during the breeding season (D.W. Holt, unpubl. data), consequently few nests have been described (Norton and Holt 1982, Bull et al. 1987). Even the natural history of this species has barely been out- lined. In this note, we describe a concealment posture previously unreported for the Northern Pygmy-Owl. Owls can be separated for identification purposes into those with horns or eartufts and those with round heads. Hereafter, horns and eartufts will be called tufts, denoting the specialized feathers arising from the heads of many owl species. Little infor- mation exists describing the adaptive significance of tufts in owls, although it is generally believed that tufts aid in concealment or hiding. Approximately 75 of 162 species of owls in the world (Amadon and Bull 1 988) possess conspicuous tufts. The majority of these species occur in the gen- era Otus and Bubo, and nest or roost in forest habitats (Burton 1973). Several species of ground-nesting owls, however, also possess inconspicuous tufts, that are erected when approached at nests or roosts (e.g., Short-eared Owl Asio flammeus, Marsh Owl A. ca- pensis and Snowy Owl Nyctea scandiaca\ pers. obser., Mikkola 1983). Methods From 1978-1989, we observed over 100 Northern Pyg- my-Owls in the wild during the breeding and non-breed- ing seasons. We used two captive Northern Pygmy-Owls to describe concealment posture and theorize reasons for this behavior. For the exercises, the owls were kept either in outdoor or indoor housing, or tethered on an experimenter’s fist. We placed a cat 10 m in front of each owl and allowed the cat to roam freely. The cat was unaware of the owl’s presence. We also tethered a Peregrine Falcon (Falco per- egrinus ) 10 m in front of one owl. The falcon was also unaware of the owl’s presence. We then approached the 59 60 Holt et al. Vol. 24, No. 3 owls ourselves or made passes by them, at and within 10 m. Each exercise was conducted ten times. We photo- graphed and described the owls’ reactions. The drawings in Figure 1 were drawn from the photographs. Results and Discussion The two owls were faced with the cat twenty times (ten times each), and one owl with the falcon ten times. On every occasion (N = 30), the owls assumed the concealing posture. Neither owl responded with the concealment posture to our approaches. Figure 1A illustrates the relaxed or normally observed pos- ture and Figure IB illustrates the concealment pos- ture. When responding to the stimuli (cat, falcon), the owls changed configuration in one continuous mo- tion. The tufts were erected. As well, the bold white eyebrows and the white rictal bristles surrounding the bill and facial feathers on the lower sides of the face were also erected. The eyes were wide open. Simultaneously, the remainder of the body feathers were compressed tight to the owl’s body and one wing was drawn across the front of the body and raised nearly to bill level. The white spotting on the flight feathers and coverts appeared as vertical lines when the wing was drawn across the body. This posture seemed to lengthen the owls’ bodies (Fig. IB). We examined Northern Pygmy-Owl study skins (N = 7) from the University of Montana Zoology Museum, Missoula, Montana, and observed that the tufts were body contour feathers. We could not dis- tinguish any differences in lengths of the tuft feathers versus other feathers of the head. In contrast, tufts of other owl species (e.g., Great Horned Owl Bubo virgtnianus, Long-eared Owl Asio otus, Short-eared Owl) readily could be distinguished and counted. Tuft erection and concealing posture was never observed during intraspecific confrontations of wild Northern Pygmy-Owls. In fact, this posture was never observed during defense of breeding or win- tering territories. Hence, the posture is probably not part of the owls’ intraspecific, agonistic behavioral repertoire. On 4 occasions in the wild, we observed Northern Pygmy-Owls exhibit “tuft” erection and conceal- ment posture when approached by mixed flocks of foraging passerines. Unlike the Boreal Owl ( Aegolius junereus) and Northern Saw-whet Owl (A. acadicus), which raise the outer crown feathers of their facial disks, and mimic tufts (Gatling 1972), Northern Pygmy-Owls actually possess tufts. The Northern Pygmy-Owl also lacks a true facial disk, and its eyes are placed near the top of the head. The tufts arise from the orbital ridge and appear as extensions of the eye- brows, which when relaxed lie horizontally above the eye (Fig. 1A). There are fifteen species of Glaucidium in the world (Amadon and Bull 1988) however, to our knowl- edge, tufts and concealment posture have been de- scribed only in the European Pygmy-Owl (G. pas- serinum) (Scherzinger 1970). Angell (1974), in his drawings of owls, mentions “plumicorns” as tiny horns just behind the eyebrows of a captive North- ern Pygmy-Owl, but did not describe them in detail. Based on our observations of captive and wild Northern Pygmy-Owls, we believe that the posture described has evolved as a cryptic strategy and has nothing to do with species recognition or predator mimicry. Our observations further indicated that this posture may have at least two functions: 1) con- cealment from potential predators, and 2) conceal- ment from potential prey or a mobbing situation. Northern Pygmy-Owls are mobbed frequently by small passerines, possibly because they often hunt by day (D.W. Holt, pers. comm.). Altmann (1956) used a number of stuffed owl species to determine mobbing behavior and predator recognition. When he placed a stuffed Northern Pygmy-Owl in an area of wintering Yellow-rumped Warblers ( Dendroica coronata ), six warblers discovered and mobbed the owl. The mobbing then attracted the rest of the flock of approximately 200 individuals. Instances such as this may contribute to selective pressures in the evo- lution of concealment posture in Northern Pygmy- Owls. Definitions. Prior to a discussion and review of literature concerning concealment pose of owls, we first address acceptable working definitions. We used terminology taken from Alcock (1975). Hiding in animals is generally achieved through cryptic coloration and behavior (Alcock 1975). Cryptic coloration includes camouflage, disruptive coloration and countershading. Camouflage is used to disguise, deceive or conceal. In animals, camou- flage effectiveness is generally dependent on the ca- pacity of an animal to remain motionless for pro- longed periods (Alcock 1975). Disruptive colorations are contrasting bold lines or patches that disrupt the outline of an animal (Alcock 1975). Attention is then drawn to these conspicuous marks which in turn distract from the more subtle features that would Autumn 1990 Concealment in Northern Pygmy-Owls 61 Figure 1. Postures of Northern Pygmy-Owls; A) normal posture, B) tufts or extended eyebrows and concealment posture. identify a particular animal (Alcock 1975). Color patterns may also be more effective than behaviors (Alcock 1975). Counter shading is not pertinent to this discussion. Literature Review on Tufts and Concealment Posture. Putman (1958) described an Eastern Screech Owl ( Otus asio ) responding to sparrows, by elongating its body, twisting sideways, then raising 62 Holt et al. Vol. 24, No. 3 and dra wing its wing across the side of its body which faced the sparrows. All feathers were compressed against the owl’s body. This is also similar to de- scriptions quoted by Bent (1938) for Eastern Screech Owls, and personal observations (D.W. Holt). Scherzinger (1971) described a posture in the Eu- ropean Pygmy-Owl (G. passerinum), identical to the posture we describe in this manuscript for the North- ern Pygmy-Owl. He termed it a concealing posture. Mikkola (1983) termed this same posture by the European Pygmy-Owl as a camouflage posture, and he felt it was a result of a potential threat. During experiments to describe the reactions of owls to predators, Scherzinger (1971) concluded that tufts on the heads of many owl species were of no “systematic” (not pertaining to systematic classifi- cation) value. He further stated that protective col- oration further de-emphasized the tufts. Mysterud and Dunker (1979) proposed a “pred- ator mimicry hypothesis,” in which they felt the selective advantage of tufts was to imitate potential mammalian predators by erection of the tufts. For example, they provided comparative drawings of owl/ predator confrontations (e.g., Eagle Owl {Bubo bubo)/ Lynx {Lynx lynx); Long-eared Owl/Marten {Martes martes); and Short-eared Owl/Red Fox {Vulpes vulpes), in which case the owl assumed a defensive posture on its nest. The connotation being, that mammalian predators would retreat when face to face with an apparent conspecific. The authors, how- ever, mention nothing of the well-developed olfactory senses in many mammals, which we think would aid them in distinguishing conspecifics. Perrone (1981) reviewed three hypotheses con- cerning the significance of tufts in owls: 1) “species recognition” (Sparks and Soper 1970, Burton 1973), 2) “broken off stub effect” (Sparks and Soper 1970), and 3) “mammalian mimicry” (Mysterud and Dunker 1979). Perrone (1981) concluded that tufts served as camouflage adaptations and concurred with hypothesis two. He also noted that tufts were more common among woodland owl species, however, many species of woodland owls also lack tufts. Ligon (1968) described the concealment pose of the Elf Owl {Micrathene whitneyi) (a round-headed owl) in which the owl changed from a normal perch- ing position, to an elongated stance with feathers compressed. The owl erected its white feathers above the eyes (eyebrows) and white feathers on the lower sides of the facial disk. Further, the owl drew its wing across the front of its body, revealing two white vertical stripes and raised the wing to bill level (sim- ilar to Fig. IB). The vertical stripes appeared to originate along the leading edge of the wing and the scapulars. The eyes were open at all times. Ligon (1968) believed that the white markings served as a disruptive camouflage tactic, and aided the owl in concealment. Gatling (1972) reported the concealment posture of Boreal Owls {Aegolius funereus) and Saw-whet Owls {A. acadicus) (round-headed) to elongate their bodies and erect the outer facial feathers of the facial disk. Although not true tufts, the posture suggested tufts and made the owls less conspicuous. In his review of concealing poses of owls, Bon- drup-Nielsen (1983) suggested that poses are similar among those species reported, however, some dif- ferences between the species suggested different functions. He cited three differences in the poses of owls, that he felt did not support the pose as a func- tion of concealment: 1) open eyes, 2) exposure of white feathers around the eyes, and 3) abrupt man- ner in which the pose is adopted. Bondrup-Nielsen (1983) felt that the three differences stated above made an owl more conspicuous and were revealing rather than concealing. Animals use cryptic coloration, behavior and physical tactics to hide. These tactics may be used singly or in combination with one another. Tufts have probably evolved as a form of cryptic morphology, which aid owls in concealment by re- sembling non-living objects such as twigs or small branches. The tufts may act as neutral stimuli to predators or mobbers, in which case they may ha- bituate to it (Alcock 1975). We feel that erection of white feather areas in the facial region and the bold white markings displayed with wing adjustment, fit well into Alcock’s (1975) definition of disruptive coloration. This would likely reduce the chances of being detected. Additionally, we see no reason why disruptive and camouflage coloration cannot act synergistically in concealing the owl. Open eyes may be advantageous, because they allow an owl to monitor the movements of a potential threat. Closed eyes could lead to disastrous results if a potential threat was lethal. If disruptive color- ation works, then open eyes may not even be detected and thus cause no harm. The Eastern Screech Owl appears to be the only owl thus far reported that has partially closed eyes during concealment posture. The abrupt or gradual change into the conceal- Autumn 1990 Concealment in Northern Pygmy-Owls 63 ment posture may relate to observer definitions, or possibly to how much time the owl has to prepare. Both the tufted and round-headed owls discussed in this manuscript achieve concealment by similar methods. This suggests convergent evolution of this behavior under similar selective pressures. However, concealment posture could simply be a basic owl behavior inherited from the first prototype owl. In any case, every owl mentioned in this manuscript has similar concealment postures. We conclude that posturing, tufts, camouflage, disruptive coloration and open eyes all contribute to concealment behavior. Acknowledgments We thank Evelyn Bull, Norman L. Ford, C. Stuart Houston, Don Jenni and Jeff Marks for reviewing and helping improve the manuscript. We thank Elwood the cat for his cooperation. Literature Cited Alcock, J. 1975. Animal behavior: an evolutionary ap- proach. Sinauer and Assoc. Inc., Sunderland, MA. Altmann, S.A. 1956. Avian mobbing behavior and predator recognition. Condor 58:241-253. Amadon, D. and J. Bull. 1988. Hawks and Owls of the world. Proc. West. Found. Vert. Zool. 3:295-357. Angell, T. 1974. Owls. Univ. Washington Press, Se- attle, WA. American Ornithologists’ Union. 1983. Check-list of North American birds, 6th edition. American Or- nithologists’ Union, Washington, D.C. Bent, A. C. 1938. Life histories of North American birds of prey. Part 2. Smithsonian Institute, U.S. National Museum, Bull. 70. Bondrup-Nielsen, S. 1983. Ambivalence of the con- cealing pose of owls. Can. Field-Nat. 97:329-330. Bull, E., J.E. Hohmann and M.G. Henjum. 1987. Northern Pygmy-Owl nests in northeastern Oregon. /. Raptor Res. 21:77-78. Burton, J.A. 1973. Owls of the world. Tanager Books, Dover, NH. Catling, P.M. 1972. A behavioral attitude of Saw-whet and Boreal owls. Auk 89:194-196. Holman, F.C. 1926. Nesting of the California Pygmy Owl in Yosemite. Condor 28:92-93. Holt, D.W. and W.D. Norton. 1986. Observations of nesting Northern Pygmy-Owls. Raptor Res. 20:39- 41. Ligon, J.D. 1968. The biology of the Elf Owl ( Mi - crathene whitneyi). Misc. Publ., Mus. Zool., Univ. Mich. No. 136. Mikkola, H. 1983. Owls of Europe. Buteo Books, Ver- million, SD. Mysterud, I. AND H. DunKER. 1979. Mimicry: a hy- pothesis on the behavioral function of owl “horns.” Animal Behavior 27:315-316. Norton, W.D. and D.W. Holt. 1982. Simultaneous nesting of Northern Pygmy-Owls and Northern Saw- whet Owls in the same snag. Murrelet 63:94. Perrone, M. 1981. Adaptive significance of ear tufts in owls. Condor 83:383-384. Putman, W.L. 1958. Use of concealing posture by a Screech Owl. Auk 75:471. SCHERZINGER, W. 1970. Zum Aktionssystem des Sper- lingskauzes (Glaucidium passerinum, L.). Zoologica 41: 1-130. . 1971. Zum Feindverhalten einiger Eulen (Strigidae). Zeitschrift fur Tierpsychologie 29:165-174. Sparks, J. and T. Soper. 1970. Owls: their natural and unnatural history. Taplinger, New York. Received 21 August 1989; accepted 23 August 1990 J, Raptor Res. 24(3): 64-67 © 1990 The Raptor Research Foundation, Inc. ENVIRONMENTAL INFLUENCES ON OSPREY FORAGING IN NORTHEASTERN NOVA SCOTIA Stephen P. Flemming 1 and Peter C. Smith Department of Biology, Acadia University, Wolfville, NS Canada BOP 1X0 ABSTRACT. — We investigated how environmental conditions influenced Osprey foraging behavior in north- eastern Nova Scotia. The number of foraging Ospreys and the dives they made peaked at dawn and dusk. Tidal direction had no effect, but the number of foragers and dive successes were highest at mid-tide. The number of foraging Ospreys decreased with diminishing water clarity, yet dive success appeared to increase when the water was murky. Only the number of foragers was affected by cloud cover. Las condiciones del ambiente y algunas de sus influencias en los habitos de pesca y alimentation de las Aguilas Pescadoras en el Nordeste de Nueva Escocia ExTRACTO. — Hemos unvestigado como las condiciones del ambiente han influenciado los habitos de pesca y alimentation del Aguila Pescadora ( Pandion haliaetus) en el nordeste de Nueva Escocia. El numero de Aguilas Pescadoras hambrientas y los buceos que hicieron, aumentaba a su maximo al amanecer y al atardecer. La direction de la marea no tuvo algun efecto, pero las cantidades de aguilas y el exito en la pesca obtuvieron su maximo a media marea. El numero de Aguilas Pescadoras que buscaban alimento decrecio con la diminution de la claridad del agua, sin embargo el exito de los buceos aumento. Solo el numero de aguilas en su afan de pesca se vio afectado con tiempo nublado. [Traduction de Eudoxio Paredes-Ruiz] Many birds alter their foraging behavior in re- sponse to changing environmental conditions (e.g., Dunn 1973, Grubb 1975, Finlay 1976). Factors af- fecting the foraging behavior of Ospreys (. Pandion haliaetus ) include chronology of the breeding season (Ueoka and Koplin 1973), time of day (Stinson 1978, Boshoff and Palmer 1983), tide (Ueoka and Koplin 1973), wind speed (Machmer and Ydenberg 1990), sunlight (Grubb 1977), water surface condition (Grubb 1977, Machmer and Ydenberg 1990), and the ecology of prey species (Swenson 1979). How- ever, in our northern Nova Scotia study area, Prevost (1977) found that dive success varied only between locations within tidal periods. He did not detect any relationships between search time or dive success with respect to environmental conditions. The first response that an animal makes to varying conditions is the decision to forage. Curiously, this is often overlooked in studies examining weather- dependent foraging, and studies of the Osprey are no exception. We examined this response, as well as 1 Present address: Department of Biology, Queen’s Uni- versity, Kingston, ON Canada K7L 3N6. dive frequency, and the percentage of dives which were successful. Our objective was to determine if environmental conditions influenced Osprey forag- ing behavior in northeastern Nova Scotia. Study Area and Methods Observations of foraging were made at Antigonish Har- bour (45°38'N 62°54'W), Nova Scotia, Canada. This shal- low estuary drains a 750 km 2 watershed, and empties into the Northumberland Strait in the Gulf of St. Lawrence The surrounding highlands are covered with deciduous and mixed forests while valley slopes and poorly drained areas are dominated by coniferous forest. Ospreys nest colonially on utility poles along powerline corridors, as well as solitarily on dead or living trees. Males of 29 breeding pairs that nested within 6 km of the estuary regularly foraged at the study site. Others from as far away as 13 km also used the Antigonish Harbour estuary (Jamieson et al. 1982). At our study area, 90% of the diet of coastally nesting Ospreys consists of Winter Flounder ( Pseudopleuronectes americanus ), a cryptic species of flatfish (Prevost 1977, Flemming unpub.). Observations of foraging (186 hr) were made from either an elevated hide or from a boat. Observation bouts of 3 hr were made during the period 0501-2000 H, 1 May- 27 August 1985 and 8 June-8 July 1986. One or two of the five possible bouts were randomly chosen for a given day. At 10 min intervals, we counted (N = 1116 counts) the number of ospreys foraging over a specified census 64 Autumn 1990 Osprey Foraging Behavior 65 Table 1. Effects of environmental conditions on Osprey foraging behavior in northeastern Nova Scotia. Reported values are X ± SD (N). Environmental Condition No. Foraging Per Count No. Dives Per Hour Percent Dive Success Time of day 0501-0800 0.79 ± 1.40 (198) 1.64 ± 2.16 (33) 50.0 (54) 0801-1100 0.66 ± 0.99 (240) 1.80 ± 1.25 (40) 74.4 (43) 1101-1400 0.36 ± 0.72 (162) 0.52 ± 0.94 (27) 57.1 (14) 1401-1700 0.60 ± 1.06 (240) 1.38 ± 1.75 (40) 63.6 (55) 1701-2000 1.21 ± 1.70 (276) 2.13 ± 2.58 (46) 63.3 (98) Direction of tide Flood 0.70 ± 0.81 (510) 1.34 ± 1.65 (85) 59.6 (114) Ebb 0.75 ± 0.91 (606) 1.49 ± 2.11 (101) 64.0 (150) Tidal amplitude Low 0.74 ± 1.10 (348) 1.17 ± 1.56 (58) 55.9 (68) Mid 0.86 ± 1.41 (444) 1.76 ± 2.17 (74) 70.0 (130) High 0.65 ± 1.30 (324) 1.22 ± 1.99 (54) 53.0 (66) Water clarity Clear 0.82 ± 1.36 (564) 1.63 ± 2.11 (94) 59.5 (153) Hazy 0.83 ± 1.39 (306) 1.25 ± 1.85 (51) 57.8 (64) Murky 0.54 ± 0.94 (246) 1.15 ± 1.64 (41) 76.6 (47) Cloud cover Clear 0.91 ± 1.45 (222) 1.27 ± 1.97 (37) 59.6 (47) Overcast 0.75 ± 1.27 (840) 1.51 ± 1.97 (140) 62.7 (212) Raining 0.32 ± 0.70 (54) 0.56 ± 1.33 (9) 60.0 (5) area (2.5 km 2 ) at Antigonish Harbour, and evaluated for each dive (prey capture attempt, N = 264 dives), whether or not the Osprey was successful in capturing prey. We measured four potential environmental influences on Osprey foraging behavior. The diurnal period was divided into 5 3-hr periods (0501-2000 H); tidal ampli- tude was divided into low, mid, and high (using tide ta- bles), and tidal direction was divided into flood and ebb categories; water clarity was categorized as clear (substrate clearly visible), hazy (objects <10 cm diameter not visible), or murky (objects <20 cm not visible) at a depth of 1 m; and cloud cover was categorized as clear (<10% cloud cover), overcast, or raining. As the counts of foraging Ospreys were not normally distributed, Kruskal- Wallis tests were used to determine if the number of foragers varied. Dive number and percent success data were normally distributed, so parametric sta- tistics were employed. Analysis of variance was used to test if the number of dives varied, and the Chi-square test was used to determine if dive success was affected. Chi- square tests were performed comparing the proportions of dives which were successful among categories (binomial data, Zar 1984). Results The effects of environmental conditions on Osprey foraging in northeastern Nova Scotia are reported in Table 1 . The time of day had an impact on Osprey foraging effort (Kruskal- Wallis F= 10.18, P= 0.01). There were more Ospreys foraging at dawn (0.79 foragers) and dusk (1.21) than at mid-day (0.36). The number of dives/hour followed the same pattern (ANOVA F = 3.58, P = 0.01). However, time of day did not affect the percentage of dives which were successful (x 2 = 6.40, P = 0.18). Dive success ranged from 50.0-74.4% throughout the day. Neither the number of foraging Ospreys (Krus- kal-Wallis F = 1.40, P = 0.50), dives/hour (AN- OVA F = 2.39, P = 0.21), nor percent dive success (x 2 = 0.40, P = 0.55) were affected by the direction of the tide. However, the number of foraging Os- preys significantly varied with tidal amplitude (Kruskal- Wallis F= 3.83, P = 0.02). More Ospreys foraged at the mid-tide (0.86 foragers) than when* the tide was low (0.74) or high (0.65). While the number of dives/hour was unaffected (ANOVA F = 1.87, P = 0.16), it was apparent that mid-tide yielded a greater percentage of dives which were successful (70.0 percent), than either low (55.9) or high tide (53.0) (x 2 - 7.77, P = 0.03). Fewer Ospreys were foraging when the water was murky (0.54 foragers), than when it was clear (0.82) or hazy (0.83) (Kruskal- Wallis F = 3.06, P = 0.05). The number of dives/hour was unaffected (ANOVA F = 1.12, P = 0.33), but there was a weak influence of water clarity on dive success (x 2 = 5.14, P = 0.08). Dive success appeared to increase when the water was murky. 66 Stephen P. Flemming and Peter C. Smith Vol. 24, No. 3 Cloud cover affected the number of foraging Os- preys (Kruskal-Wallis F = 4.63, P = 0.01), such that fewer birds foraged when it was raining (0.32 foragers), than when it was overcast (0.75) or clear (0.91). Cloud cover did not affect either the number of dives/hour (ANOVA F = 0.97, P = 0.41), or the percentage of dives which were successful (x 2 = 0.17, P = 0.60). Discussion Peaks in Osprey foraging activity have been pre- viously noted. Stinson (1978) found that more fish were brought to the nest early in the day, and Ueoka (1974) found that Ospreys concentrated their for- aging effort in the hours immediately after morning fog had dissipated. Similar to our study, Boshoff and Palmer (1983) noted a dawn and dusk pattern in Osprey hunting periodicity. It appears that foraging peaks may be most pronounced at dawn and dusk to compensate for the nocturnal non-feeding period. However, this is unlikely to be the sole explanation for foraging peaks, as Waterston (1961) and Hagan and Walters (1990) noted three and four daily peaks, respectively. Hagan and Walters (1990) reported that the time between foraging peaks corresponded to the length of time required by Ospreys to fly to the foraging area, capture prey, and return to the nest. Hence, the long foraging distance (ca. 14 km) they reported appeared to dictate multiple foraging peaks. Ospreys that nest close to foraging areas could make foraging trips whenever necessary. This would result in a greater degree of randomness in the times at which the foraging area is used. In our study area, most Ospreys nested within 3 km of the for- aging area. A few nested as far away as 13 km, but still foraged at Antigonish Harbour (Jamieson et al. 1982). These more distantly nesting Ospreys may have contributed to our observation of two foraging peaks. We found that the number of foragers and percent dive success peaked at mid-tide, suggesting that Os- preys preferentially foraged during the tidal state that resulted in the highest probability of success. Prevost (1977), who also examined Osprey foraging behavior at Antigonish Harbour, found that dive success varied among locations within tidal periods. He reported that his finding was due to differences in water depth. Hence, lower foraging activity and dive success at high tide would be expected because of the high water depth. Deeper water would inhibit capture of Winter Flounder, which is a bottom feed- er. Similarly, lower activity and success would be expected for low tide because Winter Flounders would be forced to the deeper channels, vacating the mudflats which are exposed at low tide. Tyler (1971) found that Winter Flounder also move extensively during the mid-tide. Presumably, Winter Flounders would be easier to detect at mid-tide. Our results appear to be consistent with this behavior. Ueoka and Koplin (1973) found that successful fishing efforts were highest at ebb (outgoing) tide. Stinson (1978) found the same pattern in one year of his study, but the opposite pattern in the second year. At Antigonish Harbour, we found no pattern associated with tidal direction, only tidal amplitude. Our findings appear to be related to prey behavior, and it is possible that the behavior of prey also ex- plains the different foraging responses to tide among and within other studies. Swenson (1979) found that Osprey dive success varies with prey species foraging behavior. Fewer Ospreys foraged at Antigonish Harbour when the water was murky. Dive success was similar for clear and hazy conditions, but showed a statistical trend to increase for the murky condition. Given that relatively few birds forage during murky conditions, presumably due to the poor visibility, perhaps the fish taken were the ones near the water’s surface, and thus easier to catch. Further examination is required to test this possibility. To date, no other study has examined the effect of water clarity on Osprey foraging behavior, although intuitively it would seem to be an important influence. Our data support this notion. While the number of foragers decreased as cloud cover increased, like Prevost (1977) and Machmer and Ydenberg (1990), we did not find any relation- ship with foraging success. However, Grubb (1977) found that when the sun was occluded, hovers, dives, and successful dives/min all decreased significantly. It may be that Prevost’s (1977), Machmer and Yden- berg’s (1990), and our measures of cloud cover were not fine enough to measure the more immediate for- aging responses reported by Grubb (1977). Although only four environmental influences on Osprey foraging behavior were examined in this study, all four were shown to have an effect. The results differed from a similar investigation (Prevost 1977) at the same study site that concluded there was very little environmental influence. A major rea- son for arriving at a different conclusion was that, unlike Prevost (1977), we documented how condi- Autumn 1990 Osprey Foraging Behavior 67 tions might influence the number of Ospreys which choose to forage at a given time. Acknowledgments We wish to thank the Nova Scotia Department of Lands and Forests, and the Canadian Electrical Association for financial support. The Evelyn and Morrill Richardson Graduate Fellowship (Acadia University) supported S.P.F. during this study. The field assistance of A. Evans, E. Floyd, C. Sand, D. Steward, and D. Whalen is appreci- ated. Literature Cited Boshoff, A.F. and N.G. Palmer. 1983. Aspects of the biology and ecology of the Osprey in the Cape Province, South Africa. Ostrich 54:189-204. Dunn, E.K. 1973. Changes in fishing ability of terns associated with windspeed and sea surface conditions. Nature 244:520-521. Finlay, J.C. 1976. Some effects of weather on Purple Martin activity. Auk 93:231-244. Grubb, T.C., Jr. 1975. Weather-dependent foraging behavior of some birds wintering in a deciduous wood- land. Condor 77:175-182. . 1977. Weather-dependent foraging in Ospreys. Auk 94:146-149. Hagen, J.M. and J.R. Walters. 1990. Foraging be- havior, reproductive success, and colonial nesting in Ospreys. Auk 107:506-521. Jamieson, I., N.A. Seymour and R.P. Bancroft. 1982. Use of two habitats related to changes in prey avail- ability in a population of Ospreys in northeastern Nova Scotia. Wilson Bull. 94:557-564. Lambert, G. 1943. Predation efficiency of the Osprey. Can. Field-Nat. 57:87-88. MacArthur, R.H. and E.R. Pianka. 1966. On optimal use of a patchy environment. Amer. Nat. 100:603-609. Machmer, M.M. and R.C. Ydenberg. 1990. Weather and Osprey foraging energetics. Can. J. Zool. 68:40- 43. Prevost, Y.A. 1977. Feeding ecology of Ospreys in Antigonish County, Nova Scotia. M.S. thesis, McGill University, Montreal, PQ Canada. Stinson, C.H, 1978. The influence of environmental conditions on aspects of the time budgets of breeding Ospreys. Oecologia 36:127-139. Swenson, J.E. 1979. The relationship between prey species ecology and dive success in Ospreys. Auk 96: 408-412. Tyler, A. V. 1971. Surges of Winter Flounder into the intertidal zone. /. Fish. Res. Board Can. 28:1727-1732. Ueoka, M.L. 1974. Feeding behavior of Ospreys at Humboldt Bay, California. M.S. thesis, Humboldt State University, Areata, CA. and J.R. Koplin. 1973. Foraging behavior of Ospreys in northwestern California. Raptor Res. 7: 32-38. Waterson, G. 1961. Notes on the breeding biology of the Spey side Ospreys — 1959 and 1960. Bird Notes 29: 130-135. Zar, J.H. 1984. Biostatistical analysis, 2nd ed. Prentice- Hall, Inc., Englewood Cliffs, NJ. Received 29 June 1990; accepted 11 September 1990 /, Raptor Res. 24(3):68 © 1990 The Raptor Research Foundation, Inc. Short Communications Northern Harrier Casts Pellet While in Flight Mark A. Manske 1 College of Natural Resources, University of Wisconsin, Stevens Point, Wl 54481 To my knowledge there has never been any mention of a raptor casting a pellet while in flight, but on 1 June 1986 at 0825 H on the Buena Vista Marsh in central Wisconsin I watched an adult male Northern Harrier (< Circus cyaneus ) cast a pellet while flying. He was hunting over open grassland and as he passed above an active harrier nest, he began to circle and climb until it reached a height of about 30 m. The adult female, previously color- marked, returned to the nesting area. The Harriers circled each other for approximately 30 seconds and then the female flew directly to the nest. Once she had landed, the male continued to hunt. As he flew past me, I noticed that he was not carrying anything in his talons or beak. As he continued to traverse the field, he appeared to stall in the air only 20 m from me; his wings were fully extended and tilted backwards so that they caught the wind and held the hawk motionless in the air for about 3 seconds. While 1 Present address: Route 2, May Road, Potsdam, NY 13676. the bird was stationary, I trained my binoculars on him and watched as he seemed to be trying to force something out of his crop with a series of three muscular contractions. With each contraction, the harrier lowered his head toward his breast — apparently trying to dislodge an obstruction. By the third contraction, he opened his mouth and cast a pellet. He then continued to hunt. RESUMEN. — Un Circus cyaneus macho disminuyo la ve- locidad de su vuelo, vomito residuos no digeribles en un fragmento de su vuelo y continuo en su afan de caceria. [Traduccion de Eudoxio Paredes-Ruiz] Acknowledgments I wish to thank Frances Hamerstrom for critically read- ing and editing this paper and for her support. I also thank Raymond Anderson for allowing me to work on the study area. Received 20 April 1990; accepted 29 May 1990 /. Raptor Res. 24(3):68-69 © 1990 The Raptor Research Foundation, Inc. Above-ground Nesting by Burrowing Owls Paul M. Cavanagh Department of Forestry and Wildlife Management, University of Massachusetts, Amherst, MA 01003-0070 While most Burrowing Owls ( Athene cunicularia) oc- cupy “typical” burrows (i.e., underground and either ex- cavated or expanded by an owl), some exceptions have been observed. Stoner (1933) described Burrowing Owls occupying cavities that had been dug into haystacks. Broth- erton and Brotherton (in Williams 1986) reported a Bur- rowing Owl living in a section of pipe that was in use as a parking lot barrier. Neither report involved nesting birds. Here I present an account of Burrowing Owls nesting and incubating eggs outside of burrows. I observed three Burrowing Owl nests above ground at Tamiami Airport, Kendall, Dade Co., Florida. I discov- ered these nests on 16 April, 11 May, and 17 May 1987. Each nest was a near-circular scrape in a section of main- tained lawn (Table 1). Two nests (1 and 2) were lined with debris and all contained at least one egg (Table 1). Egg dimensions were similar to those reported by Bent (1938) for Florida Burrowing Owls. I observed incubating adult owls at each nest. No eggs hatched, and all nests were eventually abandoned. 68 Autumn 1990 Short Communications 69 Table 1. Burrowing Owl nest and egg dimensions from three above-ground nests, Dade Co., Florida, 1987. Nest Dimensions (mm) Egg Dimensions (mm) 1 Nest (L x W x D) Eggs (L x W) 1 167 x 148 x 27 1 34 x 24 2 2 216 x 199 x 17 4 30.0 x 24.7 31.3 x 25.8 28.0 x 23.4 3 155 x 150 x 19 4 32.8 x 26.4 1 Measurements were taken following nest abandonment. Some eggs were missing at that time. 2 Estimated with ruler, all other eggs measured with calipers. It is unlikely that these nests were established in re- sponse to soil conditions. I observed eight active and four inactive burrows in the sections of lawn (ca. 19 ha total area) containing the above-ground nests. The entrance to one active burrow was within 2.5 m of nest 3. This suggests that soil under the nests was favorable for burrows. Burrowing Owls nesting above ground lose the ther- moregulatory and predator avoidance benefits conferred by burrows. Humidity within a burrow is greater than humidity outside a burrow, resulting in reduced water loss in adult owls (Coulombe 1971). Adults, chicks, and eggs in above-ground nests would be exposed to higher desic- cation levels than would their subterranean counterparts. Burrows also provide a place to retreat from enemies (Thomsen 1971). Above-ground nesting owls have no equivalent refuge from predators. While adult owls could escape via flight, eggs and pre-fledged chicks would be susceptible to predation. Successful nesting, therefore, is less likely to occur above ground than in a burrow. The cause of this unusual and unsuccessful nesting behavior remains unknown. Resumen. — Tres nidos de Athene cunicularia han sido ha- llados en la superficie, sobre el cuidado cesped en Florida. Las condiciones disponibles no impedia a los buhos para hacer sus nidos subterraneos, por que madrigueras ocu- padas por otros buhos y algunas madrigueras vacias habian en la vecindad. Los tres nidos sobre la superficie estaban abandonados con 9 huevos sin incubar. Las causas de este raro habito de los buhos para anidar sobre el suelo, son desconocidas. [Traduccion de Eudoxio Paredes-Ruiz] Literature Cited Bent, A.C. 1938. Life histories of North American birds of prey, part 2. U.S. Natl. Mus. Bull. 170. Coulombe, H.N. 1971. Behavior and population ecol- ogy of the Burrowing Owl Speotyto cunicularia, in the Imperial Valley of California. Condor 73:162-176. Stoner, E. A. 1933. Burrowing Owls occupying unusual quarters. Condor 35:36. Thomsen, L. 1971. Behavior and ecology of Burrowing Owls on the Oakland Municipal Airport. Condor 73: 177-192. Williams, F. C. 1986. Regional summaries: southern Great Plains region. Am. Birds 40:134-138. Received 13 October 1989; accepted 1 June 1990 J Raptor Res. 24(3):69-71 © 1990 The Raptor Research Foundation, Inc. Eagle Owl {Bubo bubo) Predation on Juvenile Bonelli’s Eagles (Hieraaetus fasciatus) Joan Real and Santi Ma5)osa Departament de Biologia Animal, Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain The predation of diurnal birds of prey by the Eagle Owl {Bubo bubo ) is well known. Mikkola (1983) lists 18 species of raptors taken. Glutz von Blotzeim and Bauer (1980) maintain that diurnal raptors can represent up to 5.4% of the Eagle Owl’s diet. None of these authors men- tion the presence of Bonelli’s Eagle {Hieraaetus fasciatus) in the diet of the Eagle Owl, although the two species are sympatric in the Mediterranean region and occupy very similar habitats. In this context, Blondel and Badan (1976) state that Eagle Owls do not interfere with Bonelli’s Ea- gles, even when they breed nearby. In contrast, Bayle (1987) mentions a case of possible predation on a Bonelli’s Eagle young, nearly fledged whose remains were found in an Eagle Owl nest in France. Other raptors of similar or 70 Short Communications Vol. 24, No. 3 greater size known to have been predated by Eagle Owls are young White-tailed Eagles ( Haliaetus albicilla) from their eyries in Norway (Wilgohs in Mikkola 1983), Os- prey Pandion haliaetus (Mikkola 1983) and Short-toed Ea- gle Circaetus gallicus (Donazar 1989). During a study of a population of 10-14 pairs of Bo- nelli’s Eagles in Catalonia, Spain from 1980 to 1988, Eagle Owls were found nesting in all eagle territories. Owls bred between 0.2 and 5.5 km from the eagles’ nests (X = 1.7 km SD = 1.56, N = 10; Table 1). In summer 1987 eleven young Bonelli’s Eagles were marked with wing tags and five of them, belonging to three different pairs, were tracked from fledging to independence 2 d in every 4 d. One of these pairs had two juveniles (a male and a female) fledged on 23 May. On 11 June, both birds began gliding flights which took them as much as 1000 m from the nest. At 0925, after one of the adults had dived at him apparently in play, the young male flew directly away from the breeding area. He was not seen again that day, or in the next few days, as opposed to the young female who roosted within 500 m of the nest every night. On 23 June, the remains of the young male (left wing, tail, sternum and one wing-tag) were discovered in a recess on a cliff some 200 m below the eagles’ eyrie. This hole was only accessible by flight or climbing ropes, so mammalian predators were unable to reach it. In the same hole there were also downy feathers, remains of prey and droppings of young Eagle Owls. In the same place, towards the evening two young Eagle Owls were heard. We interpret the presence of bones and feathers in a cliff occupied by Eagle Owls as indications that the young eagle had been taken by the owls. In the following years, an Eagle Owl pair had continued to breed in the same small cliff. The eagles had lost two other juveniles, in 1984 and 1988, during the first month after fledging. This represents a high mortality rate for this pair in six years (three fledglings out of 11, 27%). By contrast only one (4.5%) out of 22 juveniles raised by the other pairs that we monitored in 1987-88 died during the post-fledging period, and this was due to starvation. Our observations, along with that of Bayle (1987), sug- gest that young Bonelli’s Eagles are vulnerable to pre- dation by Eagle Owls. This is especially so during the first few weeks after fledging, when the juveniles tend to settle in low, accessible sites and even roost on the ground, where they are conspicuous. The proximity of the nests of eagles and owls could be a significant factor in determining predation. In our case, the pair involved had its nest much closer (200 m) to an Eagle Owl nest than any other studied pair (minimum 700 m and average 1900 m, Table 1). In the case of Bayle (1987) the nests were only 300 m apart. Therefore, when breeding in proximity to Bonelli’s Eagles, the Eagle Owl apparently can be a serious threat to young eagles during the first weeks after fledging. Table 1. Distances in metres between the nest of each pair of Bonelli’s Eagles and the nearest known pair of Eagle Owls. Eagle Pair (No.) Distance to Nearest Eagle Owl Pair (m) I 700 II 2.900 III 5.500 IV 800 V 1.500 VI a 200 VIII 1.200 IX <2.000 X 2.500 XI 1.000 XII <2.000 XIII 1.000 a Pair involved in the predation by Eagle Owl. Resumen. — Se describe un caso de predation de Buho Real ( Bubo bubo ) sobre una joven Aguila Perdicera ( Hi - eraaetus fasciatus ) unas 25 dias despues del abandono del nido, y se hace constar la desaparicion frecuente de jovenes de aguila durante este estadio en un solo territorio de aguilas (3 jovenes de un total de 1 1 desapareccieron en 6 anos, 27%). En este territorio una pareja de Buhos Reales anida a tan solo 200 m del nido de las aguilas. En con- traposition el resto de parejas de Aguilas Perdiceras con- troladas en la zona (9), muestran distancias mucho ma- yores a sus respectivos Buhos Reales vecinos ( x = 1900 m) y la mortalidad observada en 22 jovenes ha sido mucho menor (4.5%). En conclusion, se sugiere que cuando las dos especies anidan proximas, el Buho Real puede ser un predador potential de los jovenes de Aguilas Perdiceras recien salidos del nido. Acknowledgments We are particularly grateful to Xavier Ferrer and Fer- nando Hiraldo, the directors of the Bonelli’s Eagle project, and Hans Kallander, for help and suggestions. Andy El- liott assisted in correcting our English. Literature Cited Bayle, P. 1987. Decouverte des restes d’un aigle de Bonelli Hieraaetus fasciatus juvenile dans une aire de Hibou Grand-due Bubo bubo en Provence. Faune de Provence 8:49-53. Blondel, J. and O. Badan. 1 976. La biologie du Hibou Grand-due en Provence. Nos Oiseaux 362:189-219. Donazar, J. A. 1989. Variaciones geograficas y esta- Autumn 1990 Short Communications 71 cionales en la alimentation del Buho real ( Bubo bubo) en Navarra. Ardeola 36:25-39. Glutz von Blotzeim, U.N. and K. Bauer. 1980. Handbuch der Vogel Mitteleuropas. Vol. 9. Akade- mische Verlagsgesellschaft, Wiesbaden, Germany. Mikkola, H. 1983. Owls of Europe. T. and A.D. Poyser Ltd. Galton, U.K. Received 1 March 1990; accepted 17 July 1990 J. Raptor Res. 24(3):71-72 © 1990 The Raptor Research Foundation, Inc. Osprey Nestlings Fostered by Hacked Adults Two Weeks After Predation of Their Young Larry M. Rymon Department of Biological Sciences, East Stroudsburg University, East Stroudsburg, PA 18301 Hacking of Osprey ( Pandion haliaetus ) was begun in Pennsylvania in 1980 to restore a breeding population that had been extirpated by pesticide contamination and habitat alterations (Schaadt and Rymon 1983). Between 1980 and 1986, 111 donor nestlings from the Chesapeake Bay area were successfully hacked at mountain lakes and rivers in northeastern Pennsylvania. In 1986, pairs of previously hacked adults returned to produce four healthy chicks, the first to hatch in the state in many decades (Rymon 1989a). Since 1986, over 30 marked adults have returned to release sites and 16 active nests have been established. During the 1986-89 breeding season, a total of 38 chicks hatched and 31 fledged and dispersed. We are now optimistic that our hacking efforts have established the nucleus of a restored breeding population (Rymon 1989b, 1989c). During their first year of breeding, pairs frequently experience nesting failure which often appears to be re- lated to inappropriate site selection, especially those ac- cessible to climbing predators, mainly Raccoons ( Procyon lotor). Nest mortalities have also been caused by adverse weather during broodrearing. One possible remedy for lost broods appears to be brood manipulation. Manipulations have been widely conducted in nearby states New Jersey, Connecticut and Massachusetts. Poole (1989) used brood augmentation as a means of testing the ability of males to provide food. He noted that adult ospreys did not discrim- inate against transferred chicks nor did nestlings show distress or aggression when placed with others. Rymon (1987) observed fostering in Pennsylvania when a 3 yr old hacked male returned to nest unsuccessfully with an unmarked female in 1985. Seven weeks after nest failure, the male fostered nine hacked fledglings on the abandoned nest. Based on these findings I conducted a fostering experiment in 1988. Brood Replacement Among 1 6 successful nests built by hacked Ospreys that returned as adults during 1986-89, one nest failure in 1988 prompted a brood replacement. One pair, at Pocono Lake, produced two chicks on 1 3 May. This marked pair previously had raised broods there in 1986 and 1987. On the morning of 12 June, both 4 wk old chicks were missing from the predator guarded nest which was built on a nest pole located in water. The parents showed much distress and visited the nest frequently for the next several days. At the end of the second week after abandonment the adults had not layed a second clutch but were still in the area. I placed two 5.5 wk old chicks in the nest. The nestlings had been held overnight and been fed before being taken to the nest. At 0800 H they were placed on the nest. My assistants and I then observed the nest from a blind 50 m away. The adults could also be seen perched 100 m on the opposite shore. The adults remained wary but cir- cled the nest minutes after we were hidden in the blind. After this initial overflight the parents returned to perch on snags near the opposite shore. At 1025 H the female flew to the nest carrying a stick in her talons. She deposited it on the nest, looked briefly at the young and after 30 sec flew away. The adults made no further attempts to return to the nest for over 5 hr. During this period, the nestlings became restless and aggressive. They gave long intermittent beg- ging calls and vigorously pecked at each other, drawing blood several times. At 1500 H, a series of events began to unfold rapidly. Four other adult ospreys appeared over the nest and an exchange of calls began. In addition to the calling, the nestlings began begging loudly and the intended foster 72 Short Communications Vol. 24, No. 3 parent pair began a new series of calls. This exchange continued until 1512 H when a male from one of the intruding pairs landed on the nest and covered the young with his wings spread for 30 sec. The male from the foster pair then flew to the nest and drove off the intruding male. The foster female immediately joined her mate and the pair drove the four intruders away from the nest. The foster pair circled the nest site at 1520 H and then flew back to their earlier perches on the opposite side of the lake. The adults made no further vocalizations or flights until 1600 H when they both flew to the nest. They remained on the nest, with the young, until 1 630 H when the male left. While he was absent the female left the nest at 1640 H and returned to her original tree perch across the lake. At 1642 H a crow ( Corvus brachyrhynchos ) dove at the young and the female quickly returned to defend them. At 1730 H the male returned to the nest with a fish, gave it to the female and flew off once more. She then began to feed both young but after feeding them only a few bites she again flew to her tree perch. Her brief efforts to feed the young stimulated prolonged pecking between the nest- lings and again blood was drawn. At 1800 H, after a 25 min absence, the female returned to the nest and began feeding the young a second time. The male returned at 1810 H with a Small-mouthed Bass {Micropterus dolo- mieui) and the female continued to feed the young. Both parents remained on the nest until after 2100 H when the male returned to his regular night roost; the female re- mained overnight on the nest with the young. Both adults continued to care for the young and their parental activity appeared normal. The nestlings were fed well and pro- tected by their foster parents throughout the nesting pe- riod. Resumen. — En 1988, polluelos huespedes fueron puestos en el nido de dos Aguilas Pescadoras adultas, marcadas y criadas en caja abierta desde 1982, para reemplazar sus crias que dos semanas antes habian desaparecido a causa de un predador. Los adultos aceptaron los hijos adoptivos desde el dia en que reemplazaron a sus propios polluelos, y continuaron cuidando de ellos normalmente durante el periodo de anidar. Por esto se cree que si polluelos de- saparecidos son posteriormente reemplazados por otros en el nido, estos pueden ser aceptados por Aguilas Pescadoras y otras especies de aves rapaces. [Traduccion de Eudoxio Paredes-Ruiz] Literature Cited Poole, A. 1989. Ospreys-a natural and unnatural his- tory. Cambridge University Press, Cambridge, MA. Rymon, L.M. 1987. Status report: the restoration of ospreys to breeding status in Pennsylvania (1980-86). Eyas 10:34-35. . 1989a. The restoration of ospreys to breeding status in Pennsylavania by hacking (1980-86). Pages 359-362 in R.D. Chancellor [Ed.], Raptors in the mod- ern world. Proceedings of the Third World Conference on Birds of Prey, Eilat, Israel. . 1989b. Osprey restoration in three northeastern states. Pages 259-263 in Proceedings of the northeast raptor management symposium and workship. Insti- tute for Wildlife Research, Tech. Series No. 13, Wash- ington, D.C. . 1 989c. The importance of Pennsylvania’s wet- lands to raptors. Pages 195-204 in S.K, Majumdar [Ed.], Wetlands ecology, productivity and values. Pa. Acad, of Sci., Easton, PA. Schaadt, C.P. AND L.M. Rymon. 1983. The restora- tion of Ospreys by hacking. Pages 249-305 in D.M. Bird [Ed.], Biology and management of Bald Eagles and Ospreys. Harpell Press, Ste. Anne de Bellevue, P.Q., Canada. Received 22 March 1990; accepted 17 July 1990 /. Raptor Res. 24(3): 72 -74 © 1990 The Raptor Research Foundation, Inc. Daytime Activity of Little Owls ( Athene noctua) in Southwestern Spain JJ- Negro, M.J. de la Riva and F. Hiraldo Estacion Biologica de Donana, Consejo Superior Investigaciones Cientificas, Apdo. 1056, 41080 Sevilla, Spain Little Owls ( Athene noctua) do not limit their activity to darkness even though they belong to a group of nocturnal raptors. The degree of nocturnal activity likely varies be- tween geographic regions and although Val verde (1957) watched Little Owls with young in the nest hunting throughout the day in Morocco, Cramp (1985) reviewing Autumn 1990 Short Communications 73 Figure 1. Little Owl observations (•) and captures (O) in daytime. The curved lines show times of sunrise and sunset in Seville (37°22'N-6°00'W). other authors, stated that Little Owls hunt little or never during the day. In southwestern Spain we have repeatedly observed Lit- tle Owls in daytime on exposed perches such as power poles, fences or boundary stones suggesting that they could be hunting. Our data (Fig. 1) were collected between 1980 and 1986 and refer to owls seen while driving in a car along roads in Extremadura and Andalusia, through ce- real-growing areas, olive stands, wood pasture and mead- ows. The owls use exposed perches throughout the year (Fig. 1), although primarily between May and July, cor- responding to the breeding season (Cramp 1985). Most sightings were after midday and this agrees with Exo (1989) that Little Owls are more active in the second part of the day than in the first. Further evidence of daytime activity by Little Owls was obtained while trapping European Kestrels ( Falco tinnun- culus) and Lesser Kestrels ( F . naumannt) with Bal-chatris (Berger and Mueller 1959). Nine adult Little Owls were also caught, attracted by the live laboratory mouse ( Mus musculus ) used as bait. To place the Bal-chatris we fol- lowed a line trap method (Bloom 1987). We set 4 to 20 traps that were visited every 30 to 60 min. The Little Owls were caught at two sites in Sevilla Province characterized by extensive fields of cereals and sunflowers. At site one, a small rock outcrop, in 1988 and 1989 we caught 6 individuals in 7 days trapping. At site two, an old castle 15 kilometers away, we trapped for 2 days and caught 3 Little Owls on the second day. The owls were banded and released at the capture site. Why some Spanish Little Owls extend their period of activity into the day remains unclear. Jaksic (1982) pro- posed that the evolution of nocturnal activity in owls could be related to the avoidance of interference interactions with diurnal raptors. The Little Owl, being of small size, has a wide range of potential predators and competitors. It is known to occur in the diet of the Northern Goshawk ( Accipiter gentilis ), European Sparrowhawk (A. nisus ), Peregrine Falcon {Falco peregrinus) and Black Kite ( Mil - vus migrans ) (Uttendorfer 1952, Valverde 1967). In south- western Spain, specialized bird-eating raptors are rare. Goshawks and Sparrowhawks are at the southern limit of their distribution and, according to our observations, only nest in forested areas at higher altitude. Peregrines exist in our study area at their lowest nesting densities in Spain (Heredia et al. 1988). The relaxation of pressure from diurnal predators could favor Little Owls extending their hunting time into daylight hours. Supporting such an ex- planation is the fact that in Donana National Park, a location in southwestern Spain where the density and di- versity of diurnal raptors is unusually high (Valverde 1967, Garcia et al. 1989), Little Owls remain hidden during the 74 Short Communications Vol. 24, No. 3 day (M. Manez, pers. comm.). However, the degree of diurnal activity in Spanish Little Owls may also be influ- enced by other factors, such as prey availability, daily activity patterns of the prey species, or the energetic con- straints while rearing the young in summer. Resumen. — Entre los anos 1980 y 1986 se registraron 40 mochuelos {Athene noctua) posados en lugares expuestos durante el dia. Las observaciones, realizadas desde auto- movil por carreteras de Extremadura y Ahdalucia, se pro- dujeron en todas las epocas del aho, y especialmente en la epoca de cria. Posteriormente, se capturaron 10 individuos durante el dia mediante trampas Bal-chatri cebadas con ratones vivos y se obtuvo asi una nueva evidencia de la actividad de los mochuelos en horas de luz. Sugerimos que el elevado grado de actividad diurna de los mochuelos del suroeste de Espana esta relacionado con la escasez de po- tenciales predadores, como el Halcon Peregrino ( Falcoper - egrinus) o el Azor (Accipiter gentilis). No descartamos, sin embargo, que intervengan tambien factores relacionados con la disponibilidad de presas o la actividad diaria de las mismas. Literature Cited Berger, D.D. and H.C. Mueller. 1959. The Bal- chatri: a trap for the birds of prey. Bird Banding 30: 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. National Wildlife Federa- tion, Washington, D.C. Cramp, S. [Ed.]. 1985. The birds of the western Pale- arctic. Vol. IV. Oxford University Press. Exo, K.M. 1989. Tagesperiodische Aktivitatsmuster des Steinkauzes {Athene noctua). Die Vogehvarte 35:94-1 14. Garcia, L., J. Calderon and J. Castroviejo. 1989. Las aves de Donana y su entorno. Cooperativa Maris- mas del Rocio, Huelva. Heredia, B., F. Hiraldo, L.M. Gonzalez and J.L Gonzalez. 1988. Status, ecology and conservation of the Peregrine Falcon in Spain. Pages 219-226 in T.J. Cade, J.H. Enderson, C.G. Thelander and C.M. White [Eds.], Peregrine Falcon populations: their man- agement and recovery. The Peregrine Fund, Inc., Boi- se, ID. Jaksi 6, F.M. 1982. Inadequacy of activity time as a niche difference: the case of diurnal and nocturnal rap- tors. Oecologia (Bert.) 52:171-175. Uttendorfer, O. 1952. Die Ernahrung der deutschen Raubvogel und Eulen. Neudamm, Germany. Val VERDE, J.A. 1957. Aves del Sahara Espanol (estudio ecologico del desierto). Instituto de Estudios Africanos. Consejo Superior de Investigaciones Cientificas, Ma- drid, Spain. . 1967. Estructura de una comunidad de verte- brados terrestres. Monografias de la Estacion Biologica de Donana, 1, Madrid, Spain. Received 4 October 1989; accepted 12 September 1990 J. Raptor Res. 24(3):75-76 © 1990 The Raptor Research Foundation, Inc. News and Reviews 1990 Annual Meeting. Members of the Raptor Research Foundation, Inc. enjoyed a productive meeting in Allentown, Pennsylvania, from 24-28 October. Thanks to the hard-working local committee, organized by Hope Carpenter and Judy Wink, the meeting went smoothly. The first day was filled with presentations about the relationship between Great Horned Owls and their prey. The focus on the Great Horned Owl was prompted by the organizers’ concerns over local interest groups pressuring the Game Commission to remove the Great Horned Owl from the list of Pennsylvania’s protected wildlife. On the second day, at Hawk Mountain Sanctuary, participants watched migrating vultures, accipiters, buteos, eagles and harriers parade along the Appalachian “folds.” The migrants were few in number which gave the hawkwatchers plenty of opportunity to discuss the merits of various brands of binoculars, the pros and cons of the resolutions to be voted on, and the 1991 annual meeting in Tulsa. The sun smiled on the group perched on the ancient sandstones and conglomerates, outcrops to which the human anatomy could conform only so long, forcing people to mix. Three resolutions were endorsed by the membership. These resolutions were as follows: A) Whereas many raptors and avian prey species migrate between areas of varying pesticide application; and Whereas these migrations often expose the species to pesticides; and Whereas there is potential for this exposure to have an impact on these migrating species; and Whereas there is a need for dependable data on which to base wise conservation, management and political decisions; and Whereas there is a lack of relevant data and it is necessary to more adequately characterize the level of impacts on the migrating species. Therefore be it resolved that the Raptor Research Foundation, Inc.: 1 . Encourages the necessary investigations of pesticide fate and effects as they relate to migrating raptors and prey species. 2. Encourages the proper conservation, management and political decisions based on the findings. 3. Distributes this resolution to appropriate individuals, agencies and organizations. B) Whereas loss of habitat has been cited as an important cause of the historic Bald Eagle decline; and Whereas many shoreline habitats are rapidly being converted to housing developments and industrial sites; and Whereas a comprehensive nationwide survey of the security of Bald Eagle nesting, roosting and perching habitat has not been completed; and Whereas, small populations of wild species are generally at greater risk of extinction than larger populations; and Whereas some eagle populations are still very small; and Whereas the U.S. Fish and Wildlife Service, U.S.D.I., is the key federal agency charged with the responsibility of protecting endangered species and their habitats in the U.S.; and Whereas adequate protection of endangered birds and other species requires a long-term, rather than a short-term, planning horizon. Therefore, be it resolved that the Raptor Research Foundation, Inc., strongly supports the concept of regional recovery teams and urges the U.S. Fish and Wildlife Service, and U.S.D.I., to proceed with the revitalization of these teams. Be it further resolved that the Raptor Research Foundation, Inc., urges the U.S. Fish and Wildlife Service, and U.S.D.I., to: 1. Consider any changes in Bald Eagle status on a regional basis. 2. Give substantial weight to the professional input of the regional recovery teams. 3. Direct the team leaders to meet and further develop criteria for assessing and protecting the viability of Bald Eagle populations, emphasizing the security of their habitat; and 4. Direct the team leaders to initiate the above action during fiscal year 1991. C) Whereas many current forestry practices involve management of forests primarily for timber production which often leads to neglect of non-timber components and a decrease in biodiversity, as well as to both local and global environmental degradation; and Whereas the membership of the Raptor Research Foundation, Inc., recognizes that these practices seriously affect the long-term survival of the Northern Spotted Owl ( Strix occidentalis caurina ), and there exists a possibility that continued removal of mature and old-growth forest will lead to the eventual loss of the Northern Spotted Owl. Therefore, be it resolved that the Raptor Research Foundation, Inc.: 1. Applauds the U.S. Fish and Wildlife Service for its decision to list the Northern Spotted Owl as “threatened.” 2. Urges the U.S. Fish and Wildlife Service to intervene on behalf of the owl, as pursuant to their obligations under the Endangered Species Act of 1973. 75 76 News and Reviews Vol. 24, No. 3 3. Encourages the preservation of old-growth forest ecosystems and that these ecosystems be integrated into surrounding forest lands. 4. While the Raptor Research Foundation, Inc., is concerned that the recommendations of the Interagency Scientific Committee for conservation of the Northern Spotted Owl may allow a greater reduction in Northern Spotted Owls than permitted for a threatened species under the U.S. Endangered Species Act of 1973, we recommend that at least minimum provisions of the report be accepted as an initial step for the protection of the Northern Spotted Owl. The recommended two-part conservation strategy (of protection and monitoring) must be imple- mented immediately. Research must be undertaken to devise forest management practices that would permit survival of the owls. New officers were elected at the meeting. Betsy Hancock, who also chairs the committee on rehabilitation, took over as secretary when Jim Fraser retired after many years of dedicated service. Jim Fraser assumed Lynn Oliphant’s chairmanship of the committee on conservation. Lynn Oliphant and his committee have raised nearly $10,000 which, combined with the World Wildlife Fund’s contribution, provides funds for the Calakmul Biosphere Reserve in Mexico. Three winners of awards were announced at the meeting. Financial support in the amount of $1000 was given to Andrew Jenkins, from the University of Cape Town, for his study on the “Behavioral ecology of the Peregrine Falcon in South Africa.” Tim Kimmel, from Pennsylvania State University, received an award for the best student presentation entitled “Evaluation of a habitat model for directing a census of Northern Goshawks in Pennsylvania.” Bryan Kimsey, from eastern New Mexico, was awarded the Koplin Travel Award for his paper entitled “Differential migration of small accipiters through northeastern Nevada.” See you in Tulsa on 6-10 November 1991! Request for Assistance in Locating Marked Bald Eagles. Since 1985, the Texas Parks and Wildlife Department has banded and color marked 114 eaglets along the Texas Gulf Coast. Each eagle wears a standard metal band, a color band and two patagial markers. The right patagium is marked with a yellow tag bearing letters and numbers T 1 to T 114 on the ventral surface, and a black spot on the dorsal surface. The left wing is marked with a light blue tag bearing a yellow spot. The wing markers usually can be seen only with the eagle in flight. Anyone seeing these eagles is asked to please send the date of observation, exact location, color of leg band, which leg color band is on, and a description of patagial markers to the Bird Banding Laboratory, Laurel, MD 20708 and to David W. Mabie, Texas Parks and Wildlife Department, 715 South Bronte, Rockport, TX 78382. Recent Reports Available. A Copy of “Amphibians and reptiles in the diets of North American raptors,” by David A. Ross, is available free of charge. This 33-page Wisconsin Endangered Resources Report (#59) is based on a computer search of over 200 journals. Write to: Bureau of Endangered Resources, Wisconsin Department of Natural Resources, P.O. Box 7921, Madison, WI 53707. A copy of “Behavior and productivity of nesting Prairie Falcons in relation to construction activities at Swan Falls Dam,” by Anthonie M.A. Holthuijzen, is available free of charge. This 77-page final report is the result of a cooperative study between the U.S. Bureau of Land Management, Idaho Power Co., and Pacific Gas and Electric Co. Write to: Idaho Power Co., Box 70, Boise, ID 83707. THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966) OFFICERS PRESIDENT: Richard J. Clark SECRETARY: James D. Fraser VICE-PRESIDENT: David M. Bird TREASURER: Jim Fitzpatrick BOARD OF DIRECTORS EASTERN DIRECTOR: Keith L. Bildstein CENTRAL DIRECTOR: Patrick T. Redig MOUNTAIN & PACIFIC DIRECTOR: Stephen W. Hoffman EAST CANADA DIRECTOR: David M. Bird WEST CANADA DIRECTOR: Paul C. James INTERNATIONAL DIRECTOR: Bernd U. Meyburg DIRECTOR AT LARGE #1: Michael W. Collopy DIRECTOR AT LARGE #2: Robert E. Kenward DIRECTOR AT LARGE #3: Jeffrey L. Lincer ft******************* EDITORIAL STAFF EDITOR IN CHIEF: JOSEF K. SCHMUTZ, Department of Biology, University of Saskatchewan, Sas- katoon, SK., Canada, S7N 0W0 ASSOCIATE EDITORS Keith L. Bildstein Susan B. Chaplin Charles J. Henny C. Stuart Houston Robert E. Kenward Eudoxio Paredes-Ruiz Patricia P. Rabenold Patrick T. Redig 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 (8 Yi 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.