(ISSN The Journal of RAPT( >r Research Vo I, II ME 28 June 1 994 Number 2 Contents Bone Digestion and Intestinal Morphology of the Bearded Vulture. David C. Houston and Jamieson A. Copsey 73 Behavior of Colonial Common Kestrels (Falco tinnunculus ) During the Post-Fledging Dependence Period in Southwestern Spain. Javier Bustamante . . 79 Goshawk Diet in a Mediterranean Area of Northeastern Spain. Sand Manosa . . 84 The Antipredator Vocalizations of Adult Eastern Screech-Owls. Thomas McKell Sproat and Gary Ritchison 93 Behavior and Activity of Rehabilitated Buzzards ( Buteo buteo) Released in NORTHERN ITALY. Davide Csermely and Carlo Vittorio Corona 100 Short Communications Parathion Poisoning of Mississippi Kites in Oklahoma. J. Christian Franson 1 08 Status and Reproduction of the Peregrine Falcon at a Coastal Lagoon in Baja California Sur, Mexico. Aradit Castellanos, Federico Salinas-Zavala and Alfredo Ortega-Rubio 110 Successful Nesting by a Pair of Bald Eagles at Ages Three and Four. Daniel W. Mulhern, Michael A. Watkins, M. Alan Jenkins and Steve K. Sherrod 113 Traps for Capturing Territorial Owls. S. M. Redpath and I. Wyllie 115 Letters 118 Dissertation Abstracts 123 The Raptor Research Foundation, Inc. gratefully acknowledges a grant and logistical support provided by Weber State University to assist in the publication of the journal. 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 ad- dress to Jim Fitzpatrick, Treasurer, 14377 11 7th Street South, Hastings, Minnesota 55033, U.S.A. The Journal of Raptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $24.00 per year and to libraries and institutions for $30.00 per year from The Raptor Research Foundation, Inc., 14377 117th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental United States.) Second class postage paid at Hastings, Minnesota, and additional mailing of- fices. POSTMASTER: Send address changes to The Journal of Raptor Research, 14377 117th Street South, Hastings, Minnesota 55033, U.S.A. Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A. Copyright 1994 by The Raptor Research Foundation, Inc. Printed in U.S.A. © This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. Vol. 28 June 1994 No. 2 J Raptor Res. 28(2):73-78 © 1994 The Raptor Research Foundation, Inc. BONE DIGESTION AND INTESTINAL MORPHOLOGY OF THE BEARDED VULTURE David C. Houston and Jamieson A. Copsey Applied Ornithology Unit, Zoology Department, Glasgow University, Glasgow G12 Scotland, U.K . Abstract. — The diet of the bearded vulture ( Gypaetus barbatus) consists largely of bone. Two experimental birds fed a diet of sheep ribs had a mean digestive efficiency of 50%, with most of the food being digested within 24 hr. The digestive tract of bearded vultures is not unusually long for a scavenging bird of its size, and does not contain a region for mechanical breakdown of the food. The stomach contains a high concentration of acid-secreting cells, and experiments with bone fragments in acid solutions suggested that this is the chief mechanism for decalcification. A bone diet may have a higher caloric content than an equivalent weight of soft tissues. The ecological consequences of this unusual diet are that this species is able to survive in areas with a very low availability of carcasses. Key WORDS: bearded vulture; bone digestion; Gypaetus barbatus; intestinal morphology. Digestion de huesos y morfologia intestinal de Gypaetus barbatus Resumen. — La dieta de Gypaetus barbatus consiste esencialmente de huesos. Dos individuos experimentales se sometieron a una dieta de huesos de oveja, con un promedio de eficiencia digestiva del 50%, donde la mayoria del alimento llego a digerirse en 24 h. El tracto digestivo de G. barbatus no es inusualmente largo para un carronero de su tamano y no contiene una region para la trituration mecanica del alimento. El estomago contiene una alta concentration de celulas secretoras de acido, y experimentos con fragmentos en soluciones acidas sugieren que este es el principal mecanismo para la descalsificacion. Una dieta de huesos puede tener un mayor contenido calorico que un peso equivalente de tejidos blandos. Las consecuencias ecologicas de esta dieta inusual, serian que esta esta especie podria sobrevivir en areas con muy baja disponibilidad de carrona. [Traduction de Ivan Lazo] The bearded vulture ( Gypaetus barbatus ) is a scav- enger on the carcasses of large mammals in mountain regions in Africa, Asia, and Europe. It is unusual in that it eats bones. Small bones are swallowed whole and larger ones are dropped repeatedly onto rock slabs to break them into small enough fragments to be swal- lowed (Huxley and Nicholson 1963, Brown 1988). Several studies recently have shown that bone is not just an occasional food item, but the predominant food of the bearded vulture. Bone forms 70-90% of all food items (Hiraldo et al. 1979, Cramp and Simmons 1980, Brown and Plug 1990). Even owl pellets are eaten for their bone content (Heredia et al. 1990). Brown and Plug (1990) showed that if wild bearded vultures were presented with a choice of bone items and meat, they would select the bone, and old, dried bones significantly more frequently than fresh bones. Some mammalian carnivores, notably the spotted hyena ( Crocuta crocuta), can also digest bone, but this forms only a small pro- portion of their normal diet (Kruuk 1972). The beard- ed vulture is the only vertebrate known to have a diet consisting largely of bone. We present here preliminary results from feeding trials to determine the digestive efficiency of bearded vultures on this unusual diet, and the time they required for digestion. We also carried out postmortem examinations to consider whether the 73 Vol. 28, No. 2 74 David C. Houston and Jamieson A. Copsey Time after feeding (hrs) Figure 1. The time of fecal production from a pair of bearded vultures after ingestion of a bone meal. intestine of the bearded vulture showed any special- izations, and finally we speculate on the ecological implications of their diet. Methods Feeding trials were carried out on two adult bearded vul- tures housed in the Research Zoo of Tel Aviv University, Israel in September 1992. It was not possible to separate the pair; all results presented here are mean values for the two. The cage floor was lined with sheeting to allow total fecal collection. A weighed quantity of 4-cm lengths of sheep rib bones was provided each afternoon and removed the following morning. A control sample of bone was also left outside the cage, to correct for dehydration of the bone samples left in the cage. All uneaten bone fragments were weighed and corrected for water loss to determine wet weight of bone eaten. A sample of the bone diet was dried at 70°C to constant weight to determine mean water content. This figure was used to calculate dry food intake. Bone samples were then ashed in a furnace at 535°C and ash weight used to determine mineral content of the diet. Organic content was derived from weight loss during ashing. All feces were collected daily, separated from uric acid material, and dried to constant weight at 70°C. Percent digestive efficiency was calculated as 1 — total dry weight feces/total dry weight bone eaten x 100. Four feeding trials were conducted over 13 d. Birds were deprived of food for 24 hr before the start of each trial. The digestion time for food was recorded by starving the birds for 48 hr, providing them with food at 0630 H, and removing all uneaten food after they had finished feeding. The birds were then observed continuously and the time of all fecal production noted. Feces were collected and dried at 70°C. Birds were not fed again until 24 hr after the last appearance of fecal material. For security reasons, fecal col- lections could not be made at night. The form in which calcium was present in the feces was investigated using X-ray diffraction analysis using Fe-filtered Co k radiation at scanning speed 2 9 min and range 4-64 29. The effects of pH and time on the rate of bone decalci- fication was investigated. Pieces of sheep rib bone from ma- ture animals, as used in the feeding trials, were placed in hydrochloric acid solutions, buffered with N sodium acetate (Hale 1953), at pH 0.8, 1.1, and 1.5. The pHs used were within the range of acidity recorded from the stomachs of other raptor species (Herpol 1967, Duke et al. 1975). So- lutions were maintained at 40°C in a water bath. The pH was checked every few hours and the solution replaced if necessary. The weighed bone pieces were each placed in individual vials and maintained there for 6, 12, 24, or 48 hr, after which time excess liquid was removed with paper tow- elling. Bone pieces were then reweighed, dried to constant weight at 70°C, and ashed in a furnace at 525°C for 24 hr Five bone samples were used for each of the experimental treatments. We also simulated the digestive effect of combined acid and pepsin, using commercial porcine pepsin solutions in the same range of pH conditions and the time periods outlined above. The intestinal morphology of two bearded vultures was examined in postmortem examinations. The birds died in captivity, and had been part of the breeding program for the reintroduction of bearded vultures into the Alps (Frey and Walter 1989). Samples of alimentary tract were prepared for histological examination with Mallory, haematoxylin/eosin, and periodic acid-Schiff/alcean blue stains (Gurr 1962). Results The rib bones used in the feeding trials and the decalcification study had a mean water content of 32% ±1.8 (SE, N = 12), and dry bone weight was com- posed of 54% ±1.7 (SE) mineral content and 46% ± 1 .7 (SE) organic content. The mean digestive efficiency, as measured from total collection of fecal material, was 49.8% ±1.3 (SE). The digestion time for food could, unfortunately, only be measured on one occasion, when the birds ate 146 g of bone. Most fecal production occurred within 24 hr after feeding (Fig. 1). Unfor- tunately, it was not possible to be with the birds over- night to record when the peak fecal production oc- curred. Virtually all fecal material was ejected within a few hours of dawn, because fecal material was not dehydrated when collected at 0600 H. Dehydration would have occurred in the dry air conditions in Tel Aviv if feces had been produced early in the night. The dimensions of the digestive tract of the two birds were: esophagus lengths 25 and 21 cm; stomach lengths were both 17 cm, stomach widths 6 and 5 cm; small intestine lengths (including duodenum) 184 and 185 cm; wet weight of stomachs (empty) 80 and 75 g; and wet weights of small intestines (empty) 40 and 47 g. The length of the small intestine of the bearded vulture is shown in Fig. 2 in relation to its body size and in comparison with a range of other raptor species (for method of scaling for body size see Barton and June 1994 Bone Digestion by Bearded Vultures 75 Body (mm) Figure 2. A comparison of the length of the small intestine of the bearded vulture in relation to an index of body size (sternum length x sternum diagonal) 14 , with data from other birds of prey which have a scavenging diet and an active chase form of predation (from Barton and Houston 1994). Houston 1994); the intestinal length is close to that predicted for a scavenging raptor. The digestive tract showed some specialization. The esophagus was highly elastic and expandable to allow the passage of large food items, but no clearly defined crop (a diverticulum off the esophagus) was present. The bearded vulture is the only species of vulture to lack this large storage region in front of the stomach. Irregularly shaped fragments of bone would be difficult to store in a crop and then later retrieve for passage to the stomach. Bearded vultures must use the esoph- agus to store food; Brown (1988) recorded birds swal- lowing bones at least 250 mm long and 35 mm wide, which would be too large to contain in the stomach. Bearded vultures are also occasionally seen flying with the end of a bone still projecting from the mouth. The esophagus had a mean wall thickness of 1.3 ± 0. 1 mm (SE, N = 20), contained no mucus glands (as is typical of vertebrates), but did have a thickened epithelial layer from 23-126 nm thick with some kera- tinization underlaid by a connective tissue layer from 23-207 /im thick. These layers, together with the elas- ticity of the esophagus, must provide some protection from sharp bone pieces. The gastric stomach contained

and other raptors have been recorded with gastric pH as low as 0.7 (Herpol 1967). The stomach wall in the bearded vulture con- tains a high density of acid-secreting cells, and must be capable of producing a highly acidic environment. The feces of bearded vultures contained calcium hy- droxyapatite, the same form of calcium as in bone. Therefore, the mineral salts seem to be leached from the bone tissue without chemical transformation. We only have one observation on the time taken for di- gestion, but this suggested that bearded vultures com- plete digestion within about 30 hr. An acid solution of pH 0.8 alone would not have completed deminerali- zation within this time, but bone probably breaks down in the stomach much faster than in our acid solutions June 1994 Bone Digestion by Bearded Vultures 77 because of two factors. Firstly, there will be mechanical agitation from contractions of the stomach walls. Jack- son et al. (1987) showed that even gentle movement of food samples resulted in significantly greater break- down than stationary conditions. Bone fragments be- came comparatively soft after a period in strong acid, and gentle grinding together would have substantially increased their rate of breakdown. Secondly, the action of the acid will be augmented by pepsin activity to break down the collagen matrix. We were not able to obtain a commercial form of pepsin which remained active in our experimental conditions. Pepsins operate over very narrow pH ranges, which vary considerably between species (Withers 1992). Presumably bearded vultures have protein- splitting enzymes that have op- timum activity in highly acidic solutions. Very little is known of calcium metabolism in rap- tors, but bearded vultures are obviously adapted for a diet which has a highly unusual calcium/phosphorus ratio and exceptionally high calcium levels. Recom- mended feeds for domestic chickens should contain no more than 1.2% calcium (Scott et al. 1982) whereas bone contains 15-18% calcium. Brown (1988) showed that mammal bones have a higher energy content than muscle tissue (6.7 and 5.8 KJ/g respectively) partly because of their high fat content. Brown and Plug (1990) calculated that a bearded vulture taking a diet of 70% bone, 25% muscle, and 5% skin (the best estimate available of natural diet) would ingest 674 KJ energy per 100 g, compared to 586 KJ energy for an equivalent weight of muscle. We have shown the digestive efficiency of bone to be 50%, and if w r e assume 75% efficiency for soft tissues, then for each 100 g of bone-dominated diet the bird would absorb 387 KJ compared to 440 KJ on a pure muscle diet. A bone-based diet is therefore energetically almost as valuable as a meat-based diet. A bone-based diet, however, has one major advantage in that it does not decompose. A skeleton left on a mountain hillside will rapidly dehydrate sufficiently to prevent bacterial breakdown of the mineralized tissues and the fatty marrow. Bearded vultures are known to return to skel- etons after several months to continue feeding. All other scavenging birds which feed on soft tissues are faced with a race against time when they locate a carcass. If they do not consume the meat within a short period of time it will be destroyed by bacteria or insect larvae (Houston 1979). This has major implications for the availability of food for bone-eating and meat-eating scavengers. If, for example, bones remain in an edible condition for 10 times the length of time that soft tissues remain in an edible condition, this means that a bone- scavenger can survive with only one-tenth the number of carcasses within its foraging range compared to a meat scavenger. This is probably why bearded vultures are so successful in high mountain regions, such as Tibet and the Himalayas. Such areas have extremely low ungulate biomass and few carcasses become avail- able. But when they do a bearded vulture can rely on them for a long period of time. If bone is such a useful diet, why do other raptors not exploit it? Bone is a heavy food which takes a comparatively long time to digest. It is notable that even bearded vultures prefer to eat old bones rather than fresh (Brown and Plug 1990), probably because they will have lost about 30% of their weight. All vultures have extremely low energy flight costs because of their dependence on soaring. Other raptors which rely on powered flight, less efficient gliding, or species living in regions with less powerful soaring conditions, might expend too much energy' when flying with a stomach full of heavy bone to warrant feeding on this diet. In addition, the slow time required for digestion of bone will preclude small species from using this diet, for their higher metabolic rates require a faster delivery of energy from the digestive tract. Perhaps only a very large, soaring bird living in a mountainous habitat with powerful upcurrents could afford to specialize in this way. Acknowledgments We are extremely grateful to Yoram Yom-Tov for per- mission to carry out the feeding trials at the Research Zoo of the Zoology Department, Tel Aviv University. Ofer Bahat and all the staff of the zoo gave a great deal of practical help with these trials, for which we are extremely grateful. Hans Frey and Knuth Niebuhr kindly allowed us to carry out post- mortem examinations on two birds, and went to considerable trouble to send them to us in excellent condition. We would also like to thank Kate Orr, who prepared the histological sections of the gut tissue, Roger Downie for helping interpret them, and Allan Hall who arranged the X-ray diffraction analysis. S.N. Wiemeyer and G. Bartolotti made many help- ful comments on the manuscript. Literature Cited Alexander, R.M. 1983. Animal mechanics. Blackwells, Oxford, U.K. Barton, N.W.H. and D.C. Houston. 1993a. A com- parison of digestive efficiency in birds of prey. Ibis. 135. 363-372. AND . 1993b. The influence of gut mor- phology on digestion time in raptors. Comp. Biochern. Physiol. A Comp. Physiol. 105:571-578. AND . 1994. Morphological adaptation 78 David C. Houston and Jamieson A. Copsey Vol. 28, No. 2 of the digestive tract in relation to feeding ecology in raptors. /. Zool, Lond. 232:133-150. Brown, C.J. 1988. A study of bearded vultures Gypaetus barbatus in southern Africa. Ph.D. dissertation, Univ. Na- tal, Pietermaritzburg, South Africa. AND I. Plug. 1990. Food choice and diet of the bearded vulture Gypaeus barbatus in southern Africa. South. Afr. J. Zool. 25:169-177. Cramp, S. and K.E.L. Simmons. 1980. The handbook of the birds of the western Palearctic. Oxford Univ. Press, Oxford, U.K. Duke, G.E., A.A. Jegers, G. Loff and O.A. Evanson. 1975. Gastric digestion in some raptors. Comp. Biochem. Physiol. A Comp. Physiol. 50:649-656. Frey, H. and W. Walter. 1989. The reintroduction of the bearded vulture Gypaetus barbatus into the Alps. Pages 341-344 in B.-U. Meyburg and R.D. Chancellor [Eds.], Raptors in the modern world. World Working Group on Birds of Prey, Berlin, Germany and London, U.K. Gurr, E. 1962. Staining animal tissues: practical and the- oretical. Leonard Hill, London, U.K. Hale, L.J. 1953. Biological laboratory data. Methuen, London, U.K. Heredia, R., J.A. Donazar and O. Ceballow. 1990. Ingestion of eagle owl Bubo bubo pellets by lammergeiers Gypaetus barbatus. Ibis 132:127. Herpol, C. 1967. Etude de Pactivite proteolytique des divers organes du systemes digestif de quelques especes d’oiseaux en rapport avec leur regime alimentaire. Z. Vgl. Physiol. 57:209-217. Hiraldo, F., M. Delibes and J. Calderon. 1979. El quebrantahuesos Gypaetus barbatus sistematica, taxon- omia, biologia, distribucion y proteccion. Publ. Inst. Nac Conserv. Nat. Monogr. 22. Madrid, Spain. Houston, D.C. 1979. The adaptations of scavengers. Pages 263-286 in A.R.E. Sinclair & M. Norton Griffiths [Eds.], Serengeti; dynamics of an ecosystem. Univ. Chicago Press, Chicago, IL U.S.A. and J.E. Cooper. 1975. The digestive tract of the white-backed griffon vulture and its role in disease trans- mission among wild ungulates. J. Wildl. Dis. 11:306-313 Huxley, J. and E.M. Nicholson. 1963. Lammergeier Gypaetus barbatus breaking bones. Ibis 105:106-107. Jackson, S., D.C. Duffy, and J.F.G. Jenkins. 1 987. Gas- tric digestion in marine vertebrate predators: in vitro stan- dards. Fund. Ecol. 1:287-291. Kruuk, H. 1972. The spotted hyaena. Univ. Chicago Press, Chicago, IL U.S.A. Robbins, C.T. 1983. Wildlife feeding and nutrition. Ac- ademic Press, New York, NY U.S.A. Scott, M.L., M.C. Nesheim, and R.J. Young. 1982. The nutrition of the chicken. M.l. Scott & Associates, Ithaca, NY U.S.A. Withers, P.C. 1992. Comparative animal physiology. Saunders, Fort Worth, TX U.S.A. Received 30 July 1993; accepted 6 January 1994 J Raptor Res. 28(2):79-83 © 1994 The Raptor Research Foundation, Inc. BEHAVIOR OF COLONIAL COMMON KESTRELS (. Falco tinnunculus ) DURING THE POST-FLEDGING DEPENDENCE PERIOD IN SOUTHWESTERN SPAIN Javier Bustamante Estacion Biologica de Donana, CSIC, Pabellon del Peru , Avda. Marta Luisa s/n, 41013 Sevilla, Spain Abstract. — Common kestrel ( Falco tinnunculus) chicks from a small breeding colony in southwestern Spain fledged an average of 31 d after hatching and remained at the colony, depending on their parents for food, an average of 16 more days. Fledglings perched close to and socialized with their siblings and unrelated fledglings. Fledglings started to use hovering flights a mean of 9.7 d after fledging. Social play, in the form of chases among fledglings, manipulative play with objects, and the capture of insects by the fledglings were observed before fledglings became independent. Key WORDS: fledging; post-fledging dependence period; play; common kestrel; Falco tinnunculus. Comportamiento del cernicalo vulgar ( Falco tinnunculus ) durante el periodo de emancipation en suroeste de Espana Resumen. — En una pequena colonia de cernicalos vulgares {Falco tinnunculus) en el suroeste de Espana, los polios volaron por primera vez una media de 31 dias despues de la eclosion y permanecieron en la colonia una media de 16 dias mas dependiendo de sus padres. Los jovenes tenian un comportamiento social y se posaban junto a sus hermanos y junto a otros jovenes no emparentados. Los jovenes empezaron a cernirse una media de 9.7 dias despues del primer vuelo. Antes de que los jovenes se independizaran se observaron juegos sociales, bajo la forma de persecuciones entre jovenes, juegos de manipulation de objetos y capturas de insectos. [Traduction Autor] The post-fledging dependence period, defined as the period after the first flight during which young birds continue to depend on their parents for food, has received little attention in raptors. The common kestrel {Falco tinnunculus ) is a well-studied species, and its breeding cycle has been relatively well doc- umented (e.g., Newton 1979, Cramp and Simmons 1980, Cade 1982, Village 1990). However, infor- mation about the duration of the post-fledging de- pendence period and behavior of parents and off- spring during this period is scarce. From casual observations, it is estimated that the young remain near the nest for at least 2-3 wk after fledging (Vil- lage 1990). Tinbergen (1940) provided some obser- vations of the behavior of a wild brood during 20- 25 d of post-fledging dependency. Komen and Myer (1989) described the behavior of nine fledglings held in captivity and released at the time of fledging. These fledglings continued to return for food for an average of 42 d. Komen and Myer (1989) estimated the duration of the post-fledging dependence period of a wild brood of three fledglings to be 37 d. This study gives the estimated duration of post- fledging dependency in common kestrels from a small colony in southwestern Spain, and describes the adult and fledgling behavior during this part of the breed- ing cycle. Study Area and Methods Observations were carried out in the spring and summer of 1989 in a mixed colony of common kestrel and lesser kestrel {Falco naumanni) in an abandoned sandstone quar- ry (37°29'N, 5°38'W) near Carmona, Seville, southwestern Spain. Common kestrels (12-15 pairs started breeding) nested on ledges and in holes of a cliff approximately 20 m high and 200 m long. The minimum distance between neighboring nests was 6 m. The area surrounding the quarry was a flat and open agricultural plain with small fields of cereals (wheat and barley), sunflowers, olive and fruit trees. We banded 22 common kestrel chicks from five nests when they were 19-30 d old with laminated plastic bands with an alphanumeric code that could be read with a telescope. Brood sizes at the time of banding were three, four, four, five, and five chicks. One of the chicks had already fledged when banded and it was not known from which nest it came. At least one other nest produced two 79 80 Javier Bustamante Vol. 28, No. 2 fledglings that were not banded. Four chicks, each from a different nest, were equipped with radiotransmitters attached with a backpack harness (Beske 1978; weight with harness 9 g. 4% of body mass). The eight chicks without radiotransmitters from both of the nests with five chicks, were marked with a 2.5 cm strip of colored SAF- LAG pierced on the upper part of the wing (Young and Kochert 1987), which allowed individual recognition also in flight. Adult common kestrels were not marked, and they could not be identified once they started feeding the fledglings out of the nest. Observations were performed by one observer from a variable point 130 m from the cliff, with 10 x binoculars and a 60-80 x field scope. The whole colony was observed for approximately 4-hr periods, between 0630-2000 GMT, every 1-3 d (47 hr in 13 d). Observations started 17 June, when some of the chicks were starting to fledge, and ended 14 July when all but five banded kestrels (one radiotagged) had left the vicinity of the colony. Fledglings still at the colony on the last observation day spent most of the time away from the cliff and were observed infrequently. The quarry was again visited on 18, 22, and 27 July, for 30 min each day, to check if any fledglings were present or any radiotransmitter signal could be detected. No fledg- lings were seen and no radiotransmitter signal was detected after 18 July. Behavioral observations were dictated on a tape. Every 30 min the perching location of every fledgling on the cliff was recorded. Distances between each fledgling and its nest, nearest sibling, and nearest unrelated fledgling were estimated later on an enlarged photo of the cliff with 0.5 m precision. I considered that fledglings were perched in groups when distance between fledglings was <2 m. The age of 1 5 of the chicks at the time of banding was estimated from the equation: Age (d) = 8.14 + 0.17 x 8th primary length (mm), obtained from growth data of common kestrel chicks in central Spain (Veiga 1985). Fledging age was the first day a chick was seen flying or on a perch it had to reach flying. I considered the date of independence of a fledgling to be the mean between the last day the fledgling was seen at the colony and the first day the fledgling was no longer seen. Radio-tagged fledg- lings showed that not all fledglings present at the colony were observed on every 4-hr period, indicating that the duration of the post-fledging dependence period of fledg- lings without radiotransmitters could have been under- estimated. Fledglings with radiotransmitters, even if they were not seen, were considered still dependent if their signals could be located at the colony. None of the fledg- lings with radiotransmitters were observed or located by telemetry after leaving the colony cliff for the first time. I believe no radiotransmitters were lost, but some fledg- lings could have died before independence. I found remains of at least one unidentified fledgling eaten by a predator. Results Common kestrel chicks fledged at a mean age of 31 d (range 27-36 d, SD = 2.8, N = 15). There were no significant differences in fledging age be- tween fledglings with radiotransmitters (x = 33 d, N = 4) and those without ( x = 30.5 d; t = 1.46, df = 13, P = 0.17). Fledglings became independent on average 16 d after fledging (range 8-25 d, SD = 5.2, N = 20), and there were no differences between fledglings with radiotransmitters (x = 15.5 d, N '= 5) and those without (x = 16.1 d; / = —0.21, P = 0.83). Neither fledging date (F = 1.02, df = 1,18, P = 0.31), fledging age ( F = 0.085, df = 1,13, P = 0.78), brood-size (F = 0.446, df = 2,17, P = 0.65) nor order within the brood (F = 1.683, df = 4,9, P = 0.24) had any significant effect on the duration of the post-fledging dependence period. Fledglings of the same brood did not become independent on the same day and the maximum difference in indepen- dence dates within a brood averaged 11.6 d (SD = 5.6, N = 5). Two banded chicks without radiotrans- mitters were never observed at the colony after fledg- ing and probably died before independence (9% mor- tality, N = 22). Fledgling Behavior. Common kestrel fledglings returned infrequently to their nests after fledging (only 4% of the observations were at < 2 m from the nest). They perched on the ledges and on top of the cliff, alone (54% of observations) or in groups (46% of observations, N - 307). Groups ranged from 2- 5 fledglings ( x = 3.6 fledglings, SD = 1.4, N = 76) and most of them, 84%, included fledglings from different broods. Of 20 marked fledglings observed, 19 were seen at least once in a group with unrelated fledglings. Fledglings perched closer to unrelated fledglings than to their nest (paired /-test for median distances, t = 2.11, df = 14, P = 0.049), or to their siblings (t = 2, df = 14, P = 0.06), although the last difference was not significant. Median distance to the nearest sibling was not significantly different from median distance to the nest ( t = —0.99, df - 18, P = 0.34; Fig. 1). Fledglings frequently begged for food, perched or in flight, from any adult kestrel coming to the colony. On at least six instances they begged for food un- successfully from lesser kestrels. I also observed four juveniles eating insects 4-13 d after fledging. Al- though the capture was not witnessed, adults were never observed delivering insects to the fledglings. I observed four fledglings engaged in play behav- ior with objects 16, 16, and 18 d after fledging. The age of the fourth bird was unknown. On separate occasions two fledglings flew low over the cliff per- forming prey catching and plucking movements on small roots hanging from the cliff. A similar behavior June 1994 Common Kestrel Post-fledging 81 was performed on a small twig, a stone, and an airborne feather in quick succession by another fledgling. The fourth fledgling performed prey plucking movements on an object carried with its talons. The most frequent play behavior were fast flight chases by two or more fledglings. Fledglings chased each other and dove toward other fledglings perched on the cliffs making them fly. The roles between chaser and chased changed frequently, sug- gesting some kind of social play. Chases among fledg- lings — from the same and different broods — were observed on 15 occasions, 5-13 d after fledging. Beaking, a behavior in which one individual nib- bles at the beak and lore area of another (Sherrod 1983), was observed in one instance between two fledglings from different broods. Fledglings were ob- served hovering for the first time a mean of 9.7 d after fledging (SD = 6.5, N = 10). Adult Behavior. Adult common kestrels were only seen at the colony when delivering prey to the fledg- lings. Both male and female adults fed the fledglings during the post-fledging dependence period. Of 22 prey deliveries in which the sex of the adult was recorded, nine were performed by males and 13 by females. Twice a male was seen transferring the prey to the female before she fed the fledglings. No aerial prey transfers to fledglings were observed, and all prey transfers took place on cliff perches or on the ground. After all chicks had fledged, 85.3% of the prey transfers took place on perches different from the nest (N = 34). All prey delivered were birds and small mammals. The average prey delivery rate by adult common kestrels at the colony was 0.9 prey/ hr. Correcting for the number of fledglings present, each fledgling received an average of 1.1 prey/d. After young fledged, adults frequently transferred prey to groups of fledglings from more than one nest. Adults did not seem to select the fledgling in the group to which they transferred the prey. As adults were not marked, it was not clear if adults were feeding only their offspring or occasionally feeding other fledglings. Aggression. I never observed aggressive behavior among common kestrel fledglings. Most of the ag- gressive behavior observed was allospecific. A lesser kestrel adult female took 0.5 hr to expel a common kestrel fledgling from her nest that had accidentally landed there. An adult common kestrel attacked a lesser kestrel female who had previously attacked a common kestrel fledgling. An adult male common kestrel dove four times toward a fledgling who was <2 17 37 57 77 97 117 137 157 177 197 217 Distance to nest (m) OB . O0 77 97 117 137 157 177 197 217 > 252 (c) 17 37 57 Distance to sibling (m) 40% r W CO 3 30% H5 c 0 20 % N - 299 4 3 10 % cd o 3 0 % JB < 2 17 37 57 77 97 117 137 167 177 197 217 > 260 Distance to unrelated fledgling (m) Figure 1. Frequency distribution of the observations of perched common kestrel fledglings in relation to distance to their nest (a), distance to the nearest sibling (b), and distance to the nearest unrelated fledgling (c), during the post-fledging dependence period. Data on all fledglings were pooled. The values are given in 5 m intervals, except the first interval, <2 m, and the last interval, >252 m. Arrows indicate the medians. Distances were measured every 30 min with 0.5 m precision. 82 Javier Bustamante Vol. 28, No. 2 begging in a fluttering flight after him and forced the fledgling to perch on the cliff’. Discussion Common kestrel chicks fledged in southwestern Spain at an average age of 31 d, similar to that reported by other authors in Europe (27-32 d; Cramp and Simmons 1980) and in Africa (34 d; Steyn 1982). The average duration of the post-fledging depen- dence period I observed, 16 d, was shorter than those reported both in Europe (20-25 d, Tinbergen 1940; 1 mo, Cramp and Simmons 1980; 30 d, Masman 1980 in Komen and Myer 1989), and in Africa (1 mo, Steyn 1982; 41.5 d, Komen and Myer 1989). I do not think that the kestrel family groups I observed continued together somewhere else after leaving the colony. Siblings would have disappeared on the same day, but they did not. It is still possible that I underestimated the post-fledging dependence period of the fledglings without radiotransmitters, because on average only 66% of the dependent fledg- lings were observed on each 4-hr period. Also, the death of some fledglings before independence could have remained unnoticed, but the mean duration of the post-fledging period of the five fledglings with radiotransmitters was not significantly different from that of the fledglings without. This supports the idea that I did not underestimate the duration of the post- fledging dependence period. Some species of raptors have shorter post-fledging dependence periods in populations breeding at high- er latitudes (Bustamante 1993, unpubl. data). The high variability among individuals in the duration of the post-fledging dependence period, small sample sizes in all studies, and this latitudinal effect prob- ably explain the high variability among estimates from different authors. Also, the short post-fledging dependence period I observed could be related to the conditions (possibly, high abundance of prey) that permit that common kestrels nest colonially in this area. My observations also confirm that the nest is rare- ly used by common kestrels after fledging (Tinber- gen 1940), and that fledglings play with objects dur- ing the post-fledging period (Komen and Myer 1989), possibly as a way to develop and train their hunting skills. Also, the first prey caught were insects as observed by Komen and Myer (1989), and this has been observed in many other species of raptors (e.g., Baker-Gabb 1978, Mueller et al. 1981, Sherrod 1983, Oliphant and Tessaro 1985, Varland et al. 1991, Lawrence and Gay 1991, Varland and Loughin 1992). Although Newton (1979) contended that most fledgling raptors perch apart from their siblings, common kestrel fledglings perched close to each oth- er, were never aggressive toward other fledglings, and engaged in social behavior (beaking) and social play (chases) with their siblings and with other fledg- lings. Siblings of other species of falcons also socialize during the post-fledging dependence period. Allo- preening and beaking have also been observed (Sher- rod 1983, Lett and Bird 1987, Varland et al. 1991, Varland and Loughin 1992). Fledglings from different broods intermingled during the post-fledging dependence period because nests were close and fledglings did not avoid perching close to fledglings from other broods. Groups of fledglings were not caused by fledglings trying to stay close to their own nests, where it could be ex- pected that parents came with prey, or by fledglings trying to maintain a close group with their siblings at some point on the cliff, where they could be easily found and fed by their parents. Adults provided prey to fledglings that were usu- ally in groups and did not seem to be able to select who finally obtained the prey. They never behaved aggressively toward fledglings and never chased fledglings from other broods away from the vicinity of their nests, in contrast to what has been observed in the colonial lesser kestrel (Bustamante and Negro in press). Also fledglings were not selective to whom they directed their begging. All this suggests that adults could have accidentally provided food to fledg- lings that were not their own. Even lesser kestrels, which seem to be able to recognize their offspring after fledging and behave aggressively toward un- related juveniles near their nests, have been recorded accidentally feeding fledglings from other nests (Bus- tamante and Negro in press) and adopting unrelated nestlings (Donazar et al. 1991, J.L. Telia pers. comm.). The capacity to recognize its own offspring after fledging could be less developed in the common kes- trel than in the lesser kestrel. The common kestrel is generally territorial and a solitary nester. Breeding colonies, like the one I studied, are uncommon (Cramp and Simmons 1980, Village 1990). It is probably not necessary for common kestrels to dis- criminate between their offspring and unrelated ju- veniles during the post-fledging dependence period under normal circumstances, and hence the lack of June 1994 Common Kestrel Post-fledging 83 adult discrimination of offspring and lack of ag- gression toward unrelated fledglings I observed in this colony. Acknowledgments I am grateful to Dr. F. Hiraldo for his guidance, to J. Komen, D.M. Bird, D.E. Varland, and J.J. Negro, for helpful comments on a previous draft, and to S. Nadeau for corrections of the English text. This work is part of a doctoral dissertation at the Universidad Autonoma de Ma- drid. Funds were provided by project PB87-0405 DGI- CYT, and fellowships from the MEC and CSIC. Literature Cited Baker-Gabb, D.J. 1978. Aspects of the biology of the Australasian harrier Circus aeruginous approximans, M.S. thesis, Massey Univ., Palmerstron, New Zealand. Beske, A.E. 1978. Harrier radio-tagging techniques and local and migratory movements of radio-tagged juvenile harriers. M.S. thesis, Univ. Wisconsin, Stevens Point, WI U.S.A. Bustamante, J. 1993. The post-fledging dependence period of the black-shouldered kite ( Elanus caeruleus ). J. Raptor Res. 27:185-190. AND JJ. Negro. In press. The post-fledging dependence period of the lesser kestrel Falco naumanni. J. Raptor Res. Cade, T.J. 1982. The falcons of the world. Collins, London, U.K. Cramp, S. and K.E.L. Simmons. 1980. Handbook of the birds of Europe the Middle East and North Africa. Vol II. Oxford Univ. Press, Oxford, U.K. Donazar, J.A., J. J. Negro and F. Hiraldo. 1991. A note on the adoption of alien young by lesser kestrels Falco naumanni. Ardea 79:443-444. Komen, J. AND E. Myer. 1989. Observations on post- fledging dependence of kestrels ( Falco tinnunculus rup- icolus) in an urban environment. J. Raptor Res. 23:94- 98. Lawrence, S.B. and C.G. Gay. 1991. Behaviour of fledgling New Zealand falcons ( Falco novaeseelandiae) . Notornis 38:173-182. Lett, D.W. and D.M. Bird. 1987. Postfledging be- havior of American kestrels in southwestern Quebec Wilson Bull. 99:77-82. Mueller, H.C., N.S. Mueller and P.G. Parker. 1981. Observation of a brood of sharp-shined hawks in On- tario, with comments on the functions of sexual di- morphism. Wilson Bull. 93:85-92. Newton, I. 1979. Population ecology of raptors. T. & A.D. Poyser, Berkhamsted, U.K. Oliphant, L.W. and S.V. Tessaro. 1985. Growth rates and food consumption of hand-raised merlins. J. Raptor Res. 19:79-84. Sherrod, S.K. 1983. Behavior of fledgling peregrines The Peregrine Fund, Inc., Ithaca, NY U.S.A. Steyn, P. 1982. Birds of prey of southern Africa. David Philip, Cape Town, South Africa. Tinbergen, L. 1940. Beobachtungen uber die Arbeit- steilung des Turmfalken ( Falco tinnunculus ) wahrend der Fortpflanzungszeit. Ardea 29:63-98. Varland, D.E. and T.M. Loughin. 1992. Social hunt- ing in broods of 2 and 5 American kestrels after fledg- ing. J. Raptor Res. 26:74-80. , E.E. Klaas and T.M. Loughin. 1991. De- velopment of foraging behavior in the American kestrel. J. Raptor Res. 25:9-17. Veiga, J.P. 1985. Crecimiento de los polios de Falco tinnunculus en el centro de Espana, aspectos energeticos y ecologicos. Ardeola 32:187-201. Village, A. 1990. The kestrel. T. & A.D. Poyser, Lon- don, U.K. Young, L.S. and M.N. Kochert. 1987. Marking tech- niques. Pages 125-156 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline and D.M. Bird, [IEds.], Raptor management techniques manual. Nat. Wildl. Fed., Washington, DC U.S.A. Received 20 September 1993; accepted 8 March 1994 J. Raptor Res. 28(2):84-92 © 1994 The Raptor Research Foundation, Inc. GOSHAWK DIET IN A MEDITERRANEAN AREA OF NORTHEASTERN SPAIN SANTI MAftOSA Departament de Biologia Animal, Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal, 645, 08028 Barcelona, Catalonia, Spain Abstract. — The diet of the goshawk ( Accipiter gentilis) is described throughout the year in La Segarra, a Mediterranean area of Catalonia (NE Spain) where one of the densest goshawk populations recorded in Europe was found. Red-legged partridge ( Alectoris rufa), European rabbit ( Oryctolagus cuniculus ), wood pigeon {Columba palumbus), jay {Garrulus glandarius), magpie {Pica pica), thrushes {Turdus spp.) and red squirrel {Sciurus vulgaris) formed the bulk of the goshawk diet. Nestling and fledgling birds were very important during the breeding period, but the rabbit was the main source of biomass for most of the year, especially in winter. In the breeding season, pairs in heavily forested areas captured more squirrels and less rabbits than those in lightly forested areas. Changes in the diet involving a decrease in rabbit consumption and an increase in the proportion of red-legged partridge were detected following a rabbit population crash caused by the viral haemorrhagic disease. Key WORDS: Accipiter gentilis; goshawk; Spain ; Mediterranean; food habits. Dieta del azor en una zona mediterranea del noreste de Espana Resumen. — Se describe la dieta del azor {Accipiter gentilis) a lo largo del ano en la Segarra, una zona mediterranea de Cataluna (NE de Espana) donde se encontro una de las poblaciones mas densas de azor hasta ahora registradas en Europa. La perdiz roja {Alectoris rufa), el conejo {Oryctolagus cuniculus), la paloma torcaz {Columba palumbus), el arrendajo {Garrulus glandarius), la urraca {Pica pica), los zorzales y mirlos {Turdus spp.) y la ardilla {Sciurus vulgaris) fueron las presas principales. Las aves jovenes constituyeron una buena parte de las presas del azor durante el periodo reproducer, pero el conejo fue la principal fuente de biomasa durante la mayor parte del ano, especialmente en invierno. Las parejas de las zonas mas forestadas capturaron mas ardillas y menos conejos que las parejas de las zonas abiertas. La drastica reduction de las poblaciones de conejo como consecuencia de la pneumonia hemorragica virica, condujo a una diminution de su consumo y a un aumento del de perdiz. The food habits of the goshawk {Accipiter gentilis) have been described in northern and central Europe (e.g., Sulkava 1964, Opdam et al. 1977, Wikman and Tarsa 1980, Marquis and Newton 1982, Gosz- czynski and Pilatowski 1986, Widen 1987), but not in the Mediterranean region. Although there are some some general descriptions of goshawk food habits from several regions of Spain (Morillo and Lalanda 1972, Veiga 1982, Garrigues et al. 1990, Manosa et al. 1990), these are limited to the breeding season and a detailed study on this subject in a Mediter- ranean area is still lacking. The objectives of this paper are (1) to describe the diet of a goshawk pop- ulation in a Mediterranean area of Catalonia, (2) to analyze diet changes throughout the year, and (3) to study diet variation in relation to changes in prey availability between habitat types and years. Study Area and Goshawk Population The study area was within the universal transverse mercator squares 31TCG50, 31TCG51, 31TCG60, 31TCG61, and 31TCF59 in La Segarra County in the northeastern portion of the Iberian peninsula. The relief of the area is tabular, altitude lies between 500-800 m, and the climate is a transition between continental Med- iterranean and submediterranean. Natural vegetation communities cover only 30% of the area, the remainder being occupied mainly by cereal crops. Depending on the exposure and soil characteristics, different types of sec- ondary pine forest {Pinus nigra, P. sylvestris, and P. hale- pensis) or oak forest {Quercus faginea and Q. ilex) cover the areas not suitable for agriculture. The southern and eastern parts of the study area are more forested, while the northern and western parts are mostly devoted to crops Nest sites were classified as heavily forested if more than 50% of the area within a 1-km radius of the nest was covered by wood or lightly forested if that percentage was less than 50%. From 1987-89 the maximum number of goshawk pairs nesting simultaneously in a well-searched 176 km 2 area was 22, but the estimated total population from the pat- terns of use and distribution of nest sites was 26 pairs, giving a maximum density of 1 pair/6.8 km 2 , one of the highest in Europe (see Kalchreuter 1981, Thissen et al 1981, Bijlsma 1991). The mean nearest-neighbor distance between the geometric mean locations of the nesting sites 84 June 1994 Goshawk Diet in La Segarra 85 Table 1. Percentage of prey obtained when analyzing goshawk diet by different methods (see Methods section) during the nestling period at two nests in 1989. (N = number of prey individuals.) Obser- vations Nest From Hide Remains N = 74 N = 82 Pellets N = 29 Mixed N = 102 Reptilia 0.0 1.2 0.0 1.0 Phasianidae 21.6 25.6 6.9 21.6 Columbidae 18.9 15.8 17.2 17.6 Estrigiformes 0.0 2.4 0.0 2.0 Picidae 1.3 1.2 17.2 4.9 Turdidae 17.6 11.0 0.0 8.8 Corvidae 17.6 15.8 20.7 14.7 Sturnidae 0.0 3.7 6.9 4.9 Other Passer. 9.5 3.7 6.9 4.9 Other birds 4.0 2.4 3.4 2.9 Leporidae 4.0 14.6 10.3 11.8 Sciuridae 5.4 2.4 10.3 4.9 of every pair was 1535 m (SD • 455 m, range = 825- 2800 m, N = 26). Pair dispersion, measured by the G statistic (Brown and Rothery 1978), showed a value of 0 844, indicating a regular distribution of pairs (Tjernberg 1985). The average laying date during the 1986-90 period, estimated by inspection of the nests every two days from mid-March until the first egg was laid, was 5 April ± 7.96 d (N = 73, range = 21 March-29 April). Methods Prey Identification and Classification. Prey remains, bones, fur, nails and feathers found on nests, plucking sites and pellets were identified by macroscopic comparison with skeleton and skin reference collections. Arthropods were only considered as possible goshawk prey when found on the nests, but not in pellets, and were identified to taxonomic order. I tried to identify all vertebrate remains to species. When possible, the sex and age of prey was recorded. For nidicolous birds, I considered three age cat- egories: nestlings, fledglings, and adults. Young red-legged partridges ( Alectoris rufa ) were considered nestlings if their size was less than three-fourths the adult size and fledg- lings if larger. Assigning avian prey to age class was based on size, plumage, feather characteristics, and degree of ossification. The adult category might have included some young birds no longer distinguishable from adults. Eu- ropean rabbits ( Oryctolagus cuniculus ) and red squirrels (Sciurus vulgaris) were classified as young or adult ac- cording to size or degree of ossification. When a prey could not be classified to age, it was not considered in the age selection analysis. Prey found complete or nearly complete were weighed with a spring balance. Otherwise, the live biomass was estimated using bibliographic information (Geroudet 1946-57) or data from the study area according to the age and, if necessary, sex of the prey. No wastage was considered, therefore the biomass figures in this paper refer to captured biomass. Quantification of Diet During the Breeding Season. Between 1985-89, I studied nestling diet (May- July) by repeated visits to nest sites to collect all prey remains (feathers, fur, and bones) and pellets at the nests and known plucking sites. Recently delivered or partially eaten prey were recorded as prey remains, but not collected. In 1985 and 1986 nest visits were sporadic. From 1987-89, all nests containing chicks were visited every 4 d from hatching to a few days after fledging. To minimize dis- turbance, sampling was reduced during the laying and incubation periods (April). The identity of the prey remains and the minimum number of prey individuals necessary to explain their pres- ence was established for each visit, according to the number of bones or flight feathers encountered. All pellets from a visit were pooled into a single sample and analyzed to- gether. The presence of different prey types in these sam- ples was recorded, but no attempt was made to quantify the number of individuals represented. To avoid counting the same prey individual twice in the same visit (i.e., in remains and in pellets), prey found in pellets were com- puted only if they had not been found as remains in the same visit. I avoided counting the same prey individual in successive visits by comparing prey from successive col- lections: prey found in pellets or as an old remain were not considered if they had been detected in the previous visit as a fresh or partially eaten prey. In both cases, however, all methods of detection were recorded. To assess the reliability of the method noted above, 322.5 hours were spent observing in hides installed 15-20 m away from two nests in 1989. During the nestling period, observation started at 1200 FI, lasted until 1900 H and was continued the following day from 0500-1200 H. The process was alternated between the two nests until the young fledged. Only prey observed being delivered to the nest were recorded and identified with the aid of a 20- 60 x telescope. Sixty-seven out of 74 (90.5%) prey were identified to the species. The remaining seven prey were either unidentified small passerines or nestling birds. The results of these observations, which were assumed to be an unbiased sample of the nestling diet, were compared with the results obtained at the same nests and year by pellet counts alone, prey remains alone, and the combi- nation of both as described above. The results given by none of these methods were significantly different from those obtained by direct observation, but the combined method gave the nearest approximation (x 2 = 7.50, df = 6, P = 0.277; x 2 = 11-47, df = 6, P = 0.075; x 2 = 6.09, df = 6, P = 0.412, respectively; Table 1). However, it still overestimated the percentage of rabbits in the diet and underestimated the proportion of thrushes ( Turdus sp.) and other small birds (Table 1). Quantification of Diet Outside the Breeding Season. Diet outside the breeding season (August-March) was studied from 1986-88 by looking for prey remains at plucking sites (Opdam et al. 1977, Ziesemer 1983). I tried to standardize the scanning pattern over different months and to avoid finding prey of common buzzards ( Buteo buteo) or sparrowhawks ( Accipiter nisus ) by scanning only goshawk nesting areas. Two monthly inspections were 86 Santi Manosa Vol. 28, No. 2 Table 2. Prey items of goshawk in La Segarra during 1987-89. Weight in grams. Species with N < 10 are grouped and listed underneath. N (%) Total Weight (%) Arthropods 3 8 (0.40) 17 (0.00) Reptiles 21 (1.05) 2906 (0.51) Lacerta lepida 18 (0.90) 2728 (0.48) Other reptiles b 3 (0.15) 178 (0.03) Birds 1519 (75.85) 326 502 (56.90) Alectoris rufa 362 (18.07) 140 845 (24.54) Coturnix coturnix 21 (1.05) 2100 (0.37) Columba palumbus 196 (9.79) 67 169 (11.70) Columba livia 13 (0.65) 3950 (0.69) Unidentified pigeon 39 (1.95) 11 470 (2.00) Streptopelia turtur 28 (1.40) 3920 (0.68) Otus scops 27 (1.35) 2160 (0.38) Athene noctua 18 (0.90) 3060 (0.53) Picus viridis 31 (1.55) 6160 (1.07) Picoides major 15 (0.75) 1200 (0.21) Turdus merula 134 (6.69) 10 989 (1.91) Turdus viscivorus 38 (1.90) 4232 (0.74) Unidentified thrush 25 (1.25) 1887 (0.33) Garrulus glandarius 184 (9.19) 28 197 (4.91) Pica pica 54 (2.70) 9345 (1.63) Sturnus vulgaris 79 (3.94) 6516 (1.14) Fringilla coelebs 23 (1.15) 529 (0.09) Unidentified passerine 87 (4.34) 3504 (0.61) Unidentified bird 36 (1.80) 3190 (0.56) Other birds c 109 (5.44) 16 079 (2.80) Mammals 455 (22.72) 244 486 (42.60) Oryctolagus cuniculus 333 (16.63) 220 526 (38.43) Sciurus vulgaris 86 (4.29) 21 330 (3.72) Other mammals' 1 36 (1.79) 2630 (0.46) Total 2003 573 858 a Arthropods: Scolopendra sp., Orthopterans, Coleopterans. b Other reptiles: Anguis fragihs, Psammodromus algirus, unidentified reptiles. c Other birds: Accipiter gentilis (nestlings from the same nest), Accipiter msus, Phasianus colchicus, Scolopax rusticola, Gallinula chloropus, Columba oenas, Clamator glandarius, Cuculus canorus, Tyto alba, Strix aluco, unidentified owls, Caprimulgus europaeus, Capnmulgus sp , Merops apiaster, JJpupa epops, Galerida sp., Lullula arborea, unidentified lark, Luscinia megarhynchos, Turdus philomelos, Sylvia sp., Parus caeruleus, Parus major, Certhia brachydactila, Onolus onolus, Lanius excubitor, Corvus corone, unidentified crow, Passer domesticus , Serinus sennus, Carduelis carduelis, unidentified Fringillidae, Miliaria calandra. d Other mammals: Crocidura russula, Eliomys quercinus, Microtus duodecimcostatus; Apodemus sylvaticus, Mus spretus, Rattus noruegicus. Rattus rattus, unidentified mice, unidentified rodents. made at 10 previously selected sites, but fresh remains found in sporadic visits to other nesting areas were also recorded. I recorded all fresh kills, bones, fur or feathers found, and established the minimum number of prey nec- essary to explain their presence according to the number of bones and flight feathers found. Because of the char- acteristics of the autumn and winter common buzzard diet in Catalonia, consisting mainly of small mammals and invertebrates (Manosa and Cordero 1992), little confusion should have arisen with that species. However, some spar- rowhawk prey could have been confused with goshawk prey. They can be distinguished by the extent of the feather plucking (larger and usually scattered in the goshawk) and the presence of legs or bill remains left by the spar- rowhawk (Opdam 1975). When the predator identity could not be established with confidence, the prey was not con- sidered. Prey Availability Counts. European rabbit counts were carried out at dusk 1-5 times each month. A 19.7-km route (A) across the whole study area was covered with a June 1994 Goshawk Diet in La Segarra 87 vehicle, at a maximum speed of 40 km/h, from July 1987 to December 1989. All rabbits seen on the route were recorded and abundance was expressed as number of rab- bits seen per kilometer. Another 25.4-km route (B), cov- ering only the south of the study area, had been traversed in the same way between October 1986-October 1988. The results of the counts during the period when both transects were conducted simultaneously (July 1987-Oc- tober 1988) were used to obtain a conversion index be- tween them, which was used to obtain a estimate of rabbit abundance for the whole area from October 1986-June 1987 from counts conducted in route B. To obtain rough estimates of red-legged partridge abundance, I conducted car counts in April and May during the morning or before dusk, at a maximum speed of 20 km/h. A total of 57 km in 10 counts of different length and location within the study area were done in 1987 and 102 km in 19 different counts in 1989. Results were expressed as number of par- tridges seen per kilometer. Data Analysis and Statistics. Chi-square tests were used to compare diet composition by numbers of prey at different times of the year, and one-way analysis of vari- ance (ANQVA) combined with the Scheffe’s test (Zar 1984) were used to compare average prey weights. Vari- ations in the diet of the 1987-89 breeding seasons were analyzed by habitats (heavily forested versus lightly for- ested) and years. Prey were sorted according to the dif- ferent nest sites and years. Samples containing less than 20 prey were discarded (to reduce bias caused by differ- ential sampling), leaving 34 diet samples from 18 different nest sites, totaling 1590 prey items. The coefficient of variation between samples in the percentage of each prey type in each sample was calculated to determine the degree of homogeneity in the consumption of different groups of prey. Chi-square tests for mutual and partial indepen- dence in three-dimensional tables were performed follow- ing Zar (1984). When a two-dimensional chi-square test was globally significant, observed cell frequencies were considered to be significantly different from the expected frequencies when the absolute value of the standardized residual was >Z a/2 . Statistical significance level was set at a = 0.05. Statistical analyses were performed with SPSS (1990). The Shannon- Weaver index (II', log base 2) was used to describe dietary diversity (Margalef 1982). When appropriate, mean ± standard deviation are indicated. Results General Diet Description. Samples for the nest- ling period (May-July) included 27 prey items in 1985-86, 391 prey items from 13 nests in 1987, 871 prey items from 26 nests in 1988 and 452 prey items from 12 nests in 1989. Only 23 prey items were obtained during the laying and incubation periods (April), and 239 prey were determined for the Au- gust-March period. The diet of goshawks in La Segarra included 61 different types of prey (Table 2). Prey weight ranged from only a few grams to more than 1000 g for some adult rabbits. The average weight of prey was 286 ± 235 g ( N = 2003), Arthropods were incidental and in no case did we have evidence that they had been captured by the goshawk (i.e., they could be prey of goshawk prey). Reptiles w r ere only consumed during the nestling period. The diet consisted almost exclusively of endothermic vertebrate prey (98.9%). Red-legged partridge, European rabbit, wood pi- geon (Columba palumbus), jay (Garrulus glandarius), magpie (Pica pica), blackbird ( Turdus merula ), Eu- ropean starling ( Sturnus vulgaris ) and red squirrel formed the 71.3% of goshawks’ captures. In terms of biomass, the rabbit was the basic prey, followed by the red-legged partridge and the wood pigeon, which altogether accounted for 74.7% of the captured biomass. Seasonal Variation. Only 1898 prey individuals could be assigned to a particular month of the year. Frequencies of capture varied significantly by season (x 2 = 144.34, df = 28, P < 0.001; Table 3). Rabbits and passerines accounted for more than 64% of the prey in the January-April period. In May and June passerines and game birds were the main prey, but rabbits, pigeons, and corvids were also important. In July, passerines lost their preponderant position in the diet and game birds made up the largest pro- portion of it, followed by pigeons, corvids and rab- bits. In the August-December period rabbits were again the main prey, followed by pigeons and game birds. In terms of biomass, much less variation oc- curred, the rabbit being the dominant prey through- out the year, especially outside the breeding season. Game birds had a peak contribution in May, pigeons in the July- December period, and corvids in the June-July period. Globally, diet was more diverse and contained smaller prey during the nestling period (May-July, Table 3). ANOVA showed significant differences in the average weight of prey between periods (F 4 1893 ■ 16.63, P < 0.01), being lower in May, June and July than in the January-April and August-De- cember periods (Table 3). Between May and July, nestling and fledgling birds accounted for 37.5% of the 781 birds for which age could be determined, or 18.1% of biomass (185 kg). Extrapolating to all prey, 28.8% of prey and 10.8% of the total biomass cap- tured were young birds. The proportion of immature birds (both nidicolous and precocial) in relation to fully grown ones increased from the beginning of May to the end of July (x 2 = 32.38, df =5 , P < 0.001; Fig. 1) as the nesting season progressed. For nidicolous birds alone, the proportion of nestlings 88 Santi MaAosa Vol. 28, No. 2 Table 3. Percentages by numbers (AO and weight (W) of different prey categories found in the diet of the goshawk at different times of the year in La Segarra. (Only N% were tested for significance.) Jan- April May June July Aug- December N W N W N W N W N W Phasianidae 13.4 16.3 22.4 35.3 17.0 24.6 21.5 17.4 20.3 19.6 Columbidae 14.9 14.4 10.5 12.9 12.8 13.6 16.5 18.8 21.9 a 21.1 Corvidae 0.7 a 0.4 9.4 5.3 14.6 a 8.4 16.2 a 10.5 8.6 3.5 Passeriformes 29.1 4.0 28.3 a 7.3 22.7 5.8 12.8 a 3.5 12.5 a 2.1 Other birds 2.2 a 1.1 4.7 a 1.6 9.9 6.5 12. l a 5.8 7.8 3.2 Leporidae 35. l a 60.9 15.0 30.8 14.3 35.3 14.5 40.3 26. 6 a 49.9 Sciuridae 2.2 1.4 5.6 5.0 5.0 4.7 3.4 3.2 0.8 a 0.5 Other prey 2.2 1.3 4.0 1.7 3.7 1.0 3.0 0.2 1.6 0.1 Number of prey 134 446 893 297 128 Total weight (kg) 53.1 122.4 240.7 76.9 50.5 Average weight (g) 396 ± 276 274 ± 207 270 ± 235 259 ± 241 395 ± 256 H' 2.26 2.70 2.83 2.80 2.57 a Significantly different from expected frequency. decreased and that of fledglings increased throughout the breeding season (May 32.8% and 14.3%, N = 119; June 21.3% and 27.1%, N = 314; July 13.6% and 28.8%, N = 66, respectively; x 2 = 14.65, df = 4, P < 0.005). The proportion of nestling corvids decreased from May to July as the proportion of fledglings increased (x 2 = 23.66, df = 4, P < 0.01; Fig. 2). The proportion of young partridges captured increased from May (0%) to July (74.6%, x 2 = APRIL MAY JUNE JULY INCUBATION YOUNG IN NEST FLEDGE Figure 1. Proportion of young birds in relation to all birds (nidicolous and precocial) captured by goshawks in successive 2-wk periods during the breeding season. Num- bers above the bars refer to the sample size used to estimate age composition in each case. The approximate timing of goshawk breeding is shown underneath. 124.80, df = 2, P = 0.01; Fig. 2). Similar but non- significant trends were found for pigeons and star- lings, while thrushes showed a reverse trend (Fig. 2). The proportion of young to adult rabbits in May (100%, N = 38), June (69.6%, N = 79) and July (59.1%, N = 22) showed a significant decrease (x 2 = 17.33, df = 2, P < 0.01). The proportion of young to adult squirrels in May (20%, N = 5), June (13%, N = 8) and July (0%, N = 5) did not show a sig- nificant trend (x 2 = 1.04, df = 2, P ~ 0.594). Year-to-year and Habitat Variation. Significant variation in diet composition occurred between the 34 samples analyzed (x 2 = 392.62, df = 231, P < 0.001). According to the coefficients of variation of the different prey groups, game birds (G.V. = 31.2%), passerines (G.V. = 36.2%) and corvids (C.V. = 43.3%) were the prey more homogeneously repre- sented in the samples, whereas squirrels (G.V. = 89.2%) and other prey (C.V. = 105.8%) were the most unevenly consumed groups. Pigeons (C.V. = 51.1%), rabbits (G.V. = 57.9%) and other birds (G.V. = 74.6%) showed intermediate levels of variation. Year-to-year and habitat differences in prey avail- ability might be partially responsible for this vari- ation. A test for mutual independence of prey com- position, year, and habitat showed dependence of all three variables (x 2 = 132.69, df = 37, P < 0.001). Test for partial independence showed habitat being dependent on year and prey (x 2 = 94.90, df = 23, P < 0.001), year being dependent on prey and hab- itat (x 2 = 70.82, df = 30, P < 0.001) and prey being dependent on habitat and year (x 2 = 121.93, df = June 1994 Goshawk Diet in La Segarra 89 PARTRIDGE PIGEONS STARLING CORVIDS THRUSHES 25 JUNE PARTRIDGE PIGEONS STARLING CORVIDS THRUSHES 25 CD CtZ La-1 0 - 20 55 1 O - O — P AR TRIDGE J U LY 25 1 8 PIGEONS STARLING CORVIDS THRUSHES Figure 2. Percentages of nestlings, fledglings, and adult birds of some relevant groups in the diet of the goshawk in May, June, and July. Numbers above the bars refer to the sample size used to estimate age composition in each case. 35, P < 0.001). In consequence, three two-dimen- sional tables comparing diet between habitats in- dependently for each year, and two two-dimensional tables comparing diet between years independently for each habitat were tested. In all three years, diet differences between heavily forested and lightly for- ested areas were statistically significant (1987, x 2 = 21.53, df = 7, P = 0.003; 1988, x 2 = 39.39, df = 7, P < 0.001; 1989, X 2 = 18.83, df = 7, P = 0.009; MONTH Figure 3. Changes in the index of European rabbit ( Oryctolagus cuniculus ) availability in La Segarra during the period 1986-89. Table 4). When the three years were pooled, dif- ferences between habitats remained significant (x 2 = 66.24, df = 7, P < 0.001). Compared with lightly forested areas, diet in heavily forested areas included significantly less rabbits and more squirrels (Table 4). Habitat differences in the proportion of game birds, pigeons, corvids and passerines were non-sig- nificant, but consistent between years. Although the trends were similar in both habitats, year-to-year variation was significant in the lightly forested area (x 2 = 33.69, df = 14, P = 0.002) but not in the heavily forested area (x 2 = 21.54, df = 14, P = 0.09). A decrease in dietary diversity was noticed in both areas in 1989. After pooling the two habitats, dif- ferences between years remained significant (x 2 = 41.84, df = 14, P < 0.001). Diet in 1987 was char- acterized by a higher proportion of corvids, while diet in 1989 was characterized by a decrease in the proportion of rabbits and an increase in that of game birds (Table 4). The changes detected in 1989 fol- lowed a decline in the availability of rabbits (Fig. 3), whereas partridge availability had remained con- stant throughout the study period (1987: 1.02 par- tridges/km; 1989: 0.94 partridges/km). Discussion The diet of the goshawk in La Segarra showed three main peculiarities when compared to other European areas: (1) presence of reptiles, (2) high proportion of red-legged partridges, and (3) high proportion of rabbits. The first characteristic was also found in all Iberian localities studied (Morillo 90 Santi MaAosa Vol. 28, No. 2 Table 4. Goshawk diet variation in La Segarra according to year and habitat. (L: lightly forested area; H: heavily forested area.) 1987 1988 1989 L H L H L H Phasianidae 13.5 17.8 16.5 19.3 22. 8 a 24.1 Columbidae 11.9 15.5 8.7 14.0 14.6 17.9 Corvidae 22. 7 a 15.5 14.5 10.9 12.2 10.5 Passeriformes 16.7 20.1 20.2 24.6 22.8 30.9 Other birds 7.0 11.5 11.2 9.7 9.1 4.3 Leporidae 21. l b 9.8 b 22. 4 b 10.1 b 14.6 a>b 4.9 b Sciuridae 1.6 6.9 2.5 b 7.5 b 2.4 6.2 Other prey 5.4 2.9 4.0 3.9 1.6 1.2 N 185 174 401 414 254 162 H' 2.74 2.84 2.76 2.82 2.69 2.54 a Significantly different from expected frequency when compared with the same habitat in other years. b Significantly different from expected frequency when compared with the other habitat in the same year. and Lalanda 1972, Veiga 1982, Garrigues et al. 1990, Manosa et al. 1990), but only in some Eu- ropean localities (Sladek 1963, Goszczynski and Pi- latoski 1986), and might be correlated with the abun- dance of ocellated lizards ( Lacerta lepida ) in the Mediterranean regions of the Iberian peninsula. Game birds, mostly red-legged partridges, was the group most frequently captured and the least vari- able between samples and seasons, which might be caused by a certain degree of preference or local abundance of that prey. However, even taking into consideration that our methodology may over esti- mate the frequency of rabbits in the diet, in terms of biomass this was the more important prey species for goshawks in La Segarra especially outside the breeding season. Although rabbits have also been reported as an important prey for goshawks in other areas of Europe (Tinbergen 1936, Sladek 1963, Brull 1964, Marquis and Newton 1982), only the Iberian localities studied so far shared this characteristic in a consistent geographic pattern. The different methods used, as well as true sea- sonal trends, might be partially responsible for the differences between breeding and non-breeding sea- son diet, because smaller or less conspicuous prey might be hard to detect when searching for pluckings outside the nesting season (Opdam et al. 1977). Also, seven of the 10 regularly surveyed pairs outside the breeding season were in the lightly forested area, which might have contributed to an overestimate of the proportion of rabbit in the diet of the whole population at this time of the year. However, the seasonal trends detected in dietary diversity and av- erage weight of prey are consistent with those found in other European areas (Opdam et al. 1977, Widen 1987). This suggests that goshawk diet composition in La Segarra was largely determined by the diver- sity and availability of vulnerable prey, which was higher in spring and summer. The lowest proportion of resident and summer birds (Phasianidae, Corvi- dae and other birds) in the diet were reached in the January- April period, and coincided with their low- est population levels. This was not found for pigeons and passerines, in which the autumn and winter populations may be increased by wintering or mi- grant birds. The abundance of young birds could be as well a crucial factor determining the importance of different species in the spring and summer diet, and the goshawk would switch from one to another as they become available: from May- July, the total proportion of pigeons and corvids in the diet in- creased as the proportion of fledgling pigeons and fledgling corvids in the diet increased, whereas the total proportion of passerines decreased as fledgling thrushes (the main passerine group in the diet) de- creased. Also, the increase in the consumption of partridges from June- July paralleled the increase in the proportion of young partridges in the diet. Similar importance of young birds and mammals in the diet of goshawks has been reported in other regions (Schnell 1958, Sulkava 1964, Opdam et al. 1977, Wikman and Tarsa 1980, Reynolds and Meslow 1984). The versatility of feeding by the goshawk was June 1994 Goshawk Diet in La Segarra 91 further emphasized when comparing lightly forested and heavily forested areas. Rabbits and corvids on one hand, and squirrels and pigeons (mainly wood pigeon) on the other, favor farmland and forest hab- itats respectively, and goshawks took advantage of them differentially in each habitat type. However, the proportion in the diet of other prey types (game birds) did not seem to reflect relative abundance in each environment, which might be a consequence of the unit-sum constraint of proportions (Aebischer and Robertson 1993), or of differences in the vul- nerability of these prey between habitats, regardless of their abundance. After the sudden decline on rab- bit availability in La Segarra, probably as a con- sequence of the outcome of the viral haemorrhagic disease (Manosa 1991), goshawks showed a func- tional response involving a reduction of rabbit con- sumption and an increased predation on red-legged partridge. This response, expressed as a proportional change in rabbit consumption, was larger than that observed in golden eagles ( Aquila chrysaetos; Fer- nandez 1993). In the golden eagle (a rabbit specialist in Mediterranean areas), diet diversity increased fol- lowing rabbit population crash. This was less in the case of the goshawk, an essentially bird-eating raptor which seems to prey opportunistically on rabbits. The effect on the partridge population of that in- crease in goshawk predation will depend on the nu- merical response of goshawk after the rabbit pop- ulation crash. Further long-term monitoring of breeding densities, breeding success and diet of gos- hawks and their prey in La Segarra would provide a better understanding of the mechanisms under- laying predator-prey interactions in Mediterranean agricultural landscapes. Acknowledgments I am grateful to Fernando Hiraldo and Xavier Ferrer, who provided guidance throughout this study, to Francesc Uribe, who granted access to skin collections at the Museu de Zoologia de Barcelona, to Jorge Puig for providing the observation tower, and to Joan Real for access to his skin and skeleton reference collections. S. Sulkava, S.J. Petty and an anonymous referee made very useful comments on earlier versions of the paper. Thanks are also due to Man- dy Goddard and Marian Reed for improving the English of the manuscript. The hospitality and help of people living in La Segarra were greatly appreciated. This study was partially financed by a grant from the Comissio Interde- partamental de Recerca i Tecnologia (Generalitat de Ca- talunya), project AR87-122, a FPI-grant from the Min- isterio de Educacion y Ciencia. All nest visits, hide building and nest observations were conducted under permission of the Departament d’Agricultura, Ramaderia i Pesca of the Generalitat de Catalunya. Literature Cited Aebischer, N.J. and P.A. Robertson. 1993. Com- positional analysis of habitat use from animal radio- tracking data. Ecology 74:1313-1325. BljLSMA, R.G. 1991. Trends in European goshawks (. Accipiter gentilis ): an overview. Bird Census News 4. 347. Brown, D. and P. Rothery. 1978. Randomness and local regularity of points in a plane. Biometrika 65. 115-122. Brull, H. 1964. Das Leben Deutscher Greifvogel. 2 Aufl., Fischer. Stuttgart, Germany. Fernandez, C. 1993. Effect of the viral haemorrhagic pneumonia of the wild rabbit on the diet and breeding success of the golden eagle Aquila chrysaetos (L.). Rev, Ecol. Terre Vie 48:323-329. Garrigues, R., R. Martinez and J.A. Morata. 1990 Introduction al estudio de la biologia del azor ( Accipiter gentilis , L., 1758) en Albacete. Al-basit, Rev. Estud Albacetenses 27:123-162. Geroudet, P. 1946-57. La vie des oiseaux. Vol. 1-6 Collection de Poche. Les Beautes de la Nature. De- lachaux and Niestle S.A., Paris, France. Goszczynski, J. and T. Pilatowski. 1986. Diet of common buzzard ( Buteo buteo L.) and goshawk (Ac- cipiter gentilis ) in the nestling period. Ekol. Pol. 34. 655-667. KALCHREUTER, H. 1981. The goshawk (Accipiter gen- tilis) in western Europe. Pages 18-28 in R.E. Kenward and I.M. Lindsay [Eds.], Understanding the goshawk. The International Association for Falconry and Con- servation of Birds of Prey, Oxford, U.K. MaNosa, S. 1991. Incidencia de la pneumonia vmrica del conill sobre la comunitat de rapinyaires segarrencs. El Medi Natural del Valles 3:141-149. and P.J. Cordero. 1992. Seasonal and sexual variation in the diet of the common buzzard in north- eastern Spain. J. Raptor Res. 26:235-238. J. Real and E. Sanchez. 1990. Comparacio de l’ecologia de dues poblacions d’astor Accipiter gentilis a Catalunya: el Valles Moianes i la Segarra. El Medi Natural del Valles 2:204-212. Margalef, R. 1982. Ecologia Ed. Omega, Barcelona, Spain. Marquis, M. and I. Newton. 1982. The goshawk in Britain. Br. Birds 75:243-260. Morillo, C. and J. Lalanda. 1972. Primeros datos sobre la ecologia de las Falconiformes en los Montes de Toledo. Bol. Estac. Cen. Ecol. 2:57-70. Opdam, P. 1975. Inter and interaspecific differentiation with respect to feeding ecology in two sympatric species of the genus Accipiter. Ardea 63:30-55. 92 Santi Manosa Vol. 28, No. 2 , J. Thissen, P. Versghuren and G. Muskens. 1977. Feeding ecology of a population of goshawk (Accipiter gentilis). J. Ornithol. 118:35-51. Reynolds, R.T. and E.C. Meslow. 1984. Partitioning of food and niche characteristics of coexisting Accipiter during breeding. Auk 101:761-779. Schnell, J.H. 1958. Nesting behavior and food habits of goshawks in the Sierra Nevada of California. Condor 60:377-403. Sladek, J. 1963. Beitrag zur Nahrungsokologie des Hii- nerhabitchts. /. Ornithol. 81:44-94. SPSS-Inc. 1990. SPSS reference guide. SPSS Inc., Chi- cago, IL U.S.A. Sulkava, S. 1964. Zur Nahrungsbiologie des Habitchts, Accipiter g. gentilis (L.). Aquilo Ser. Zool. 3:1-103. Thissen, J., G. Muskens and P. Opdam. 1981 . Trends in the Dutch goshawk Accipiter gentilis population and their causes. Pages 28-43 in R.E. Ken ward and I.M. Lindsay [Eds.], Understanding the goshawk. The In- ternational Association for Falconry and Conservation of Birds of Prey, Oxford, U.K. Tinbergen, L. 1936. Gegevens over het voedsel von nederlandse haviken (Accipiter gentilis gallinarum (Brehm)). Ardea 25:195-200. Tjernberg, M. 1985. Spacing of golden eagle Aquila chrysaetos nests in relation to nest site and food avail- ability. Ibis 127:250-255. Veiga, J.P. 1982. Ecologia de las rapaces de un ecosis- tema de montana. Aproximacion a su estructura comu- nitaria. Tesis Doctoral. Univ. Complutense de Madrid, Madrid, Spain. WlDfeN, P. 1987. Goshawk predation during winter, spring and summer in a boreal forest area of central Sweden. Holarct. Ecol. 10:1-7. Wikman, M. and V. Tarsa. 1980. Food habits of the goshawk during the breeding season in southwestern Finland 1969-77. Suom. Riista 28:86-96. Zar, J.H. 1984. Biostatistical analysis. Prentice Hall, Englewood Cliffs, NJ U.S.A. Ziesemer, F. 1983. Untersuchungen zum Einfluss des Habitchts (. Accipiter gentilis ) auf Populationen seinen Beutetiere. Verlag Gunter Hartmann, Kronshagen, Germany. Received 13 November 1992; accepted 24 February 1994 J. Raptor Res. 28(2):93-99 © 1994 The Raptor Research Foundation, Inc. THE ANTIPREDATOR VOCALIZATIONS OF ADULT EASTERN SCREECH-OWLS Thomas McKell Sproat' and Gary Ritchison Department of Biological Sciences, Eastern Kentucky University, Richmond, KY 40475 U.S.A. Abstract. — Adult eastern screech-owls ( Otus asio ) used six different vocalizations (bounce songs, whinny songs, bark calls, bark-screech calls, screech calls, and bill-claps) during trials in which a human ap- proached nest sites or approached and handled nearly-fledged or recently-fledged young. Bounce songs and whinny songs were uttered more frequently during nest defense trials while bark calls, screech calls and bill-claps were uttered more frequently during trials with young owls. We suggest that bounce and whinny songs serve as low-intensity warnings to mates and nestlings. Bark calls consisted of a single, short duration note and appear to serve as warning calls, informing a mate and young of an approaching predator and informing the predator of a willingness to attack. Screech calls were short duration, high volume calls. Most screech calls were given during flights directed at the predator, and may function as a high-intensity warning call. Bark-screech calls appeared intermediate to bark and screech calls, both in structure and function. Most bill-claps were given during flights directed at the predator, often in conjunction with screech calls. We suggest that the combined vocal signal of screech calls and bill-claps represents the highest-intensity vocal warning directed at potential predators by screech-owls. Key Words: eastern screech-owl; vocalizations; antipredator; nest defense; Otus asio. Vocalizaciones antideoredadoras de individuos adultos de Otus asio Resumen. — Individuos adultos de la especie Otus asio usaron seis vocalizaciones diferentes (cantos de bravata, relinchos, llamados de tipo grunidos o ladridos, mezcia de grunidos y chillidos, solo chillidos y golpes de pico) durante ensayos en los que un humano se aproximo a los nidos o aproximo y toma a los polluelos. Tanto el canto de bravata como los relinchos fueron utilizados con mayor frecuencia durante la defensa del nido, mientras que las demas vocalizaciones fueron frecuentemente utilizadas durante el acercamiento a juveniles. Sugerimos que, tanto la como el relincho, sirven como alertas de baja intensidad para la pareja y los volantones, Los llamados de grunidos o ladridos, de una simple nota de corta duracion, parecen servir para alertar, informando tanto a la pareja como a las crias de la aproximacion de un depredador a informando al deprededor de su disposicion de ataque. Los chillidos son de corta duracion, pero son llamados de alto volumen. La mayoria de los chillidos fueron hechos durante vuelos hacia el depredador y podria corresponder a un Uamado de alterta de alta intensidad. Los llamados de chillidos y grunidos parecen estar en una categoria intermedia entre los llamados de grunidos y los de chillidos, tanto en estructura como en la funcion. La mayoria de los golpes de pico fueron realizados durante los vuelos hacia el depredador, a menudo mezclados con llamados de chillidos. Sugerimos que esta ultima combination de senales vocales representan la alerta de mayor intensidad vocal dirigidas al potencial depredador por parte de 0 . asio. [Traduction de Ivan Lazo] The responses of parent birds to an approaching predator may vary considerably, but often include vocalizations, distraction displays, or attacks. Such behaviors may enhance a parent’s reproductive suc- 1 Present address: Department of Range and Wildlife Management, Texas Tech University, Lubbock, TX 79409 U.S.A. cess but do entail some survival cost (Montgomerie and Weatherhead 1988). The extent of that cost varies with the type of response. Distraction dis- plays, such as dives and attacks, may be relatively expensive and risky (Andersson et al. 1980, Greig- Smith 1980, Curio and Regelmann 1985, Knight and Temple 1988). In contrast, vocalizing is neither particularly costly nor risky and, as a result, many parent birds respond to approaching predators by vocalizing (Greig-Smith 1980, Bjerke et al. 1985, 93 94 Thomas McKell Sproat and Gary Ritchison Vol. 28, No. 2 Table 1. Comparison of the whinny songs and bark calls of male and female eastern screech-owls. Males 3 Females 13 Comparison of Male and Female Vocalizations (Wilcoxon test) Mean SE C Mean SE C z P Whinny songs Duration (sec) 1.12 0.02 1.13 0.05 0.18 0.8577 Minimum frequency d 684.5 14.0 688.6 31.9 1.30 0.1923 Maximum frequency* 1 1101.5 16.7 1419.4 61.7 4.13 <0.0001 FMA e 940.8 15.4 1080.0 32.9 3.89 <0.0001 Bark calls Duration (sec) 0.24 0.06 0.25 0.01 1.11 0.2670 Minimum frequency 749.4 10.9 813.5 9.3 4.52 <0.0001 Maximum frequency 1092.8 11.3 1147.6 13.5 2.07 0.0382 FMA 959.4 9.5 1014.3 10.0 3.47 0.0005 a Eight males gave 80 whinny songs and nine males gave 124 bark calls. b Five females gave 35 whinny songs and 136 bark calls. c Standard error. d All frequency measurements in Hertz. e Frequency at maximum amplitude in Hertz. Veen and Piersma 1986, Knight and Temple 1986, 1988, Weatherhead 1989). Even well-armed parents (i.e., raptors) may respond to potential predators by vocalizing (e.g., Wiklund and Stigh 1983, Andersen 1990). Adult eastern screech-owls ( Otus asio) utter a va- riety of vocalizations in response to potential pred- ators (Sproat 1992, Sproat and Ritchison 1993). We previously examined the nest defense behavior of eastern screech-owls and reported the use of five antipredator vocalizations (Sproat and Ritchison 1993) but did not provide a detailed description of the vocalizations or discuss possible functions. Here we provide such a description and also discuss the possible function(s) of these vocalizations. Methods The vocal responses of male and female eastern screech- owls to potential predators approaching nest sites or young were examined during three breeding seasons (1985, 1990 and 1991) at the Central Kentucky Wildlife Management Area, located 17 km southeast of Richmond, Madison County, Kentucky. A detailed description of methods used during the nest defense trials can be found in Sproat and Ritchison (1993). Briefly, eight pairs of radio-tagged screech-owls ( N = 4 in 1990 and N = 4 in 1991) were tested repetitively while six pairs (N = 4 in 1990 and N — 2 in 1991) were tested only once. The repetitive pairs were each tested three or four times, with trials conducted at 12-14 d intervals during the approximately eight- week nesting cycle. Two people were involved in each trial, one acting as an observer and the other as the predator. During each trial, the predator spent 8 min at a point 8 m in front of the nest tree, four min at the base of the nest tree, 4 min about halfway between the ground and the cavity (using a ladder), and a final 4 min at the initial location in front of the nest tree. To obtain additional recordings, we also examined the responses of eight pairs of screech-owls (three in 1985, three in 1990, and two in 1991) to humans just prior to or after fledging of their young. Pairs tested in 1990 and 1991 had also been used for the nest defense trials while those tested in 1985 had not been tested previously. Fur- ther, only those pairs tested in 1990 and 1991 were fitted with radiotransmitters. During these nestling/fledgling trials, young were removed from nest cavities or roost sites, tethered to a branch, and approached and handled by a human. These trials varied in duration and during each trial an attempt was made to record all vocalizations ut- tered by the adults. Because paired owls were sometimes in close proximity during these trials, we were not always able to determine whether the male or female was vocal- izing. We also attempted to determine the number of dives (any break in horizontal flight directed at the predator) made by each member of the pair. During all trials we noted the number and type of vocalizations uttered by parent owls. Vocalizations were recorded by the person acting as the predator using a Uher 4000 Report Monitor tape recorder with a Dan Gibson parabolic microphone. All vocalizations recorded on tape were subsequently analyzed using a Kay Elemetrics Corp. Sonagraph (Model 5500). For each vocalization we de- termined duration, maximum frequency, minimum fre- quency, frequency at maximum amplitude (FMA), and, for bounce songs, the number of notes per song. Multiple comparisons were made using a one-way ANOVA applied to ranks (equivalent to a Kruskal- Wallis June 1994 Owl Antipredator Vocalizations 95 test; SAS Institute 1985) while paired comparisons were made using Wilcoxon tests (SAS Institute 1985). Chi- square tests were used to test for non-random distributions. All values are presented as mean ± standard error. Results Eastern screech-owls uttered six different vocal- izations during the trials: bounce songs, whinny songs, bark calls, bark-screech calls, screech calls, and bill- claps (Fig. 1). Male screech-owls gave all of these vocalizations while females gave all except bounce songs. Description of Vocalizations. The bounce songs of male screech-owls (N = 39 songs by seven indi- viduals) averaged 1.92 ± 0.06 sec in duration and consisted of an average of 25.33 ± 1.03 notes. The mean frequency at maximum amplitude (FMA) was 620.0 ±6.1 Hz. The bounce songs of males exhib- ited significant individual variation in number of notes per song (F 429 = 4.07, P = 0.0097), maximum frequency (F 4>2 9 — 4.13, P = 0.0009), minimum fre- quency (F 42 9 = 4.07, P < 0.0001), and FMA (F 429 = 5.96, P = 0.0013) but not in duration (F 429 = 1.52, P = 0.222). The whinny songs of male ( N = 8) and female (N = 6) screech-owls differed significantly in max- imum frequency and FMA but not in duration or minimum frequency (Table 1). Among males, whin- ny songs differed significantly in duration (F 7J2 — 3.95, P = 0.001), maximum (F 7>72 = 34.08, P < 0.0001) and minimum (F 772 = 21.65, P < 0.0001) frequency, and FMA (F 7J2 = 34.79, P < 0.0001). Similarly, among females, whinny songs differed sig- nificantly in duration (F 5>2 9 = 6.74, P = 0.0003), maximum (F 5 29 = 41.65, P < 0.0001) and minimum (F S29 = 6.71, P = 0.0003) frequency, and FMA (F 5>29 = 25.56, P < 0.0001). Bark calls consisted of a single note that typically exhibited a gradual decline in frequency (Fig. 1). The barks of female screech-owls were significantly higher in frequency than those of males (Table 1). Among males, bark calls exhibited significant indi- vidual variation in duration (F 9115 = 4.61, P < 0.0001), maximum (F 9U5 = 5.19, P < 0.0001) and minimum (F 9 115 = 4.65, P < 0.0001) frequency, and FMA (F 9115 = 5.83, P < 0.0001). Similarly, among females, bark calls exhibited significant individual variation in duration (_F 4131 = 5.82, P = 0.0002), maximum (F 4131 = 6.46, P < 0.0001) and minimum (F 4131 = 4.56, P = 0.0018) frequency, and FMA (F 4 ’ 131 = 6.06, P = 0.0002). Bark calls were sometimes given in bouts of two N 2 1 2 Time (sec) Figure 1. The antipredator vocalizations of eastern screech-owls, (a) bounce song, (b) whinny song, (c) three bark calls, (d) two bark-screech calls, and (e) two screech calls followed by a single bill-clap plus a screech call exhibiting frequency modulation followed by two bill-claps or more (with a bout defined as a series of the same calls with intercall intervals of 30 sec or less). The mean number of bark calls per bout ( N = 71 bouts by at least 18 individuals) was 6.42 ± 1.01. Females (N = 6) gave significantly (z = 3.21, P = 0.0013) more barks calls per bout than did males (N = 8), with males averaging 3.87 ± 0.83 calls per bout and females averaging 5.96 ± 0.86 calls per bout. Bark-screech calls were uttered by one or both members of one pair of screech-owls during a nest- ling/fledgling trial, and the characteristics of these calls were intermediate to those of bark and screech calls. Bark-screech calls (N = 19) averaged 0.21 ± 0.01 sec in duration and had a mean FMA of 793.2 ± 11.5 Hz. These calls exhibited a sharp drop in frequency, descending from a mean high frequency 96 Thomas McKell Sproat and Gary Ritchison Vol. 28, No. 2 of 943.2 ± 36.3 Hz to a mean low frequency of 523.7 ± 45.4 Hz. Screech calls were high volume calls consisting of a single note exhibiting a rapid drop in frequency (Fig. 1). Screech calls sometimes ended with a series of frequency modulations (Fig. 1). Most screech calls were given by owls in flight, often during dives. Screech calls (TV = 53) averaged 0.25 ± 0.02 sec in duration and had a mean FMA of 884.7 ± 20.5 Hz. These calls descended from a mean high frequency of 1217.1 ± 24.6 Hz to a mean low frequency of 443.2 ± 17.7 Hz. We were able to positively identify only three of the owls (two females and one male) that uttered these calls and, therefore, could not com- pare the screech calls of males and females. Bill-claps produced short duration sounds ( x = 0. 02 ± 0.0004 sec; TV = 46 by at least four individ- uals) that covered a wide range of frequencies (Fig. 1). Although most bill-claps were given immediately before or after bark calls (N = 12) or screech calls ( TV = 24), three screech-owls gave only bill-claps during dives. When given with other calls, bill-claps were given an average of 0.25 ±0.15 sec ( N = 2) before bark calls, 0.31 ± 0.08 sec (TV = 5) before screech calls, 1.36 ± 0.85 sec (TV = 7) after bark calls, and 0.17 ± 0.03 sec (TV = 13) after screech calls. No significant differences were found between the bill-claps of males and females (Wilcoxon tests, P > 0.05). Bill-claps were often given in bouts of two or more. The mean number of bill-claps per bout was 1.63 ± 0.13 (TV = 27 bouts by at least four individuals) and the mean duration of these bouts was 0.16 ± 0.03 sec. Vocal Responses During Nest Defense and Nestling/Fledgling Trials. Few vocalizations were uttered during the incubation stage (TV =19 trials). Female screech-owls ( N — 2) vocalized during two trials, with one female giving one whinny song and the other 15 whinny songs. Males (TV = 5) vocalized during five trials, with one male giving one whinny song and five bounce songs, a second male giving one bark, and three males giving bounce songs (1, 1, and 16, respectively). Screech-owls vocalized during 14 of 17 trials con- ducted during the nestling stage. Bark calls (TV = 103 by eight males and two females during eight trials) and whinny songs (TV = 94 by eight males and four females during eight trials) were the most frequently used vocalizations during the nestling stage. Screech-owls gave few bounce songs (TV =11 by three males) and screech calls (TV = 5 by two males and one female) and no bill-claps. Male screech- owls were more vocal than females, with only males vocalizing during seven trials and both the male and female vocalizing during seven additional trials. In addition, vocalizing males gave more calls, averaging 1 1 .4 bark calls (TV = 8 males) and 7.8 whinny songs (TV = 8 males). Vocalizing females averaged six bark calls (TV = 2 females) and 4.5 whinny songs (TV = 4 females). Vocalizations were uttered by adult male and fe- male screech-owls during seven of eight nestling/ fledgling trials. Screech-owls used all six vocaliza- tions during these trials, with bark calls given most frequently. During three of the seven nestling/fledg- ling trials in which adult screech-owls uttered vo- calizations, we were unable to positively identify the source (i.e., adult male or adult female) of some or all of the vocalizations. For the remaining four trials, we found that female screech-owls uttered signifi- cantly more (% 2 = 16.2, df = 3, P = 0.001) bark calls per trial than did males, with females averaging 31 ± 13.3 bark calls and males 8.3 ± 5.9 bark calls. Among those pairs tested during both types of trials (nest defense and nestling/fledgling), the use of vocalizations during the two trials differed sig- nificantly (x 2 = 47.6, df = 4, P < 0.0001). Bark calls, screech calls, and bill-claps were used more frequently during the nestling/fledgling trials while bounce songs and whinny songs were used more frequently during the nest defense trials. Discussion Eastern screech-owls in our study uttered bounce and whinny songs in an antipredator context; how- ever, these songs are also used in other contexts (Ritchison et al. 1988, Klatt and Ritchison 1993). Bounce songs given by male screech-owls in our study averaged 25.3 notes. By comparison, bounce songs given in response to playback averaged 32.3 notes (Cavanagh and Ritchison 1987) while those uttered during duets averaged 58.4 notes (Klatt and Ritchison 1993). Thus, our results support the hy- pothesis that the message conveyed by bounce songs varies with song length — shorter songs conveying increasing levels of aggression (Klatt and Ritchison 1993) or perhaps anxiety. Most bounce songs were given during the incubation period when screech- owls exhibited little nest-defense activity (Sproat and Ritchison 1993). These results suggest that bounce songs were probably directed by males toward their June 1994 Owl Antipredator Vocalizations 97 INCREASING WILLINGNESS TO ATTACK BOUNCE w WHINNY k SONG V S0NG T BARK (SINGLE OR SHORT SERIES) BARK (LONG ^ SERIES I ^ BILL-CLAPS) BARK- SCREECH ► SCREECH DIRECTED TO CONSPECIFICS SCREECH + BILL-CLAP DIRECTED TO POTENTIAL PREDATOR Figure 2, A possible antipredator communication system of adult eastern screech-owls. incubating mate and served as a low-level warning (Fig. 2). Screech-owls responded with significantly greater intensity during the nestling stage than during in- cubation (Sproat and Ritchison 1993), and most whinny songs were given during the nestling stage. Whinny songs are also given with greater volume than bounce songs (Ritchison et al. 1988). This in- creased volume, plus the association with other an- tipredator behaviors (e.g., flights and dives), suggests that whinny songs serve as a higher-level warning to mates and nestlings (Fig. 2). The characteristics of whinny songs also make a calling bird relatively easy to locate (Ritchison et al. 1988), suggesting that they may also serve to distract potential predators. Selection should favor the use of easily locatable calls as distraction displays when the caller’s position must be revealed (Greig-Smith 1980). Vocalizations that apparently serve to distract predators have been re- ported in several other species (Greig-Smith 1980, East 1981, Andersen 1990). Screech-owls in our study also uttered bark calls, bark-screech calls, screech calls, and bill-claps. These calls have been reported previously (Marshall 1967, Walker 1974, Voous 1988, Torre 1990) and are apparently uttered only in aggressive or defensive contexts (Torre 1990). Other species of owls utter similar calls in aggressive contexts. For example, boreal owls ( Aegolius funereus) utter screech calls when the nest or fledged young are approached by potential predators (Meehan 1980). Bark-like calls have been reported in snowy owls ( Nyctea scandiaca), little owls ( Athene noctua ), barred owls ( Strix varia ), spotted owls ( S . occidentalis) , and boreal owls (Voous 1988). Bill-claps have also been reported in several species of owls, and are generally uttered in ag- gressive (including nest protection) or defensive con- texts (Johnsgard 1988). Bark calls were uttered by male and female screech- owls during the nestling stage and, especially, during the nestling/fledgling trials. Our results indicate that bark calls serve to warn a mate and young that a predator is approaching. Kelso (1938:248) reported that when two juvenile screech-owls heard bark calls “. . . they crouched flat . . . and feigned death.” Calls with a similar function have been reported in other species (e.g., Greig-Smith 1980, Knight and Temple 1986, 1988, Andersen 1990). Screech-owls sometimes gave long series of bark calls, particularly during the nestling/fledgling tri- als. Previous studies suggest that a single call, or a short series of calls, may be sufficient to convey a warning of danger to a mate or young and, further, that a long series of calls are more likely directed at the predator (Powell 1974, Greig-Smith 1980). Our results support this hypothesis. Screech-owls gave relatively short bouts of bark calls during the nest defense trials and these bouts preceded a dive only once, suggesting that the calls were directed at a mate or young. In contrast, the longer series of barks given during the nestling/fledgling trials were often followed by screech calls and dives, suggesting that the calls warn a predator of a screech-owl’s increas- ing willingness to attack (Fig. 2). Most screech calls were given by screech-owls during flights at the predator, mainly during the nestling/fledgling trials when young were being handled. Kelso (1938:248) observed that screech- owls gave screech calls “. . . when a person or large animal comes near the young either while they are 98 Thomas McKell Sproat and Gary Ritghison Vol. 28, No. 2 in or out of the nest. It is usually given as the male swoops at the intruder’s head. ...” The relatively high volume of these calls and the tendency to utter them close to the predator indicate that the calls are directed at the predator and serve as a high-intensity warning (Fig. 2). Bark-screech calls were also given during the nestling/fledgling trials and appeared in- termediate to bark calls and screech calls, both in terms of structure and function (Fig. 2). All bill-claps were given during the nestling/ fledgling trials, mainly during flights at the potential predator (often in conjunction with screech calls). As with screech calls, the association of bill-claps with flights at the predator indicates that they are directed at the predator and serve as a high-intensity warning. The combined vocal signal of screech calls and bill-claps may represent the highest-intensity vocal warning given by screech-owls (Fig. 2). Male screech-owls vocalized more than females during our nest defense trials. Similarly, Sproat and Ritchison (1993) found that male screech-owls de- fended young in the nest more vigorously than did females. However, female screech-owls vocalized more than males during our nestling/fledgling trials and, in at least two pairs, females made more flights at the predator. Such results suggest that the inten- sity of defense by female screech-owls may increase when a predator poses a greater threat (i.e., is closer) to the offspring and support the hypothesis that the location of a predator relative to the nest (or fledged young) may influence the defense behavior of male and female raptors that exhibit reversed sexual di- morphism (Sproat and Ritchison 1993). In summary, eastern screech-owls use several vo- calizations in an antipredator context and we suggest that these vocalizations represent a graded system of communication (Fig. 2). Similar graded systems have been reported in other species (Morton and Shalter 1977, Miller 1979, Veen and Piersma 1986, Arm- strong 1992), and such systems permit more precise communication because individuals are able to com- municate subtle variations in motivation (Morton 1977). Acknowledgments We thank P.M. Cavanagh, J.R. Belthoff, T. Ritchison, K. Krantz, D.D. Able, A. Bowen, T. Buck, B. Moore and, especially, P.H. Klatt for assistance in the field. The comments of D.E. Andersen and two anonymous reviewers improved the manuscript. Financial support was provided by Eastern Kentucky University. Literature Cited Andersen, D.E. 1990. Nest-defense behavior of red- tailed hawks. Condor 92:991-997. Andersson, M., G. Wiklund and H, Rundgren. 1980 Parental defence of offspring: a model and an example Anim. Behav. 28:536-542. Armstrong, T.A. 1992. Categorization of notes used by female red-winged blackbirds in composite vocali- zations. Condor 94:210-223. Bjerke, T., Y. Espmark and T. Fonstad. 1985. Nest defence and parental investment in the redwing Turdus iliacus, Orms Scand. 16:14-19. Cavanagh, P.M. and G. Ritchison. 1987. Variation in the bounce and whinny songs of the eastern screech- owl. Wilson Bull. 99:620-627. Curio, E. and K. Regelmann. 1985. The behavioural dynamics of great tits (Parus major ) approaching a predator. Z. Tierpsychol. 69:3-18. East, M. 1981. Alarm calling and parental investment in the robin ( Erithacus rubecula). Ibis 123:223-230. Greig-Smith, P.W. 1980. Parental investment in nest defence by stonechats ( Saxicola torquata ). Anim. Behav. 28:604-619. Johnsgard, P.A. 1988. North American owls: biology and natural history. Smithsonian Inst. Press, Wash- ington, DC U.S.A. Kelso, L.H, 1938. A study of the screech owl ( Otus asio ). M.S. thesis, Cornell Univ., Ithaca, NY U.S.A. Klatt, P.H. and G. Ritchison. 1993. The duetting behavior of eastern screech-owls. Wilson Bull. 105:483- 489. Knight, R.L. and S. A. Temple. 1986. Nest defence in the American goldfinch. Anim. Behav. 34:887-897. AND . 1988. Nest-defense behavior in the red-winged blackbird. Condor 90:193-200. Marshall, J.T., Jr. 1967. Parallel variation in North and Middle American screech owls. Monogr. West Found. Vert. Zool. 1:1-72. Meehan, R.H. 1980. Behavioral significance of boreal owl vocalizations during the breeding season. M.S thesis, Univ. Alaska, Fairbanks AK U.S.A. Miller, E.H. 1979. An approach to the analysis of graded vocalizations of birds. Behav. Neural Biol. 27 25-38. Montgomerie, R.D. and P.J. Weatherhead. 1988. Risks and rewards of nest defence by parent birds Quart. Rev. Biol. 63:167-187. Morton, E.S. 1977. On the occurrence and significance of motivation-structural rules in some bird and mam- mal sounds. Am. Nat. 111:855-869. Morton, E.S. and M.D. Shalter. 1977. Vocal re- sponse to predators in pair-bonded Carolina wrens. Condor 79:222-227. Powell, G.V.N. 1974. Experimental analysis of the social value of flocking by starlings ( Sturnus vulgaris ) June 1994 Owl Antipredator Vocalizations 99 in relation to predation and foraging. Anim. Behav. 22: 501-505. Ritchison, G., P.M. Cavanagh, J.R. Belthoff and E.J. Sparks. 1988. The singing behavior of eastern screech-owls: seasonal timing and response to playback of conspecific song. Condor 90:648-652. SAS Institute. 1985. SAS user’s guide: statistics. 1985 ed. SAS Institute, Cary, NG U.S.A. Sproat, T.M. 1992. The nest defense behavior of east- ern screech-owls. M.S. thesis, Eastern Kentucky Univ., Richmond, KY U.S.A. and G. Ritchison. 1993. The nest defense be- havior of eastern screech-owls: effects of nest stage, sex, nest type and predator location. Condor 95:288-296. Torre, J. De La. 1990. Owls: their life and behavior. Crown Publishers, Inc., New York, NY U.S.A. Veen, J. AND T. Piersma. 1986. Causation and function of different vocal reactions of little gulls Larus minutus to intruders near the nest. Behaviour 96:241-264. Voous, K.H. 1988. Owls of the northern hemisphere. Wm. Collins Sons and Co., Ltd., London, U.K. Walker, L.W. 1974. The book of owls. A. A. Knopf, Inc., New York, NY U.S.A. Weatherhead, P.J. 1989. Nest defence by song spar- rows: methodological and life history considerations. Behav. Ecol. Sociobiol. 25:129-136. Wiklund, C.G. and J. Stigh. 1983. Nest defence and evolution of reversed sexual dimorphism in snowy owls Nyctea scandiaca. Ornis Scand. 14:58-62. Received 30 September 1993; accepted 1 March 1994 J. Raptor Res. 28(2):100-107 © 1994 The Raptor Research Foundation, Inc. BEHAVIOR AND ACTIVITY OF REHABILITATED BUZZARDS C Buteo buteo) RELEASED IN NORTHERN ITALY Davide Csermely and Carlo Vittorio Corona 1 Dipartimento di Biologia e Fisiologia Generali, Universita di Parma, Viale delle Scienze, 1-43100 Parma, Italy Abstract. — The behavior and habitat hunting of 16 rehabilitated common buzzards ( Buteo buteo) released in northern Italy were analyzed. The buzzards were released individually in different seasons, and their activity was recorded continuously for at least the first 3 d after release and intermittently thereafter until they dispersed from the release site. The birds remained in the surrounding area for more than 100 d, showing a progressive acclimation to the new environment. The released buzzards interacted frequently with wild territorial conspecifics and were attacked by several species of corvids, especially the hooded crow ( Corvus corone). Nevertheless, such interactions were not the direct cause of dispersal. Some birds defended a territory adjacent to or inside that of a wild buzzard. Prey capture was almost normal, although certainly underestimated. Small mammals and reptiles were most often caught. Although the area chosen for this study had high human population, this was not a major source of interference with the releases. Thus, the buzzards appeared to be able to cope with their new environment being minimally influenced by having been in captivity. Key WORDS: hawks; Buteo buteo; behavior; captivity; dispersal; rehabilitation; behavioral ecology. Comportamiento y actividad de los Buteo buteo rehabilitados y deyados en libertad en el norde de Italia Resumen. — Se analizo la conducta y el habitat de caza de 16 individuos rehabilitados de la especie Buteo buteo liberados en el norte de Italia. Los individuos de B. buteo fueron liberados en el area de estudio individualmente y en diferentes estaciones; su actividad fue registrada continuamente por al menos tres dias despues de su liberacion e intermitentemente hasta el momento de abandonar el sitio de liberacion. Las aves permanecieron en los alrededores del area por mas de 100 dias, mostrando una progresiva aclimatacion al nuevo ambiente. Los individuos liberdos interactuaban frecuentemente con conespecificos territoriales silvestres y fueron atacados por varias especies de covidos, especialmente Corvus corone. Sin embargo, tales interacciones no fueron la causa directa de su dispersion. Algunas aves defendieron territories vecinos o al interior de los defendidos por individuos silvestres. La captura de presa fue casi normal, aunque ciertamente subestimada. Tanto pequenos mamiferos como reptiles fueron a menudo capturados. Aunque las areas escogidas para este estudio tenian una alta poblacion humana, este factor no constituyo una gran fuente de interferencias sobre las liberaciones. En sintesis, B. buteo parece ser capaz de incertarse en su nuevo mediambiente siendo escasamente influenciado por su cautividad. [Traduccion de Ivan Lazo] Several programs for the rehabilitation of raptors have been developed in recent years by institutions devoted to the protection of birds. Standard proce- dures for raptor rehabilitation have been developed for several species (Nelson 1977, Llewellyn and Brain 1983, Pendleton et al. 1987, Weaver and Cade 1991) as well as the techniques for successful release (Sher- rod et al. 1982, Llewellyn 1991). Nevertheless, the adaptation of birds back into the natural habitat is 1 Present address: Via P. Petronia 89, 1-00136 Roma, Italy. still neglected. In fact, it is almost impossible to get information of the fate of released birds from the literature, because most data refer to survival rate and recovery distance from the release site (Servheen and English 1979, Duke et al. 1981, Ingram 1983, Hamilton et al. 1988). Moreover, little precise in- formation has been compiled on the behavior of in- dividuals after release. The objective of this study was to fill that gap, investigating in detail the behavior, activity, and in- tra- and interspecific interactions in a group of com- mon buzzards {Buteo buteo) immediately after re- lease following rehabilitation until they dispersed 100 June 1994 Behavior of Released Buzzards 101 from the area. Such an investigation is likely to be of interest to raptor rehabilitators (Meyers and Mil- ler 1992). Methods The buzzards used in this study were all wild birds, housed temporarily for rehabilitation at the Raptor Re- habilitation Centre (RRC) managed by the Italian Society for the Protection of Birds (LIPU) near Parma. They all originated in northern or central Italy within 100-200 km of the release area. When released the birds were all in perfect physical condition and flying fitness, and were chosen randomly among those ready for releasing. Those possibly imprinted to humans were not considered. A total of 16 buzzards were studied. Six were adult (two males and four females) and 10 were sub-adults (five males and five females). They were released near the end of each season, from April 1990 to November 1991. Five were studied betw r een winter and spring, four between spring and summer, three between summer and autumn, and four between autumn and winter. Thus, we avoided the most stressful climatic conditions that occur in Janu- ary-February and in July- August (Kostrzewa and Kos- trzewa 1991). The duration in captivity was variable, ranging from a few days to several months, depending on the seriousness of the injury or illness. The mean duration for nine buzzards was 295.5 ± 109.2 d. We did not know the period for the other five, but it was certainly within the same range. The release site was located within a waterfowl sanc- tuary managed by LIPU about 15 km north of Parma and 5 km from the Po River. The area is flat and without extensive woodlands but with a high human population density. The site was chosen because of the necessity to observe closely and track the buzzard behavior precisely, even for long distances if necessary. Wild buzzards are regularly present particularly during winter. Several taxa of invertebrates and terrestrial vertebrates offered an easy and variable food source. The area surrounding the release site contained several biotopes, with rather differing vegetal cover. The habitat types were evaluated using the method described by Emlen (1956). Several watercourses — the Parma River and sev- eral streams — run within the study area. Most of the trees are concentrated along them. The buzzards were released individually between 0900- 1500 H on days without precipitation. Beforehand they were kept on location in an outdoor aviary for 1-2 wk in order for them to habituate to the environment. A radiotag (9 g two stage, BIOTRACK, Wareham, U.K.) was at- tached some hours before release (Kenward 1987, White and Garrott 1990). The buzzards were followed virtually continuously from dawn to dusk each day if weather permitted for the first 3 d after release, hereafter referred as “days 1-3.” If a bird did not leave the area, it was subsequently monitored intermittently with the same schedule at 1-4 d intervals, until the bird disappeared from the surroundings. That period, including the first 3 d, is hereafter indicated as “all-days.” Observations were carried out using 8 x bin- oculars and a 1 0-40 x zoom spotting scope. The daylight period was equally divided into three sec- tions that were variable during the year based upon the photoperiod. The proportion of time spent in each habitat for each one-third of the daylight period and in every season was arcsin transformed for comparison. The exact time of sunrise and sunset for the geographical coordinates of the area were calculated every 2 wk. The days after release were counted considering the day of release as day one. The days of the year were indicated considering the spring equinox as day zero. We used the Mann- Whitney U-test to compare means, the Kruskal-Wallis one-way ANOVA (Siegel 1956) to evaluate time durations between seasons or between thirds of the day, the Spearman rank correlation to ascertain possible correlations, and the Chi-square test to compare frequencies. The means are given ± SE, and the proba- bility is always given as two-tailed. Results Most buzzards did not disappear quickly from the release site in 426.6 hr of observation (Table 1). The area used by the birds was about 2730 ha in size, almost centered around the release site. One-half of the sampled buzzards left the study area within three days. Three departed within a few hours and one on day three. This occurred in early spring and autumn. Mortality. Three buzzards died in the study area by electrocution after perching on medium-tension pylons which are widely distributed in the plains of Italy, and unfortunately are a serious problem for other species too. One bird died of a gunshot wound received during the night or at dawn before we start- ed our observation session, and another died in spring for unknown reasons during a late snowfall. Finally, one buzzard was recaptured close to starvation. Habitat Use. Habitat types within the study area were small. Their distribution was almost regular, and the buzzards moved very easily from one habitat to another. We found great individual variability in habitat use ( H = 31.79, N = 450, P < 0.001, mea- sured as minutes spent by each bird in each habitat). Birds that changed habitat frequently had been kept in captivity for the least time (Z = 2.18, N ~ 279, P < 0.05). During winter, buzzards stayed in one habitat longer than in other seasons, both during days 1-3 (H = 10.28, N = 390, P < 0.05) and in all-days (II = 17.58, N = 485, P < 0.001). The buzzards remained longer in open habitats than in areas with thick vegetation in every period considered (Kostrzewa 1989). The tendency to ex- plore different habitats immediately after release, i.e., the minutes spent in each habitat before moving to another one, decreased with time (r s — 0.10, N = 102 Davide Csermely and Carlo Vittorio Corona Vol. 28, No. 2 Table 1. The history of common buzzards released following rehabilitation near Parma, Italy. Buzzard Identifi- cation Code Sex, Age Date of Release Days Remaining Within the Study Area Duration of Observation ( hr) Cause of Observation End VR-340 M, JU 25 Oct 1990 1 1.5 Abandonment 3 AV-670 F, AD 6 Dec 1990 1 2.8 Abandonment 3 RN-700 F, JU 27 Mar 1991 1 5.2 Abandonment 3 V-525 F, AD 11 Apr 1990 3 17.4 Abandonment 3 0-790 F, JU 15 Jun 1990 4 27.0 Abandonment 3 VA-425 F, JU 19 Jun 1991 4 25.7 Abandonment 3 NM-920 M, AD 11 Sep 1991 4 28.2 Abandonment 3 VN-355 M, JU 13 Apr 1991 7 30.4 Death RN-670 F, JU 17 Nov 1990 11 37.7 Death VP-960 M, JU 20 Sep 1991 13 29.0 Death AN-690 F, AD 16 Mar 1991 14 45.2 Abandonment 3 B-355 F, JU 30 Apr 1991 18 31.3 Abandonment 3 A-260 M, JU 9 Jun 1990 29 33.9 Abandonment 3 GM-440 M, AD 3 Nov 1990 39 46.5 Recapture RS-1150 F, AD 15 Sep 1991 65 34.7 Abandonment 3 RA-450 F, AD 23 Jun 1991 103 30.2 Abandonment 3 a Buzzard left the release area. 485, P < 0.05). Habitats with trees were used most (74.8% of time), particularly tree rows (55.9%). The time spent in such habitats was inversely correlated with tree distance (r s = —0.12, TV = 310, P < 0.05). The birds preferred those areas in spring, particu- larly the “irregular” woods ( H = 11.29, TV = 147, P < 0.02) and poplar plantations ( H = 11.02, TV = 147, P < 0.02), while in summer they stayed mostly in woods with trees in rows ( H = 12.54, N = 146, P < 0.01). Such a preference changed dramatically in autumn and winter, when the birds chose prin- cipally open/cultivated areas ( H = 20.55, TV = 147, P < 0.001). In contrast, they appeared to avoid the vicinity of buildings or other areas where human presence was evident. Only six birds frequented such areas, perching close to human settlements and spending no more than 20% of the observation period there. We found no relationship between time of day and habitat preference. The birds remaining for a long time within the study area were also able to occupy a territory adjacent to or within a territory defended by a wild conspecific, but behaved as sub- ordinate to the latter. Perching Sites. The buzzards perched most fre- quently in tree branches, but also often used pylons, poles, or simply stood on the ground. In spring ( TV = 148) they perched most often on poplars ( Populus spp.; x 2 (i) = 111-90, P < 0.001) and willows ( Salix alba ; % 2 (i) = 12.99, P < 0.001), while in summer ( TV = 221) they rested in oaks ( Quercus spp.; x 2 (i) = 18.1 1, P < 0.001) and again in poplars (x 2 (i) = 42.75, P < 0.001) and willows x 2 (i) = 15.02, P < 0.001). In autumn ( TV = 237) they preferred open habitats and either perched on pylons (x 2 (i) = 21.72, P < 0.001), poplars (x 2 (i> = 27.16, P < 0.001) or de- scended to the ground, but in winter ( TV = 46) they returned to a preference for trees, again principally poplars (x 2 d) = 40.45, P < 0.001). The perching duration was unaffected by the type of perching site and averaged 30.70 ± 1.22 min (TV = 652). Perch height was negatively correlated with the perching duration in both days 1-3 (r s = —0.10, TV = 486, P < 0.05) and in subsequent time periods (r s = —0.09, TV = 652, P < 0.02). Height was strong- ly influenced (H = 37.14, N = 652, P < 0.001) by season in either period ranging from 5.26 ± 0.26 m (all-days) in spring to 3.27 ± 0.17 m (all-days) in summer and in winter. Flight Performance. The buzzards flew some distance away immediately after release, but re- mained within a range of 400-5000 m. The distance from the release site increased progressively to 1295.0 ± 217.4 m on day three. These values were greatly affected by season ( H = 18.25, TV = 551, P < 0.001), June 1994 Behavior of Released Buzzards 103 Table 2. Some parameters of flapping or gliding flights and soaring for each released buzzard. (It was not possible to ascertain the actual height of all flights.) Buzzard Identifi- cation Code Total No. of Flights Mean No. of Minutes Between Two Flights Mean No. of Hours Between Two Soaring Flights Mean (± SE) Height (m) of Flight ( N ) Mean (± SE) Length (m) of Flight (N) AV-670 6 28.3 — 11.5 ± 1.5 (2) 441.7 ± 141.8 (6) RN-700 8 38.8 5.167 — 491.9 ± 204.6 (8) VR-340 3 30.0 1.5 — 150.0 ± 57.7 (3) V-525 11 95.0 8.733 75.0 ± 0.0 (2) 336.4 ± 134.7 (11) 0-790 25 64.8 — — 173.0 ± 17.8 (25) GM-440 51 49.1 46.633 — 187.4 ± 18.2 (51) NM-920 48 35.2 28.167 9.1 ± 1.9 (26) 176.6 ± 17.6 (48) VA-425 45 34.2 — 8.2 ± 0.7 (26) 161.1 ± 14.9 (45) VN-355 76 27.2 15.217 14.8 ± 2.8 (29) 185.0 ± 20.1 (76) RN-670 90 24.8 — — 186.7 ± 18.3 (90) AN-690 54 50.2 — 18.5 ± 11.5 (52) 160.6 ± 15.0 (54) VP-960 47 37.0 5.793 18.3 ±7.1 (19) 281.4 ± 41.9 (47) B-355 42 25.4 7.829 22.1 ± 5.1 (16) 245.8 ± 37.7 (42) A-260 62 33.4 11.305 — 219.4 ± 22.1 (62) RS-1150 73 28.5 34.683 7.5 ± 1.4 (51) 186.3 ± 20.7 (73) RA-450 51 35.5 30.183 7.0 ± 0.9 (43) 132.8 ± 12.1 (51) with longer distances in autumn (1043 ± 206 m) and shorter in winter (536 ± 93 m). The time of day did not have any influence. Most flights involved flapping and gliding with soaring being recorded only at the beginning of spring and autumn. The frequency of flights was highly variable between individuals ( H = 25.11, N = 126, P < 0.05), with intervals between two flights ranging from 24.8-95.0 min/bird (Table 2). High frequency of flights was associated with short rehabilitation period (Z = 2.65, N = 11, P < 0.01). The longest flights were in autumn and spring (221.7 ± 14.5 m [N = 218] and 223.3 ± 15.0 m [N = 234], respec- tively, in all-days), showing a significant difference among seasons ( H = 12.46, N = 692, P < 0.01 in all-days). Flight length increased with distance from release site (r s = 0.13, N = 692, P < 0.001). Flight height and length were positively correlated (r s = 0.31, N = 219, P < 0.001). Predatory Behavior. We recorded 92 predation attempts, 55 of which occurred during days 1-3. Twelve birds out of the 16 studied attempted to catch prey at least once (7.67 ± 2.13 attempts/bird), with much individual variation (one attempt every 1.3 hr to one every 33.9 hr). The four buzzards that died or were recaptured had higher mean frequencies than the surviving birds (one attempt every 2.7 ± 0.5 hr vs. one attempt every 17.0 ±4.1 hr, Z = 2.12, N = 12, P < 0.05). More attempts were recorded during autumn (N = 43, one attempt every 2.9 hr) and spring (N = 32, one attempt every 4.1 hr) than in winter (N = 3, occurring every 12.5 hr). The interval between two prey capture attempts was very variable (H = 20.09, N = 48, P < 0.05). Moreover, the frequency of the attempts increased in relation to days after release (r s = 0.35, N = 48, P < 0.05). Buzzards generally hunted from perches (87.0% of total attempts). Only 12 hunts were performed by walking or standing on the ground and only three birds displayed these patterns. Range of prey taken was variable, being mainly comprised of mammals, reptiles, and insects. Although the common buzzard is well able to capture birds (Tubbs 1974), these were not included in our hunting observations in contrast to observations by Lovari (1974). When hunting from perches, buzzards started from a mean height of 4.36 ± 0.26 m. Neither the substrate nor the outcome were related to the height. The quarry was caught at a mean distance of 13.06 ± 1.11 m from the perch (range 2-60 m). The predation angle, i.e., the angle between the vertical from the perch to the ground and the path from the perch to the prey, supposing a linear glide, covered a wide range (0-85°). This angle was af- 104 Davide Csermely and Carlo Vittorio Corona Vol. 28, No. 2 fected by habitat substrate during days 1-3 ( H = 9.92, N = 50, P < 0.05). Uncultivated and grass fields accounted for the highest percentage of suc- cessful attempts ( N = 10). Banks of watercourses accounted for 42.9% of uncertain successes ( N =14), but the percentage of success related to the grass fields was only 7.1%. Uncultivated or plowed fields produced intermediate results. Unsuccessful at- tempts (N = 26) were mainly recorded in grass fields (38.4%), watercourse banks (34.6%), and plowed fields (19.2%). The season strongly influenced both the type of perch used for predation attempts (x 2 ( 3 ) = 42.65, P < 0.001) and the type of habitat substrate where the attempt was performed (x 2 ( 3 ) = 8.61, P < 0.05). In fact, buzzards preferred to hunt from rows of trees in spring (P < 0.001) and from pylons in autumn ( P < 0.001). Most predation attempts oc- curred on the grass fields during the cold season. Interactions with Conspecifics and Other Bird Species. A total of 29 interactions with resident wild buzzards was recorded involving five birds out of the 16 released. Most interactions occurred in summer and autumn (24.1% and 62.1%, respectively; cf. Kos- trzewa 1991), and we did not record any interaction in winter. Such interactions occurred soon after re- lease; in fact, approximately one-half occurred in days 1-3. The interval between two interactions de- creased markedly with days (r s = —0.56, N = 20, P < 0.05), reaching the maximum value between day 10-30 post-release. The interactions occurred mostly when the released buzzard was perched and were rather variable in duration (range: 5 sec-35 min.), and negatively correlated with perch height (r s = — 0.66, N = 15, P < 0.05). An interaction between two soaring birds was recorded only once. Vocali- zations were very frequent during interactions, as observed also by Tubbs (1974). Wild buzzards attacked first in 55.1% of inter- actions and the released bird attacked first only in 1 3.7% of times. Fighting, although of short duration, occurred in 6.8% of observations. In these cases nei- ther buzzard showed a tendency to leave. Attacks by the released buzzard never occurred on day one. Released buzzards that interacted with wild ones scored higher in predation frequency than those not interacting ( Z = 2.11, N = 12, P < 0.05). The three birds that interacted most frequently eventually died or were recaptured. The buzzards in this study interacted with several corvid species much more frequently than with con- specifics: 317 interactions involving the hooded crow ( Corvus corone), 63 involved the magpie (Pica pica), and 50 the jay (Garrulus glandarius). The mean fre- quency of interaction with the hooded crow was highest in spring and lowest in autumn. The inter- actions with the magpie were most frequent in au- tumn and very rare in winter, and those with the jay were rare in winter but similar in the other seasons. Interactions without regard to the bird spe- cies most often occurred among rows of trees, ranging from 92.0% for jays to 54.6% for hooded crow. The latter species also frequently mobbed buzzards in open areas (27.4%) and in other types of woods (17.2%). The number of mobbing individuals was highly variable with the maximum by the hooded crow (up to 12 birds and up to eight in the magpie and three in the jay). The corvids involved in mob- bing often performed true attacks on the buzzard. The latter, however, generally paid no apparent at- tention to them. The mobbing rate, without regard to the corvid species, varied between the seasons (x 2 ( 6 ) = 19.30, P < 0.01). The attacks were continuous (more than one attack/10 sec) in spring, at intervals (less than one attack/ 10 sec) in autumn, and rare (less than one attack/60 sec) in winter. The season greatly affected both the number of attacking birds and the total duration of the interaction (Table 3). The maximum number of mobbing individuals was much higher in spring and summer in all corvid species (H — 12.85, N = 317, P < 0.001 in the hooded crow; H = 9.93, N = 63, P < 0.05 in the magpie; H = 16.59, N = 50, P < 0.001 in the jay). Corvids mobbed longer in spring and summer (jay and magpie). The frequency of interaction decreased with number of days post-release for hooded crow r = 0.22, N = 92, P < 0.05) but not for the magpie and jay. Similarly, the frequency of vocalizations by the mobbing hooded crows was affected by the season (x 2 (6) = 87.48, P < 0.001). Vocalizations were almost continuous (more than one vocalization/5 sec) in spring, less frequent (less than one vocalization/5 sec) in winter, and virtually absent in autumn. Several other bird species interacted with released buzzards, but these were too infrequent to allow statistical evaluation. Seventeen interactions oc- curred with common kestrels ( Falco tinnunculus ) , mostly during spring near the kestrels’ nests. A few interactions occurred with the marsh harrier (Circus aeruginosus ) and hen harrier ( Circus cyaneus ) during autumn and winter in open habitats. Interactions with sparrowhawks (Accipiter nisus) occurred at the June 1994 Behavior of Released Buzzards 105 Table 3. The mean (±SE) duration (minutes) of interactions and the mean (±SE) number of attacking birds in three corvid species in each season. Hooded Crow Magpie Jay Season Duration No. Birds Duration No. Birds Duration No. Birds Spring 5.62 ± 0.59 1.50 ± 0.16 4.38 ± 1.13 0.83 ± 0.32 4.47 ± 0.86 1.08 ± 0.23 Summer 9.89 ± 1.21 1.56 ± 0.16 4.37 ± 0.98 0.29 ± 0.24 3.82 ± 0.95 0.69 ± 0.24 Autumn 9.42 ± 1.74 0.91 ± 0.13 1.88 ± 0.31 0.06 ± 0.04 1.05 ± 0.21 0.05 ± 0.05 Winter 14.54 ± 3.22 0.84 ± 0.18 1.85 ± 0.35 0.00 ± 0.00 2.70 + 0.30 0.00 ± 0.00 end of spring. Finally, several non-corvid Passeri- formes and two species of Columbidae interacted occasionally. Discussion Many of the buzzards were able to survive for several weeks around the release site. Although vary- ing in timing and direction, the abandonment of the release site was similar to what has been recorded for rehabilitated congeneric American species (Hamilton et al. 1988). However, we recorded a greater distance than reported for buzzards released in wooded habitat (Llewellyn and Brain 1983) sug- gesting that areas lacking large woods are likely not attractive for long-term occupation, possibly because of the lack of hiding places. The survival of buzzards for prolonged time in this study shows that release in areas heavily populated by humans is not very detrimental to the birds as was claimed by Hamilton et al. (1988). On the other hand, lack of muscle tone just after release likely reduces the readiness to disperse from the release site (Servheen and English 1979). Low muscle tone is certainly caused by prolonged captiv- ity that in turn is correlated with the frequency of flights and quick dispersal. Nevertheless, it is un- likely that it induces great vulnerability to the bird as claimed by Duke et al. (1981). Although repeated flights in training aviaries at the RRC were very important, they seemed to be inadequate for long distance flights soon after release. Nonetheless, good muscle tone and endurance appeared to be achieved in a very few days. Similar to American species (Duke et al. 1981), the season that release occurred in clearly affected the time of dispersal and the type of flight. In fact, although the Italian population is basically non-mi- gratory, the type of flights performed in spring and autumn (higher, longer, and frequent soaring) are associated with a migratory behavior. Moreover, quick departure from the release site was recorded only during the migration period. The frequency of hunting attempts by our released birds was high and possibly underestimated. Our data do not support the hypothesis by Hamilton et al. (1988) that in red-tailed hawks {Buteo jamaicen- sis) and broad-winged hawks {Buteo lineatus) un- familiarity with the new area or captive feeding neg- atively affect hunting behavior. Even other parameters related to prey catching ability, attack glide (Wakeley 1978), and the prey attack angle (Janes 1985) were similar to those of congeneric wild birds. Predatory proficiency of our birds likely improved with repetition. Prolonged captivity did not seem to be detrimental to hunting ability from perches, as previously suggested in laboratory conditions (Csermely et al. 1991). Such an ability is shown by the wide range of taxa taken as prey by our reha- bilitated birds, a range very similar to the diet of wild Mediterranean populations (Lovari 1974, Manzi and Pellegrini 1989, Manosa and Cordero 1992). The increased success of prey capture with days post-release was possibly connected to an in- creased knowledge of the environment. The increase in hunting attempts in migratory periods may have been due to increases in metabolism connected with migration. Retaliation to a wild buzzard attack was rare in the early post-release days but the frequency of interactions increased with time after release. In- teractions, although frequent during reproductive and migration periods (Brown 1989), did not cause buz- zards to leave the area which was opposite of the case for red-tailed hawks (Hamilton et al. 1988). Mobbing by corvids seemed to cause only the buz- zard’s abandonment of perches. This was true in spring and summer, when the corvids have greater parental motivation toward antipredatory behavior 106 Davide Csermely and Carlo Vittorio Corona Vol. 28, No. 2 (Roell 1982). The hooded crow, due to its large size and great sociality, is the species with the greatest ability to chase buzzards. However, antipredatory behavior by the corvids did not seem to have a very detrimental effect on buzzard releases. In conclusion, released buzzards showed a ready ability to cope with the environment and to acclimate to the wild. Prey was captured quite easily even after prolonged captivity, although a certain level of train- ing was evident. Moderate human presence around the release site did not appear detrimental. A greater source of interference likely came from mobbing corvids that sometimes forced buzzards to move from perches. From an applied point of view we can say that the rehabilitation technique was basically cor- rect, because none of the buzzards showed evident behavioral modifications related to the captivity pe- riod. Acknowledgments We are greatly indebted to Daniele Ghillani, Maurizio Ravasini, and Marco Lambertini of the Italian Society for the Protection of Birds, as well as the whole staff of the Raptor Rehabilitation Centre of Parma, for the help pro- vided and the permission to use the RRC facilities and the birds housed there. We thank also the Parma Provin- cial Administration for the permission to release the buz- zards on its territory. The comments and criticisms by Achim Kostrzewa, Santi Manosa, Gary Duke and an anonymous referee offered many valuable insights to im- prove an earlier draft of the manuscript. The basic stim- ulus for developing this study came from discussions with Nicolantonio Agostini. The research was supported by the Italian Ministero Universita e Ricerca Scientifica e Tec- nologica and the Consiglio Nazionale delle Ricerche, Literature Cited Brown, L. 1989. British birds of prey. Bloomsbury Books, London, U.K. Csermely, D., N. Agostini and D. Mainardi. 1991. Predatory behaviour in captive wild Buzzard. Birds Prey Bull. 4:133-142. Duke, G.E., P.T. Redig and W. Jones. 1981. Recov- eries and resightings of released rehabilitated raptors. Raptor Res. 15:97-107. Emlen, J.T. 1956. A method for describing and com- paring avian habitats. Ibis 98:565-576. Hamilton, L.L., P.J. Zwank and G.H. Olsen. 1988. Movements and survival of released, rehabilitated hawks. Raptor Res. 22:22-26. Ingram, K. A. 1983. Release and survival of a one-eyed golden eagle. Ann. Proc. Am. Assoc. Zoo Vet. 1983:160. Janes, S.W. 1985. Habitat selection in raptorial birds. Pages 159-188 in M.L. Cody [Ed.], Habitat selection in birds. Academic Press, London, U.K. Kenward, R. 1987. Wildlife radio tagging. Academic Press, London, U.K. Kostrzewa, A. 1989. Nest habitat separation in three European raptors: Accipiter gentilis, Buteo buteo and Pernis apivorus — A multivariate analysis. Pages 553- 559 in B.-U. Meyburg and R.D. Chancellor [Eds.], Raptors in the modern world. World Working Group Birds Prey, Berlin, Germany. . 1991. Interspecific interference competition in three European raptor species. Ethol. Ecol. Evol. 3:127- 143. Kostrzewa, R. and A. Kostrzewa. 1991. Winter weather, spring and summer density, and subsequent breeding success of Eurasian kestrels, common buz- zards, and northern goshawks. Auk 108:342-347. Llwellyn, P.J. 1991. Assessing adult raptors prior to release. Pages 33-47 in Raptor rehabilitation work- shop. London Zoo, The Hawk Trust, The Hawk Board, London, U.K. AND P.F. Brain. 1983. Guidelines for the re- habilitation of injured raptors. Int. Zoo Yearb. 23:121- 125. Lovari, S. 1974. The feeding habits of four raptors in central Italy. Raptor Res. 8:45-57. Manzi, A. and M. Pellegrini. 1989. Dati sulla bio- logia riproduttiva della poiana ( Buteo buteo) in un’area della fascia collinare abruzzese. Avocetta 13:109-114. MaAosa, S. and P.J. Cordero. 1992. Seasonal and sexual variation in the diet of the common buzzard in northeastern Spain. /. Raptor Res. 26:235-238. Meyers, J.M. and D.L. Miller. 1992. Post-release activity of captive- and wild-reared bald eagles. J. Wildl Manage. 56:744-749. Nelson, R.W. 1977. On the diagnosis and “cure” of imprinting in falcons which fail to breed in captivity Pages 39-49 in J.E. Cooper and R.E. Kenward [Eds.], Papers on the veterinary medicine and domestic breed- ing of diurnal birds of prey. British Falconers’ Club, Oxford, U.K. Pendleton, B.A.G., B.A. Millsap and K.W. Cline 1987. Raptor management techniques manual. Nat. Wildl. Fed., Sci. Tech. Ser. No. 10, Washington, DC U.S.A. Roell, A. 1982. A comparison of nest defence by jack- daws, rooks, magpies and crows. Behav. Ecol. Sociobiol 11 : 1 - 6 . Servheen, C. and W. English. 1979. Movements of rehabilitated bald eagles and proposed seasonal move- ments patterns of bald eagles in the Pacific northwest. Raptor Res. 13:79-88. Sherrod, S.K., W.R. Heinrich, W.A. Burnham, J.H. Barclay and T.J. Cade. 1982. Hacking: a method for releasing peregrine falcons and other birds of prey. The Peregrine Fund, Boise, ID U.S.A. Siegel, S. 1956. Nonparametric statistics for the be- June 1994 Behavior of Released Buzzards 107 havioral sciences. McGraw-Hill Book Co., New York, NY U.S.A. Tubbs, C.R. 1974. The buzzard. David & Charles, Lon- don, U.K. Wakeley, J.S. 1978. Hunting methods and factor af- fecting their use by ferruginous hawks. Condor 80:327- 333. Weaver, J.D and T.J. Cade (Eds.). 1991. Falcon propagation. The Peregrine Fund, Boise, ID U.S.A. White, G.C. and R.A. Garrott. 1990. Analysis of wildlife radio-tracking data. Academic Press, San Di- ego, CA U.S.A. Received 8 July 1993; accepted 8 February 1994 Short Communications J. Raptor Res. 28(2): 108-1 09 © 1994 The Raptor Research Foundation, Inc. Parathion Poisoning of Mississippi Kites in Oklahoma J. Christian Franson 1 U.S. Fish and Wildlife Service , National Wildlife Health Research Center , 6006 Schroeder Road, Madison, WI 53711 U.S. A. Key WORDS: Ictinia mississippiensis; Mississippi kite; parathion; poisoning. Parathion (phosphorothioic acid O, O-diethyl 0-[4-ni- trophenyl] ester) is a broad spectrum organophosphorus insecticide, used on a variety of crops and occasionally for mosquito control, and is highly toxic to birds (Smith 1987). Intentional poisoning with parathion is reported to have killed more than 8000 red-winged blackbirds ( Agelaius phoeniceus ), common grackles (Quiscalus quiscula), brown- headed cowbirds ( Molothrus ater) and European starlings (Sturnus vulgaris ) in two separate instances (Stone et al. 1984), Use of parathion on wheat fields has resulted in the mortality of about 1600 Canada geese ( Branta cana- densis) and other waterfowl in one instance (White et al. 1982) and about 200 Canada geese in another (Flickinger et al. 1991). More than 200 laughing gulls (Larus atricilla) died near cotton fields treated with parathion (White et al. 1979). Secondary poisoning of raptors, resulting from the consumption of prey exposed to parathion, has been reported experimentally and in the field. Stone et al. (1984) found two dead red-tailed hawks ( Buteo jamaicensis) , a Cooper’s hawk (Accipiter cooperii) and an American kestrel ( Falco sparvenus) that had fed on blackbirds killed by parathion. One of four American kestrels died after being fed cricket frogs (Acris crepitans) that had been exposed to 10 ppm parathion for 96 hr (Fleming et al. 1982). The Mississippi kite ( Ictinia mississippiensis) is highly insec- tivorous (Brown and Amadon 1968) and is thus subject to secondary poisoning resulting from consumption of in- sects exposed to pesticides. I report here an instance of secondary parathion poisoning in wild Mississippi kites. Study Area and Methods On 25 August 1988, two sick and 14 dead Mississippi kites were collected at the edge of a golf course near Altus in southwest Oklahoma. One owl, two rabbits, and several 1 Present address: U.S. National Biological Survey, Na- tional Wildlife Health Research Center, 6006 Schroeder Road, Madison, WI 53711 U.S. A. ground squirrels, all of unidentified species, were also found dead in proximity to the kites but were not exam- ined. Adjacent to the golf course were cotton fields recently sprayed with pesticides and, although inquiries were made, the specific compound(s) used remain unknown. There was no history of recent pesticide application to the golf course. Three of the dead kites were sent to the National Wildlife Health Research Center for necropsy. Brains from these three carcasses, and from one bird collected as a control by shooting, were tested for cholinesterase activity by the method of Ellman et al. (1961) as modified by Hill and Fleming (1982). Stomach contents were pooled from the three birds found dead and sent to the Patuxent Wild- life Research Center and analyzed by column extraction and gas chromatography for 24 organophosphorus com- pounds and six carbamates (Belisle and Swineford 1988, Patuxent Analytical Control Facility standard operating procedure 0-25.00). The lower limit of reportable residues was 0.1 ppm wet weight for organophosphorus compounds and 2.45-4.90 ppm wet weight for carbamates. Results and Discussion Clinical signs exhibited by the two sick birds included frothy oral discharge, weakness, inability to stand, and stumbling gait — all compatible with exposure to an an- ticholinesterase agent (Grue et al. 1991). These birds re- covered after being given ground beef and water. Exam- ination of the three carcasses revealed that two were adult females and the third was a male of undetermined age. All three were in fair body condition with only traces of subcutaneous fat, had large amounts of unidentified insect remains in their stomachs, and no lesions suggestive of trauma or infectious disease. Brain cholinesterase activities in the three birds found dead were 1. 0-1.1 jumol/min/g (wet weight), compared with 9.2 jumol/min/g (wet weight) for the control bird. These results suggested death was due to an anticholinesterase pesticide (Ludke et al. 1975) and incubation of the sample for 18 hr at 37°C resulted in no increase of brain cholinesterase activity, implicating an organophosphorus compound (Hill and Fleming 1982). Parathion (0.69 ppm wet weight) was the only pesticide found in detectable levels in the sample of pooled stomach contents, and its presence in the sample was confirmed by gas chromatography/mass spectroscopy. The history of recent pesticide application to adjacent cotton fields, the proximity of sick Mississippi kites ex- 108 June 1994 Short Communications 109 hibiting clinical signs compatible with anticholinesterase poisoning, and laboratory findings in kites found dead point to parathion as the cause of mortality in this event. The presence of insect remains and parathion in the stom- achs of these birds suggest they were secondarily poisoned after consuming insects exposed to parathion, probably applied to cotton fields adjacent to the golf course. This is the first documentation of Mississippi kites dying of an- ticholinesterase poisoning and parallels a case in south Texas where laughing gulls died after feeding on insects in cotton fields recently sprayed with parathion (White et al. 1979). Resumen. — El 25 de agosto de 1988 se encontraron dos individuos enfermos de Ictinia mississippiensis y 14 indi- viduos muertos, en el campo de golf Altus, Oklahoma. Las senales clinicas observadas sugirieron un envenenamiento por anticolinesterasa. Se diagnostico un envenenamiento por “parathion,” luego que la evaluation de laboratorio revelo inhibition de colinesterasa cerebral de un 88-89% y la presencia de “parathion” (0.69 ppm, peso humedo), en el contenido estomacal. Cultivos de algodon adyacentes al campo de golf habian sido recientemente rociados con un (os) pesticida (s) desconocido (s). No hubo antecedentes recientes de aplicacion de pesticidas al campo de golf. El contenido estomacal consistio en restos de insectos y es probable que los individuos de I. mississippiensis se hayan envevenado secundariamente, luego de consumir insectos expuestos a la aplicacion de “parathion” en los campos de algodon. [Traduction de Ivan Lazo] Acknowledgments I thank J. Andreasen for bringing this case to my at- tention and staff at the National Wildlife Health Research Center and Patuxent Wildlife Research Center for labo- ratory support. T. Custer and L. Glaser reviewed the manuscript. Literature Cited Belisle, A. A. and D.M. Swineford. 1988. Simple, specific analysis of organophosphorus and carbamate pesticides in sediments using column extraction and gas chromatography. Environ. Toxicol. Chem. 7:749- 752. Brown, L. and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw-Hill Book Co., New York, NY U.S.A. Ellman, G.L., K.D. Courtney, V. Andres, Jr. and R.M. Featherstone. 1961. A new and rapid col- orimetric determination of acetylcholinesterase activity Biochem. Pharmacol. 7:88-95. Fleming, W.J., H. De Chacin, O.H. Pattee and T.G Lamont. 1982. Parathion accumulation in cricket frogs and its effect on American kestrels. J. Toxicol Environ. Health 10:921-927. Flickinger, E.L., G. Juenger, T.J. Roffe, M.R. Smith and R.J. Irwin. 1991. Poisoning of Canada geese in Texas by parathion sprayed for control of Russian wheat aphid. J. Wildl. Dis. 27:265-268. Grue, C.E., A. D.M. Hart and P. Mineau. 1991. Bi- ological consequences of depressed brain cholinesterase activity in wildlife. Pages 152-209 in P. Mineau [Ed.], Cholinesterase-inhibiting insecticides: their impact on wildlife and the environment. Vol. 2. Elsevier, Am- sterdam, The Netherlands. Hill, E.F. and W.J. Fleming. 1982. Anticholinester- ase poisoning of birds: field monitoring and diagnosis of acute poisoning. Environ. Toxicol. Chem. 1:27-38. Ludke, J.L., E.F. Hill and M.P. Dieter. 1975. Cho- linesterase (ChE) response and related mortality among birds fed ChE inhibitors. Arch. Environ. Contam. Tox- icol. 3:1-21. Smith, G.J. 1987. Pesticide use and toxicology in re- lation to wildlife: organophosphorus and carbamate compounds. U.S. Fish Wildl. Serv. Resour. Publ. 170, Washington, DC U.S.A. Stone, W.B., S.R. Overmann and J.C. Okoniewski. 1984. Intentional poisoning of birds with parathion. Condor 86:333-336. White, D.H., K.A. King, C.A. Mitchell, E.F. Hill and T.G. Lamont. 1979. Parathion causes second- ary poisoning in a laughing gull breeding colony. Bull Environ. Contam. Toxicol. 23:281-284. , C.A. Mitchell, L.D. Wynn, E.L. Flickinger and E.J. Kolbe. 1982. Organophosphate insecticide poisoning of Canada geese in the Texas panhandle. J Field Ornithol. 53:22-27. Received 20 November 1993; accepted 3 February 1994 /. Raptor Res. 28(2):1 10-1 12 © 1994 The Raptor Research Foundation, Inc. Status and Reproduction of the Peregrine Falcon at a Coastal Lagoon in Baja California Sur, Mexico Aradit Castellanos, Federico Salinas-Zavala and Alfredo Ortega-Rubio Centro de Investigaciories Biologicas del Noroeste, S.C., Div. de Biol. Terr., Apdo. Postal 128, La Paz, B.C.S, Mexico Key WORDS: peregrine falcon; nesting; Mexico; Baja Cali- fornia; Falco peregrinus. The peregrine falcon ( Falco peregrinus) is considered an endangered species worldwide (King 1981). Its status is not well known in Mexico (Banks 1969, Fyfe et al. 1976). Peregrine distribution has been considered to be restricted to the north and northwest of Mexico (see Thelander 1978), with the largest numbers in the Gulf of California and the Baja California peninsula (Banks 1969, Porter et al. 1988). Banks (1969) estimated the Gulf of California and the Baja California peninsula peregrine populations to contain about 66 nests, 38 of them on the Pacific side. However, later reports show the population on the west coast of the peninsula to be very small, declining drasti- cally, or even disappearing (Anderson 1976, Porter et al. 1978, 1988). This decline was apparently at least partly caused by high levels of organochlorine pesticides (Porter et al. 1978, 1988, Kiff 1988). Since 1977, when only one peregrine nest site was known on the Pacific side of Baja California, little additional information has been obtained for the west coast (Porter et al. 1988). During 1993, we found several active nests in the Ojo de Liebre (Scammon’s) Lagoon, a location without historical nesting records. Here, we report on the peregrine status at this location, and provide information on nesting chronology and reproductive success. Study Site and Methods Ojo de Liebre Lagoon is located on the west coast of the middle Baja California peninsula, about 650 km south of the United States/Mexico border (Fig. 1). It is the largest of three lagoons (360 km 2 ) that open to the Vizcaino Bay. Descriptions of the lagoon can be found in Lewis and Ebeling (1974) and Saunders and Saunders (1981). To locate peregrine nests, we explored potential sites, such as man-made structures located on the lagoon by boat, and investigated the islets on foot. Each nest found was checked directly at least four times between the third week of March and the third week of June. A nest where eggs were laid was considered active; a nest where at least one young fledged was considered productive. Results and Discussion We found three breeding peregrine pairs in the lagoon. Two nests were on top of metallic, 3-m high, channel markers in the water near the sand dunes on the coast. These towers were constructed after 1967 (J. Peralta pers. comm.). The third nest was on the ground, in a small conical rocky cavity (40 x 60 x 120 cm), on a low islet. This islet was visited by coyotes {Canis latrans ) which periodically eradicated the ground-nesting ospreys {Pan- dion haliaetus ) there (Kenyon 1947, Jehl 1977, Henny and Anderson 1979, Castellanos 1983). According to Banks (1969), no breeding peregrines were sighted at the Ojo de Liebre Lagoon. Since then, there have been no additional peregrine sightings or reported nests in this area (see Banks 1969, Porter et al. 1988, Wilbur 1987). However, there are several unpublished sightings of resident peregrines and nesting pairs in this area for 1977 (C. Henny and D. Anderson pers. comm.), 1984, and 1992 (F. Jaramillo and F. Heredia pers. comm.) Nesting occurred between the first part of March, when the eggs were laid, to late June, when all the young had abandoned their nests or were able to fly. Laying seems to have occurred between February and March, which is consistent with previous reports of egg laying dates (Porter et al. 1988). Eggs apparently hatched between the last week of March and the third week of April. The young fledged between the second week of May and the third week of June. The clutch size averaged 3.3 eggs. The occurrence of two sets of three eggs is consistent with Bancroft (1927) who explained that on the Baja California peninsula, three egg clutches are more frequently laid than clutches of four An average of 3.0 nestlings and 2.6 fledglings was pro- duced in each active nest; both values are greater than those reported (nestlings = 2.17, fledglings = 1.74) for the Gulf of California peregrines during 1976-1984 (Porter et al. 1988). There was no significant difference between the average number of fledglings produced on the Gulf of California and this study ( t = 1.76, df = 28, P > 0.05) Our exploration revealed a limited number of potential nesting sites such as cliffs or relatively secure man-made structures in the study area. Indeed, we believe that the observed peregrines represented the total number of res- ident breeding pairs in the Ojo de Liebre Lagoon. Two of the nests were located on towers constructed in the late 1960s and the third was in a site which had been visited by coyotes for several years, presumably preventing per- egrine nesting. Thus, we believe that peregrine falcons have been nesting in the lagoon for no more than 20 yr Our data suggest that Ojo de Liebre Lagoon is an im- portant peregrine breeding location in the middle west coast of Baja California. However, commercial fishing, tourism and channel markers maintenance activities are the primary threats to the peregrines in the area. The ground nest is accessible by walking visitors and fishermen who use the islet as a base. Nests on towers can be disturbed by fishermen operating around the towers or by the main- tenance workers. Consequently, we believe that a special 110 June 1994 Short Communications 111 0J0 DE LIEBRE LAGOON Cedros Is. Natividad Is SAN IGNACIO LAGOON O STUDY AREA SCALE " I " ' ■f 8 3 Figure 1. Location of the Laguna Ojo de Liebre (Scammon’s Lagoon), Baja California Sur, Mexico. 112 Short Communications Vol. 28, No. 2 effort needs to be made by government agencies to protect these nesting sites. Resumen. — El halcon peregrino ( Falco peregrinus ) esta considerado mundialmente en peligro y su estatus en Mex- ico es poco conocido. En recientes reportes se considera a la poblacion anidante en la costa del Pacifico de la pen- insula de Baja California desapareciendo o muy reducida en numeros. Durante 1993, nosotros encontramos tres pa- rejas de peregrino en la laguna Ojo de Liebre, en la costa del Pacifico de la peninsula, donde no habia registros pre- vios de anidamiento. Los nidos estaban ubicados uno di- rectamente en el suelo y dos sobre torres de senalamiento maritimo dentro del agua. El anidamiento ocurrio entre la primera mitad de marzo y finales de junio. El numero promedio de volantones producido por nido activo fue de 2.6. La principal fuente de amenaza para los peregrinos en el area de estudio es la perturbation humana. Reco- mendamos la protection efectiva de los sitios de anida- miento. [Traduction Autor] Acknowledgments We thank M. Acevedo for his assistance in the field work, F. Jaramillo, F. Heredia, C. Henny and D. An- derson for their additional data on peregrine records, S. Arguelles and H. Romero for their academic support, M. Layman and A. Jenkins for providing us with literature, and R. Bowers for clarifying the English. The manuscript benefitted from comments of D.W. Anderson and C.J. Henny. This work was financed by the Centro de Inves- tigaciones Biologicas del Noroeste, the Secretaria de Ed- ucation Publica and the Consejo National de Ciencia y Tecnologia. We also appreciate the support provided by the Secretaria de Desarrollo Social-Delegation B.C.S. and the Compama Exportadora de Sal, S.A. Literature Cited Anderson, D.W. 1976. The Gulf of California, Mex- ico. Pages 270-271 in R.W. Fyfe, S.A. Temple, and T.J. Cade [Eds.], The North American peregrine fal- con survey. Can. Field-Nat. 90:228-273. Bancroft, G. 1927. Notes on the breeding coastal and insular birds of central Lower California. Condor 29: 188-195. Banks, R.C. 1969. The peregrine falcon in Baja Cali- fornia and the Gulf of California. Pages 81-91 in J.J. Hickey (Ed.), Peregrine Falcon Populations. Univ. Wise. Press, Madison, WI U.S.A. Castellanos, A. 1983. Observaciones sobre distribu- tion, abundancia y productividad del aguila pescadora en la laguna Ojo de Liebre-Guerrero Negro, B.C.S., Mexico. Pages 98-103 in Reunion sobre “La Fauna y su Medio Ambiente” Noroeste de Mexico-Suroeste Estados Unidos de America. Gen. Tech. Rept. WO- 36S. U.S.D.A. Forest Serv., Washington, DC U.S.A. Fyfe, R.W., S.A. Temple and T.J. Cade. 1976. The 1975 North American peregrine falcon survey. Can. Field-Nat. 90:228-273. Henny, C.J. and D.W. Anderson. 1979. Osprey dis- tribution, abundance, and status in western North America: III. The Baja California and Gulf of Cali- fornia Population. Bull. South. Calif. Acad. Sci. 78:89- 106. Jehl, J.R., Jr. 1977. History and president status of ospreys in northwestern Baja California. Pages 241- 245 in J.C. Ogden [Ed.], Trans. N. Am. Osprey Res. Conf. U.S. Natl. Park Serv. Washington, DC U.S.A. Kenyon, K.W. 1947. Breeding populations of the Os- preys in Lower California. Condor 49(4):152-158. Kiff, L.F. 1988. Changes in the status of the peregrine in North America: an overview. Pages 123-139 in T. Cade, J. Enderson, C. Thelander and C. White (Eds.), Peregrine falcon populations: their management and recovery. The Peregrine Fund, Inc. Boise, ID U.S.A. King, W. 1981. Endangered birds of the world. The ICBP bird red data book. Smithsonian Inst. Press. Washington, DC U.S.A. Lewis, L.R. and P.E. Ebeling. 1974. Sea guide. Vol. II Baja California. SEA publications, Inc. Newport Beach, CA U.S.A. Porter, R.D., G. Craig, D. Ellis, J. Enderson and W. Hunt. 1978. Status of the peregrine falcon in the Rocky Mountains and the southwestern United States, Baja California and Mexico (South of Texas). Pages 26-32 in P.P. Schaeffer and S.M. Ehlers (Eds.), The current status of peregrine falcon populations in North America. Nat. Audubon Soc., Western Educa- tion Center, Tiburon, CA U.S.A. , M.A. Jenkins, M.N. Kirven, D.W. Anderson and J.O. Keith. 1988. Status and reproductive per- formance of marine peregrines in Baja California and the Gulf of California, Mexico. Pages 105-114 in T. Cade, J. Enderson, C. Thelander and C. White (Eds.), Peregrine falcon populations: their management and recovery. The Peregrine Fund, Inc. Boise, ID U.S.A. Saunders, G. and D. Saunders. 1981. Waterfowl and their wintering grounds in Mexico, 1937-64. U.S.D.I., Fish Wildl. Serv. Res. Publ. 138. Washington, DC U.S.A. Thelander, C.G. 1978. The status of peregrine falcons in California— past and present. Pages 3-12 in P.P. Schaeffer and S.M. Ehlers (Eds.), The current status of peregrine falcon populations in North America. Nat. Audubon Soc., Western Education Center, Tiburon, CA U.S.A. Wilbur, S.R. 1987. Birds of Baja California. Univ. Calif. Press. Berkeley, CA U.S.A. Received 7 November 1993; accepted 10 February 1994 /. Raptor Res. 28(2):113-114 © 1994 The Raptor Research Foundation, Inc. Successful Nesting by a Pair of Bald Eagles at Ages Three and Four Daniel W. Mulhern U.S. Fish and Wildlife Service, 315 Houston St., Suite E, Manhattan, KS 66502-6172 U.S.A. Michael A. Watkins U.S. Army Corps of Engineers, Natural Resources Management Branch, 700 Federal Building, 601 E. 12th St., Kansas City, MO 64106-2896 U.S.A. M. Alan Jenkins and Steve K. Sherrod G.M. Sutton Avian Research Center, Inc., P.O. Box 2007, Bartlesville, OK 74005-2007 U.S.A. Key Words: bald eagles; Kansas; nesting; plumage; sub- adult. Sexual maturity in the bald eagle ( Haliaeetus leucoce- phalus) is commonly thought to occur after the bird attains a completely white head and tail, typically at age 4 yr (Clark and Wheeler 1987). Various factors probably in- fluence initial reproductive attempts by individual eagles, so plumage is not always a reliable indicator of age or reproductive readiness (McCollough 1989). In 1993, a pair of bald eagles in subadult plumage nested in eastern Kansas. The nesting pair consisted of a 4-yr-old male and 3-yr-old female, and they successfully fledged one eaglet. Observations The nesting eagles were found at Hillsdale Reservoir in eastern Kansas, 40 km south of Kansas City. The pair occupied a nest in a large dead tree standing in water. They were first observed on the nest on 25 March 1993. Each bird wore a standard U.S. Fish and Wildlife Service aluminum band on one leg and a colored band on the opposite leg, and could thus be traced to its origin. The male parent was one of two males fledged in 1989 from a nest approximately 45 km northwest of the Hillsdale nest site. That was the first year bald eagles were docu- mented nesting in Kansas since presettlement; Goss (1891) reported the bald eagle as resident in Kansas, with egg laying beginning in March, but provided no information on specific nests or locations. This eagle and its sibling fledged 16 July 1989, and were live trapped and banded 23 July. They left the area 9 August 1989, and neither was reported again until 1993. The female hatched 16 January 1990 at the G.M. Sutton Avian Research Center in Bartlesville, Oklahoma, from an egg taken from a nest in Osceola County, Florida. She fledged 8 April from a hack tower at Eufaula Reservoir in eastcentral Oklahoma, approximately 345 km south of the Hillsdale nest, and was last seen in the area on 29 May 1990. She was not reported again until 1993. Ra- diotracking of previously hacked eagles by Sutton Center personnel indicate they sometimes initially disperse north as far as Canada. We saw the parents exhibiting nestling feeding behavior on 7 and 8 April, but no eaglets were visible. No subse- quent feeding behavior was observed over the next several days until 16 April, when one parent was observed feeding a small chick. We do not know if it was the same eaglet fed on 7 April. The eagles were monitored periodically from April through June. Between 25 and 29 June the eaglet fledged, and was last seen at the reservoir on 17 July. High water levels in the reservoir during much of July and early August prevented adequate monitoring, so we do not know the actual departure date. Reports of nesting by bald eagles in subadult plumage are rare. Hoxie (1910) reported successful reproduction by a pair in which both birds were in immature plumage, though the female was “beginning to show distinct traces of white in the tail.” One hacked bird in Saskatchewan may have bred when only 3 yr old (Gerrard and Bortolotti 1988), and Hatcher (1991) reported successful nesting by a 3-yr-old male released in Tennessee. There are infrequent reports of birds in subadult plumage mating with an adult (Bent 1937, Stalmaster 1987). Sherrod et al. (1976) re- ported two different females in “eye-stripe” plumage that mated with males in adult plumage; one female laid eggs that did not hatch, but the other successfully produced two eaglets. “Eye-stripe” plumage, believed to “precede that of adult,” is described as a basically white head with a brown eye stripe, and a white tail with brown banding or blotching (Sherrod et al. 1976). This plumage is analogous to subadult plumage E reported for bald eagles by Stal- master (1987). We observed a pair at another reservoir in eastern Kansas in 1993, one of which showed plumage similar to subadult E. This pair appeared to be incubating, but for unknown reasons abandoned the nest prematurely. Hancock (1973) reported that three of four pairs of adult bald eagles that eventually hatched eggs in captivity produced infertile eggs their first year of nesting, and no fertile eggs were produced until both parents were at least 5 yr old. Maestrelli and Wiemeyer (1975) speculated that the initial failure to reproduce by a captive 5-yr-old male and an 8-yr-old female was due to the male’s physical immaturity. Captive bald eagles and golden eagles ( Aquila chrysaetos ) may attain adult plumage and begin repro- ducing later than wild birds, possibly due to diet and other factors (Jollie 1947, McCollough 1989). Sandeman (1957) reported that subadult golden eagles sometimes occupy territories, form pairs, and construct nests, but generally produce no eggs. However, Teresa 113 114 Short Communications Vol. 28, No. 2 (1980) reported an adult and a bird in subadult plumage which fledged two young. Teresa (1980) also stated that breeding by subadults in most eagle species occurs only under unusually favorable or unfavorable conditions. In Kansas, recent bald eagle nestings occurred after many decades of absence, and many suitable nesting sites are available. This may be creating an unusually favorable condition for population growth. The bald eagle nest at Hillsdale Reservoir provided a unique opportunity to observe known-age birds in their first nesting attempt and to document plumage character- istics in wild birds of known age. The plumage of the male was virtually identical to subadult plumage E de- scribed by Stalmaster (1987). The plumage of the female closely matched Stalmaster’s subadult plumage D. Had we not known this bird’s age, we might have concluded that she was a 4-yr-old in delayed plumage. That conclu- sion would have been reinforced by her nesting success. The origin of the 4-yr-old male, a product of the first Kansas nest documented since presettlement, indicates the importance of ensuring breeding success by bald eagles initially colonizing a nesting area. Resumen. — Una paraja de individuos de la especie Ha- liaeetus leucocephalus con plumaje subadulto establecieron un territorio de nidificacion sobre una reserva al este de Kansas y en la primavera de 1993. Ambos individuos tenian anillos coloreados en sus patas, las que permitieron conocer sus edades y lugares de origen. El macho de cuatro anos de edad, con plumaje de volanton en 1989, corres- pondiente al primer nido activo documentado en Kansas desde la precolonizacion. La hembra de tres anos de edad, fue registrada en Oklahoma en 1990. La pareja empollo exitosamente un polleulo. [Traduccion de Ivan Lazo] Acknowledgments We thank the Kansas Department of Wildlife and Parks, the Corps of Engineers, and volunteer Eva Willis for as- sistance in monitoring eagle nests. We also thank Michael Lockhart, George Allen, Vernon Tabor, Eva Willis, and John Ramsey for reviewing drafts of this manuscript. Literature Cited Bent, A.C. 1937. Life histories of North American birds of prey. Part I. U.S. Natl. Mus. Bull. 167. Clark, W.S. and B.K. Wheeler. 1987. A field guide to hawks. Houghton Mifflin Company, Boston, MA U.S. A. Gerrard, J.M. and G.R. Bortolotti. 1988. The bald eagle; haunts and habits of a wilderness monarch Smithsonian Inst. Press, Washington, DC U.S.A. Goss, N.S. 1891. History of the birds of Kansas. G.W. Crane & Co., Topeka, KS U.S.A. Hancock, D. 1973. Captive propagation of bald eagles Hahaeetus leucocephalus — a review. Int. Zoo Yearb. 13 244-249. Hatcher, R.M. 1991. Computer model projections of bald eagle nesting in Tennessee. J. Tenn. Acad. Sci. 66 225-228. Hoxie, W.J. 1910. Notes on the bald eagle in Georgia. Auk 27:454. Jollie, M. 1947. Plumage changes in the golden eagle. Auk 64:549-576. Maestrelli, J.R. andS.N. Wiemeyer. 1975. Breeding bald eagles in captivity. Wilson Bull. 87:45-53. McCollough, M.A. 1989. Molting sequence and aging of bald eagles. Wilson Bull. 101:1-10. SANDEMAN, P.W. 1957. The breeding success of golden eagles in the northern Grampians. Scott. Nat. 69:148- 152. Sherrod, S.K., C.M. White, and F.S.L. Williamson. 1976. Biology of the bald eagle on Amchitka Island, Alaska. Living Bird 15:143-182. Stalmaster, M.V. 1987. The bald eagle. Universe Books, New York, NY U.S.A. Teresa, S. 1980. Golden eagles successfully breeding in subadult plumage. Raptor Res. 14:86-87. Received 18 October 1993; accepted 1 March 1994 J Raptor Res. 28(2):1 15-1 17 © 1994 The Raptor Research Foundation, Inc. Traps for Capturing Territorial Owls S. M. Redpath and I. Wyllie Institute of Terrestrial Ecology, Monks Wood Experimental Station , Abbots Ripton, Huntingdon , Cambridgeshire, PEI 7 2LS. U.K. Key WORDS: lures ; Strix aluco; tawny owl; territorial be- havior; trapping , A variety of techniques have been used to capture rap- tors (e.g., Berger and Hamerstrom 1962, Meng 1971, Fuller and Christenson 1976, Kenward et al. 1983, Bull 1987). Raptors are generally easier to capture during the breeding season when they can be caught in nest boxes (e.g., owls) or by placing traps at or near the nest. Outside the breeding season birds are more difficult to catch as their position at any one time is harder to predict. Excep- tions to this are some North American owls which can be caught with comparative ease (Forsman 1983, Bull 1987). Many owls defend territories, and can be caught by exploiting their behavior toward intruders. For example, the tawny owl (Strix aluco) vigorously defends territories throughout the year (Southern 1970), and can be caught using tape lures to attract birds to mist nets (Hirons 1976). Outside the breeding season tawny owls have also been caught while roosting in nest boxes (Baudvin and Dessolin 1992) or with the use of live prey as lures (Hardy 1992). Methods During the winters of 1990-91 and 1991-92, three techniques were tested in an attempt to capture tawny owls in woods in Cambridgeshire, southeast England. Two of these traps rely on the fact that territorial owls defend their territory against intruders. The third uses prey to attract owls to the traps. Mist Net and Tape Lure. Nets were set up inside known owl territories with a continuous tape of a hooting male placed underneath. These were watched for ap- proximately 2 hr. Large Modified Chardoneret Trap. This trap had three compartments; a large lower one containing a male tawny owl, and two upper ones in which owls were caught (Fig. 1). The lure owl was provided with suitable perches and cover from rain. The lid above each of the top com- partments had a piece of stiff wire running down its center, which extended beyond its base and, when the trap was set, rested in a hole in the wooden trigger. The trigger was held against the wall of the trap by pressure from the lid wire. The perch was fixed to the wall of the trap and to the trigger. Pressure on the perch pulled the trigger down, which released the wire, allowing the lid to shut. The trap was held shut by two hooks at the end of the lid which snagged on the wire of the trap. The whole trap was constructed of 5 cm weldmesh. The trap was set with perches just above and in front of the open lids. It was placed in a territory at dusk, and checked at dawn. Small Modified Chardoneret Traps. These traps op- erated as for the above trap, but this time the lower com- partment was smaller (10 cm high) and contained prey species (house sparrows [Passer domesticus ] or laboratory mice) as lures. The traps were similar in design to the falling-lid trap described by Kenward et al. (1983), based on an original design by Hamilton (Lundberg 1933). The lower compartment had a mesh size of 1 cm and contained food, water, and shelter for the lure species. Again, the traps were set with a perch just above and in front of the open lid. One or two of these traps were placed in each territory just before dusk and checked at dawn. Results and Discussion None of the six capture attempts using nets was suc- cessful. Owls were twice seen to be attracted to the taped calls, but flew over or around the net. Due to the length of time required to set up and watch these nets, this method was dropped in favor of the traps. When the success rate of the two types of trap was compared, we found that the trap using the live owl (11 owls caught in 32 trap nights) was significantly more successful (x 2 = 50.3, P < 0.001) than the trap using live prey lures (5 owls caught in 253 trap nights). No more than one owl was ever caught per night per territory. All the owls were fitted with radio- transmitters and all were found to be territorial birds. Some North American owls such as spotted owl ( Strix occidentals ) and great grey owl ( Strix nebulosa ) appear relatively unafraid of humans and can be caught with apparent ease (Forsman 1983, Bull 1987). This is not the case with tawny owls which invariably fly when humans approach their roost sites. Outside the breeding season, tawny owls have previously been caught either in nest boxes (Baudvin and Dessolin 1992), with mist net and tape lures (Hirons 1976), or using live prey as lures (Har- dy 1992). The use of nest boxes for roosting in the winter appears to depend on habitat type (Petty 1992), with birds less likely to use boxes where natural cover (e.g., coniferous trees) is abundant. In the present study owls rarely used boxes to roost in, preferring the cover of plants such as old man’s beard ( Clematis vitalba ) or ivy (Hedera helix ) The use of nets and tape lures to catch owls also proved ineffective and time consuming. The modified Chardoneret traps had an advantage in that they could be easily set and left overnight. Placing a live owl inside a bird’s territory proved more effective at attracting owls to the trap than using prey species and this technique presents an effective method of capturing territorial owls, which compares favorably to other designs used to capture raptors outside the breeding season (see Kenward et al. 1983). Resumen. — Rapaces, tales como Strix aluco son a menudo dificiles de capturar en la estacion no reproductiva. Es- 115 116 Short Communications Vol. 28, No. 2 hooks shelter trigger perch lure 5cm weldmesh Figure 1. Large modified Chardoneret using a captive owl as a lure. Owls flew from an external perch into one of the top compartments, landing on the internal perch and releasing the trigger, thereby allowing the lid to close. June 1994 Short Communications 117 tudios previos describen la captura de aves mientras des- cansan en nidos caja, o usando redes de niebla y graba- ciones senuelo. En este estudio, las aves fueron raramente encontradas descansando en nidos caja, de manera que otras tres tecnicas fueron comparadas. Primero, redes de niebla fueron levantadas sobre una grabacion senuelo y observadas durante dos horas. Los buhos fueron atraidos por la grabacion pero volaron sobre o alrededor de la red. No hubo captura en seis intentos. Segundo, una Trampa Chardoneret modificada fue construida, se uso un macho vivo de S. aluco como senuelo. El buho cautivo se mantuvo en el compartimento inferior y las capturas se realizaban en el superior. El propio peso del buho aterrizando sobre una percha en el compartimento superior accionaba el mecanismo de cierra de la trampa. En la tercera tecnica se utilizo una pequena version de la Trampa de Char- doneret modificada, aunque esta vez se utilizaron especies presa como senuelo y dispuestas en el fondo del compar- timento. De las dos trampas, la primera (con buhos vivos) fue mas efectiva (11 buhos en 32 noches-trampa) que la trampa que utilize especies presas (cinco buhos en 253 noches-trampa). La diferencia fue significativa (x 2 = 50.3, P < 0.001). Esta trampa utiliza la conducta agresiva de buhos territoriales hacia intrusos y representa un efectivo metodo para capturar buhos territoriales. [Traduction de Ivan Lazo] Literature Cited it Baudvin, H. and J.L. Dessolin. 1992. Analyse de la morphometric de la chouettes hulottes Strix aluco en Bourogne. Alauda 60:93-104. Berger, D.D. and F. Hamerstrom. 1962. Protecting a trapping station from raptor predation. J. Wildl. Man- age. 26:203-206. Bull, E.L. 1987. Capture techniques for owls. Pages 291-294 in R.W. Nero, R.J. Clark, R.J. Knapton and R.H. Hamre [Eds.], Biology and conservation of north- ern forest owls. Gen. Tech. Rep. RM-142. U.S. Forest Service, Rocky Mountain Forest and Range Exper. Sta., Fort Collins, CO U.S.A. Forsman, E.D. 1983. Methods and materials for lo- cating and studying spotted owls. U.S. Forest Service Gen. Tech. Rep. PNW-162. Portland, OR U.S.A. Fuller, M.R. and G.S. Christenson. 1976. An eval- uation of techniques for capturing raptors in east-cen- tral Minnesota. Raptor Res. 10:9-19. Hardy, A.R. 1 992. Habitat use by farmland tawny owls Strix aluco. Pages 55-63 in C.A. Galbraith, I.R. Taylor and S. Percival [Eds.], The ecology and conservation of European owls. UK Nature Conservation No. 5, Peterborough, Joint Nature Conservation Committee. Hirons, G. 1976. A population study of the tawny owl (Strix aluco ) and its main prey species in a woodland. Ph.D. dissertation, Oxford Univ., Oxford, U.K. Kenward, R.E., M. Karlbom and V. Marcstrom. 1983. The price of success in goshawk trapping. Rap- tor Res. 17:84-91. LUNDBERG, A. 1933. Handbook for jaktvardare. Fahl- cranz & Co., Stockholm, Sweden. Meng, H. 1971. The Swedish goshawk trap. J. Wildl Manage. 55:832-835. PETTY, S.J. 1992. Ecology of the tawny owl Strix aluco in the spruce forests of Northumberland and Argyll Ph.D. dissertation, Open Univ., Milton Keynes, U.K. Southern, H.N. 1970. The natural control of a pop- ulation of tawny owls ( Strix aluco). J. Zool. Lond. 1 62* 197-285. Received 11 November 1993; accepted 6 February 1994 Letters /. Raptor Res. 28(2): 1 18-1 19 © 1994 The Raptor Research Foundation, Inc. Flush-hunting and Nest Robbing by Peregrine Falcons Between 0610-1000 H on 25 November 1992, we observed the hunting behavior and interactions of an adult pair of peregrine falcons ( Falco peregrinus ) and their two fledged nestlings, in a steep- walled gorge on the lower Orange River, South Africa (28°S, 20°E). The young were still dependent on their parents for food, most of which was provided by the adult male. At 0824 H the adult female was observed making an aerial transfer of food to the juvenile male. The prey appeared to be a half-grown rock pigeon {Columba guinea ) squab. At 0827 H the adult female flew about 50 m to a rock pigeon nest, situated on a grass tussock on an open ledge about 20 m above the floor of the gorge, on the north wall. She removed a nestling, flew to a nearby perch and ate it. While raiding the nest, the peregrine was attacked by an adult rock pigeon. By 0833 H the adult female falcon had finished eating the squab, and returned to the now empty pigeon nest. She was again attacked by the pigeon, which actually landed on the peregrine’s back and dislodged her from the ledge. The falcon fell backwards, turned and caught the pigeon, which managed to break free and fly down the gorge The peregrine chased the pigeon for about 200 m before it found cover among some large boulders in the river bed At 0835 H the peregrine female was seen to visit the pigeon nest for the third time. Again the pigeon defended its nest, but this time the falcon was able to grab and hold on to its attacker, and flew with the pigeon to a ledge 30 m upstream, where she killed it, plucked it and fed on it until 0947 H, when she flew out into the gorge and passed the remains of the pigeon to the juvenile male. At 1 1 15 H on 7 May 1993, ARJ watched a female peregrine at the same site land at a ledge where she was mobbed by two rock pigeons. The falcon tried to catch one of these pigeons and chased it down the gorge for about 200 m before flying back to perch on the cliff. At 1420 H the peregrine flew from a perch about 100 m upriver and landed at the same ledge, and had been perched there for about 5 min before she was again attacked by a pigeon which she caught, apparently very easily, without leaving the ledge. Although the hunting falcon was not seen to rob a pigeon nest at the ledge where this incident took place, this may have occurred sometime previously. Large falcons, and especially peregrines, feed mostly on flying birds, which are caught in aerial chases. Observations of nest robbing by large falcons are infrequent in the literature (W. Fischer 1967, Der Wanderfalk, Ziemsen, Wittenburg; R.B. Treleaven 1981, Br. Birds 74:97; J.L.B. Albuquerque 1984, M.S. thesis, Brigham Young Univ., Provo, UT U.S.A.; A.J. van Zyl 1991, Gabar 6:68), although nestling birds (mostly of ground-nesting species) sometimes are identified from remains gathered at nesting and roosting sites (D.A. Ratcliffe 1980, The peregrine falcon, T. & A.D Poyser, Calton, U.K.; R. Mearns 1983, Bird Study 30:81-90). In contrast, records of common kestrels (F. tinnunculus ) robbing nests are quite frequent (e.g., D.W. Yalden 1980, Bird Study 27:235-238; F. van der Merwe 1986, Promerops 176:12-13; R.A. Pettifor 1990, An. Behav. 39:821-827; A.J. van Zyl 1991; S.K. Woolley 1992, Br. Birds 85:188). Kestrels are relatively slow, active-search hunters, which may account for the higher number of incidents of nest robbing reported for this species than for fast, pursuit-hunting falcons. Given that a nest full of young birds is probably not a typical search image for these high-speed, aerial hunters, we are drawn to speculate on the conditions under which a peregrine might discover and utilize such a food source. African peregrines ( F , p. minor ) apparently “flush-hunt” on their nest cliffs relatively frequently (K. Hustler 1983, Ostrich 54:161-171; W. Tarboton 1984, Raptor Res. 18:131-136; ARJ pers. obs.). This hunting technique can involve the systematic searching of areas of the cliff, either from a perch or from the air, in order to locate, flush and then chase birds perched on the cliff. Falcons that flush-hunt regularly may be more likely to find nestling birds and prey on them than those that do not. We suspect that the frequency with which falcons flush-hunt may increase in situations where cliff-dwelling prey species are abundant in a pair’s hunting range or, at the other extreme, where the frequency with which potential prey fly past cliff sites is low. The former conditions probably occur at the seabird colonies on the western Pacific islands, where flush-hunting by immature peregrines has also been reported (C.M, White cited in Tarboton 1984), and at temperate sea cliffs, where flush-hunting has been observed (A. Parker 1979, Br. Birds 72 104-114) and nest robbing at a gull colony has been recorded (R.B. Treleaven 1981, Br. Birds 74:97). The latter conditions may prevail at lower latitudes (see A.R. Jenkins 1991, Gabar 6:20-24), and flush-hunting has been observed in Argentina (C.M. White cited in Tarboton 1984), southern Brazil (Albuquerque 1984) and Mexico (D.V. Lanning et al. 1977, Nat. Geog. Res. 18:377-388), as well as in tropical Africa. In the first incident described here, the adult male peregrine made at least 17 hunting attempts at flying prey during 118 June 1994 Letters 119 the morning observation period, all within a 1-km stretch of the river gorge, and was successful on four (23.5%) occasions. The pair obviously was not subject to a low availability of flying prey. They were exploiting a prey base that was spatially concentrated in a short length of river gorge, and temporally concentrated by a common activity peak in the early morning. This prey base consisted of an abundance of aerial insectivores and other species found in close association with the river or the cliffs of the river gorge. Rock pigeons, and presumably their nests, were numerous m the gorge. We suspect that nest robbing is a fairly frequent occurrence in this pair. We thank the Foundation for Research Development for financial support. — Andrew R. Jenkins and Anthony J. van Zyl, Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch 7700, South Africa. J Raptor Res. 28(2): 1 19-120 © 1994 The Raptor Research Foundation, Inc. Cannibalism of a Young Barn Owl {Tyto alba) by its Parents Cannibalism occurs fairly frequently in broods of many raptor species (C. Ingram 1959, Auk 76:218-226; C.H. Stinson 1979, Evolution 33:1219-1225; J.K. Terres 1980, Aud. Soc. Encycl. North Am., Alfred A. Knopf, New York, NY U.S.A.). This behavior is adaptive in predatory species in times of food shortages, severe weather conditions, and disturbance at the nest, and contributes to their individual fitness. Cannibalism among barn owls {Tyto alba) has been reported (D.S. Bunn et al. 1981, The barn owl, Buteo Books, Vermillion, SD U.S.A.; B.A. Colvin 1984, Ph.D. diss., Bowling Green, OH U.S.A.; G.M. Lenton 1984, Ibis 126:551-575; Marti 1992, Barn owl, Birds of North Am., Acad Nat. Sci., Phila. 1:1-15), although it occurs less frequently than is popularly believed (D.S. Bunn et al. 1981). When food is abundant, nestling barn owls have been observed to share food with their younger siblings (C.D. Marti 1989 Wilson Bull. 101:132-134); however, when food is scarce, young barn owls have been observed to kill and consume their siblings, an act that could permit them to survive periods of severe food shortages (D.S. Bunn et al. 1981). The killing of an owlet by an adult and feeding it to the other young is the most unlikely of seven different cannibalism scenarios and has not been documented (D.S. Bunn et al. 1981). Reports of adult barn owls killing one of their own injured young and eating it or feeding it to their remaining young has also not previously been reported. Some circumstantial evidence exists to suggest that both of these scenarios can occur in North American barn owls (B.A Colvin 1984). In the process of studying a pair of nesting barn owls, I observed evidence of cannibalism in which one or both of the adults presumably killed and consumed one of their offspring during a period when food was becoming scarce. I observed a pair of barn owls and their offspring on an abandoned herbicide manufacturing facility in Houston, Texas. I visited the site at 1-2 wk intervals from 10 April 1988 through 19 August 1989. The owls used a small brick structure (4.6 x 2.4 x 3.0 m) as a roosting/nesting site. A wooden box (0.3 x 1.2 x 0.3 m) above a small doorway, the only opening to the structure, served as a nest box. On 23 October 1988, a clutch of seven eggs was found in the nest. This was the second of three clutches produced by the owls during this 16-mo period. By 30 October, the first two eggs had hatched and by 12 November, a third egg had hatched and one egg remained in the nest; the other three eggs were missing. The remaining egg never hatched and disappeared within a week. The three owlets were last observed in the nest together on 17 December. On 24 December, both parents were seen at the roost and there were only two young still in the nest. The oldest owlet (57-59 d) was found dead on the floor and I observed the adult male sitting next to it. The owlet appeared to have been dead for about 1-2 d. Its body cavity had been ripped open, and it had been almost completely eaten. Only the wings, feet, skull, and stripped skeleton remained. It was not decapitated as is usually done with live prey and cannibalized young (D.S. Bunn et al. 1981) and its feathers were not scattered around the roost (K.L. Hamilton 1980, Texas J. Sci. 32:175). A necropsy on the dead owlet revealed a broken right humerus. I suspect that this occurred during practice flying within the small enclosed area, but may have been a result of falling out of the nest to the floor (about 2.6 m). The barn owl roost and nest box were inaccessible to the few potential mammalian predators at the site and other avian predation was highly unlikely. In addition, the condition of the owlet’s carcass strongly suggested that it had been eaten by the owls and not by another predator. The hunger of either the parents or the remaining owlets, combined with the colder than normal temperatures at the time, probably led to this cannibalism. Pellet analyses indicated that prey were becoming scarce as winter progressed into 1989, and many birds and insects were found in the diet (unpubl. data). Feeding behaviors such as cannibalism of healthy or injured young can be important in predatory species such as 120 Letters Vol. 28, No. 2 barn owls during times of food shortage. However, this behavior usually is difficult to witness. More observations at raptor nest sites are needed to document the fate of nestlings that mysteriously disappear from their nests and to determine how frequent this behavior is and under what circumstances it occurs. I thank W. McClure for field assistance with the ongoing barn owl study at this site, and J. Shaw, B. Colvin, J Marks, and two anonymous reviewers for valuable comments on an earlier version of the manuscript. — Steven R. Sheffield, Department of Zoology, Oklahoma State University, Stillwater, OK 74078 U.S.A. J. Raptor Res. 28(2): 1 20 © 1994 The Raptor Research Foundation, Inc. Ospreys {Pandion haliaetus ) Scavenging Fish ON Ice The diet and foraging behavior of ospreys ( Pandion haliaetus ) have been studied extensively in North America (A.C. Bent 1937, U.S. Nat. Mus. Bull. 167:352-379; T.C. Dunstan 1974, Wilson Bull. 86:74-76; J.E. Swenson 1978,/. Wildl. Manage. 42:87-90; A. Poole 1989, Ospreys, Cambridge Univ. Press, Cambridge, U.K.; S.P. Fleming et al. 1992, Auk 109:649-654), and other parts of the world (Y.A. Prevost 1982, Ph.D. thesis, Univ. Edinburgh, Scotland; S. Cramp and K.E.L. Simmons 1980, The birds of the western Palearctic, Vol. 2, Oxford Univ. Press, Oxford, U.K.). Live fish, caught by plunging into shallow water, comprised over 99% of the diet in each osprey population studied thus far (Poole 1989). In this paper we provide details of ospreys scavenging dead and dying fish, caught by fishermen, from the ice surface during the first week of nest site occupation in Canada. Between 1 April and 6 April 1993, two ospreys were noted on artificial nest platforms in the Honey Harbour area of Georgian Bay, Lake Huron (44°5TN, 79°49'W). Ice cover was complete during this period on all water bodies within at least 8 km of these nest sites, and the main melt did not occur until the second week of April. In 1991 and 1992 the first ospreys were noted in this area on 7-8 April, and some of these birds flew up to 12 km to reach open- water fishing areas. On at least three separate occasions in the 1-6 April period in 1993, the two ospreys were seen by one of us (EC) soaring and hovering above ice-fishing holes in a small bay 2 km from the nest sites. Fishermen were catching large numbers of black crappie ( Pomoxis nigromaculatus ) at this time, and usually left 15-30 cm fish on the surface of the ice. Since many different ice holes were fished by up to 50 people on some days, dead and dying black crappies were sometimes left unattended beside ice holes for up to 30 min. On several occasions both ospreys swooped down to the ice surface about 100 m from the nearest fishermen, and each flew off with a black crappie. Ospreys have been noted previously to pick up dead or dying fish from the water surface or from shoreline rocks (Bent 1937, Dunstan 1974), but these appear to be the only published accounts of such behavior. We know of no other accounts of ospreys taking fish from the ice surface, but elsewhere in Lake Huron, fledgling ospreys occasionally take fish scraps thrown to them by fishermen (W. Davis pers. comm.). Ospreys regularly use large fish carcasses for nesting material (Bent 1937, Poole 1989), and we have noted this behavior in the Great Lakes. We have also recorded a male osprey picking up and eating a dead largemouth bass ( Micropterus salmoides ) floating at the water surface in Georgian Bay. Ospreys arriving back at nest sites in northern parts of North America are often confronted with extensive ice coverage of foraging areas during the pre-laying period. These observations of freshly caught fish taken at ice-fishing holes reflect the osprey’s adaptability in foraging techniques, and its remarkable tolerance of human presence. The studies of osprey in the Great Lakes basin were funded by the Canadian Wildlife Service-Ontario Region, Environment Canada’s Great Lakes Action Plan, and the Ontario Ministry of Natural Resources. We are also grateful to various colleagues at the Canada Centre for Inland Waters for logistical assistance. — Peter J. Ewins, Canadian Wildlife Service, Environment Canada, Canada Centre for Inland Waters, P.O. Box 5050, Burlington, Ontario, L7R 4A6 Canada, and Elmer Cousineau, Brandy’s Island, Honey Harbour, Ontario POE 1E0, Canada. /. Raptor Res. 28(2):120-121 © 1994 The Raptor Research Foundation, Inc. Unusual Parental Behaviors by Male Northern Goshawks The parental role of male raptors during nesting is typically limited to providing food for their mates and young It is uncommon for male raptors to participate directly in brood rearing, such as brooding or feeding nestlings (L. June 1994 Letters 121 Brown 1976, Birds of prey: their biology and ecology, A&W Publ. Inc., New York, NY U.S.A.; L Newton 1979, Population ecology of raptors, Buteo Books, Vermillion, SD U.S.A.), though it has been documented for some species (L. Brown and D. Amadon 1968, Eagles, hawks and falcons of the world, McGraw-Hill Book Go., New York, NY U.S.A.). The aggressiveness of hungry and physically larger female nestlings may make adult male raptors reluctant to provide care (I. Newton 1978, J. Zool. 184:465-487; 1979). This may be especially true among accipiters, a genus possessing strong reversed sexual size dimorphism. P.A. Johnsgard (1990, Hawks, eagles, and falcons of North America, Smithsonian Inst. Press, Washington, DC U.S.A.) postulated that male accipiters never feed their young, but there are conflicting reports. For example, when female sparrowhawks ( Accipiter nisus) are killed or are absent from the nest, the males will deliver food to the nestlings but will not feed them (D.A. Bannerman 1956, The birds of the British Isles, Vol. 5, Oliver & Boyd, Edinburgh & London U.K.; Newton 1979). N.F.R. Snyder (pers. comm.), however, observed a male Cooper’s hawk (A. cooperii) that brooded and fed nestlings after the female had been killed. R.S. Palmer (1988, Handbook of North American birds, Vol. 4, Yale Univ. Press, New Haven, CT U.S.A.) reported that female northern goshawks ( A . gentilis ) will not allow males to remain in the nest area after the nestlings are a few days old. Conversely, Bannerman (1956) suggested that male northern goshawks will feed their nestlings but did not provide any supporting evidence. Here we describe one observation of a male goshawk feeding nestlings and another of a male goshawk brooding nestlings in northern Arizona during the breeding seasons of 1990 and 1991. To our knowledge this is the first documentation of male goshawks providing direct parental care to nestlings while the female was present during all or part of the interaction. The study area and methods are described in C.W. Boal (1993, M.S. thesis, Univ. Arizona, Tucson, AZ U.S.A.). On 13 July, 1990, at 0735 H, an adult male goshawk delivered a golden-mantled ground squirrel ( Spermophilus lateralis) to a nest under observation. The nest contained two 30-34-d-old unattended nestlings. The male goshawk stood on the nest rim for a few moments, then fed the nestlings for 8 min. He stopped feeding the nestlings and flew out of view when the female goshawk approached the nest and gave “dismissal” vocalizations (J.H. Schnell 1958, Condor 60:377-403) at 0743 H. We detected no differences between the behavior of the male and female goshawks in feeding the nestlings or in the nestlings’ responses to being fed by the male or female parent. Neither adult bird was banded, but identification of the sexes was possible by size comparison, plumage characteristics, and the behavior and vocalizations when interacting. The second observation occurred at a nest where the adult female goshawk was banded but the adult male was not. On 22 June, 1991, the male brought a tassel-eared squirrel ( Sciurus aberti) to a perch approximately 40 m from the nest tree at 1129 H. The female took the squirrel from the male, brought it to the nest, and began feeding the two 15-17-d-old nestlings. At 1225 H the male goshawk perched in a tree 15 m from the nest tree and made “cluck” vocalizations (Schnell 1958). The female goshawk immediately flew from the nest with the squirrel and began giving “dismissal” vocalizations from an unseen location in the nest stand. The male goshawk flew to the nest at 1228 H. He walked about the nest and then assumed a brooding position, though he was unable to completely cover the nestlings. The nestlings allowed the male to brood them without displaying any indication of alarm. The female goshawk stopped vocalizing at 1245 H but remained out of view. The male continued to brood the nestlings until 1335 H, at which time he stood, stretched, and flew from the nest. Nest defense is not the primary role of male goshawks during brood-rearing (Schnell 1958), thus a non-aggressive response to intruders would be expected in contrast to the vocal and aggressive nest defense behavior of female goshawks (Schnell 1958). To observe the males’ response to human intruders while brooding, nest observations continued while two field assistants searched the nest area for prey remains and castings between 1300 and 1320 H. Expected behavior of an adult female goshawk at this stage of the nesting cycle would be to leave the nest, perch in a nearby tree while vocalizing, and making low attacking flights at the intruders. The male goshawk, however, showed little concern over the intrusions and remained in a brooding position, even closing both of his eyes for short intervals. These two incidents were observed during 1539 hr of nest observations. Participation in the feeding and brooding of nestlings by male goshawks is apparently uncommon. However, this report documents that male goshawks can and occasionally do provide direct care to their nestlings. These observations were made during a study funded by a cost-share agreement between the Southwestern Region of the USDA Forest Service and the University of Arizona. Kaibab Forest Products, the Arizona Wildlife Federation, and the Arizona Falconers Association also provided funding. We thank T.S. Estabrook, D.N. Gossett, and two anonymous reviewers for providing helpful comments and suggestions on an earlier draft of this manuscript. — Clint W. Boal, School of Renewable Natural Resources, University of Arizona, Tucson, AZ 85721 U.S.A.; Erin L. Bibles, USDA Forest Service, Safford Ranger District, Safford AZ 85548 U.S.A.; Raymond E. Brown, RR1 Box 445, Appleton, ME 04862 U.S.A. J. Raptor Res. 28(2): 1 22 © 1994 The Raptor Research Foundation, Inc. Bald Eagle Attacks Adult Osprey Kleptoparasitism and agonistic interactions between bald eagles ( Haliaeetus leucocephalus ) and ospreys ( Pandion haliaetus ) are well documented (A.C. Bent 1937, U.S. Natl. Mus. Bull. 167; J.C. Ogden 1975, Wilson Bull. 87:496- 505; J.M. Gerard et al. 1986, Blue Jay 34:240-246; Y. Prevost 1979, Auk 96:413-414). The details of only one attack by a bald eagle on an osprey have been documented, in this case a nestling which had just received a fish from one of its parents (S.P. Flemming and R.P. Bancroft 1990, J. Raptor Res. 24:26-29). The observers were unable to determine the fate of the nestling. Here, we describe an attack that resulted in the death of an adult osprey and we discuss possible reasons for the attack. The observation was made at a distance of 200 m at a 300 ha lake in northeastern Nova Scctia within 15 km of where the only other described attack (S.P. Flemming and R.P. Bancroft 1990, /. Raptor Res. 24:26-29) occurred. At 0615 H on 4 May 1993, a mature bald eagle was seen pursuing a male osprey. The tail and approximately 7 cm of the body of a 12 cm-long white perch ( Morone amencana) could be seen protruding from the osprey’s mouth. The osprey flew in an erratic trajectory at heights from 3-12 m above the lake surface in an apparent attempt to evade the eagle. A second eagle joined the chase from where it had been perched in a tree along the shoreline. Both eagles closed to within a few m of the osprey and after about 45 s one of the eagles grabbed the osprey with its talons. Both birds immediately fell to the water at which point the second eagle departed. The osprey ceased struggling within 30 sec of hitting the water and the eagle immediately began using its wings to paddle to the shore 125 m away, pulling the osprey behind it. The eagle began to pluck the osprey as soon as it reached the shore. It then dragged the osprey to higher ground, about 3 m away, and remained there for 45 min while eating it. We retrieved the remains of the osprey after the eagle had departed. Except for parts of the digestive tract, the viscera had been eaten, along with the entire breast musculature and that of one wing and both legs. The head of the osprey was intact and it still had the perch protruding from its mouth. The crop and pharynx were engorged with a mass (approx. 0.25 kg) of tissue of fish that could not be identified. This tissue was in an advanced stage of digestion, apparently the osprey had been attempting to regurgitate it. The completely undigested white perch was lodged in the buccal cavity in a way that suggested the osprey had been trying to regurgitate it also. It appeared that regurgitating the fish would have been difficult for the flying bird because of the size and shape of the fish and the way the erect dorsal fin was protruding into the palate of the osprey. The only other attack of a bald eagle on an osprey (S.P. Flemming and R.P. Bancroft 1990, /. Raptor Res. 24:26- 29) apparently began as kleptoparasitism, a common occurrence, but the eagle was opportunistic in attacking the osprey. Kleptoparasitism can potentially lead to predation, although this has not been documented in birds (H.J Brockmann and C.J. Barnard 1979, Anim. Behav. 28:487-514). It is probable that the attack described here was also a case of intended kleptoparasitism which led to predation; there was no evidence that the perch had been touched by the eagle. A possible reason for the eagle’s attack is that it somehow recognized that the osprey was in distress and therefore vulnerable to predation. We thank the St. Francis Xavier University Council for Research for supporting research on the social behavior of ospreys. — J. MacDonald, Department of Physical Education and N.R. Seymour, Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G ICO Canada. 122 / Raptor Res. 28(2):123 © 1994 The Raptor Research Foundation, Inc. Dissertation Abstract Regulation of Bald Eagle ( Haliaeetus leucocephalus) Productivity in the Great Lakes Basin: an Ecological and Toxicological Approach The bald eagle population, within and adjacent to the Great Lakes Basin, constitutes the greatest single population within the contiguous United States. Bald eagles were largely extirpated from the Great Lakes by the mid-1960s, due to the effects of DDE. Eagles began to repopulate and raise young again along the shores of the Great Lakes, with the exception of Lake Ontario, by the 1980s. The studies reported here focused on factors limiting bald eagle populations. Ecological factors investigated included food habits, nest tree use, winter habitat use, and the identification of potential nesting habitat. Bald eagles primarily foraged on fish (suckers, bullheads, northern pike, carp, and freshwater drum). Eagle nests were built primarily in white pines, but in cottonwoods near Lake Erie. Potential nesting habitat exists along the shorelines of all Great Lakes, primarily along Lakes Huron and Superior. Habitat availability, however, may limit the Lake Erie subpopulation, which has little unoccupied habitat and great density of nesting eagles. Toxicological aspects investigated included monitoring concentrations of PGBs and p,p'-DDE in plasma, mercury and selenium in feathers. Hematological biomarkers were used to assess health of eaglets. Bill deformities in nestlings were also investigated. Concentrations of p,p'-DDE or PCBs, but not mercury or selenium, were significantly, and inversely correlated with regional reproductive productivity and success rates. Lesser reproductive productivity in some lesser contaminated areas are believed to be related to greater nesting density. Reproductive productivity of bald eagles within this population is primarily regulated by concentrations of organo- chlorine compounds along the shorelines of the Great Lakes, and density dependant factors in the interior, relatively uncontaminated areas. The continuing recovery of this population will depend on maintaining greater productivity in interior areas to compensate for lesser fecundity and greater adult mortality along the shorelines of the Great Lakes. — William Wesley Bowerman IV. 1993. Ph.D. dissertation, Department of Fisheries and Wildlife, Institute for Environmental Toxicology, Ecology and Evolutionary Biology Program, Michigan State University, East Lan- sing, MI 48824 U.S.A. Present address: Department of Animal Science, Michigan State University, East Lansing, MI 48824 U.S.A. J Raptor Res. 28(2):123-124 © 1994 The Raptor Research Foundation, Inc. Dissertation Abstract Facultative Manipulation of Hatching Asynchrony in the American Kestrel (. Falco sparverius) The consequences of hatching asynchrony for nestling birds have been well studied, but the adaptive significance of hatching patterns is the subject of considerable controversy. My questions centered around the role of food in determining costs and benefits of asynchrony at different stages in the breeding cycle and in particular, whether American kestrels might practice individual optimization of hatching spans. I conducted experiments in both the pre-laying and brood- rearing stages and in the process, tested four hypotheses: 1) brood reduction, 2) sibling rivalry, 3) peak load, and 4) energetic constraints during laying. I explored the costs and benefits of brood reduction from a theoretical perspective. I developed a model of facultative manipulation (individual optimization) of hatching based on the brood reduction hypothesis and the assumption that hatching patterns have different fitness payoffs in good and bad food years. When food resources during the nestling period were partly predictable from those during the pre-laying period, facultative manipulation of hatching seemed advantageous in many types of environments. Correlation analysis showed that small mammal numbers in summer were sometimes, but not always, predictable from those in spring. Next, I examined the costs and benefits of asynchrony during the brood-rearing period. I measured growth and mortality of nestlings within four treatment groups (asynchronous, synchronous, food-supplemented, unsupplemented) 123 124 Dissertation Abstracts Vol. 28, No. 2 to test the brood reduction hypothesis. Fledging success did not differ between synchronous and asynchronous broods when food was poor, but consistent with the brood reduction hypothesis, nestlings died at a younger age in asynchronous broods. Asynchronous young did better in terms of growth when food was scarce but when food was more abundant, youngest nestlings in asynchronous broods still died despite apparently adequate food for the brood. Overall, the patterns of growth and mortality supported the brood reduction hypothesis for kestrels when food was limited, but not when it was abundant. To test whether asynchrony affected parental effort, I measured provisioning rates to synchronous and asynchronous broods. Parents of synchronous broods made up to 31% more visits to the nest than parents of asynchronous broods by the time nestlings were 25-d old. Despite the higher provisioning rate, nestlings from synchronous broods weighed less at fledging. Patterns of food provisioning were consistent with the sibling rivalry hypothesis but not with the peak load hypothesis. Finally, I examined the proximate effect of food on asynchrony during the pre-laying period. In good food years, the hatching spans of clutches were more synchronous than in poor years. Similarly, parents on good territories and females in good physical condition had synchronous broods compared to parents with less food. Kestrels that were supplemented in the pre-laying period laid larger eggs and hatched those eggs more synchronously. These results were consistent with the hypothesis of facultative manipulation of hatching spans but not with the energetic constraint hypothesis. Kestrels seemed to “choose” an appropriate degree of asynchrony based on food levels in the pre-laying period. — Karen L. Wiebe. 1993. Ph.D. dissertation, Department of Biology, University of Saskatch- ewan, Saskatoon SK, Canada S7N 0W0. Present address: Department of Forest Sciences, 2357 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z4, Canada. THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966) OFFICERS PRESIDENT: Michael W. Collopy VICE-PRESIDENT: David M. Bird SECRETARY: Betsy Hancock TREASURER: Jim Fitzpatrick BOARD OF DIRECTORS EASTERN DIRECTOR: Brian A. Millsap CENTRAL DIRECTOR: Thomas Nicholls MOUNTAIN & PACIFIC DIRECTOR: INTERNATIONAL DIRECTOR #2: M. Isabel Bellocq DIRECTOR AT LARGE #1 : Jim Bednarz DIRECTOR AT LARGE #2: Robert E. Kenward DIRECTOR AT LARGE #3: Keith L. Bildstein DIRECTOR AT LARGE #4: Josef K. Schmutz DIRECTOR AT LARGE #5: Paul F. Steblein DIRECTOR AT LARGE #6: Katherine McKeever Karen Steenhof CANADIAN DIRECTOR: Paul C. James INTERNATIONAL DIRECTOR#!: Jemima Parry-Jones EDITORIAL STAFF JOURNAL EDITOR: Carl D. Marti, Department of Zoology, Weber State University, Ogden, UT 84408-2505 U.S.A. ASSOCIATE EDITORS 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 arti- cles, letters to the editor, thesis abstracts and book reviews. Contributors should submit a typewritten original and three copies to the Editor. All submissions must be typewritten and double-spaced on one side of 216 X 278 mm ( 8 V 2 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. 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 nu- merals. 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 ( 6 th ed., 1983) or an- other authoritative source for other regions. Subspecific identification should be cited only when per- tinent 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 poli- cy are outlined in “Information for contributors,”/. Raptor Res., Vol. 27(4), and are available from the editor. Keith L. Bildstein Gary R. Bortolotti Charles J. Henny Fabian Jaksic Patricia L. Kennedy Erkki Korpimaki BOOK REVIEW EDITOR: Jeffreys. Marks EDITOR OF RRF KETTLE: Richard J. Clark 1994 ANNUAL MEETING The Raptor Research Foundation, Inc. 1994 annual meeting will be held on 3-6 November at the Little America Hotel in Flagstaff, Arizona. Details about the meeting and a call for papers will be mailed to Foundation members in the summer, and can be obtained from Dan Varland, Scientific Program Chairperson, ITT Rayonier, Inc., Northwest Forest Resources, P.O. Box 200, Hoquiam, WA 98550, (telephone 206 533-7000), and Patricia Hall, Local Chairperson, 436 E. David Drive, Flagstaff, AZ 8601 1 U.S.A. (telephone 602 774-0041) . For information about the associated symposia contact: Susi MacVean (northern goshawk) , Arizona Game and Fish Department, 2222 W. Greenway Road, Phoenix, AZ 85023 U.S.A. (telephone 602 789-3581); Joseph Ganey (Mexican spotted owl), USDA Forest Service, Rocky Mountain Forest and Range Research Station, 2500 Pine Knoll Drive, Flagstaff, AZ 86011 U.S.A. (telephone 602 556-2156); Michael Fry (Swainson’s hawk), Department of Avian Science, University of California, Davis, CA 95616 U.S.A. (telephone 916 752-1201) . Raptor Research Foundation, Inc., Awards Recognition for Significant Contributions 1 The Dean Amadon Award recognizes an individual who has made significant contributions in the field of systematics or distribution of raptors. Contact: Dr. Clayton White, 161 WIDE, Department of Zoology, Brigham Young University, Provo, UT 84602 U.S.A. Deadline August 15. The Tom Cade Award recognizes an individual who has made significant advances in the area of captive propagation and reintroduction of raptors. Contact: Dr. Brian Walton, Predatory Bird Research Group, Lower Quarry, University of California, Santa Cruz, CA 95064 U.S.A. Deadline: August 15. The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significantly to the understanding of raptor ecology and natural history. Contact: Dr. David E. Andersen, Department of Fisheries and Wildlife, 200 Hodson Hall, 1980 Folwell Avenue, University of Minnesota, St. Paul, MN 55108 U.S.A. Deadline: August 15. Recognition and Travel Assistance The James R. Koplin Travel Award is given to a student who is the senior author of the paper to be present- ed at the meeting for which travel funds are requested. Contact: Dr. Petra Wood, West Virginia Cooper- ative Fish and Wildlife Research Unit, P.O. Box 6125, Percival Hall, Room 333, Morgantown, WV 26506-6125 U.S.A. Deadline: Deadline established for conference paper abstracts. The William C. Andersen Memorial Award is given to the student who presents the best paper at the annual Raptor Research Foundation Meeting. Contact: Ms. Laurie Goodrich, Hawk Mountain Sanctuary, Rural Route 2, Box 191, Kempton, PA 19529-9449 U.S.A. Deadline: Deadline established for meeting paper abstracts. Grants 2 The Stephen R. Tully Memorial Grant for $500 is given to support research, management and conservation of raptors, especially to students and amateurs with limited access to alternative funding. Contact: Alan Jenkins, George Miksch Sutton Avian Research Center, Inc., P.O. Box 2007, Bartlesville, OK 74005- 2007 U.S.A. Deadline: September 10. The Leslie Brown Memorial Grant for $500-$l,000 is given to support research and/or the dissemination of information on raptors, especially to individuals carrying out work in Africa. Contact: Dr. Jeffrey L. Lincer, 9384 Hito Court, San Diego, CA 92129-4901 U.S.A. Deadline: September 15. 1 Nominations should include: 1) the name, title and address of both nominee and nominator, 2) the names of three persons qualified to evaluate the nominee’s scientific contribution, 3) a brief (one page) summary of the scientific contribution of the nominee. 2 Send 5 copies of a proposal (<5 pages) describing the applicant’s background, study goals and methods, anticipated budget, and other funding.