(ISSN 0892-1016) The Journal of Raptor Research Volume 25 Spring 1991 Number 1 Contents Altitudinal Distribution and Conservation of Raptors in Southwestern Colombia. jean-Marc Thioiiay 1 Development of Foraging Behavior in the American Kestrel. Daniel E. Varland, Erwin E. Klaas and Thomas M. Loughlin 9 Short Communications Nest Site and Prey of a Pair of Sharp-Shinned Hawks in Alberta. Michael S. Quinn ... 18 Ornate Hawk- Eagle Feeding on Green Iguana. Jack Clinton-Eitniear, Michael R. Gartside and Mark A. Kainer 19 Notes on a Successful Nesting by a Pair of Yearling Peregrine Falcons ( Falco peregrinus). Annie M. Wendt and Greg A. Septon 21 Non-Breeding Diet of Long-Eared Owls in Massachusetts. Denver W. Holt and Nancy N. Childs 23 The Raptor Research Foundation, Inc. gratefully acknowledges a grant and logistical support provided by the University of Saskatchewan 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 address to Jim Fitzpatrick, Treasurer, 12805 St. Croix Trail, Hastings, Minnesota 55033, U.S.A. The Journal of Raptor Research (ISSN 0892-1016) is published quarterly for $18.00 per year by The Raptor Research Foundation, Inc., 12805 St. Croix Trail, Hastings, Minnesota 55033, U.S.A. Second class postage paid at Hastings, Minnesota, and additional mailing offices. Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A. Copyright 1991 by The Raptor Research Foundation, Inc. Printed in U.S.A. THIS PUBLICATION IS PRINTED ON ACID-FREE PAPER. THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. Vol. 25 Spring 1991 No. 1 J. Raptor Res. 25(1):1 —8 © 1991 The Raptor Research Foundation, Inc. ALTITUDINAL DISTRIBUTION AND CONSERVATION OF RAPTORS IN SOUTHWESTERN COLOMBIA Jean-Marc Thiollay Laboratoire d’Ecologie, Ecole Normale Superieure, 46 rue d’Ulm , 75230 Paris, Cedex 05, France Abstract. — Diurnal raptors were surveyed during four weeks along a gradient from sea level to 4000 m on the Pacific slopes of the Andes in southwestern Colombia. However, most of the work on habitat selection, density estimates and conservation problems was done within the subtropical level (1200-2400 m) in the 3200-ha forest reserve of La Planada and its surrounding mosaic of pastures, cultivated fields and disturbed forest. Twenty-two raptor species were recorded. Forest species richness does not change noticeably at successive levels between 0 and 1000 m, but this richness decreases rapidly above 1500 m. The number of open grassland species tends to increase with elevation. Extensive deforestation is a major threat to the survival of several forest raptors, including endemics from the humid western slope of the Andes. Some sufficiently large areas of relatively undisturbed forest, suitable for raptor conservation, still remain between 500 and 2000 m but very few can be found above or below this level. Distribution y conservacion de aves de rapina en diversos niveles de altitud en el sudoeste de Colombia Extracto. — Raptoras diurnas fueron inspeccionadas durante 4 semanas a lo largo de una gradiente comprendida entre el nivel del mar y los 4000 metros, en las pendientes andinas del Pacifico en el sudoeste de Colombia. Sin embargo, la mayor parte del trabajo de selection de habitat, estimaciones de densidad y problemas de conservacion, ha sido hecho dentro del nivel subtropical (1200-2400 m) en las 3200-ha. de la reserva forestal La Planada, y el mosaico de sus alrededores con pastos, campos cultivados y alterada floresta. 22 especies de aves de rapina han sido registradas. La riqueza de las especies raptoras de floresta no cambia notablemente en los sucesivos niveles entre 0 y 1000 m, pero si decrece rapidamente a partir de los 1500 m. El numero de las especies de las areas de pastos tiende a crecer con la elevation. La extensiva deforestation constituye el mayor peligro para la supervivencia de las aves raptoras de floresta; esto es cierto tambien para las especies de las humedas pendientes occidentales de los Andes. Areas suficientemente grandes de floresta relativamente inalterada, apropiadas para la conservacion de aves raptoras, aun se encuentran entre los 500 y los 2000 m, pero muy pocas pueden encontrarse por encima o por debajo de este nivel. [Traduction de Eudoxio Paredes-Ruiz] Colombia is ornithologically one of the richest countries in the world with at least 1695 species of birds reliably recorded, including 75 Falconiformes, as summarized by Hilty and Brown (1986). The extreme southwestern part of the country is among the least studied areas. Yet this Pacific slope of the Andes, called southern Choco, which extends into northwestern Ecuador, is both rich in endemic taxa and threatened throughout by rapid deforestation, especially in the lowlands. Moreover, diurnal rap- tors are usually poorly surveyed because specific sur- vey methods are required to establish the presence, or to assess the relative abundance, of many species. These methods are time consuming and are often appropriate for only a particular subset of the raptor assemblage (Thiollay 1989a). The birds in this study area proved to be no exception. The present study of the distribution of raptors along a gradient from sea level to 4000 m was of interest for several reasons. Little was known about the area and its endemic species; the gradient had a wide altitudinal range but within a relatively narrow 1 2 Jean- Marc Thiollay Vol. 25, No. 1 strip; comparative data were drawn in 1987 from a personal survey of raptors in nearby northwestern Ecuador; this was among the first uses of raptors as sensitive indicators for the management of a Bio- sphere Reserve (UNESCO-MAB) proposed in the area; several species may soon become extinct be- cause of the current high rate of deforestation. Study Area and Methods The southwestern corner of Colombia (Narino), along the Ecuadorian border, provides all 5-km-wide gradient from the upper ridge of the western Andes, dominated by the Cumbal Volcano (4764 m), down to the Pacific coast. It is crossed by the Pasto-Tumaco road of which the El Espino- Altaquer section has been the most intensively sur- veyed during this study (Fig. 1). This Pacific slope of the northern Andes (Choco) has the heaviest rainfall in the Americas (Hilty and Brown 1986), ranging from over 3000 mm on the coast to an average of 10 000 mm in the foothills (500-1000 m) and decreasing to about 4-5000 mm at the subtropical and montane levels. The heavy cloud cover tends to increase with altitude. The mean temperature drops by about 6°C with each 1000-meter increase in elevation. The altitudinal gradient was divided into five main zones (Holdridge 1967). 1) The Paramo extends from the tree line (3200-3400 m) to the upper limit of vegetation (around 4500 m). The Rosette Shrub ( Espeletia sp.) was charac- teristic of the lower part of this wet alpine grassland where some patches of low, dense Polylepis woodland still re- mained in the ravines. The upper part of the Paramo was dominated by grasslands. Strong winds, cool temperatures, moderate rains and extensive cloud cover occurred almost daily. 2) The temperate or montane forest was found main- ly from 2500-3500 m between El Espino, Miraflores and Piedrancha. Trees were usually under 20 m tall and cov- ered with epiphytes. Stunted trees and shrubs dominated a so-called elfin forest near the tree line. 3) From 2400 m down to 1200 m, a subtropical, humid or premontane forest was found. Many trees reached 25-30 m in height and were heavily covered by epiphytes (e.g., ferns, mosses, bromeliads). Trees were dominated by the genera Cassia, Clusia, Ficus , Miconia, as well as palms. The dense and wet undergrowth had many tree ferns. 4) From 1200 m to 500 m, in the Altaquer- Junin-Barbacoas-El Diviso area, the foothills bore a tropical wet forest (rain forest of Hold- ridge 1967). It was the elevation with the heaviest rainfall, covered by a dense, evergreen forest, with trees reaching 30-35 m. The highest tree species diversity may be found at this level (C. Samper, pers. comm.). 5) Below 500 m, the lowland wet forest was the tallest (35-45 m) with comparatively less undergrowth and still high tree species Spring 1991 Raptors in Southwestern Colombia 3 richness. A wide belt of mangroves fringed the coast. All along the gradient, much of the original forest cover has been converted to cattle pastures and cultivated fields; shrubs predominated on lightly grazed or abandoned areas. Most of my observations were made in and around La Planada Natural Reserve, within the subtropical zone. This 3200-ha reserve was at an altitude of 1500 to 2200 m and covered with primary forest. Over 200 ha were regenerating, after being either converted into pasture or logged for valuable timber 10-20 years ago. The mature forest was on average 20-30 m high with a dense, very wet undergrowth and a discontinuous canopy. Palms and tree ferns were numerous and epiphytes were omnipresent. Two hundred resident bird species have been identified (unpubl. list from numerous observers), including 25 Cho- co endemics. Mammals (squirrels, monkeys, carnivores) usually existed at low densities. The largest mammals were the Spectacled Bear, Tremarctos ornatus and the Brocket Deer, Mazama americana. On the eastern border of the reserve, the deep valley of Pialapi was partly cleared for shifting cultivation and the remaining forest patches were often disturbed. Along the northeastern side, the slopes of the Rio Miraflores valley were used for cattle ranching, but substantial areas of forest still covered the upper slopes. The large valley of the Rio Guiza was densely populated and cultivated, with pastures on the upper slopes. Some patches of forest re- mained only on the steepest slopes, ridges and ravines. The lower and upper parts of the valley are here defined from the position of La Planada (at the level of Chucunes- Ricaurte) 25-30 km downstream to Altaquer and up- stream to Mallama. The upper valley was more deforested but less cultivated than the lower section. The entire area of La Planada-Pialapi and the valley from Altaquer to Mallama were surveyed on foot between 24 June and 26 July 1988. Three additional days were spent in the montane zone (around Cumbal and Azufral Volcanoes) and two days in the lowlands. Rain and fog were of almost daily occurrence and lowered the detect- ability of raptors. Using all available trails and roads, I searched the area for raptors from dawn to dusk, making intensive use of clear late morning hours. I spent more time in openings (treefall gaps, landslides, clearings, ridg- es) from where most raptors could be seen in flight. The secretive forest falcons (Micrastur sp.) were mostly located by their calls in early and late hours. The data were expressed as the mean number of in- dividuals recorded per hour spent under three different conditions affecting raptor detectability and defined as op- timal, suboptimal and unsuitable. Based on prior expe- rience (Thiollay 1989a), and according to the behavior of each species, these conditions included: habitat (i.e., inside or outside the forest), time of day and weather. A mean frequency of occurrence per hour was then calculated, using only optimal conditions. This index of abundance was comparable within a given species between different localities but not between species, which usually vary widely in their behavior and conspicuousness. Most of La Planada Reserve was covered in this survey and all resident species are thought to have been recorded or confirmed by previous records. Conservative density estimates are presented based on the mapping of all ob- servations and the behavior of adult birds monitored. This minimum number of pairs of each species is probably too low for the secretive small forest species but much more accurate for the conspicuous large soaring species. Pairs of displaying Leucopternis or Leptcdon and even calling Micrastur were widely separated and thus easy to distin- guish from each other without a complete mapping of their territory. Around the 3000-ha forest of La Planada, an additional area of about 7000 ha of mixed pastures, cultivated fields, old clearings and disturbed forests was surveyed mainly for easily detectable (soaring) species. A minimum number of pairs was estimated for this total area of approximately 10 000 ha (see species status). The aim of the census was to provide some basic data about the ecological require- ments of such species if their survival is to be considered in a future management plan for this part of the western Andes. More details about census are given elsewhere (Thiollay 1989a). Results Altitudinal Distribution. The distribution of raptors along the altitudinal gradient is presented in Figure 2. It was not possible to give a more quan- titative picture of the species’ distribution because of the brevity of the survey in the foothills and lowlands. Table 1 emphasizes the relative abundance of species in the subtropical-temperate zone where most of the work was carried out. Below I describe the raptor assemblage in each successive altitudinal zone but species wall be cited only in the upper level of their range and not repeated in each of the following ones (see Fig. 1). Especially in the least surveyed areas, some species may have been overlooked. This is why I mention the species that I have not seen but that have been recorded by J. Orejuela (pers. comm.) or that were known formerly and are still likely to exist at similar level in western Narino (Hilty and Brown 1986). In the Paramo zone, the Carunculated Caracara ( Phalcoboenus carunculatus ) was still common and widespread in the highest grasslands and often came down to 3000 m or lower into ploughed fields.'The Red-backed Hawk (Buteo polyosoma) was even more common, but was mostly associated with the lower paramo (up to 3800 m) and the montane grasslands down to 1 800 m and even 1 600 m in the La Planada area. Although considered merely a non-breeding migrant in Colombia by Hilty and Brown (1986), I found this species breeding on the slopes of the Azufral Volcano, above El Espino. An adult brought prey to a nest near the tree line at 3400 m on 7 July and another adult was followed by a calling, newly fledged young. Two Cinereous Harriers ( Circus ci- 4 Jean- Marc Thiollay Vol. 25, No. 1 TROPICAL MONTANE Altitude (meters) Cathartes aura Coragyps atratus Leptodon cayanensis Chondrohierax uncinatus Elanoides forficatus Elanus leucurus Circus cinereus Accipiter striatus Accipiter collaris Accipiter superciliosus Accipiter bicolor Leucopternis princeps Leucopternis semiplumbea Geranoaetus melanoleucus Buteo magnirostris Buteo brachyurus Buteo polyosoma Oroaetus isidori Phalcoboenus carunculatus Herpetotheres cachinnans Micrastur ruficollis Falco sparverius Lowland! 0 Foothill 1000 Subtropical 2000 Temperate 3000 Paramo 4000 Figure 2. Altitudinal distribution of Falconiformes recorded in July 1988 along the Pacific slope of the Andes in southern Colombia. Solid lines represent regular observations. Dashed lines are ranges cited by Hilty and Brown (1986) but not confirmed during this study, or personal observations that are out of the known breeding level given by these authors. Fifteen additional species were formerly reported and are still likely to occur in the area, mainly in lowland forest. Table 1. Raptor population of the subtropical zone in southwestern Narino, Colombia. Numbers represent the percentage of optimal detectability hours in which the species were recorded. Mean number of individuals seen per hr are in parentheses. The five habitats are arranged in increasing order of visually estimated deforestation. The total number of suitable census hrs ranged from 11-101. La Planada PlALAPI Rio Lower Upper Reserve Valley Miraflores Rio Guiza Rio Guiza 1500-2200 m 1200-1900 m 1500-3300 m 1200-1500 m 1600-2500 m Coragyps atratus 14 (2.0) 72 (4.2) 82 (4.1) 75 (5.3) Cathartes aura 14(1.0) 24 (1.0) 55 (1.8) 12 (4.0) Leptodon cayanensis 28 (1.0) 20 (1.0) Chondrohierax uncinatus 20 (2.0) Elanoides forficatus 30 (1.0) 43 (6.7) 24 (5.6) 37 (18.3) Accipiter collaris 6(1.0) 3(1.0) Accipiter bicolor 4(1.0) Leucopternis princeps 30 (1.5) 72 (1.8) 73 (2.2) Leucopternis semiplumbea Geranoaetus melanoleucus 1 (1.0) 25 (2.0) Buteo magnirostris 14(1.0) 57 (2.2) 79 (2.2) 45 (1.8) 12 (2.0) Buteo brachyurus 9 (1.0) 12 (2.0) Buteo polyosoma Oroaetus isidori 14(1.0) 27 (1.3) 14(1.0) Micrastur ruficollis Falco sparverius 17(1.1) 38 (1.3) Species richness 10 7 7 5 6 Diversity index (H') 2.150 1.376 1.582 1.143 1.106 Spring 1991 Raptors in Southwestern Colombia 5 nereus) were seen in the lower paramo and meadows of the same area. The Andean Condor ( Vultur gry- phus) formerly widespread (Goodfellow 1902), is now very rare in Narino (Orejuela, pers. comm.) and was not seen. It is still present in northern Ecuador (pers. obs.). In the temperate montane zone, numerous Black Vultures ( Coragyps atratus ) were foraging in the cat- tle pastures and cultivated fields. They occurred up to 3300 m in the Cumbal-Espino-Tuquerres valley and were common in densely populated areas all along the gradient down to the coast. The American Kestrel ( Falco sparverius) was locally common from 3200 m down to 1600 m. Two pairs of Black-chested Buzzard- Eagles ( Geranoaetus melanoleucus ) were lo- cated in the upper Rio Guiza valley around 2500 m and 2900 m. The nest of one of them, on a cliff ledge, contained a fully feathered fledgling on 17 July. I saw other pairs in similar grassy and rocky slopes near cliffs above El Pedregal and in the Rio Paste Canyon near Chachagui. The only temperate forest raptor recorded was the Sharp-shinned Haw r k {Ac- cipiter striatus) between 3000 m and 3500 m. Three individuals, including one in dark phase, were hunt- ing around a 200-ha forest remnant, along edges, shrubby areas, pastures and lower paramo at the foot of the Azufral Volcano. A feather was even found by C. Samper (pers. comm.) at 4000 m. The White-throated Hawk ( Buteo albigula) which is a typical species of similar temperate forests in north- ern Ecuador, has not been observed here and is not cited from Narino (Hilty and Brown 1986). In the subtropical zone, the Turkey Vulture ( Ca - thartes aura), which was more common in the low- lands, extended here up to 2200 m and occasionally 2600 m but it was less numerous at this elevation than the Black Vulture. The Gray-headed Kite ( Leptodon cayanensis ) reached its upper limit at this level (2100-2200 m). It may breed up to 1900 m where a display flight was recorded, but it was more common in the coastal plain. The Hook-billed Kite ( Chondrohierax uncinatus ) which was seen at 1800- 2000 m, may not be breeding at this upper limit of its range. The Swallow-tailed Kite ( Elanoides forfi- catus ) was seen commonly between 1200 and 2400 m, sometimes in flocks of 11 to 32 individuals. It was less abundant in the deforested lowlands. The little-known Semicollared Hawk ( Accipiter collaris) and the much more conspicuous Barred Hawk ( Leu - copternis princeps) were the two most characteristic species of this altitudinal level and among the most frequent. I saw a pair of Barred Hawks down to 800 m below Junin. The Semi-collared Hawk is also known to extend down to the foothills (Hilty and Brown 1986). I observed both species up to 2200 m. The Bicolored Hawk {Accipiter bicolor) probably reaches its upper limit at La Planada Reserve where I recorded it several times around 1700 m. I saw it also in the lowlands and thus its range overlaps completely with that of Accipiter superciliosus and with most of that of A. collaris. The Roadside Hawk {Buteo magnirostris) was the most common hawk in the cleared semi-wooded areas, from sea level to 1900 m. It overlapped with the American Kestrel in the upper 200-300 m of its range. Individuals of the Short-tailed Hawk {Buteo brachyurus) were occa- sionally seen hunting up to 1 900 m, but the highest established pair was recorded at 1300-1400 m. The White-rumped Hawk {Buteo leucorrhous) has been recorded in the La Planada area, but was not seen during this study. The Black-and-chestnut Eagle {Oroaetus isidori) is a rare, spottily distributed and threatened species, typically associated with the un- disturbed, wet, subtropical forest of this level. I iden- tified it six times, only in the La Planada area. The Barred-forest Falcon {Micrastur ruficollis) was the only common and widespread forest falcon, seen be- tween 1500-2200 m, and may be the most abundant raptor in the natural forest undergrowth. In the tropical foothills, no new species were re- corded. However, two presumably rare Choco forest endemics, the Plumbeous Hawk {Leucopternis plum- bea ) and the Plumbeous Forest-falcon {Micrastur plumbeus) are known from this area, which several lowland species also may reach (Hilty and Brown 1986). The lowlands were visited only briefly. This area was almost entirely deforested and devoted to cattle raising and cultivation. The only remaining forest patch was too small to include a representative sam- ple of the natural raptor community. The species not previously recorded on the gradient were the Black-shouldered Kite {Elanus leucurus) and the Laughing Falcon {Herpetotheres cachinnans) in open pastures and secondary woodlands. Both may extend to 1000 m and more. The semiplumbeous Hawk {Leucopternis semiplumbea) and the Tiny Hawk {Ac- cipiter superciliosus ) were seen in and around forest fragments. I also recorded the former once at 1600 m in La Planada Reserve but it may not be resident at that altitude. Up to 10 additional forest species were known (Hilty and Brown 1986), and are still 6 Jean- Marc Thiollay Vol. 25, No. 1 SPECIES NUMBER Figure 3. Highest number of primarily forest (hatched) and grassland or open-woodland species (cross-hatched) recorded in this study, or likely to occur (Hilty and Brown 1986), along the altitudinal gradient in SW Narino. All regular species are included, regardless of their abundance or breeding status. Occasional vagrants are excluded. likely to occur in the coastal plain. These include the Double-toothed Kite (Harpagus bidentatus ), Plumbeous Kite ( Ictinia plumbea), Common Black Hawk ( Buteogallus anthracinus ), Crested Eagle ( Morphnus guianensis), Black-and-white Hawk-ea- gle ( Spizastur melanoleucus) , Ornate Hawk-eagle (Spizaetus ornatus), Red-throated Caracara ( Dap - trim americanus), Slaty-backed Forest-falcon ( Mi - crastur mirandollei), Collared Forest-falcon ( Micras - tur semitorquatus) and Bat Falcon ( Falco rufigularis). Some of them may survive in the area but at least the eagles require large areas of relatively undis- turbed forest (Thiollay 1989b) that may no longer exist at low elevation. Habitat Selection in the La Planada Area. The raptors studied may be divided into several categories according to their natural habitat and their observed susceptibility to deforestation. Obligate forest species occur only in sufficiently large areas of primary or old secondary forest. Micrastur ruficollis has never been seen outside dense forest undergrowth. Oroaetus isidori was apparently hunting only over large tracts of forest, flying directly and high above clearings and second growth. Both species are likely to be the most sensitive to forest degradation or fragmentation. Some primary forest species may hunt regularly along edges, in some openings, second growth and disturbed forest. Leptodon cayanensis, Accipiter col- laris, A. bicolor and probably Chondrohierax uncinatus are representatives of this category. They may sur- vive forest disturbance and fragmentation better than obligate forest species, but they do not take advantage of it and cannot persist in heavily deforested areas. Other forest species, such as Leucopternis princeps, are readily using, or even consistently associated with, natural or man-made openings inside the forest, including large wooded pastures along edges. Elan- oides forficatus hunts for insects over the canopy of both unbroken and fragmented forest, as well as over open woodlands. They appear to benefit from a mod- erate amount of deforestation (at least L. princeps is rarer or absent in large unbroken tracts of forest) but they still avoid areas that are extensively cleared. Originally nonforest species are still associated with partly wooded areas, forest edges and clearings (e.g., Cathartes aura, Buteo magnirostris, B. brach- yurus). They increase their hunting and/or breeding range at least in the early stages of deforestation, since they readily colonize newly deforested areas. Most open grassland species invade formerly wooded areas in advanced stages of deforestation (Fig. 3). Geranoaetus melanoleucus, Buteo polyosoma and Falco sparverius were here typical representatives of the fauna replacing that of the former temperate forest. The number of pairs of each species recorded dur- ing this one-month survey is probably too conser- vative. Some pairs may have been overlooked. How- ever, the difference between the actual and observed densities cannot be great and is likely to provide a reasonable estimate of the current carrying capacity of the area. Two different pairs of Leptodon caya- nensis were located on opposite sides of the 3000-ha La Planada Reserve. Their home ranges extended beyond the reserve’s limits. An additional record may have represented a third pair within the 10 000-ha area. Only one pair of Chondrohierax uncinatus was seen flying over the reserve. One flock including 2 to 13 Elanoides forficatus, and sometimes additional isolated birds, were seen every day moving all over the area. The resident population within the 1 0 000 ha may not have exceeded 15 birds. I made several observations within the reserve of Accipiter collaris, including individuals carrying prey. The existence of a minimum of two pairs can be assumed. This species was not seen outside the re- serve. Similarly the presence of one pair of Accipiter bicolor was inferred from the spatial grouping of the six different records within the 3000-ha protected forest. However, these two secretive little hawks are Spring 1991 Raptors in Southwestern Colombia 7 easily overlooked and their actual population may have been higher. Leucopternis princeps was the only common large hawk. Six pairs were located on the 10 000-ha area. Three of the home ranges overlapped the limits of the 3000-ha reserve but probably none of them was completely included in it. At least seven pairs of Buteo magnirostris were identified, always associated with clearings. Only one pair was on the reserve. One pair of Buteo polyosoma with a fledged young was hunting regularly in the northern part of the study area, outside the reserve. One adult Oroaetus isidori was seen several times over the western and southwestern parts of the reserve, often ranging well outside the boundary of the protected area. It is unlikely that more than one pair of this rare eagle occurred within the 10 000-ha study area and the protected forest zone was apparently not large or suitable enough to meet all of its requirements. At least, three well separated pairs of Micrastur ruficollis were located (direct observations and dawn or dusk calls), within the central part of the reserve. It was probably the most abundant forest raptor and the only one for which the 3000-ha reserve may be large enough to support a significant, if not self- sustainable, population. Discussion Community Composition. Twenty-two raptor species were recorded and at least fourteen additional ones are expected. Altogether, two-thirds (24) are forest species, and only 12 are grassland or very open-woodland species. The marked succession and turnover of communities found along altitudinal gra- dients in the Andes (see Terborgh 1971, Terborgh and Walker 1975) were also found here, although the incomplete censuses at lower levels preclude a detailed analysis. Some species had narrow altitu- dinal distributions, replacing each other along the gradients while others had wider and overlapping distribution ranges (Figure 1). The genus Accipiter offers striking examples of three altitudinal special- ists, with A. supercihosus under 1000 m, A. collaris between 1000 and 2500 m and A. striatus above 2500 m. The range of a larger species, A. bicolor, over- lapped with that of collaris and super ciliosus. The total species richness, and the number of for- est species, quickly decreased with altitude, but only above 1000 m (Figs. 2 and 3). At mid-level of the gradient (subtropical), the loss of forest species through deforestation was partly balanced by the invasion of species originating from grasslands and upper levels. At this elevation, the grassland com- munity became richer than that of the forest alone. But the overall man-induced richness of the forest- grassland mosaic was still 26% lower than that of the tropical forest alone. At higher elevation, more raptor species were favored than were lost when the forest cover was destroyed. Conversely, below about 1500 m, many more species were lost than gained through large scale deforestation. The bird assem- blages of small degraded patches of woodlands among fields and pastures were probably much poorer than those of the original forest. These patterns may be explained by the former rarity of open habitats below the temperate zone and the evolution of few species adapted to open areas in the humid lowlands. More- over, apart from paramo specialists, most of grass- land species benefiting from deforestation were geo- graphically widespread and often common species, whereas the disappearing forest birds were poten- tially threatened everywhere and are therefore in more urgent need of conservation. Conservation Problems. Raptors face a major threat from the extensive and rapid deforestation at all altitudinal levels, for cattle grazing more than for cultivation. Logging is now very important every- where (first for valuable timber, then for fuelwood and charcoal) and it often precedes and prompts forest clearing. Erosion prevents regeneration and further aggravates deforestation. Pollution and hunting pressure seemed to have only a local and minor impact. No comparable censuses, with statistically testable results, have been made in different forest types. However, at least within the best studied area, both abundance and diversity of forest raptors decreased with the reduction and degradation of forest patches (Table 1). A higher proportion of records per unit of time or distance covered was obtained from high primary forest in the reserve, on moderate slopes with deep, well-drained soils. Unfortunately these areas are also the most accessible and are said to be the most valuable for timber production and agri- culture. Therefore they are the first to be logged and cleared. The remaining forest patches tend to be of the poorest type, i.e., on steep slopes, at high eleva- tions, in ravines, on narrow ridges or swampy flats. The wet Pacific slope of the Andes of Colombia and western Ecuador is well known for its numerous endemic bird species. Among the Falconiformes alone, several species have restricted ranges ( Micrastur 8 Jean-Marc Thiollay Vol. 25, No. 1 plumbeus, and to a lesser extent, Leucopternis plum- bea and L. princeps) or very scattered distributions (e.g., Accipiter collaris, Oroaetus isidori). Moreover, they are very little-known forest species whose long- term conservation may be dependent on national parks in Colombia and Ecuador which are currently in small number and understaffed. Although the minimum size of a viable population of raptors is still debated, it can hardly be lower than several pairs. Thus the size of an isolated forest patch required for the long-term survival of a raptor population must be large. The 3200-ha reserve of La Planada harbors at best a few pairs of the most abundant species and not a single complete home range of the rarest ones. Fortunately, several species here use edges, clearings or secondary vegetation around the forest (all Accipiter and Leucopternis spe- cies) or can cross wide expanses of degraded wood- lands between primary forest patches (Oroaetus). The small forest falcons ( Micrastur ), although restricted to forest undergrowth, may have small territories (under 100 ha) and reach relatively high densities (this study, Klein & Bierregaard 1988, Thiollay 1989b). These behavioral traits may reduce the area of forest reserves necessary for the survival of viable populations of these species. Within the study area, both the lowland and the temperate zones are so deforested that there is little hope of preserving a viable natural community of forest raptors or even to afford the persistence of every forest species. In the La Planada-Pialapi area, significant expanses of suitable forest still remain. If deforestation can be stopped (e.g., through a man- agement plan of the proposed Biosphere Reserve), the original raptor community may survive. How- ever, the best prospects for conservation lie with the large tracts of little-disturbed forest that still remain on lower slopes (500-1000 m, notably the Junin- Barbacoas area). The very heavy rainfall may pre- vent large scale agricultural development and most of the easily accessible timber has already been logged. It is the last opportunity to take conservation mea- sures in an area that probably harbors most of the species of the lower and upper levels, as well as endemics of its own. Ackowledgments The study was funded by the UNESCO-MAB project (Paris). It has been made possible thanks to the help and logistic support of the team of the La Planada Reserve, especially its director Jorge Orejuela and its manager Guillermo Cantillo. D. and B. Snow as well as G. Samper were also helpful both in the field and through their com- ments on a first draft of the manuscript, which was typed by F. Thiollay. To all of them, I am very grateful. Literature Cited Goodfellow, W. 1902. Results of an ornithological journey through Colombia and Ecuador. Ibis 8:207- 233. Hilty, S.L. and W.L. Brown. 1986. A guide to the birds of Colombia. Princeton University Press, Prince- ton, NJ. Holdridge, L.R. 1967. Life zone ecology. Tropical Science Center, San Jose, Costa Rica. Klein, B.C. and R.O. Bierregaard. 1988. Movement and calling behavior of the Lined Forest-Falcon (Mi- crastur gilvicollis) in the Brazilian Amazon. Condor 90, 497-499. Terborgh, J. 1971. Distribution on environmental gra- dients: theory and a preliminary interpretation of dis- tributional patterns in the avifauna of the Cordillera Vilcabamba, Peru. Ecology 52:23-40. and J.S. Walker. 1975. The role of competition in the distribution of Andean birds. Ecology 56:562- 576. Thiollay, J.M. 1989a. The census of diurnal raptors in a primary rain forest: comparative methods and species detectability. J. Raptor Res. 23:72-84. . 1989b. Area requirements for the conservation of rain forest raptors and game birds in French Guiana. Conservation Biology 3:128-137. Received 19 May 1989; accepted 25 September 1990 J. Raptor Res. 25(1):9-17 © 1991 The Raptor Research Foundation, Inc. DEVELOPMENT OF FORAGING BEHAVIOR IN THE AMERICAN KESTREL Daniel E. Varland and Erwin E. Klaas U.S. Fish and Wildlife Service , Iowa Cooperative Fish and Wildlife Research Unit , Iowa State University, Ames, I A 50011 Thomas M. Loughin Agricultural Experiment Station, Department of Statistics, Iowa State University, Ames, I A 50011 ABSTRACT. — We observed the development of foraging behavior after nest departure in 12 sibling groups of American Kestrels ( Falco sparverius). Perch resting decreased whereas perch hunting, eating self- captured prey, and flying increased over the 5-wk period that young were observed. Kestrels used perch hunting more than other types of hunting and fed exclusively on invertebrates, primarily grasshoppers. Perch hunting success (captures/pounces) increased significantly 3 wk after fledging. After this period there was no significant change. Significant increases in capture rate (captures/hour) occurred 4 and 5 wk after fledging due to increased pounce rates. We observed social hunting among siblings, families, and also among unrelated kestrels. Social hunting occurred during both perch hunting and ground hunting. Social foraging in these kestrels was imitative rather than cooperative. Desarrollo de los habitos de caceria en los Halcones Cernicalos Extracto. — Hemos observado el desarrollo de los habitos de busqueda de alimento en Halcones Cernicalos {Falco sparverius) con 12 grupos de hermanos. Despues de un periodo de 5 semanas de observation, notamos que estos jovenes halcones disminuyeron la frecuencia del posarse para descansar, mientras que aumentaron la frecuencia en el posarse para cazar, el comer su presa capturada, y el volar. La caceria desde una percha ocurrio mas que otros tipos de caceria. Se alimentaron exclusivamente de invertebrados, principalmente de saltamontes o longostas. El exito de la caceria desde una position perchada (captura/ embestida) crecio significativamente despues de 3 semanas de haber dejado el nido. Despues de esto no hubo cambio significativo. Un notable incremento en la proportion de capturas (captura/hora) ocurrio entre 4 y 5 semanas despues de dejar el nido, y se debio al incremento en la proportion de embestidas. Se observo cacerias en grupos entre hermanos, familias, y tambien entre individuos sin parentesco. Las cacerias en grupo se realizaron o bien desde el suelo o desde una percha. La provision de comida en grupo en estos cernicalos fue mas bien imitativa que cooperativa. [Traduction de Eudoxio Paredes-Ruiz] The post- fledging period, here defined as the pe- riod of parental dependency for food in young birds after leaving the nest (see van Tyne and Berger 1966), has received relatively little attention in avian research. This is partly because of the difficulties in observing the behavior of young once they leave the nest (e.g., Brown and Amadon 1968, Newton 1979, Alonso et al. 1987). The post-fledging period and the subsequent pe- riod of recent independence from parents are im- portant life history stages, when young develop for- aging skills essential to survival (Weathers and Sullivan 1989). High mortality rates of recently in- dependent juveniles and others during their first year of life reflects the critical nature of this time (e.g., Lack 1954, Henny 1972, Sullivan 1989). In 1988 we began a study of American Kestrels nesting in nest boxes attached to the backs of high- way signs along Interstate Highway 35 (1-35) in Central Iowa. In this paper we describe the devel- opment of foraging behavior in young kestrels during the post-fledging phase and during the period of recent independence from parents. Study Area and Methods Several years prior to the initiation of this study, kestrel nest boxes were attached to the backs of highway signs along 1-35 at approximately 2-km intervals, from northern Polk County to northern Worth County in northcentral Iowa. The study area was a corridor approximately 2 km wide on either side of 1-35 from 18 km south to 99 km north of Ames. Land bordering 1-35 was farmed inten- sively with row crops. We banded 97 fledglings observed in 1988 and 1989 9 10 Varland et al. Vol. 25, No. 1 with U.S. Fish and Wildlife Service leg bands, and indi- vidually marked them with colored vinyl leg jesses before they fledged. We captured 76 percent (35/46) of the adult kestrels in the nest box or with bal-chatri noose traps (Berger and Mueller 1959). We banded and individually marked adults with colored vinyl leg jesses. To locate fledged young for behavioral studies we used the signals from back-mounted radio transmitters (Holohil Systems, Ltd., Woodlawn, Ontario, Canada). We attached transmitters to birds several days before fledging. In 1988 we attached radio transmitters to 12 nestlings in 10 nest boxes. Survival of radio-marked kestrels was high (11 of 1 2 survived the post- fledging period) and siblings generally maintained close contact for 4 to 5 wk after fledging. This confirmed the technique’s usefulness and feasibility for monitoring family group activity. We made observations in 1988 to gain insight into American Kestrel post-fledging behavior and to develop an efficient data recording system. These data are not part of the present analysis. We tested the transmitters used in 1989 along the high- way right-of-way at a height of 1 m. Signal range averaged 2.3 km (N — 13, SD = 0.60, range — 1.1-3. 5 km). In 1989, we radio-tagged one randomly selected nestling from each of 13 nests. Young observed in 1989 (50 individuals from 1 3 nests) fledged between 27 and 3 1 d after hatching (mean = 29.2, SD = 1.4), from 13 June to 3 July. One radio-tagged nestling died 7 d after fledging before we could collect behavioral data. We lost signals from 3 of the remaining 12 transmitters within 5 d after the tagged birds fledged. For two of these sibling groups, we were unable to determine whether the transmitters failed or if the individuals left the area. For the third, transmitter failure became evident when we observed the radio-marked kestrel with another sibling group in the study 37 d after fledging. Despite the early loss of signals from these three transmitters, we were able to collect data on behavior of individuals in these broods. We observed fledglings between 0600 and 1300 H at a distance of 70-100 m with a 20 x or 20-60 x spotting scope. We did not use a blind because birds under obser- vation frequently changed locations. We monitored fledg- ling groups on a rotational basis at 1-3 d intervals until we lost contact with the brood. When we could not find a brood, we searched by vehicle an area of approximately 6 km 2 around their last known location. We adopted Wyllie’s (1985) definition of dispersal, which is movement of a fledged bird farther than 1 km from its nest without return. We determined time of dispersal only for kestrels with transmitters known to be functioning 1 wk after fledging (N = 9). At the beginning of each observation session, we ran- domly selected one fledgling, which was not necessarily the one with the transmitter, as the focal bird (Altmann 1974). Two people observed behavior; typically one in- dividual collected data on a sibling group while the other observed another group elsewhere on the study area. In 39 cases two people collected data simultaneously on two birds in the same sibling group, or one person made con- secutive observations on different birds in the same sibling group. For analysis, we combined these simultaneous or consecutive observations into one observation session. Sessions lasted 5 to 60 min or until the focal bird dis- appeared from view. We did not use data if the bird left in <5 min. We analyzed data for 93 observation sessions (mean length = 57.5 min, SD = 32.0). A metronome timing device (Wiens et al. 1970), set at 20 sec intervals, cued spot observations of behavior and social activity. At each sound of the tone, we recorded behavior and social activities of the focal kestrel. We re- corded four main classes of activity: general behavior, so- cial behavior, hunting behavior, and allopreening and beaking. We recognized nine subclasses of general behav- ior and five of social behavior. General Behavior. “Perch resting” describes a kestrel perched and not engaged in any other observed behavior. Rudolf (1982) and Toland (1987) distinguished “perch hunting” from other perching activity by alert posture, erect body or body leaning slightly forward, frequent star- ing at ground (Fig. 1), and head bobs. Because young kestrels that have never hunted may exhibit some of these behaviors without attempting prey captures, behavior was not recorded as perch hunting until at least one pounce was observed. Flights to/and from the ground and flights between perches during perch hunting bouts were included in perch hunting behavior. We defined “ground hunting” as a bird on the ground searching for prey for >20 sec. Searches of shorter duration involving flight from a perch were considered perch hunting. “Flight” was any non- hunting flight. We use the term “eating” only for kestrels eating self-captured prey. “Maintenance activity” includ- ed preening, plumage rousals (shaking), and stretching. “Lying on belly” describes a posture young kestrels often assumed on fenceposts, utility poles, and large tree branch- es. “Begging” was solicitation of food from parents. “Out of sight” refers to a focal kestrel concealed by vegetation or other objects. A session was discontinued when a bird was out of sight >5 min. “Other” was used to categorize behaviors observed relatively infrequently, and included walking, hover hunting, aggressive interactions among sib- lings, parent-to-young prey transfers, and eating prey caught by parents. During observation sessions, one or both adults frequently vocalized aggressively at us. We therefore suspect that the interactions with parents oc- curred less frequently than they would have in the absence of observers. Social Behavior. Lett and Bird (1987) defined social behavior for American Kestrel fledglings as any behavior which occurred within 2 m of one or more siblings. We adopted this operational definition with two modifications. We extended the distance to 3 m and included non-sibling kestrels in social interactions (adults late in the post-fledg- ing period which no longer feed their young and kestrels from outside the parent/sibling family unit). “Associa- tion” was any activity of the focal kestrel except social hunting, which occurred <3m from one or more kestrels. “Social hunting” was hunting activity by the focal kestrel which occurred <3m from one or more kestrels that also were hunting (Fig. 1). “Nonsocial” refers to activity of the focal kestrel occurring > 3 m from one or more kestrels. When we could not see whether other kestrels were <3 m from the focal kestrel because of dense vegetation we recorded its social status as “Undetermined.” Foraging Behavior. We recorded pounces, captures, and prey type. Foraging success was the percentage of Spring 1991 Foraging in Kestrels 11 Figure 1. American Kestrels hunting socially after fledging. pounces with known outcomes that were successful. Out- comes were unknown in 5% of the observed pounces (18/ 345). We converted pounces and captures to hourly rates based on session length. Allopreening and Beaking. We recorded the frequen- cies and the individuals involved in allopreening and beak- ing, forms of direct social contact. Allopreening is the preening of a conspecific individual’s plumage. Our ob- servations of beaking paralleled those of Sherrod (1983: 182), who adopted the term beaking to describe behavior in young Peregrine Falcons ( Falco peregrinus ) in which “one falcon nibbles at the beak and lore area of its sibling.” Statistical Analysis. We grouped behavioral data ac- cording to 7-d intervals starting with fledging. The ex- perimental unit (n) was the sibling group, and observations of the number of groups observed ranged from 12 during the first wk after fledging to 4 during the fifth. We com- puted statistics for behavior, social, and hunting activity for each sibling group in each 7-d, post-fledging interval for which data were available. We used the general linear model procedure (PROC GLM, SAS 1985) to obtain an analysis of variance (ANO- VA) and tested for linear trends in specific behaviors dur- ing 5 wk post-fledging. Because not all sibling groups were represented in all weeks and data were missing from some cells, we used Type III sum of squares to calculate P values. We selected 0.05 as the level of significance for linear trends in behavior. Because behaviors were not in- dependent, we adjusted the significance level of P values using Bonferroni’s inequalities (Snedecor and Cochran 1989:116). Thus, the level of significance for these tests is 0.05 divided by the total number tests being made on a set of non-independent behaviors. To compare differences in means for foraging activity between weeks after fledging, we used least significant difference (LSD) £-tests (SAS 1985). We selected 0.05 as the level of significance for t -tests. Results Kestrels spent progressively less time inactive and more time foraging as they grew older (Table 1). A significant decrease occurred in perch resting be- havior ( P < 0.001) with weeks post-fledging, where- as significant increases occurred in perch hunting ( P < 0.001), eating self-captured prey ( P < 0.001), and flying (P < 0.002). We did not observe young eating prey captured by their parents after the third week post- fledging. Mean time of dispersal for ra- dio-marked kestrels ( N = 9) was 23.6 d after fledg- ing. Perch hunting constituted a greater percentage of foraging time than ground hunting in all 5 wk post- fledging (Table 1). Significant increases occurred with time in perch hunting pounces (P < 0.001), captures (P < 0.001), and success (P < 0.05; Fig. 12 Varland et al. Vol. 25, No. 1 Table 1. Time (mean % ± SE) spent engaged in 10 behavior categories by post-fledging American Kestrels in Iowa. Weeks Post-Fledging Behavior 1 Mean ± SE 2 Mean ± SE 3 Mean ± SE 4 Mean ± SE 5 Mean ± SE 1-5 F-Values® Perch resting 75.3 ± 4.0 53.8 ± 5.2 41.4 ± 3.3 19.5 ± 7.2 23.8 ± 2.1 <0.0010 Perch hunting 0.2 ± 0.2 6.0 ± 2.0 18.3 + 2.7 43.4 ± 8.8 48.6 + 2.8 <0.0010 Ground hunting 0.0 0.9 ± 0.7 3.6 ± 1.6 10.0 ± 5.4 1.8 ± 1.1 0.0580 Flying 0.4 ± 0.1 2.1 ± 0.4 3.9 ± 0.9 5.8 ± 3.3 7.5 ± 2.6 0.0018 Eating self-captured prey 0.0 <0.1 ± 0.1 1.5 ± 0.8 6.6 ± 2.6 7.9 ± 0.8 <0.0010 Maintenance 14.5 + 2.0 19.1 ± 4.2 17.4 ± 3.4 9.3 ± 3.8 8.7 ± 0.8 0.3215 Lying on belly 4.1 ± 3.2 7.3 ± 4.1 2.9 ± 1.6 0.0 0.0 0.1750 Begging 1.7 ± 1.1 2.5 ± 0.6 2.6 ± 0.9 0.0 0.0 0.1394 Out of sight 2.3 ± 0.9 5.4 ± 1.2 7.9 ± 2.4 5.3 + 1.6 1.6 ± 0.6 0.1794 Other 1.4 ± 0.4 2.8 ± 1.4 0.4 ± 0.2 0.1 ± 0.1 0.1 ± 0.1 0.0547 a F-values are based on AN OVA F-tests for linear trends across 5 wk post-fledging (df = 1, 27). All tests for lack of fit were not significant (P > 0.05). 2). Ground hunting success also increased signifi- cantly ( P < 0.01). We identified nearly all prey items caught by young kestrels as grasshoppers (order Orthoptera). We saw one kestrel feeding on a dragonfly (order Odonata), and some items were too small to identify. During four sessions we observed seven brief bouts of hover hunting in birds 12-37 d post-fledging. None of these attempts were successful. We observed five flycatching attempts (see Suring and Alt 1981) among birds 23-25 d post-fledging during three ses- sions, four were successful. When perch resting, fledged kestrels became pro- gressively less social with time. The significant de- crease in association ( P < 0.001) and the significant increase in nonsocial behavior ( P < 0.001; Table 2) reflect this trend. Allopreening and beaking exchanges occurred Table 2. Time (mean % ± SE) spent engaged in social and nonsocial activity by post-fledging American Kestrels in Iowa. Behavior by Weeks Post-Fledging 1-5 Social Activity 1 2 3 4 5 F-Values® Perch resting (N) b (12) (10) (10) (6) (4) Association 57.7 ± 10.8 48.9 ± 8.2 38.3 ± 6.0 25.8 ± 16.3 13.5 ± 8.2 <0.0010 Social hunting — — — — — — Nonsocial 28.2 ± 7.5 48.9 ± 8.1 56.1 ± 5.8 74.2 ± 16.3 86.5 ± 8.2 <0.0010 Undetermined 14.1 ± 8.6 2.2 ± 1.0 5.6 ± 3.3 0.0 0.0 0.2722 Perch hunting (N) (1) (6) (10) (6) (4) Association 0.0 17.3 ± 11.7 19.4 ± 6.8 6.6 ± 6.0 3.3 ± 1.7 0.1658 Social hunting 0.0 11.6 + 5.3 21.3 ± 7.1 30.4 ± 16.2 14.5 ± 8.4 0.0772 Nonsocial 100.0 69.8 ± 12.5 53.0 ± 6.1 63.0 ± 18.3 82.2 ± 8.5 0.4673 Undetermined 0.0 1.3 ± 0.8 6.3 ± 4.9 0.0 0.0 0.7646 Ground hunting (N) (0) (5) (7) (5) (3) Association 0.0 15.0 ± 15.0 21.7 ± 10.3 1.2 ± 1.2 0.0 0.0955 Social hunting 0.0 20.4 ± 13.6 33.6 ± 13.9 45.9 ± 22.7 0.0 0.9385 Nonsocial 0.0 44.6 ± 17.5 44.6 ± 8.4 52.9 ± 22.1 100.0 0.4887 Undetermined 0.0 20.0 ± 20.0 0.0 0.0 0.0 — a F-values are based on ANOVA F-tests for linear trends across 5 wk post-fledging. Perch resting df = 1, 26; perch hunting df = 1, 12; hunting on ground df = 1, 7. All tests for lack of fit were not significant (F > 0.05). * Number of sibling groups observed. (a) Perch Hunting Hunting on Ground 2 3 4 * Weeks Post— fledging 24 22 20 IB IB 14 12 10 a 6 4 2 Pounces/hr (n.s.) +/- 1 SE 2 3 4 * Weeks Post-fledging (b) Perch Hunting Hunting on Ground (C) Perch Hunting Hunting on Ground 14 12 10 B 0 4 2 0 0 1 2 3 4* 5* Captures/hr (P < 0.001) j. - +/- 1 SE J3 I ] U B 4 » 1 1 L. 14 12 10 B a 4 2 0 0 1 2 3 4* 5 Captures/hr (n.s.) - +/- 1 SE ,u. Weeks Post-fledging Weeks Post-fledging Figure 2. Mean foraging pounce (a), percent success (b), and capture rates (c) for post-fledging American Kestrels at weekly intervals. P values are based on AN OVA F-tests across 5 wk post-fledging (perch and ground hunting pounce and capture rate df = 1, 27; perch and ground hunting success df = 1, 10). Weekly means with * differ significantly (F < 0.05, least significant difference i-test) from the preceding week. 14 Varland et al. Vol. 25, No. 1 during 15% (14/93) of the sessions. We observed the behaviors in 9 of 1 2 family groups among young ranging from 3-23 d post-fledging. Kestrels were social while perch and ground hunt- ing and spent a substantial amount of time in these activities (Table 2). We observed social hunting dur- ing 41% (20/49) of the sessions in which hunting occurred. We saw social hunting in 10 of 12 sibling groups and quantified it in 8. In three of these eight groups, social hunting involved siblings and nonsib- lings. We saw extra-familial social hunting in 20% (4/20) of the sessions with social hunting. In one of these groups we observed social hunting involving siblings, a parent, and a non-sibling female of un- known age. The female parent did not feed the young but called and flew aggressively at a Red-tailed Hawk (Buteo jamaicensis) perched within 20 m of the group, causing the hawk to leave the area. Social hunting among non-sibling groups occurred just before or after dispersal from the natal area. We observed social hunting on one or two occasions and then lost contact due to signal loss from the radio-tagged kes- trel. We are uncertain whether these groups re- mained together. Discussion Association. Association among fledgling kestrels occurred mostly during the first 2 wk after fledging, when young are most dependent on parents. Moreno (1984) found that fledgling Northern Wheatears ( Oenanthe oenanthe ) fed by one parent perched closer to each other than fledglings fed by both parents, and that a tendency for fledglings to associate (perch < 1 m apart) diminished as they became increasingly more independent. Distance between sibling Spanish Imperial Eagles ( Aquila heliaca ; Alonso et al. 1987) and Black Kites ( Milvus migrans; Bustamante and Hiraldo 1990) increased with age, and there was a positive correlation between increased sibling dis- tance and flying proficiency. Wittenberger (1981) suggested that the allopreen- ing in breeding birds is important in maintaining pair bonds. Our observations of allopreening and beaking provide evidence that American Kestrels are social after fledging. Thus, fledgling kestrels do not perch close together merely to improve their chances of being fed or because they lack flying skills. We suggest allopreening and beaking may maintain so- cial bonds between siblings during the post-fledging period. Both behaviors occur in the social repertoire of fledgling Peregrine Falcons (Sherrod 1983), and Komen and Meyer (1989) observed allopreening in fledgling Common Kestrels ( Falco tinnunculus). Other researchers have reported close associations among fledged American Kestrels (Sherman 1913, Cade 1955, Roest 1957, Smith et al. 1972, Balgooyen 1976, Wheeler 1979, Lett and Bird 1987), but we have not found any reference in the literature to allo- preening or beaking. Development of Foraging Behavior. Bird and Palmer (1988) described various foraging methods used by American Kestrels. Toland (1987) grouped American Kestrel foraging methods into three cat- egories: perch hunting (which he observed 70-97% of the time); hover hunting (2-20%); and horizontal flight (<5%). The American Kestrel is a generalist predator of invertebrates and small vertebrates, and its diet varies with season and geographic area (Heintzelman 1964, Bent 1938). In this study, young kestrels progressed from rel- ative inactivity to active foraging within 3 to 4 weeks of leaving the nest (Fig. 2, Table 1). The two hunting methods observed most frequently, perch hunting and ground hunting, were probably least dependent on flying ability. Early reliance on hunting tech- niques requiring relatively simple flight patterns has been reported for post-fledging Common Kestrels (Shrubb 1982), Peregrine Falcons (Sherrod 1983), Red-tailed Hawks (Johnson 1986), Northern Wheatears (Moreno 1984), and Spotted Flycatchers (Muscicapa striata ; Davies 1976). Fledged American Kestrels fed on easily-caught invertebrate prey. Dunstan (1970), Johnson (1986) and Shrubb (1982) reported invertebrates as the ear- liest prey of Great Horned Owls ( Bubo virginianus ) , Red-tailed Hawks, and kestrels. Toland (1987) found an 82% success rate among American Kestrels (both sexes, all ages) hunting invertebrates, with lower rates for rodents (66%) and birds (33%). Collopy (1973) reported that kestrels wintering in California had 64% hunting success for invertebrates and 25% for vertebrates. Smallwood (1987) found kestrels wintering in Florida fed only on arthropods, with comparable success rates for males (76%) and fe- males (73%). In this study, mean perch hunting success in- creased significantly from 3.3% in the second week after fledging to 49.7% in the third, but did not change significantly thereafter (Fig. 2). These suc- cess rates for invertebrates are substantially lower than rates cited above and indicate that kestrels fur- ther develop their foraging skills after dispersal. We Spring 1991 Foraging in Kestrels 15 observed significant increases in mean capture rates by perch hunting kestrels at 4 and 5 wk post-fledging due to increased pounce rates (Fig. 2). The observed increases in perch hunting success and pounce rates may be at least partially due to increases in grass- hopper density during the post-fledging period. Grasshoppers were abundant in central Iowa in July and August 1989 (Rice 1989). Reports of increasing numbers of kills by matur- ing Peregrine Falcons released from hack sites (Sher- rod 1983) and increasing hunting success with age in fledged Red-tailed Hawks (Johnson 1986) were supported by few quantitative data. Increased hunt- ing success over time was quantified for fledgling Ospreys ( Pandion haliaetus; Edwards 1989a) and passerines, including Northern Wheatears (Moreno 1984), Spotted Flycatchers (Davies 1976), and Yel- low-eyed Juncos (Junco phaeonotus; Sullivan 1988). Social Hunting. Wilson (1975:51) described two types of social foraging, imitative and cooperative. The net effect of such social hunting probably is greater foraging efficiency. During imitative foraging, individuals observe others in the group and may initiate, copy, increase, or learn foraging behavior. All of these may occur during social hunting but are difficult to differen- tiate. Communication among imitative foragers probably is indirect, and group members do not co- ordinate their efforts during the hunt. Several in- vestigators reported feeding benefits associated with imitative foraging (e.g., Krebs 1973, Rubenstein et al. 1977, Sullivan 1984). Edwards (1989a, 1989b) compared the foraging behavior of sibling pairs of Ospreys and single young and found that pairs and singles both reached the same level of success but that siblings developed their skills sooner. Sibling pairs also used similar foraging techniques and had similar diets. Edwards suggested these differences were a result of observational learning between sib- lings. Hector (1986) listed six characteristics distin- guishing cooperative foraging from imitative forag- ing, including division of labor and use of signals to coordinate movements. He reported that mated pairs of Aplomado Falcons ( Falco femoralis ) cooperatively hunting for birds had greater success (45%) than when alone (21%). Group size in cooperatively for- aging Harris’ Hawks ( Parabuteo unicinctus ) was positively correlated with capture (Bednarz 1988). After the breeding season American Kestrels may hunt in social groups of 10-20 juveniles and adults (Cade 1955, Wheeler 1979, Wilmers 1982). We also observed post-breeding adults and juveniles hunting in groups, but social hunting was observed most frequently among siblings prior to or just after dis- persal. Young kestrels hunted socially from 12-46% of the time (Table 2). We saw nothing to indicate that individuals in groups were coordinating their efforts or using signals to coordinate movements. Thus, social foraging in these kestrels was imitative rather than cooperative. We considered the possibility that differences might exist between the hunting efficiency of kestrels hunt- ing socially and those hunting nonsocially, but the study design was not adequate to test this idea. Fur- ther research is needed to document whether social hunting influences foraging efficiency in the Amer- ican Kestrel. Acknowledgments This paper is a contribution of the Iowa Cooperative Fish & Wildlife Research Unit, U.S. Fish & Wildlife Service; Iowa State University; Iowa Department of Nat- ural Resources; and the Wildlife Management Institute. It is Journal Paper No. J- 14074 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 2845. Support was received from the Iowa Department of Natural Resources Nongame Program, Iowa Ornithologists’ Union, North American Bluebird Society, Iowa Science Foundation, Big Bluestem Audubon Society of Ames, Iowa, Max McGraw Wildlife Foun- dation, Iowa Agriculture Experimental Station, and the Iowa State University Department of Animal Ecology. For assistance in the field we are grateful to ISU students T. Holmes, K. Moeller, P. Emge, V. Windsor, and D. Mallinger and to DNR Nongame Technicians B. Ehres- man and P. Schlarbaum, We thank Carroll Rudy (W3866 Highway H, Chilton, WI 53014) for drawing the socially hunting kestrels. Thanks also to the following individuals who read drafts of the paper and provided helpful com- ments: G. McLaughlin, J. Bednarz, L. Best, J. Dinsmore, P. Delphy, J. Gionfriddo, K. Shaw, R. Bowman, J. Small- wood and J. Bustamante. Literature Cited Alonso, J.C., L,M. Gonzalez, B. Heredia and J.L. GonzAlez. 1987. Parental care and the transition to independence of Spanish Imperial Eagles Aquila heliaca in Doiiana National Park, southwest Spain. Ibis 129: 212-224. Altmann, J. 1974. Observational study of behavior: sampling methods. Behaviour 49:227 -267 . Balgooyen, R.G. 1976. Behavior and ecology of the American Kestrel ( Falco sparverius) in the Sierra Ne- vada of California. Univ. Calif. Publ. Zool. 103:1-87. Bednarz, J.C. 1988. Cooperative hunting in Harris’ Hawks ( Parabuteo unicinctus). Science 239:1525-1527. 16 Varland et al. Vol. 25, No. 1 Bent, A.C. 1 938. Life histories of North American birds of prey. Part II. Bull. U.S. Nat. Mus. No, 167. Berger, D.D. and H. Mueller. 1959. The bal-chatri: a trap for birds of prey. Bird-Band. 30:19-27. Bird, D.M. and R.S. Palmer. 1988. American Kestrel. Pages 253-290, in R.S. Palmer [Ed.], Handbook of North American birds: diurnal raptors. Yale Univer- sity Press, New Haven, GT. Brown, L.H. and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw-Hill Book Co., New York. Bustamante, J. and F. Hiraldo. 1990. Factors influ- encing family rupture and parent-offspring conflict in the Black Kite Milvus migrans. Ibis 132:58-67. Cade, T.J. 1955. Experiments on winter territoriality of the American Kestrel, Falco sparverius. Wilson Bull. 67:5-17. COLLOPY, M.W. 1973. Predatory efficiency of the Amer- ican Kestrel wintering in northwestern California. Raptor Res. 7:25-31. Davies, N.B. 1976. Parental care and the transition to independent feeding in the young Spotted Flycatcher ( Muscicapa striata). Behaviour 39:280-295. Dunstan, T.C. 1970. Post-fledging activities of juvenile Great Horned Owls as determined by radio telemetry. Ph.D. thesis. University of South Dakota, Vermillion, SD. EDWARDS, T.C. 1989a. Similarity in the development of foraging mechanics among sibling Ospreys. Condor 91:30-36. . 1989b. The ontogeny of diet selection in fledg- ling Ospreys. Ecology 70:881-896. Hector, D.P 1986. Cooperative hunting and its rela- tionship to foraging success in an avian predator. Ethol- ogy 73:247-257. Heintzelman, D.S. 1964. Spring and summer Sparrow Hawk food habits. Wilson Bull. 76:323-330. Henny, C.J. 1972. An analysis of the population dy- namics of selected avian species. U.S. Fish and Wildl. Serv., Wildl. Res. Report 1:1-99, Washington, D.C. Johnson, S.J. 1986. Development of hunting and self- sufficiency in juvenile Red-tailed Hawks. Raptor Res. 20:29-34. Komen, J. and E. Meyer. 1989. Observations on post- fledging dependence of kestrels ( Falco tinnunculus rupi- colus ) in an urban environment. J. Raptor Res. 23:94- 98. Krebs, J.R. 1973. Social learning and the significance of mixed-species flocks of chickadees ( Parus spp.) Can. J. Zool. 51:1275-1288. Lack, D. 1954. The natural regulation of animal num- bers. Clarendon Press, Oxford, U.K. Lett, D.W. and D. M. Bird. 1987. Post-fledging be- havior of American Kestrels in southwestern Quebec. Wilson Bull. 99:77-82. MORENO, J. 1984. Parental care of fledged young, di- vision of labor and the development of foraging tech- niques in the Northern Wheatear ( Oenanthe oenanthe ). Auk 101:741-752. Newton, I. 1979. Population ecology of raptors. Buteo Books, Vermillion, SD. Rice, M.E. 1989. Crops, soils, and pests newsletter. Iowa State University Ext. Entomol. Newsletter IC- 458(17), Ames, IA. Roest, A.I. 1957. Notes on the American Sparrow Hawk. Auk 74:1-19. Rubenstein, D.I., R.J. Barnett, R.S. Ridgely and P.H. Klopfer. 1977. Adaptive advantages of mixed- species feeding flocks among seed eating finches in Costa Rica. Ibis 119:10-21. Rudolf, S.G. 1982. Foraging strategies of American Kestrels during breeding. Ecology 63:1268-1276. SAS Institute. 1985. SAS/STAT Guide for Personal Computers. Version 6. SAS Institute, Cary NC. Sherman, A.R. 1913. The nest life of the Sparrow Hawk. Auk 30:406-418. Sherrod, S. 1983. Behavior of fledgling peregrines. The Peregrine Fund, Inc., Ithaca, NY. Shrubb, M. 1982. The hunting behavior of some farm- land kestrels. Bird Study 29:121-128. Smallwood, J.A. 1987. Sexual segregation by habitat in American Kestrels wintering in southcentral Flor- ida: vegetative structure and responses to differential prey availability. Condor 89:842-849. Smith, D.G., C.R. Wilson and H.H. Frost. 1972. The biology of the American Kestrel in Central Utah. Southwest Nat. 17:73-83. Snedecor, G.W. and W.G. Cochran. 1989. Statistical methods. Iowa State University Press, Ames, IA. Sullivan, K.A. 1984. The advantages of social foraging in Downy Woodpeckers. Anim. Behav. 32:16-21. . 1988. Ontogeny of time budgets in Yellow-eyed Juncos: adaptation to ecological constraints. Ecology 69:118-124. . 1989. Predation and starvation: age-specific mortality in juvenile juncos (Junco phaeonotus). J. Anim. Ecol. 58:275-286. Suring, L.H. and C.J. Alt. 1981. Flycatching behavior by American Kestrels. Southwest Nat. 26:76. Toland, B.R. 1987. The effect of vegetative cover on foraging strategies, hunting success and nesting distri- bution of American Kestrels in central Missouri. J. Raptor Res. 21:14-20. van Tyne, J. and A.J. Berger. 1966. Fundamentals of ornithology. John Wiley and Sons, New York. Weathers, W.W. and K.A. Sullivan. 1989. Juvenile foraging proficiency, parental effort, and avian repro- ductive success. Ecol. Monogr. 59:223-246. Wheeler, S. 1979. New Hampshire kestrels. New Hampshire Audubon Annual. Spring:25-27. Spring 1991 Foraging in Kestrels 17 Wiens, J.A., S.G. Martin, W.R. Holthaus and F.A. I WEN. 1970. Metronome timing in behavioral ecology studies. Ecology 51:350-352. Wilmers, T.J. 1982. Kestrel use of nest boxes on re- claimed surface mines in West Virginia. M.S. thesis. West Virginia University, Morgantown, WV. WILSON, E.O. 1975. Sociobiology: the new synthesis. Belknap Press, Boston, MA. WlTTENBERGER, J.F. 1981. Animal social behavior. Duxbury Press, Boston, MA. Wyllie, I. 1985. Post-fledging period and dispersal of young Sparrowhawks Accipiter nisus. Bird Study 32: 196-198. Received 13 July 1990; accepted 13 December 1990 J. Raptor Res. 25(1):18— 19 © 1991 The Raptor Research Foundation, Inc. Short Communications Nest Site and Prey of a Pair of Sharp-Shinned Hawks in Alberta Michael S. Quinn 1 Department of Forest Science , University of Alberta, Edmonton, AB Canada T6G 2H1 Sharp-shinned Hawks ( Accipiter striatus) nest mainly in coniferous and mixed coniferous/deciduous forests (Platt 1976, Evans 1982, Reynolds et al. 1982) where they prey on small to medium-sized birds (e.g., Snyder and Wiley 1976, Duncan 1979, Reynolds and Meslow 1984). Infor- mation on prey delivered to the nest is available from few regions within this hawk’s range. Here I present data on the food habits of a pair of Sharp-shinned Hawks in the aspen parkland of Alberta, and describe their nesting hab- itat. Methods I found the Sharp-shinned Hawk nest containing three young on 6 July 1987, 0.6 km from the southeast shore of Beaverhill Lake, Alberta (53°24'N 112°31'W). Based on size and feather development (Brown and Amadon 1968), I judged the young to have hatched about 27 June. The nest was observed from a blind 6.6 m east of the nest tree during 18 observation periods, from 14-24 July. Ob- servation periods were 1. 5-2.0 hr long for a total of 31 hr of observation. The adult male and female could be dis- tinguished by size, plumage, and after 2 d of observation, by vocalization. I identified prey items, as well as which adult caught and delivered the prey, for each observed feeding. I compared prey remains (mainly feathers) found in or below the nest to specimens in the University of Alberta Zoology Museum collection. Results The Sharp-shinned Hawks had three young and one egg that did not hatch. After fledging on 20 July and 22 July, the hawks continued to use the nest as a feeding site for at least 5 days. Young were seen in the immediate vicinity of the nest until 7 August. The Sharp-shinned Hawks nested in deciduous forest. The nest was 2.4 m high in a stunted Trembling Aspen ( Populus tremuloides; height = 4.5 m). The nest was con- cealed within a dense stand of willows (Salix spp.; 65, 820 stems/ha, X height = 3.5 m). Canopy closure was 82.5%. Horizontal cover at heights up to 3 m (Noon 1981) ranged from 74-100%. Forest tent caterpillars ( Malacosoma dis- stria) reduced foliage density throughout the nesting pe- riod. The ground below the nest was ephemerally wet. Sixteen of the deliveries to the nest were by the female, 1 Present address: Faculty of Physical Education and Rec- reation, University of New Brunswick, Box 4400, Fred- ericton, NB Canada E3B 5 A3. 3 by the male, and 2 were undetermined. The adult female rarely left the nest area whereas the male was rarely seen there. Prey transfers were initiated by the male calling from about 20 m south of the nest. The female then flew toward the male and returned within 1 min with prey. I observed the male Sharp-shinned Hawk hunting on four occasions. Two were unsuccessful attempts to capture fledgling Red-winged Blackbirds (Agelaius phoeniceus). The other two observations were at dusk when the hawk caught two large moths in flight. Twenty-one prey items were delivered to the nest in 31 hr of observation: 20 birds and one small mammal resem- bling a vole ( Microtus sp.). I was able to identify 12 of the 21 items to species. Six were fledgling Red- winged Black- birds and one each of Yellow Warbler (Dendroica petechia), American Goldfinch ( Carduelis tristis ), flycatcher ( Empi - donax sp.), American Robin ( Turdus migratorius ) and a Tree Swallow ( Tachycineta bicolor ). In addition, prey re- mains consisted of Black-billed Cuckoo ( Coccyzus erythrop- thalmus ), flycatchers ( Empidonax sp.), Purple Martin ( Progne subis), Black-capped Chickadee (Pants atricapil- lus ), House Wren (Troglodytes aedon), Veery (Catharus fuscescens), American Robin, Savannah Sparrow (Passer- culus sandwichensis). Clay-colored Sparrow (Spizella pal- lida), Red-winged Blackbird, American Goldfinch, Yellow Warbler, Tree Swallow, Downy Woodpecker (Picoides pubescens), Wilson’s Phalarope (Phalaropus tricolor), and Meadow Vole (Microtus pennsylvanicus). I found 14 celluloid color bands in regurgitated pellets. These bands were from fledgling House Wrens studied in the same area (Quinn 1989). No bands from adult House Wrens were found, although the majority of the population had been banded (74% of known breeding population). The Sharp-shinned Hawk nest was located on the west edge of a 7.65 ha study grid containing 71 nest boxes, 50 of which were occupied by House Wrens. Discussion The tree species composition and height of canopy at the Beaverhill Lake nest-site differed from those previ- ously described in the literature (Platt 1976, Reynolds et al. 1982). There were no conifers within 5 km of the nest and the crown height of the nest tree was only 4.5 m. Similarities in nesting habitat between the Beaverhill Lake nest and those previously reported are the high vegetation density, well developed canopy, mesic conditions and close proximity to water. The dominance of avian prey in the present study is consistent with previously reported data (Snyder and Wi- 18 Spring 1991 Short Communications 19 ley 1976, Duncan 1979). The relatively high number of juvenile Red-winged Blackbirds and especially House Wrens in the prey sample suggests selection for juvenile birds. Resumen. — Una pareja de Gavilan Pechirrojo Menor ( Accipiter striatus), en epoca de anidar, ha sido observada cerca de Beaverhill Lake, Alberta. El nido estaba ubicado a 2.4 m sobre el suelo en un bajo Alamo Temblon (Pop ulus tremuloides ) dentro de una area densa de sauces (Salix spp.). La hembra puso cuatro huevos, tres de los cuales incubaron bien, y las crias emplumaron hasta volar. El macho fue el que hizo la mayoria de la caza, haciendo presa, predominantemente, de jovenes Tordos Sargento (Agelaius phoeniceus) y de Trogloditas Continental ( Trog- lodytes aedon). Se observo que el macho capturaba y con- sumia grandes polillas. [Traduccion de Eudoxio Paredes-Ruiz] Acknowledgments I thank Sheila Braun, Valerie Kerr, Dick Decker and Matt Besko for assisting with the observations. I am grate- ful to the Beaverhill Bird Observatory for cooperation on the research area. The comments of Drs. W.M. Samuel and G.L. Holroyd on this manuscript were greatly ap- preciated. This research was supported by the Canadian Wildlife Service, the University of Alberta and the Alberta Summer Temporary Employment Program through a grant to the Edmonton Natural History Club. Literature Cited Brown, L. and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw-Hill Book Co., NY. Duncan, S. 1979. An analysis of the stomach contents of some Sharp-shinned Hawks (Accipiter striatus). J. Field Ornithol. 51:178. Evans, D.L. 1982. Status reports on twelve raptors. USDI Fish and Wildlife Service, Special Scientific Re- port — Wildlife, No. 238. Noon B.R. 1981. Techniques for sampling avian hab- itats. Pages 42-50 in D.E. Capen [Ed.], The use of multivariate statistics in studies of wildlife habitat, Workshop proceedings. U.S. Forest Service, General Technical Report RM-87, Fort Collins, CO. Platt, J.B. 1976. Sharp-shinned Hawk nesting and nest site selection in Utah. Condor 78:102-103. Quinn, M.S. 1989. Factors regulating the breeding pop- ulation, reproductive success and mating system of House Wrens (Troglodytes aedon ) at Beaverhill Lake, AB. M.Sc. thesis, Department of Forest Science, Uni- versity of Alberta, Edmonton. Reynolds, R.T. and E.C. Meslow. 1984. Partitioning of food and niche characteristics of coexisting accipiter during breeding. Auk 101:761-779. , E.C. Meslow and H.M. Wight. 1982. Nest- ing habitat of coexisting accipiter in Oregon. J. Wildl. Manage. 46:124-138. Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size dimorphism in hawks and owls of North America. Ornithological Monographs No. 20, American Orni- thologists’ Union, Lawrence, KS. Received 19 June 1990; accepted 28 November 1990 /. Raptor Res. 25(l):19-20 © 1991 The Raptor Research Foundation, Inc. Ornate Hawk-Eagle Feeding on Green Iguana Jack Clinton-Eitniear Center for the Study of Tropical Birds, Inc., 218 Conway, San Antonio, TX 78209-1716 Michael R. Gartside P.O. Box 20219, Charleston, SC 29413 Mark A. Kainer Department of Biology, Southwest Texas State University, San Marcos, TX 78666 The Ornate Hawk-eagle (Spizaetus ornatus ) is a scarce resident of dense subtropical and tropical forests from southern Mexico to northern Argentina (Eitniear 1986, 1988, Brown and Amadon 1968). The species is stated to be the rarest of the three hawk-eagles in Belize (Hartshorn el al. 1984). Lyon and Kuhnigk (1985) documented both mammalian and avian prey species but considered the Ornate Hawk-eagle a specialist on birds. This note doc- 20 Short Communications Vol. 25, No. 1 uments an additional sighting of the species feeding on Green Iguanas ( Iguana iguana) in Belize. On 28 May 1990, we observed an Ornate Hawk-eagle feeding on a Green Iguana while perched in a tree on the banks of the Raspaculo branch of the Rio Guacamayo, 4 km upstream from the confluence of the Raspaculo and Guacamayo. Several minutes after our arrival the hawk- eagle attempted to carry the prey to another branch in a nearby tree. The hawk-eagle was unable to lift the iguana, however, and both plummeted into the underbrush, where the hawk-eagle continued to feed on the lizard. The entire episode was documented on video tape, which is deposited in the video library of the Center for the Study of Tropical Birds, Inc. An earlier sighting was made by Mick Fleming in the fall of 1987. In the same area as the 1990 sighting, Fleming’s party observed an Ornate Hawk-eagle flying across the Raspaculo with an adult Green Iguana in its talons. The bird alighted in a nearby tree where it con- sumed its prey (Fleming 1987). In Tikal National Park, 70-80 km northwest of the Raspaculo River, Lyon and Kuhnigk (1985) observed Or- nate Hawk-eagles feeding upon a young tinamou (Tinam- idae), a Plain Chachalaca ( Ortalis vetula ), a young Crested Guan {Penelope purpurascens) , a Gray-headed Dove {Lep- totila plumbeiceps) and a leaf-nosed bat (Phyllostomidae). More recently, also in Tikal National Park, Flatten et al. (1989) recorded 52 Ornate Hawk-eagle prey items of which 21 (40.4%) were identified as avian, 24 (46.1%) as mam- malian, and 7 (13.5%) were unidentifiable. Klein et al. (1988) reported that 63.5% of prey items were avian, including macaws (Ara spp.). The Ornate Hawk-eagle has been reported to feed upon Great Curassow {Crax rubra) (Russell 1964), Kinkajoo (Potus flavus) (Brown and Amadon 1968), and Guiana Cock-of-the-Rock {Rupicola rupicola) (Trail 1987). An additional report of this species feeding on a reptile was made by Klein et al. (1988) who mentioned that the hawk-eagle fed upon an unidentified snake and a lizard (Teiidae) in Manaus, Brazil. Since previous studies of this raptor have not been con- ducted along rivers where Green Iguanas are abundant, our sighting (despite abundant avian prey items) suggests that the Ornate Hawk-eagle, like most raptors, will take vulnerable prey species when they become available. Therefore, the Ornate Hawk-eagle should be considered more opportunistic than previously believed. Resumen. — Los autores observaron un Aguila Elegante {Spizaetus ornatus) consumir una iguana {Iguana iguana) en Belice. Se considera que esta especie se alimenta prin- cipalmente de aves. Sin embargo, este registro, asi como los dos documentados y publicados previamente, indican que el aguila exhibe el mismo comportamiento oportunista documentado en aves rapaces que habitan zonas de clima templado del norte. Acknowledgments We thank Lloyd Kiff for his comments on this manu- script and Mick Fleming and Mr. Oscar Rosado for shar- ing their previous experiences with the species and the region. Literature Cited Brown, L. and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw-Hill Book Co., New York. ElTNIEAR, J.C. 1986. Status of the large forest eagles of Belize. Bull. Int. Council Bird Preservation, World Working Group on Birds of Prey 3:107-110. . 1 988. Status of the Ornate Hawk-eagle in Mex- ico and Central America. The Eyas 11(2):8-10. Flatten, C.J., J.A. Madrid, A.E. Hernandez and R.P. Gerhardt. 1989. Observations at the nest of an Ornate Hawk-eagle {Spizaetus ornatus). Maya Project, Progress Report 11:69-80. Fleming, M. 1987. Wild animal sightings on the Ras- paculo. Newsletter of the Belize Audubon Society, De- cember. Hartshorn, G., L. Nicolait, L. Hartshorn, G. Be- vier, R. Brightman, J. Cal, A. Cawich, W. David- son, R. Dubois, C. Dyer, J. Gibson, W. Hawley, J. Leonard, R. Nicolait, D. Weyer, H. White and C. Wright. 1984. Belize country environmental profile. Imprenta Trejos, San Jose, Costa Rica. Klein, B.C., L.H. Harper, R.O. Bierregaard, and G.V. Powell. 1988. The nesting and feeding behavior of the Ornate Hawk-eagle near Manaus, Brazil. The Con- dor 90:239-241. Lyon, B., A. Kuhnigk. 1985. Observations on nesting Ornate Hawk-eagles in Guatemala. Wilson Bull. 97: 141-147. Russell, S.M. 1964. A distributional study of the birds of British Honduras. Ornithol. Monogr., No. 1. Trail, P.W. 1987. Predation and antipredator behavior at Guiana Cock-of-the-Rock leks. Auk 104:496-507. Received 9 August 1990; accepted 3 December 1990 Spring 1991 Short Communications 21 J. Raptor Res. 25(1):21— 22 © 1991 The Raptor Research Foundation, Inc. Notes on a Successful Nesting by a Pair of Yearling Peregrine Falcons ( Falco peregrinus ) Annie M. Wendt Wisconsin Peregrine Society, P.O. Box 1148, Milwaukee, WI 53210-1148 Greg A. Septon Milwaukee Public Museum, 800 W. Wells St., Milwaukee, WI 53233 It is rare for yearling male Peregrine Falcons {Falco peregrinus ) to breed; occasionally an immature female will pair with an adult male. When yearlings attempt to breed, many fail to produce eggs or lay a smaller than normal clutch; if eggs are produced, young seldom fledge (Hagar 1965, Hickey 1965, Cade 1982, Mearns and Newton 1984, Ambrose and Riddle 1988, Newton and Mearns 1988). In Milwaukee, Wisconsin, in 1988, a pair of yearling peregrines produced and fledged young. This is the first known record of successful nesting by a pair of yearlings. Study Site The First Wisconsin Center, overlooking Lake Mich- igan, is the tallest building in Wisconsin. The top floor is an observation deck, with full length glass windows on all sides. The nest was in a hack box (Sherrod et al. 1982) that had been installed on a 2 m ledge outside the windows on the west side of this floor, 178 m above street level. Fourteen young peregrines had been released from the site in 1987. History of Falcons The male of the pair, a F. p. pealei x F. peregrinus, had been released in 1987 in Ft. Sheridan, Illinois, with 10 other youngsters. He was described as a dominant bird (J. McCoy and M. Spreyer, in litt.). The female, a F. p. anatum, was one of 20 young released in Rochester, Min- nesota, in 1987. Breeding Activity A peregrine was seen hunting near the First Wisconsin Center on 21 March 1988. Within 10 d a second falcon had joined it. Both birds were in juvenile plumage, except for a spattering of adult feathers on their backs and a fair amount of white on the crop area. Both falcons molted quickly. By mid-June they looked adult, especially from a distance. By July, their heads, backs and well over 75% of their undersides had molted and they were replacing their flight feathers. Both falcons were seen regularly through 18 May. We inspected the hack box on 13 May, but found no evidence of nesting. When sightings stopped abruptly after 18 May, we thought the pair had left the area. But on 15 June we found the female in the hack box brooding two new chicks, one male and one female. These were the first peregrines hatched in the wild in Wisconsin in over 20 years. Because of precarious footing in front of the hack box, we feared for the safety of the nestlings so we barred the front of the box on 10 July. The parents continued to feed the young through the bars. We added two captive-pro- duced chicks on 15 July. We banded all four chicks, color- marked them with fluorescent spray paint, and released them from the box on 26 July, at an age of 38-42 days. All four young fledged. The male was strongly aggres- sive toward the young, stooping and striking once they were in the air or when they perched on exposed ledges. His attack was particularly intense when the flight of the young falcons appeared unsteady; at times he actually knocked them out of the air. Although stooping became less intense with time, each fledgling was driven to the ground at least once. While stooping, the male often gave creaking calls as described by Ratcliffe (1980). One youngster broke a femur when it hit the ground after an attack and later died of complications. Another died after hitting a glass window. The third youngster was injured twice, but survived and was relocated to a hack site in Omaha, Nebraska. The fourth stayed in Milwaukee and was last seen in early September. Discussion Most reports of juvenile peregrines attempting to breed come from relatively recent observations of an expanding, reintroduced population. As Hunt (1988:673) pointed out, “There is little information on the ecological age of first breeding in stable, undisturbed populations of peregrines.” Competition for nest sites has been recognized as a factor limiting the number of breeding yearlings. From 1935- 1957, Hagar (1969) observed only one mated juvenile female on a highly rated cliff; six others were found on low rated cliffs. None of these seven nests were successful. Today, tall buildings in cities are providing more high- quality nest sites, and without a stable population of adult peregrines, these sites are available for juveniles to attempt to nest. Newton and Mearns (1988) suggest that breeding might be delayed because juveniles that are inefficient foragers or are confined to areas where prey is scarce cannot develop the body reserves necessary to breed and cannot afford to spend time defending a territory. This is especially true for young males, for whom the increased burden of feeding a mate and family requires well developed hunting skills. The western shore of Lake Michigan is a well-documented migration route, and the availability of prey may have 22 Short Communications Vol. 25, No. 1 played a role in the pair of falcons selecting Milwaukee as a nest site and breeding successfully as yearlings. According to Ratcliffe (1980:341), paired juveniles “are often in transitional plumage, with a mixture of dark brown and slate grey.” He also noted that breeding adults “do not usually begin to molt until nesting is well advanced or actually over.” Our juvenile pair molted very quickly; both looked adult by the time the eggs had hatched, es- pecially when viewed from a distance. We agree with Ambrose and Riddle (1988:680), who feel that “there may be other cases of one year old birds attempting to breed which were not detected because of their nearly adult plumage.” It is possible that the hormone levels necessary to initiate and maintain breeding behavior might affect the rate at which mated juveniles attain their adult plum- age. Skutch (1976) suggests that when parent birds drive fledglings from the air or from exposed perches, this may be a response that reduces detection by predators. Also, “surviving subadult falcons which returned to hack sites from the preceding year appeared to react somewhat like parents with this respect. The aggressive stoops by which the subadults forced the young down, however, were of a more serious nature, and they often hit the youngsters a forceful blow. The stimulus in this case seems to be a ‘new falcon’ flying in the area, and aggression is the response” (Sherrod 1983:144). The young age of the male in our study may well have caused his strongly aggressive behavior. We do not know if adding the bars to the hack box contributed to his ag- gression by limiting his contact with the chicks, but had the young left the box prematurely, they might have been knocked off the ledge by the male’s attacks before they were old enough to fly. As a breeding adult, the male also harassed his fledged young when their flight appeared weak, but never with the same intensity and we never again saw him strike them forcefully. Resumen. — En 1988, en Milwaukee, Wisconsin, una pa- reja de Halcones Peregrinos ( Falco peregrinus) de aprox- imadamente un aiio de edad, incubo y crio hasta que las crias pudieran volar; siendo este, el primer caso que cono- cemos de una nidada con logros positivos. La pareja cambio de plumaje rapidamente; a mediados de junio, y especial- mente a la distancia, los dos tenian la apariencia adulta. El macho se mostro agresivo con sus crias, lanzandose hacia ellos y golpeandoles fuertemente. [Traduccion de Eudoxio Paredes-Ruiz] Acknowledgments We thank Clayton White, W. Kranz, and Fran Hamer - strom for reviewing this manuscript. Literature Cited Ambrose, R.E. and K.E. Riddle. 1988. Population dispersal, turnover, and migration of Alaska pere- grines. Pages 677-684 in T.J. Cade, J.H. Enderson, C.G. Thelander and C.M. White. [Eds.], Peregrine Falcon populations: their management and recovery. The Peregrine Fund, Inc., Boise, ID. Cade, T.J. 1982. The falcons of the world. Cornell University Press, Ithaca, NY. Hagar, J.A. 1969. History of the Massachusetts Per- egrine Falcon population, 1935-57. Pages 123-131 in J.J. Hickey [Ed.], Peregrine Falcon populations: their biology and decline. University of Wisconsin Press, Madison, WI. Hickey, JJ and D.W. Anderson. 1965. The Pere- grine Falcon: life history and population literature. Pages 3-42 in J.J. Hickey [Ed.], Peregrine Falcon populations: their biology and decline. University of Wisconsin Press, Madison, WI. Hunt, W.G. 1988. The natural regulation of Peregrine Falcon populations. Pages 667-676 in T.J. Cade, J.H. Enderson, C.G. Thelander and C.M. White [Eds.], Peregrine Falcon populations: their management and recovery. The Peregrine Fund, Inc., Boise, ID. Mearns, R. AND I. Newton. 1984. Turnover and dis- persal in a peregrine Falco peregrinus population. Ibis 126:347-355. Newton, I. and R. Mearns. 1988. Population ecology of peregrines in South Scotland. Pages 651-665 in T.J. Cade, J.H. Enderson, C.G. Thelander and C.M. White [Eds.], Peregrine Falcon populations: their manage- ment and recovery. The Peregrine Fund, Inc., Boise, ID. Ratcliffe, D.A. 1980. The Peregrine Falcon. Buteo Books, Vermillion, SD. Sherrod, S., W. Heinrich, W. Burnham, J. Barclay AND T. CADE. 1982. Hacking: a method for releasing Peregrine Falcons and other birds of prey. The Per- egrine Fund, Inc., Ithaca, NY. . 1983. Behavior of fledgling peregrines. The Peregrine Fund, Inc., Ithaca, NY. Skutch, A.F. 1976. Parent birds and their young. Uni- versity of Texas Press, Austin, TX. Received 30 November 1989; accepted 5 December 1990 Spring 1991 Short Communications 23 J Raptor Res. 25(l):23-24 © 1991 The Raptor Research Foundation, Inc. Non-Breeding Season Diet of Long- Eared Owls in Massachusetts Denver W. Holt Owl Research Institute, Inc., P.O. Box 8335, Missoula, MT 59807 Nancy N. Childs Habitat Institute for the Environment, 10 Juniper Road, Belmont, MA 02178 The Long-eared Owl (Asio otus ) is a widely-distributed, holarctic species (Burton 1973). In Massachusetts, Long- eared Owls are a species of special concern and little is known of their distribution, biology and ecology (Melvin et al. 1989). Long-eared Owl food habits have been extensively stud- ied in North America (Marti 1976, Marks 1984), and Europe (Nilsson 1981, Wijnandts 1984, Cramp 1985). At least 23 800 prey items in North America (Marti 1976) and over 360 000 prey items in Europe (Wijnandts 1984) have been identified. To our knowledge, nothing has been published on the diet of these owls in Massachusetts. We located only one study in Connecticut, which reported diet of this species for New England (Choate 1971). Here, we compare non-breeding season diet of Long-eared Owls from two locations in Massachusetts. Pellets were collected from Nantucket Island and the mainland town of Belmont, approximately 176 km apart. Nantucket Island (130 km 2 ) is composed of moraines and out- wash plains from Pleistocene glaciation (Woodsworth and Wigglesworth 1934). It is also unique in its compo- sition of maritime heaths or “moorlands” (Tiffney and Eveleigh 1985). Belmont is a densely settled suburban town approximately 12 km west of Boston. The topog- raphy is geologically a drumlin, dominated by deciduous woods with pockets of conifers. Abandoned orchards and large meadows occur throughout the woodlands. The owls’ non-breeding season was defined as 1 August to 1 April. Owls were observed at roost sites after detection of their pellets or “whitewash.” Pellets were collected be- tween November 1984 and February 1985 at irregular intervals. Pellets were air dried for four weeks and then dissected. Prey items were identified by comparing skulls, mandibles, long bones and feathers with museum speci- mens. Differences in frequencies of prey between sites were tested using a chi-square test of independence (Siegel 1956). Dietary overlap between sites was calculated using Schoe- ner’s (1968) symmetric index. Food niche-breadth was calculated using the antilog of the Shannon- Wiener equa- tion (see Marti 1987). Biomass was calculated using mid- points of weight ranges reported by Godin (1977) for mammals and Dunning (1984) for birds. We used mid- points because weights of prey can vary with habitat, season, age and sex. Mean weights reported in the liter- ature are most often those of adult specimens and could lead to overestimates of biomass calculations. Three owls were observed at each roost site. The Nan- tucket roost was in a dense stand of White Pine ( Pinus strobus ) forest, within 1 km of open moorlands and beach grasslands. The Belmont roost was in a Pitch Pine ( Pinus rigida) stand, within a mixed deciduous/coniferous forest, and within 0.5 km of meadows and orchards. Smith (1981) and Bosakowski (1984) stated that Long-eared Owls pre- fer dense stands of coniferous trees. Bosakowski (1984) felt foliage density may afford protection from environ- mental factors and predation. Our roost sites were also in dense cover. We recorded 915 prey items from two study sites (Table 1). Four species of mammals and two species of birds were identified. Meadow voles ( Microtus pennsylvanicus ) were the most numerous prey by number and biomass (Table 1). This is consistent with other studies (Marti 1976, Nilsson 1981, Marks 1984, Wijnandts 1984). Choate (1971) reported 91% (N = 128) meadow voles in the Long- eared Owl diet from Connecticut, the only New England study. Between the two locations, the owls had similar diets (overlap = 99.2%); however, prey species proportions dif- fered significantly (x 2 = 28.4, df = 3, P < 0.005). This was due to higher proportions of white-footed mice ( Pero - myscus leucopus ) from Nantucket owls and higher pro- portion of short-tailed shrews ( Blarina brevicauda) from Belmont owls (Table 1). Food niche-breadth values were similar from the two sites (1.85 at Nantucket and 1.89 at Belmont) and were in the range of values reported for North American Long-eared Owls that feed primarily on voles (1.60-2.30; see Marks 1984). Resumen. — Las dietas de buhos de la especie Asio otus, en la estacion no reproductiva, en dos areas de estudio en Massachusetts, han sido determinadas por medio del ana- lisis de egagropilas. Novecientos quince items conteniendo residuos de presa han sido identificados. En la Isla Nan- tucket, la dieta (N = 657) estuvo constituida en el 79% por ratones de la especie Microtus pennsylvanicus. 24 Short Communications Vol. 25, No. 1 Table 1. Non-breeding season diet of Long-eared Owls in Massachusetts. Prey weights (g) are given in parentheses. Nantucket Belmont Species No. % Biomass % No. % Biomass % Meadow Vole (20-64) 516 78.5 21 672 87.6 206 79.8 8652 88.6 White-footed Mouse (16-29) 122 18.6 2684 10.8 26 10.1 572 5.8 Short-tailed Shrew (12-24) 12 1.8 216 0.9 19 7.4 342 3.5 Meadow Jumping Mouse (13-23) 4 0.6 72 0.3 0 Blue Jay (64-109) 1 0.2 86 0.3 1 0.4 86 0.9 Northern Flicker (92-129) 0 1 0.4 110 1.1 Unid. Birds 2 0.3 — — 5 1.9 — — Totals 657 100.0 24 730 99.9 258 100.0 9762 99.9 mientras que el 19% corresponds a ratones de la especie Peromyscus leucopus. En Belmont, la dieta (N = 258) estuvo constituida en el 80% por ratones de la especie M. penn- sylvanicus, 10% corresponds a ratones de la especie P. leucopus, y 7% a musaranas de la especie Blarina brevi- cauda. Los buhos de cada una de las areas de estudio mostraron dietas similares en un 99.2%. Sin embargo, hubo diferencia significativa en la proportion de las es- pecies de presa capturada. [Traduction de Eudoxio Paredes-Ruiz] Acknowledgments William Barnard, Evelyn Bull, John Coleman, Jim Duncan, Jeff Marks and Christian Rohner made helpful comments on the manuscript. Nancy Claflin and Edith Andrews helped locate owls. Literature Cited Bosakowski, T. 1984. Roost selection and behavior of the Long-eared Owl wintering in New Jersey. Rap. Res. 18:137-142. Burton, J.A. [ed.]. 1973. Owls of the world. Tanager Books, Dover, NH. Choate, J.R. 1971. Notes on geographic distribution and habits of mammals eaten by owls in southern New England. Trans. Kans. Acad. Sci. 74:212-216. Cramp, S. [Ed.]. 1985. The birds of the Western Pa- learctic. Vol. 4. Oxford University Press, Oxford, U.K. Dunning, J.B., JR 1984. Bird weights of 386 species of North American birds. Western Bird-Banding As- sociation Monograph No. 1. Godin, A.J. 1977. Wild mammals of New England. Johns Hopkins University Press, Baltimore, MD. Marks, J.S. 1984. Feeding ecology of breeding Long- eared Owls in southwestern Idaho. Can. J, Zool. 62: 1528-1533. Marti, C.D. 1976. A review of prey selection by the Long-eared Owl. Condor 78:331-336. . 1987. Raptor food habits studies. Pages 67-79 in B.G. Pendleton, B.A. Milsap, K.W. Kline and D.A. Bird [Eds.], Raptor Management Techniques Manual, Nat. Wildl. Fed. Tech. Ser. No. 10, Washington D.C. Melvin, S.M., D.G. Smith, D.W. Holt and G.R. Tate. 1989. Small owls. Pages 88-96 in Proc. Northeast Raptor Management Symposium and Workshop. Nat. Wildl. Fed., Washington, D.C. Nilsson, I.N. 1981. Seasonal changes in food of the Long- eared Owl in southern Sweden. Ornis Scand. 12:216- 223. SCHOENER, T.W. 1968. The Anolis lizards of Bimini: resource partitioning in a complex fauna. Ecology 49: 704-726. Siegel, S. 1956. Nonparametric statistics for the be- havioral sciences. McGraw-Hill Book Co., New York. Smith, D.G. 1981. Winter roost site fidelity by Long- eared Owls in central Pennsylvania. Am. Birds 35:339. Tiffney, W.N., Jr. and D.E. Eveleigh. 1985. Nan- tucket’s endangered maritime heaths. Pages 1093-1109 in O.T. Morgan [Ed.], Coastal zone 85, Vol. 1, MD. Wijnandts, H. 1984. Ecological energetics of the Long- eared Owl. Ardea 72:1-92. WOODSWORTH, J.B. AND E. WlGGLESWORTH. 1934. Ge- ography and geology of the region including Cape Cod, the Elizabeth Islands, Nantucket, Martha’s Vineyard, No Man’s Land and Block Island. Mem. Mus. Comp. Zool., 52, Harvard University, Boston, MA. Received 26 October 1990; accepted 21 December 1990 THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966) OFFICERS PRESIDENT: Richard J. Clark SECRETARY: Betsy Hancock VICE-PRESIDENT: Michael W. Collopy TREASURER: Jim Fitzpatrick BOARD OF DIRECTORS EASTERN DIRECTOR: Keith L. Bildstein CENTRAL DIRECTOR: Patrick T. Redig MOUNTAIN & PACIFIC DIRECTOR: Stephen W. Hoffman EAST CANADA DIRECTOR: David M. Bird WEST CANADA DIRECTOR: Paul C. James INTERNATIONAL DIRECTOR #1: Fabian M. JaksiC INTERNATIONAL DIRECTOR #2: Eduardo E. ISigo-Elias DIRECTOR AT LARGE #1: Michael W. Collopy DIRECTOR AT LARGE #2: Robert E. Kenward DIRECTOR AT LARGE #3: Jeffrey L. Lincer DIRECTOR AT LARGE #5: James A. G ess am an DIRECTOR AT LARGE #6: Gary E. Duke &)|M|e9|(4cj|!:|cafe3|l9|g:|C3|s4ll|E]fel9E&3festE!fc EDITORIAL STAFF EDITOR IN CHIEF: Josef K. Schmutz, Department of Biology, University of Saskatchewan, Sas- katoon, SK., Canada, S7N 0W0 ASSOCIATE EDITORS Keith L. 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