(ISSN 0S92-1016) The Journal OF Raptor kesearch Volume 32 December 1998 Number 4 Contents In MeMORIAM: Frances HAMERSTROM. Dale E. GawUk and Raymond K. Anderson ii INTRA- AND EXTRA-PAIR COPULATIONS AND FEMALE REFUSAL OF MATING IN Montagu’s Harriers. Massimo Pandolfi, Roberto Pagliarani and Giancarlo Olivetti 269 Sex Identification in Raptors Using PCR. Kim h. Norris-Caneda and James D. Elliott, Jr. 278 Hematology and Hematozoa of Adult and Nestling Cooper’s Hawks in Arizona. Clmt W. Boal, K. stormy Hudelson, R. William Mannan and Tracy S. Estabrook 281 Egestion of Chitin in Pellets of American Kestrels and Eastern Screech Owls. Chikako Akaki and Gary E. Duke 286 An Infrared Video Camera System for Monitoring Diurnal and Nocturnal Raptors. David K. Delaney, Teryl G. Grubb and David K. Garcelon 290 Prey of Breeding Northern Goshawks in Washington. James w. Watson, David W. Hays, Sean P. Finn and Paul Meehan-Martin 297 Food Habits of the Great Horned Owl {Bubo virginianus) in a Patagonuvn Steppe in Argentina. Ana Trejo and Dora Grigera 306 Short Communications Habitat Use of Crowned Eagles {Harpyhauaetus coronatus) in the Southern Limits of the Species’ Range. M. Isabel Bellocq, Stella M. Bonaventura, Favio N. Marcelino and Maria Sabatini 312 A Comparison of Methods to Evaluate the Diet of Golden Eagles in Corsica. Jean- Francois Seguin, Patrick Bayle, Jean-Claude Thibault, Jose Torre and Jean-Denis Vigne 314 A Record of a Harpy Eagle from Eastern Paraguay. Thomas M. Brooks. 318 Letters 322 Commentary. Edited by Daniel E. Varland On the Evidence Needed for Listing Northern Goshawks {Accipiter gentius) Under the Endangered Species Act; A Reply to Kennedy. K. Shawn Smallwood 323 The Value of Demographic and Habitat Studies in Determining the Status of Northern Goshawks {Accipiter gentius atricapillus) with Special Reference to Crocker-Bedford ( 1990 ) AND Kennedy ( 1997 ). D. Coleman Crocker-Bedford 329 Evaluating Northern Goshawk {Accipiter gentius atricapiuus) Population Status: A Reply TO Smallwood and Crocker-Bedford. Patricia L. Kennedy 336 Determining the Status of Northern Goshawks in the West: Is Our Conceptual Model Correct? Stephen DeStefano 342 Book Reviews. Edited by Jeffrey S. Marks 349 Information for Contributors 351 Index to Volume 32 355 The Raptor Research Foundation, Inc. gratefully acknowledges a grant and logistical support provided by Boise State University to assist in the publication of the journal. J. Raptor Res. 32(4):ii-iv © 1998 The Raptor Research Foundation, Inc. IN MEMORIAM: FRANCES HAMERSTROM Dale E. Gawlik Everglades Systems Research Division, South Florida Water Management District, 3301 Gun Club Road, West Palm Beach, FL 33406 U.S.A. Raymond K. Anderson University of Wisonsin-Stevens Point, Field Research Station, Clam Lake, WI 54317 U.S.A. 4 Frances Hamerstrom died 29 August 1998 at age 90 in Port Edwards, Wisconsin, U.S.A. Fran (pronounced Fron) was well known for her work on Greater Prairie Chickens {Tympanuchus cupido). Sharp-tailed Grouse {Pedioecetes phasianellus) and Northern Harriers {Circus cyaneus). She published over 150 scientific papers, dozens of popular articles and 12 books. She once remarked that “if you are the kind of person who wakes up every morning wanting to make the world a better place, it gives a certain zest to everything you do.” Those who knew Fran will agree; there was a certain zest to everything she did. Despite the societal stuffiness of her privileged childhood, Fran was drawn to wild animals at an early age. Her fondness for raising young wild animals and nursing sick ones to health reinforced in her mind that she was different from other people in her social setting. It also laid the foundation for a “hands-on” style of wildlife research that emphasized personal contact with the animals of study. To Fran, bringing free-flying raptors into her household to study them just made good sense. It seemed odd to her to think that a scientist could ask meaningful research questions without having first-hand knowledge of an animal’s daily needs. Fran’s research style and personality complimented those of her husband and teammate, Frederick (known to his fnends as Hammy), who preceded her in death by eight years. This exceptional life-long team was appropriately labeled a “super organism” by an anonymous apprentice. Thus, it is virtually impossible to refer to them individually in their wildlife careers. That is not to say that they behaved alike. Fran was often spontaneous and impulsive whereas Frederick was methodical and meticulous. Fran was sometimes outspoken and prone to embellishment whereas Frederick was the quiet master of understatement. Both were fiercely committed to saving our natural heritage. They accomplished so many things together because their differences strengthened their sum. Fran was in the vanguard of “equal opportunity” for women in wildlife biology long before it was popular or even considered. The male-oriented profession precluded specific employment in her early professional life and signifi- cantly limited it later on. Fran was keenly aware of the male chauvinism associated with the embryonic wildlife profession and would subtly call attention to this fallacy by physically out-manning men in the field. Her relatively recent book, “Is She Coming Too?” is testament to this historic awareness. When Frederick gained an educational appointment, or employment, Fran accompanied him and participated as a volunteer, or pursued complimentary avenues. Her efforts were soon recognized and occasionally rewarded with a token salary, but more often the agency got two highly qualified people for the price of one. Thus, the Hamerstroms jointly conducted field research on pheasant. Northern Bobwhite {Colinus virginianus) , hawks and owls under Paul L. Errington at Iowa State College from 1932-35, and research on prairie chickens, Sharp-tailed and Ruffed {Bonasa umbellus) Grouse, Sandhill Cranes {Grus canadensis), furbearers, and Great Horned Owls (Bubo virginianus) for the U.S. Resettlement Administration in central Wisconsin from 1935-37. While at Iowa, Fran received an award for “the woman most likely to succeed in research”. The Hamerstroms studied prairie chickens as Research Fellows under Aldo Leopold at the University of Wisconsin (1937-41), where Fran became the only woman to ever earn a graduate degree (M.S.) under Professor Leopold. They conducted joint research on deer, songbirds, small mammals, prairie chickens, and Sharp-tailed Grouse through the University of Michigan Museum of Zoology (1941-49) with a leave for military duty (1943-46) during which time, Fran was a medical technician in the laboratory of U.S. Army Beaumont General Hospital, El Paso, TX U.S.A. They became project leaders of the Wisconsin Department of Natural Resources Prairie Grouse Management Research Unit with headquarters in Plainfield, WI U.S.A. (1949-72). During this tenure, they gained international recognition for their scholarship and successful efforts to ensure a permanent place for prairie chickens on the Wisconsin landscape. Fran was awarded an honorary doctorate degree from Carroll College in Waukesha, WI U S.A. in 1961. Upon retirement from the Wisconsin Department of Natural Resources in 1972, they became unsa- laried Research Associates at the University of Wisconsin-Stevens Point and continued wildlife research until their respective deaths. Their lifetime achievements are even more remarkable when one considers that they conducted exhaustive field studies on harriers. Osprey {Pandion haliaetus), kestrels, Harris Hawks {Parabuteo unicinctus) and several other species coincident with their tenure on other official projects. They were stellar role models. 11 December 1998 In Memoriam 111 Although Fran’s research on grouse was more noteworthy to many, she always held a special fascination with raptors. Her first major scientific paper (co-authored with Errington and Frederick) was on the food habits of Great Horned Owls. It won The Wildlife Society’s Terrestrial Publication Award in 1940. Ironically, the paper was a disappointment to her. As a woman in a male-oriented profession, she felt a strong need to prove herself by publishing her first significant paper as the sole author. Errington just assumed she would want her relatively small contribution to become part of his major paper. She went on to publish 70 papers on birds of prey and to receive The Wildlife Society’s publication award (as a co-author with Frederick and Os Mattson) a second time in 1957 for her work on prairie chicken management. One of Fran’s most exhaustive studies was a long-term project on the breeding ecology of Northern Harriers in central Wisconsin. From the 1950s to 1980s she and co-workers banded close to 300 adult and 650 nestling harriers, and conducted over 20,000 small mammal trap nights. She documented that food abundance was the mechanism regulating harrier mating systems and local population densities. She also noted that those relationships changed during the years that the pesticide DDT was used. Keeping with her habit of maintaining several research projects simultaneously, Fran also conducted a long-term nest box study of American Kestrels {Falco sparverius) . During the winters of their later years, she and Frederick conducted studies on Harris Hawks in Texas and Ospreys in Mexico Raptors held more than a scientific interest for Fran. She was an accomplished falconer who, at age 12, took her first quarry with a male kestrel. Later she helped pioneer artificial insemination techniques with Golden Eagles {Aqmla chrysaetos ) . It was not uncommon for Fran to apply traditional falconry techniques in her raptor research projects She maintained close ties to falconers throughout her life and was a member of the North American Falconers Association, the British Falconers Association and the Great Lakes Falconers Association. Her lifetime interest in raptors also made Fran an early supporter of the Raptor Research Foundation. She received the President’s Award from the Foundation and was the Central Director in 1975-76. In 1990, the Foundation created an award in the Hamerstrom name given to individuals who made significant contributions to the understanding of raptor ecology or natural history. In 1992, the Journal of Raptor Research dedicated a special issue to the Hamer- stroms’ contribution to science. Upon Frederick’s death, Fran journeyed to tropical rainforests, a region that appar- ently always intrigued her but which Frederick had little desire to visit because of the heat and humidity. She initially traveled to the Congo where she “hunted with the pygmies” as she put it. She made at least five consecutive trips to the Amazon basin, always traveling alone and training physically for the ordeal beforehand. She was initially interested in the hunting practices of rainforest societies and started to collaborate on a book on that subject with a native. But, like the birds she studied, Fran returned to Wisconsin each spring to continue her research on kestrels Few people in the profession of wildlife biology have earned so many awards from such a breadth of organizations She received the Josselyn Van Tyne Award from the American Ornithologist’s Union, the Chapman Award from the American Museum of Natural History, the United Peregrine Society Conservation Award and the Edwards Prize from the Wilson Ornithological Society. A sample of other organizations that bestowed awards include the Raptor Research Foundation, The Wildlife Society, National Wildlife Federation, International Crane Foundation, Citizens Natural Resources Association, Deutschen Ornithologen — Gesellschaft, Wisconsin Department of Natural Resources, Wiscon- sin Society for Ornithology and Wisconsin Academy of Sciences, Arts and Letters. Fran was a member of over 20 scientific societies including all the major North American and several European ornithological societies, The Wildlife Society, Raptor Research Foundation, Ecological Society of America and the American Society of Mammalogists. She also was a member of several wildlife conservation societies and writers associations. In the last 20 years of her life, Fran devoted more time to writing popular books and preferred to be defined as a writer rather than an international wildlife biologist. Her book “Strictly for the Chickens” won the August Derleth Award. One of Fran’s least-recognized contributions to the field of science was her service as an educator and role model. The Hamerstroms employed a European model of apprenticeship whereby they allowed qualified individuals to live in their home and become part of their daily lives. The 100 or so apprentices were called gabboons. The terra means slaves that conduct the lowest form of labor. During the banquet at a Raptor Research Foundation annual meeting, Fran looked around the room and pointed out the large number of Foundation officers and meeting attendees who had been through the Hamerstrom household. It was a testament to the influence the Hamerstroms have had on the field of raptor research. The gabboon system ensured that science was only part of an apprentice’s learning experience. Gabboons were treated to introductions with visiting professionals from all over the world. Since before World War II, the Hamer- stroras had strong connections to European scientists. Gabboons were schooled in subjects as diverse as proper table manners, correct English and carpentry. They also enjoyed Fran’s fine cuisine, which was the subject of her wild foods cookbook. Anyone who washed dishes and put the antique china back in the cupboards quickly realized that every piece had its place and it was not negotiable. Certain strict household rules evolved as a defense mechanism against legions of houseguests each year. Like Leopold, the Hamerstroms imparted on gabboons a strong appreciation for fine art and disdain for the trappings of technology. The walls of their unpainted pre-civil war construction IV In Memoriam VoL. 32, No. 4 farmhouse in rural central Wisconsin were adorned with original art work. The house had no indoor plumbing but each person was allowed private bathing time at “the pond” where they had a chance to see a Green Heron {Butorides stnatus) or a brood of Wood Ducks {Aix sponsa) . Fran’s model for a biologist was one with more field sense than statistical prowess or experimental design skills. This view was also evident in most of her publications, which often lacked statistical rigor but were rich with high- quality data. Her thoughts on statistics were that if a pattern wasn’t obvious from a look at the raw data, it either wasn’t real or more samples were needed to know for sure. She lamented the fact that contemporary students often knew very little basic biology about the animals they were studying even though they may have had a good grasp on the scientific process. The Hamerstroms set the standard for a dedicated work ethic. They used their home as a research center, they brought gabboons into their daily lives and they believed that if animals did not recognize weekends and eight-hr days, it didn’t make sense for researchers to do so either. It was obvious that wildlife research was more of a passion for the Hamerstroms than a job. This philosophy stemmed from Leopold’s expectations of his graduate students and was the basis for the “Hamerstrom rule of thirds”. The rule is that researchers should spend one-third of their time on the bureaucratic folly required by their employer, another one-third of their time should be spent on tasks both the employer and the researcher want to do and one-third of their time should be spent doing exactly what the researcher pleases. Fran was quick to note that this last one-third was beyond a regular 40-hr week, and she maintained It was that portion of their time that made the prairie chicken work a success. Even while in Michigan from 1943- 46, she and Frederick took personal time to visit the booming grounds in central Wisconsin each year to monitor their marked birds. Fran also was a model in her advocacy of keeping wild pets. She believed that if the public was to really appreciate wild animals they must be allowed to experience them first hand, much as she had done as a child. She believed the risk of harm to an individual wild pet was less than the benefit of letting a child feel the wonder and responsibility of caring for that pet. Although Fran rehabilitated many injured wild animals over her lifetime, she realized in mid life that emphasizing the welfare of an individual animal over that of the population was misguided. In her book Strictly for the Chickens, Fran tells the story of capturing a hen prairie chicken with a nasty infection. Frederick was ready to end the bird’s suffering and make a study skin from it. Fran intervened and cleansed the wound, stitched it up and released the bird. Years later she fecaptured the same hen and thus became somewhat of a heroine for saving its life. Of that incident Fran wrote, “But year after year I watched the range of our prairie chickens disappear under the plow and drainage. And I began to grow up. I came to realize that the saving of one individual for sentimental reasons is nothing compared to preservation of habitat for a species. Frederick knew this all the time.” Even in death Fran was a role model. She saw countless life and death cycles through harrier and vole population highs and lows. Better than most people she knew that in nature, death was necessary and healthy for the good of the population. As with her husband, Frederick, and former professor, AJdo Leopold, there was no funeral so that death would be mourned; funerals are for the living and the commercial enterprises that materialize out of the death event. Instead she slipped quietly away to become part of that natural cycle she spent her life preserving. THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. VoL. 32 December 1998 No. 4 J. Raptor Res. 32(4):269-277 © 1998 The Raptor Research Foundation, Inc. INTRA- AND EXTRA-PAIR COPULATIONS AND FEMALE REFUSAL OF MATING IN MONTAGU’S HARRIERS Massimo Pandolfi, Roberto Pagliarani and Giancarlo Olivetti University ofUrbino, Istituto di Scienze Morfologiche, Via M. Oddi, 21-61029 Urbino, Italy Abstract. — ^We studied the mating behavior of Montagu’s Harriers ( Circus pygargus) and recorded the incidence of extra-pair copulations (EPC) and refusal of females to copulate. The average duration of copulations was 4.9 sec and they were most frequent between 1000-1400 H. Each pair averaged 105 successful copulations per clutch (range = 31-245). About 59% of 114 within-pair copulation (WPG) attempts were unsuccessful and, in 14 cases, the female rejected its mate. For the majority of cases, the cause of copulation failure was not identified. While the frequency of copulation attempts was not correlated with food-pass frequency, the duration of copulations was influenced by the presence of food brought by the male. Copulation attempts peaked early in the breeding season (3 wk prior to the beginning of egg laying) and outside the fertile period of females. Successful copulations peaked early in the breeding season (wk 4) and during the females’ fertile period (wk 1). Copulation early in the breeding season may function to assess male competence in Montagu’s Harriers allowing a way for females to evaluate the quality of males. Refusal is an aspect of female behavior that could help us to understand if, and in what way, female choice is based on the capacity of the male to successfully transfer sperm. Keywords: Circus pygargus; Montagu’s Harrier, copulation] extra-pair copulation] copulation refusal. Intra- and extra-pair copulations j rechazo de la hembra de ser montada en el Aguilucho Cenizo Resumen. — El motivo de este estudio es de presentar observacione de las montas del Montagu’s Harriers ( Circus pygargus) j de discutirlo en relacion a extra-pair copulations (EPC) j el rechazo de la hembra de ser montada. La media de duracion de la monta era 4.9 y las copulas eran mas frecuentes entre 1000- 1400 H. Cada pareja lleva a cabo una media de 105 copulas exitosas por puesta (rango = 31-245). Alrededor del 59% de 114 WPC intentos fueron fallidos y en 14 casos observamos que la hembra rechazaba su macho. Para la mayoria de los otros casos no identificabamos cual era la causa del fallo en la copula. La frequencia de los intentos en la copulacion no esta correlacionada con la frecuencia de trasferencia de alimentos, pero la duracion de las copulaciones se ha encontrado que esta influen- ciada por la presencia del alimento llevada por el macho que lleva a cabo la mayoria de los intentos cuando la probabilidad de exito es mayor, y por tanto cuando la hembra ha recibido o esta comiendo la presa. La variacion estacional en los intentos de copula muestran un pico temprano en la temporada de cria (tres semanas ante de la deposicion de los huevos, o semana 3) y fuera del periodo fertil de la hembra. La frequencia exitosa de copulas muestran dos picos: uno temprano en el periodo reproductor (semana 4) y otro durante el periodo fertil de la hembra (semana 1). Por lo tanto, la copula, especial- mente aquellas durante las etapas tempranas del periodo reproductor, pueden tener una funcion social importante en el Montagu’s Harrier. Para la hembra pudiera ser una forma de evaluar la calidad del macho y el rechazo es un aspecto del comportamiento de la hembra, que podria ayudarnos a entender si, y en que manera, la eleccion de la hembra esta basada en la capacidad del macho para alcanzar copulas exitosas. [Traduccion de Fernando Hiraldo] 269 270 Pandolfi et al. VoL. 32, No. 4 The Montagu’s Harrier {Circus pygargus) is gen- erally monogamous (Cramp and Simmons 1980) but occasionally is polyandrous (Pandolfi et al. 1995, Arroyo 1996) or polygynous (Hens 1926 in Cramp and Simmons 1980, Dent 1939, Underhill- Day 1990). Its copulation behavior is relatively un- known. In monogamous species investing heavily in parental care, Trivers (1972) predicted that nat- ural selection should favor males that pursue a mixed reproductive strategy. Therefore, males in- crease their fitness by mating with and fertilizing females that have already mated and whose young will be reared without their help. The benefits of extra-pair copulations (EPC) for females are not as clear, especially when females actively resist (Mc- Kinney et al. 1984). On the other hand, females apparently go in search of EPCs and data suggest that they sometimes solicit EPCs from males with higher quality than their partners (Birkhead and Mpller 1992, Kempenaers et al. 1997). Numerous instances have been reported of females refusing to mate with their partners (Indigo Buntings [Pas- serina cyanea], Westneat 1987; Tree Swallows [Tach- ydneta bicolor], Venier and Robertson 1991; White Storks [ Ciconia ciconia] , Tortosa and Redondo 1992; Willow Warblers [Phylloscopus trochilus], Ar- vidsson 1992; Red-billed Gulls {Larus novaehollan- diae]. Mills 1994; Razorbills [Alca torda], Wagner 1996; Ospreys [Pandion haliaetus], Birkhead and Lessells 1988; African Marsh-Harriers [Circus rani- vorus], Simmons 1990; Black Kites [Milvus mig- rans], Koga and Shiraishi 1994). This study was undertaken to observe the mating behavior of Montagu’s Harriers in reference to EPCs and refusals by females to copulate. Study Area and Methods We observed the behavior of the Montagu’s Harrier at two sites in the Pesaro-Urbino area (Monte della Mattera; 43°46'20", 12°51'20" and Montefabbri: 43°46'00", 12“40'50"), Marche region, Italy from 1991-96. Breeding sites were in the foothills of the Apennines (altitude 200- 500 m) and consisted of uncultivated steep badlands and wheat crops. Four to six pairs of Montagu’s Harriers nested in loose colonies at the two sites. Individuals were identified by molt and plumage color and consistent use of perches. We were able to identify individual birds in six of the 24 pairs studied and only data derived from these six pairs are presented. We collected 512 hr of observations on these six pairs from the time they arrived at nesting sites until the time they left. Observations were made between sunrise and sunset for five consecutive hours of obser- vation each day. This allowed us to cover all daylight hours over the period of one week with three shifts. Ob- servations were made using 10X50 binoculars and a 30X spotting scope. The term copulation attempt was used to refer to cop- ulation attempts by males regardless of their success. We assumed that the time needed for the male to balance on the back of the female before cloacal contact was at least 3 sec; therefore all attempts lasting <4 sec were clas- sified as unsuccessful (Simmons 1990). Copulation at- tempts were considered as individual cases even if they occurred during a succession of attempts by the male. Refusals to mate by females were only counted if we were certain that their behavior did not allow males to land on their backs, or if their behavior caused males to lose their balance and take flight within 1 sec. In birds, the length of the female’s fertile period de- pends on various factors: duration of sperm storage in the female reproductive tract, time interval between the fertilization of an egg and its subsequent deposition, and number of days in which the clutch is completed (Birk- head 1988, Birkhead and M0ller 1992). The duration of sperm storage and the time interval between fertilization of an egg and its subsequent deposition have not yet been established in the Montagu’s Harrier; therefore, in order to hypothesize the duration of the presumed fe- male fertile period, we used data for the American Kes- trel {Falco sparverius. Bird and Buckland 1976), where the duration of sperm storage in the female lasts about 8 d. We assumed that sperm storage in female Montagu’s Harriers was about 6 d prior to egg laying, given that this is the shortest period of sperm storage known (Birkhead and M0ller 1992). The time between ovulation and de- position of an egg is about 24 hr in domesticated fowl (Birkhead and M0ller 1992). Fertilization takes place within one hour of ovulation, so we assume a period of one day between fertilization and egg deposition for the Montagu’s Harrier. We assumed that the female fertile period began on the seventh day (6 + 1) before the de- position of the first egg and ended about one day before the deposition of the last egg. Egg laying was determined by observing nests with the aid of a mirror which allowed us to see the eggs while maintaining a distance of about 3 m from the nest. We counted back 29 d (Cramp and Simmons 1980) from the date of hatching in order to obtain the date on which egg laying occurred. The date of hatching was estimated by counting back from the age of the oldest chick which was estimated from morpho- logical characters (Cramp and Simmons 1980). We as- sumed an average of 2 d between laying of each egg (Cramp and Simmons 1980, Glutz et al. 1971). We divided the reproductive season into weeks, calling the week in which eggs were laid wk 0. The courtship period included wk —4, — 3, — 2; the presumed female fer- tile period was wk —1 and wk 0. We assumed that egg laying started on first day of wk 0. We recorded behavior 5 min before and 5 min after copulation attempts. Because both males and females can show more than one display during this 5-min period, the proportion of each display type (expressed as a per- centage) exceeded 100%. The various displays are de- fined in Pandolfi and Pino D’Astore (1990). With the term “sky-dance” we mean sky-dancing plus spiraling sen- Simmons (1991). December 1998 Copulation in Montagu’s KL\rrier ■o 0) (D (/) n O i/i c o « Z3 D. O O 0) X3 in IT 5 Duration of copulations in Montagu's Harrier (sec) Figure 1. Duration of copulations in Montagu’s Harriers in the Pesaro-U rhino area, Italy. 271 Results and Discussion Montagu’s Harriers mated on the ground (89% of 111 copulations) and on perches such as poles or shrubs (11%). Prior to copulation, the most fre- quent activity observed involving both members of the pair was a food pass (48% of 94 cases) . In 17% of the cases, the pair had previously performed copulation, while in 5% of the cases there had only been flight play. Males were perched in breeding areas in 14% of the cases and in 28% of the cases for females. Males performed a sky-dance in 1% of ^ Copulation attempts/hr cases, and showed intraspecific aggressiveness in 5% of the cases. In four of these cases, males at- tacked other males (three neighbors and one not identified) and, on one occasion, a male attacked a female neighbor. Males flew in front of females and turned sharp- ly (in a hook-flight) to land on their backs. If males came from behind, they simply glided onto the fe- males’ backs. Males balanced themselves by stretch- ing out and beating their wings while females low- ered and raised their tails to allow cloacal contact. I I Successful copulations Time of the day Figure 2. Diurnal fluctuation in frequency of copulation in Montagu’s Harriers in the Pesaro-Urbino area, Italy 272 Pandolfi et al. VoL. 32, No. 4 Figure 3. Seasonal variation in successful (a), unsuccessful (b) and total copulation attempts (c), relative to the beginning of egg laying (i) in Montagu’s Harriers in the Pesaro-Urbino area, Italy. Y-axes show means and SE. The average duration of successful mounts was 4.9 sec (SD = 2.1; N — 115) and 87% of 115 copula- tions lasted between 3—8 sec (Fig. 1), There were no significant differences (Kruskal-Wallis test, H = 0.1085, df = 2, P — 0.09) in the duration of cop- ulations between the three time periods into which we divided the day (dawn-0900 H, 0900-1400 H, and 1400 H-sunset). Following each copulation, both males and fe- males perched in the area in the m^ority of 94 cases (53% for males, 69% for females). In 15% of the cases, there was further copulation. In 21% of these, males left nesting areas while females left in 9%. In the remaining cases, we recorded activities such as intraspecific aggressiveness (3% for males: two cases toward other males and one case toward a female; 2% for females: one case toward another female), flight play (1%), and other behaviors (9% for males, 4% for females) . Copulation attempts occurred unevenly throughout the day (x^ = 16.10, df = 6; P< 0.05), showing a higher frequency between 1000-1400 H. December 1998 Copulation in Montagu’s Harrier 273 After 1400 H, there was a marked reduction in cop- ulation frequency, apart from a smaller peak be- tween 1700-1800 H (Fig. 2). The seasonal trend in copulation attempts car- ried out by males showed a peak during the court- ship period in wk —3 (3 wk prior to the beginning of egg laying) when 0.68 copulation attempts/hr was recorded. Another smaller peak occurred in wk —1, with 0.45 copulation attempts/hr (Fig. 3c). We found a significant difference in the total cop- ulation attempts/hr during the various weeks (Kruskal-Wallis test H = 17.44, df = 7, P = 0.0147) with a constantly decreasing trend from wk 4 to wk + 2, after which no further copulation attempts were recorded in the six focal pairs. The frequency of successful copulations peaked at 0.24 copulations/hr during wk —4, with a sec- ond peak of 0.22 copulations/hr during wk — 1 (Fig. 3a) but copulation frequency did not vary sig- nificantly over time (Kruskal-Wallis test H = 9.37, df = 7, P = 0.2271). Both Goshawks (Accipiter gen- tilis) (M0ller 1987) and Lesser Kestrels (Falco nau- manni) (Negro et al. 1992) show a similar bimodal pre-egg laying peak in copulations. The frequency of unsuccessful attempts was very high during the courtship period and decreased after wk —1 (Fig. 3b). The variation in frequency between the various weeks was statistically signifi- cant (Kruskal-Wallis test H = 16.13, df = 7, P = 0.0239). During the courtship period (21 d, wk —4,— 3,— 2) and the presumed female fertile period (13 d for a modal clutch of four) , we observed 40 successful cop- ulations during 192 hr of observations, yielding a fre- quency of 0.2 successful copulations/hr. Considering that daily harrier activity spans 15 hr, each pair {N = 6) successfully copulated about 102 times per clutch (range = 31—245) . The range was very wide but was comparable with other raptors. In fact, for the Afri- can Marsh-Harrier ( Circus ranivorus) , Simmons (1990) estimated 37—160 successful copulations per clutch whereas Birkhead and Lessels (1988) reported a range of 20-97 successful copulations per clutch for Osprey. Copulations during the courtship period oc- curred outside the female fertile period. In other species of raptors, copulations have been recorded both during and outside the female fertile period; Goshawks (M0ller 1987), Cape Vultures {Gyps co- protheres) (Robertson 1986) , Ospreys (Birkhead and Lessels 1988), African Marsh-Harriers (Simmons 1990), Merlins {Falco columbarius, Shodi 1991), Lesser Kestrels (Negro et al. 1992) and Black Kites {Milvus migrans, Koga and Shiraishi 1994). Various explanations have been given to explain copulation in the early stages of the breeding sea- son. For example, males may try to copulate early on in the pre-laying period to increase their pater- nity insurance, given that it is not certain when the female will lay the first egg (Birkhead and Mqller 1992). Alternatively, it may be in the female’s in- terest to hide her fertile period to exchange cop- ulations for food (Moller 1987). The latter hypoth- esis is not very probable for Montagu’s Harriers, as there is no relation between the hourly rate of suc- cessful copulations and the hourly rate of food passes during these weeks (Spearman correlation coefficients r^ = 0.1567, N = 30, P = 0.408). An- other possibility is that copulation attempts at the beginning of the breeding season are part of a eval- uation mechanism by females (Tortosa and Redon- do 1992) . They could also function to establish and maintain the pair bond (Newton 1979) , given that Montagu’s Harriers remate every year (Cramp and Simmons 1980). The peak of successful copulations during wk — 1 corresponded to the presumed female fertile pe- riod and might be explained both by fertilization and sperm competition hypotheses. In fact, most harriers produce unhatched eggs (Simmons 1990) and the six pairs that we studied produced 25 eggs, 20% of which did not hatch. This suggests that fre- quent copulation limits infertility of eggs while di- luting the sperm of other males. Hatching failure might also be due to defects in eggs rather than a lack of sperm, but we do not have information on this possibility. Given that copulations recorded during the in- cubation period continued until wk +2, they may function to provide sperm for replacement clutch- es in the case of nesting failure, as suggested by Birkhead et al. (1987). They may also serve to maintain the pair bond. Because only males en- gage in play and feeding activity with young during the post-fledging period (Giacchini and Pandolfi 1994, Pandolfi 1996), the pair bond is probably weakened. This could explain why copulations were not recorded later in the breeding season as happens in Cape Vultures (Robertson 1986), Gos- hawks (M0ller 1987) and African Marsh-Harriers (Simmons 1990). For Cape Vultures, pair bonds are lifelong (Robertson 1986) and African Marsh- Harrier pairs bond for >1 yr (Simmons 1990). The Goshawk is a nonmigratory species and pair bonds 274 Pandolfi et al. VoL. 32, No. 4 certainly last longer than in the migratory Monta- gu’s Harrier. Of 118 copulations we observed, 4 EPC attempts were observed (3.4%). EPCs involved two extra- pair males, and two females that belonged to focal pairs. Two EPCs occurred 7 d before the start of egg laying, while the other two occurred 2 d before egg laying. All four attempts occurred during fe- males’ presumed fertile periods (two females in- volved). Two of the four EPCs were successful (i.e., the male stayed on the back of the female for >4 sec). In three of the cases, the female’s mate was absent. In the one case when her mate was present, his behavior showed indifference, but the EPC was unsuccessful. Females never rejected the attempts of the extra-pair males and all females were already mated in the colony. One of the males involved already had a mate and belonged to the colony, while the other was not identified. The percentage of EPCs recorded in our study was slightly less than that reported by Arroyo (1996) for Montagu’s Har- rier in Spain. The fact that the four cases we ob- served all fell within the presumed female fertile period and that females never resisted suggests that this strategy effectively allows pursuing males, even only occasionally, to increase their reproduc- tive success at the expense of others. Although Simmons (1990) reported an EPC of 2% in African Marsh-Harriers, he found that the males copulated more frequently when they nested in colonies. His finding supports the sperm competition hypothesis suggesting that such a low number of EPCs could trigger mechanisms of sperm competition benefit- ting those males that use them and take the nec- essary countermeasures. Montagu’s Harrier males spent more time (x^ = 59.94, df = 1, P < 0.01, Yates corrected) in the nesting area near their part- ner during the female fertile period (43%) than during wk +1, +2, +3 (35%), a pattern that is common in other raptors such as African Marsh- Harriers (Simmons 1990), Ospreys (Birkhead and Lessells 1988) and Goshawks (M0ller 1987). Be- having in this way, males may deter access to fe- males by other males (Birkhead and Lessells 1988) . This form of male mate-guarding could explain the low proportion of EPCs observed. For females, the risks regarding the loss of pa- rental care (Trivers 1972) could be minimized if the intruder were to carry out the EPC attempts in the absence of their males, as in fact happened in three out of four cases we observed. The fact that the females did not dissuade these males suggests that they already knew these males and they were of “high quality.” Even though one of the two males was unidentified, it probably belonged to the colony under observation, which comprised five pairs during the reproductive season. The risks could be too high for females accepting EPCs from unknown males since a male of unknown quality could fertilize their eggs (Birkhead and Mqller 1992). However, females may gain by increasing the genetic quality or diversity of chicks (Birkhead and M0ller 1992). Indeed, numerous cases have been recorded of broods not genetically related to their putative father (Avise 1996). Data available on raptors suggests that this phenomenon is not widespread (Swatschek et al. 1994, Korpimaki et al. 1996, Negro et al. 1996) but is present nonetheless. In 48% of 94 cases, food passes occurred 5 min before copulations. However, copulation frequency was not correlated with food passes during the first six weeks of the breeding season (Spearman cor- relation coefficient, r^ = 0.16, N = 30, P = 0.4). There was also no significant correlation between the frequency of successful copulations and food- pass frequency over the various weeks (r^ = 0.1567, N = 30, P = 0.408) . These data are similar to those found by Picozzi (1984) for Hen Harriers (Circus cyaneus) and by Simmons (1990) for African Marsh- Harriers that showed food passes to be important, but not essential, correlates of copulation. Conse- quently, we examined whether the duration of a copulation was influenced by the presence of food provided by males. The median duration of copu- lation attempts when food was present (4 sec) was significantly higher than the median duration of copulation when food was not present (0 sec, Mann-Whitney Latest, U = 691.5; P = 0.01). This difference remained significant even when only at- tempts in which males effectively landed on fe- males’ backs (food present median = 5 sec; food absent median = 3 sec; U = 152.5; P = 0.0496). When food was present, males were successful in 29 out of 56 cases (52%); without food, only 5 out of 35 attempts (14%) were successful (x^ = 11.39, df = 1, P < 0.01, Yates corrected). Of 91 attempts, 56 (62%) were carried out in the presence of food, while 35 (38%) were attempted in the absence of food, a difference that is statistically significant (x^ = 4.4, df = 1, P < 0.05, Yates corrected). There- fore, the duration of copulations was influenced by the presence of food brought by males and they attempted copulations when the probability of suc- cess was highest (i.e., when females had received December 1998 Copulation in Montagu’s Harrier 275 or were eating prey) . For African Marsh-Harriers, Simmons (1990) found that, while food was not a prerequisite for copulation and did not even influ- ence the duration, males had a higher probability of being unsuccessful if food was absent. For Os- preys, Poole (1985) reported that feedings were not an immediate stimulus for copulations but that efficient food transfers among courting Ospreys appeared to be a requirement for successful cop- ulations. We observed 14 copulation rejections by female harriers in 114 within-pair copulations, 47 (41%) of which were successful. This was considerably lower than the 73% estimated for African Marsh- Harriers (Simmons 1990). The unsuccessful at- tempts resulted directly from the female’s behav- ior. In the other 53 cases, two of the failures were attributable to external factors (e.g., males left to fight off female intruders or left to fight off crows [Corvus spp.]). For the remainder of cases we could not identify the reason for the copulation failure. Of the 14 cases in which the female refused to copulate, 13 occurred during courtship and only one occurred during fertile period. The possibility that females simply were not physiologically ready is little supported by our data. In fact, from the beginning of the courtship period, we observed successful copulations (Fig. 3). During the day- time, 10 out of 14 refusals were observed between 1000—1400 H, when the frequency of successful copulation attempts/hr was high (Fig. 2). In four cases food was present, in six it was absent, and in the remaining four cases the presence or absence of food was unrecorded. We have no data on prey size in these cases, so we cannot control for any correlation betwen prey size and female refusal. We observed the following female behaviors dur- ing copulation refusals: in four cases, males had begun landing when females lay flat on the ground keeping their wings semiopen and flattened with their tails toward the ground; in seven cases, fe- males opened and beat their wings; a female flew away once; once a female jumped away; and once a female hit the male with her talons claws while landing. The first behavior was also described by Studinka (1942) as soliciting behavior for copula- tion by the female. We interpreted this as a refusal because when examining the 13 cases in which fe- males behaved in this way (seven cases observed in two out of the six focal pairs and six cases observed in two other pairs) , the male copulated successfully Proportion of copulation attempts that 100% are: 90% 80% ■ Successful 70% 60% □ Unsuccessliil 50% 40% ^ Relused by females 30% 20% 10% 0% Courtship Female Incubation fertile Periods ofthe breeding season Figure 4. Proportion of successful and unsuccessful copulation attempts and refusal by female Montagu’s Harriers during various periods of the breeding season in the Pesaro-Urbino area, Italy. on only one occasion. Sudden opening of wings by the female followed by flattening on the ground are movements which make it difficult for males to land. The fact that females spread their tails toward the ground could have been a signal indicating un- willingness to copulate since the tail must be raised for cloacal contact. Even though there was not a significant differ- ence between the proportion of successful copu- lation attempts, copulation attempts that failed be- cause of refusal by the female, and those that failed for other reasons during the three periods consid- ered (x^ = 6.71, df = 4, P > 0.05) females refused 18% of the attempts by the males during the court- ship period and refused only 3% of attempts dur- ing their presumed fertile period (Fig. 4). The in- crease in the proportion of successful copulations during the fertile period appeared to be due, at least in part, to the lower number of female refus- als. Simmons (1990) reported nine (4.6%) cases of refusal by female African Harriers out of 196 at- tempted copulations. This rate is similar to that re- ported by Koga and Shiraishi (1994) for Black Kites, where 4.1% of 246 copulation attempts were refused by females. In both cases, however, the pe- riods in which refusals took place were not report- ed. In White Storks ( Ciconia ciconia, Tortosa and Re- dondo 1992) and Lesser Kestrels (Negro et al. 1996), males copulate frequently even in the ab- sence of sperm competition. It has been suggested 276 Pandolfi ex al. VoL. 32, No. 4 that these males may advertise their good condi- tion by performing energetically costly copula- tions; therefore, copulations are part of a process of mate assessment involved in the acquisition and maintenance of the pair bond (Tortosa and Re- dondo 1992, Negro et al. 1996). This may also be the case in the Montagu’s Harrier, Intense copu- lation activity carried out by males despite female refusals could serve to indicate the general health of males, assuming that copulations are expensive in terms of sperm production and physical court- ship activity (Dewsbury 1982). Furthermore, in re- fusing, females could test the ability of males to copulation and fertilization. A rather long period would be advantageous to establish the quality of males in order to limit the risks of being deceived. If these characteristics were inherited, it would be advantageous for females to fertilize her eggs with these males (Birkhead and Mpller 1992). In conclusion, while the frequent copulation pattern observed in Montagu’s Harrier may be ex- plained with the sperm competition hypothesis, copulations may also have an important social function during the courtship period. For females, it could be a way of evaluating the quality of males. Therefore, refusal is an aspect of female behavior that could help us to understand if, and in what way, female choice is based on the capacity of males to transfer sperm. Acknowledgments We thank Rob Simmons, Keith Bildstein, Miranda Henning, Daniel Varland, and an anonymous reviewer for their very helpful suggestions. We thank Marco Roc- chi for his help with the statistical analysis and Sian Beale for translating the text. 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The status and breeding bi- ology of Marsh Harrier and Montagu’s Harrier in Brit- ain since 1900. Ph.D. dissertation. National Council for Academic Awards, London, U.K. Venier, L.R. and R.J. Robertson. 1991. Copulation be- haviour of the Tree Swallow, Tachycineta bicolor, pater- nity assurance in the presence of sperm competition. Anim. Behav. 42:939-948. Wagner, R.H. 1996. Why do female birds reject copula- tions from their mates? Ethology 102:465-480. Westneat, D.F. 1987. Extra-pair copulations in a predom- inantly monogamous bird: observations of behaviour Anim. Behav. 35:865-876. Received 21 November 1997; accepted 1 August 1998 J. Raptor Res. 32(4):278-280 © 1998 The Raptor Research Foundation, Inc. SEX IDENTIFICATION IN RAPTORS USING PGR Kim H. Norris-Caneda and James D. Elliott, Jr. South Carolina Center for Birds of Prey, P.O. Box 1247, Charleston, SC 29402 U.S.A. Abstract. — Recent discovery of a gene on the W-chromosome of birds provides a method for sexing in a variety of avian taxa. We investigated the possible use of polymerase chain reaction (PCR) primers specific to the CHD-W (chromodomain-helicase-DNA-binding on the W-chromosome) gene to identify sex in nine species of raptors. Blood was collected from birds of known-sex (female and male) and DNA was extracted. PCR, using primers P2 and P3, was performed followed by restriction enzyme digestion of the PCR products. Primers P2 and P3, specific to the CHD genes, reliably confirmed the sex in all 38 birds tested representing nine species and four families. A convenient, inexpensive and effective procedure was developed for blood collection, stoi age and subsequent DNA isolation and PCR analysis. Key Words: CHD gene; sex identification; raptors-, W-chromosome; PCR. Identificacion de sexo en aves rapaces mediante la utilizacion de la RCP Resumen. — El reciente descubrimiento de un gene en los cromosomas W de las aves es un metodo para sexar una variedad de taxones aviares. Hemos investigado el posible uso de la reaccion de la cadena polymersa (RCP) con el fin de identificar el sexo en nueve especies de rapaces. Muestras de sangre fueron obtenidas de seis aves de las cuales se conocia su sexo (machos y hembras), el ADN fue extraido. La RCP fue obtenida mediante la utilizacion de P2 y P3 y la restriccion de la enzima digestiva de los productos de la RCP. Este metodo permitio, en forma confiable identificar el sexo en las 30 aves, las cuales representaban nueve especies y cuatro familias. Un metodo conveniente y poco costoso fue desarrollado para la recoleccion de muestras de sangre, alamacenaje y el subsecuente aislamiento del ADN y el analisis de la RCP. [Traduccion de Cesar Marquez] The identification of sex is often a problem when studying raptors because sexes are not dis- tinct morphologically. This problem is especially true in juveniles and hatchlings. One effective so- lution is to exploit DNA markers to diagnose sex. Birds show female heterogamety in having one W- and one Z-sex chromosome whereas males have two Z-chromosomes. Because of this, a simple poly- merase chain reaction (PCR) technique can be used to identify sex across a broad range of bird taxa at any stage of development (Griffiths et al. 1996). PCR is a robust technique which can target and amplify specific sequences of DNA (Mullis and Faloona 1987). The PCR primers, P2 and P3, am- plify a highly conserved region on the W-sex chro- mosome known as the CHD (chromodomain-heli- case-DNA-binding) gene. A second version of the CHD gene (CHD-NW), not W-linked, is also am- plified by the primer pair and is present in both female and male birds. Recently, CHD-NW has been shown to be linked to the Z-chromosome in chickens (Griffiths and Korn 1997). This finding indicates that, among a wide variety of bird species, amplification using the single set of PCR primers followed by restriction digestion of the PCR prod- ucts will allow for discrimination between the pres- ence of the W-linked CHD gene (unique to female birds) and the CHD-NW gene. A specific restric- tion enzyme will cut the CHD-NW amplification product but not the W-linked version. The pres- ence/absence of a 110 base pair (bp) band, follow- ing enzyme digestion, is diagnostic for sex identi- fication in all bird species previously tested (Griffiths et al. 1996). Our objective for this study was to determine the reliability of PCR primers P2 and P3 in the sexual identification of a variety of raptors. Materials and Methods Blood was collected from 38 individuals of known-sex from each of the following species: Bald Eagle {Haliaeetus leucocephalus) , Red-tailed Hawk {Buteo jamaicensis), Red- shouldered Hawk (Buteo lineatus), Osprey (Pandion hal- iaetus) , American Kestrel (Falco sparverius) , Merlin (Falco columbarius) , Black Vulture ( Coragyps atratus) , Barred Owl (Strix varia) and Great-horned Owl (Bubo virginianus) . 278 December 1998 Sex Identification in Raptors 279 The sex of each bird was determined through necropsy, reproductive behavior and/ or morphometric and behav- ioral data. Blood was drawn from the brachial vein of the wing using a 1-3 ml syringe with a 22-25 gauge needle (depending on the species) after swabbing the area with alcohol. Approximately 100 pi of blood was transferred from the syringe to a heparinized microhematocrit tube (Becton Dickinson, Franklin Lakes, NJ U.S.A.) for DNA extraction purposes. Both ends of the tube were plugged with microhematocrit tube sealer (Becton Dickinson). The microhematocrit tube was stored at 4°C for one day to several weeks prior to DNA extraction. If longer stor- age was required, tubes were placed at — 20°C. DNA was extracted from whole blood using InstaGene Whole Blood Kit (BioRad, Hercules, CA U.S.A.) accord- ing to manufacturer’s protocol with the following modi- fications. Five microliters of whole blood per sample were added to a 1.5 ml microcentrifuge tube containing 1 ml of the supplied lysis buffer. The tube was incubated 8-15 min at room temperature and the supernatant discarded. The remaining pellet was washed twice with lysis buffer, carefully removing the supernatant each time. Two hun- dred microliters of InstaGene matrix was added to the pellet and the tube incubated 8 min at 70°C. The sample was then vortexed, incubated at 95°C for 4 min and cen- trifuged (15 000 rpm) for 1 min. The resulting superna- tant was stored at — 20°C per kit instructions until used in PGR analysis. Standardized PGR reactions were performed twice on DNA from all birds using a 96-well microtiter plate for- mat (Falcon) in a MJ Research Model PTG-100 Program- mable DNA Thermal Gontroller to determine repeat- ability of PGR reaction conditions. A PGR reaction volume of 20 (xl per sample contained: IX Ta^DNA poly- merase buffer, 200 |jlM each dNTPs, 3.5 mM MgGl 2 primers P2 (5'TGTGGATGGGTAAATGGTTT3') and P3 (5 ’ AGATATTGGGGATGTGATAGTGA3' ) (National Biosciences, Inc., Plymouth, MN U.S.A.) at 1 pM each, 100-200 ng of genomic DNA (5 pi of DNA extraction reaction) and 0.5 units of AmpliTaq DNA polymerase (Perkin Elmer, Foster Gity, GA U.S.A.) . Gycling parame- ters were 94°G for 1.5 min, followed by 56°G for 15 sec, 72°G for 15 sec, 94°G for 30 sec, for 30 cycles and one cycle of 56°G for 1 min and 72°G for 5 min. Negative controls containing water were run with every PGR and precautions were taken to avoid contamination (Thomas and Paabo 1993). Following PGR, all samples were subjected to restric- tion enzyme digest with Haelll. Five units of Haelll (New England Biolabs, Beverly, GA U.S.A.) were used to cut 7 pi of each PGR reaction following manufacturer’s rec- ommendations for appropriate buffer and temperature. Restriction enzyme digestion reaction components were prepared as a master mix to ensure consistent results across all samples. Samples were electrophoresed on a 2.0% agarose gel (1:1 Amersham Life Sciences, Arlington Heights, IL U.S.A.; Life Technologies, Gaithersburg, MD U.S.A.) at 100 V for 1-2 hr in IX TBE buffer (90 mM Tris-borate, 2 mM EDTA pH = 8.0) followed by staining for 20 min in 0.5 pg/ml ethidium bromide solution (Maniatis et al. 1982). Results For all species tested in this study, primers P2 and P3 produced PGR products of 110 bp in size in both female and male birds. These primers are specific to both versions of the CHD gene, CHD- W, on the W-chromosome (unique to females) and CHD-NW on a non-W-chromosome (present in both sexes) (Griffiths et al. 1996, Ellegren 1996). This results in the presence of two PCR fragments in females, both 110 bp in size. Males have only one fragment type, CHD-NW. Digestion of the CHD-NW product with a restriction enzyme allows for discrimination between the two PCR products and the determination of sex. The restriction en- zyme Haelll was used to cut the CHD-NW product (into two fragments of 45 bp and 65 bp); the CHD- W product remained intact (Fig. 1). For 34 birds, the sex of each was correctly identified by the PCR/ Hag/// enzyme digest reaction. Haelll did not digest the CHD-NW products for the four Barred Owl samples. This PCR product was subsequently isolated from a known-male sample and se- quenced. The sequence data revealed the loss of the Haelll site and provided a candidate MboII site for testing. Upon testing in four known-sex sam- ples, MboII provided accurate discrimination be- tween female and male samples. Discussion We found that PCR primers P2 and P3 located on the CHD genes of birds reliably sexed the rap- tors we studied. Primers P2 and P3 confirmed the sex in all 38 species of raptors sampled represent- ing nine species and four families. Other molecu- lar methods have been used to sex raptors but are not useful across taxa and can be a challenge in terms of technique and resources (Longmire et al. 1991, May et al. 1993). PCR is a more straightfor- ward, less labor-intensive technique and more ame- nable to implementation in less technical settings. Our study developed a convenient, inexpensive and effective procedure for blood collection, stor- age and subsequent DNA isolation. Blood is col- lected in heparinized microhematocrit tubes that can be stored at 4°C for several weeks prior to DNA extraction and still yield viable, high molecular weight DNA. Preparation of DNA from whole blood using a commercial DNA extraction kit ex- pedited the procedure and eliminated the use of hazardous reagents. The PCR protocol works well in a 96-well format allowing for the processing of a large number of samples at one time. Although 280 Norris-Caneda and Eluott VoL. 32, No. 4 std RTHA ' RSHA GHOW BLVU - BAEA OSPR std 1 -f F M F M F M F M F M F M 12 3 4 12 3 4 12 3 4 12 3 4 12 3 4 12 3 4 1 § — mm • • Figure 1 . PCR products cind corresponding Haelll enzyme digests from one known female and one known male from six of nine raptor species evaluated. For each species (RTHA = Red-tailed Hawk; RSHA = Red-shouldered Hawk; GHOW = Great Horned Owl; BLVU = Black Vulture; BAEA = Bald Eagle; OSPR = Osprey), the first two lanes (1 and 2) represent the one female sample; the next two lanes (3 and 4) represent the one male sample. Lanes 1 and 3 show the 110 bp PCR products generated using primers P2 and P3. Lanes 2 and 4 show the results from the //««/// enzyme digestion. The ‘std’ lanes contain a 100 bp molecular weight size standard (Life Technologies). blood was the tissue source for DNA in this study, the sensitivity and specificity of the PCR technology should allow for the use of other tissue sources such as feathers. Based on the fact that sex iden- tification was not shown through the use of a single enzyme {Haelll) for every species tested in this study (Barred owl required MboII ) , known-sex birds from untested species could be initially eval- uated using a panel of restriction enzymes. Grif- fiths et al. (1996) suggested several enzymes that appear to be appropriate over a broad range of avian families and would provide a reasonable starting point. Future modifications of this tech- nique to include primers to the CHD genes that amplify across an intron may eliminate the need for restriction enzymes in some species (Ellegren and Shelton 1997). Acknowledgments We appreciate the generous support from Westvaco Corp.’s Forest Genetics and Biotechnology Center. We also gratefully acknowledge blood samples kindly provided by The Carolina Raptor Center. Special thanks to Kim James, Linda Flanagan, Kathy Dolan, Les Pearson, Sally Schwuch- ow. Will Rottmann, Elizabeth Stone and Jessica Young for providing assistance with this project. We also wish to thank Arnaldo Ferreira for his skillful support and Richard Griffiths, Hans Ellegren, Phil Dunham and Jay Coke for their comments on earlier drafts of this manuscript. Literature Cited Ellegren, H. 1996. First gene on the avian W-chromo- some (CHD) provides a tag for universal sexing of non-ratite birds. Proc. R. Soc. London Ser. B 263:1635— 1641. and B. Shelton. 1997. New tools for sex identi- fication and the study of sex allocation in birds. Trends Ecol. EvoL 12:255-259. Griffiths, R., S. Daan and C. Dijkstra. 1996. Sex iden- tification in birds using two CHD genes. Proc. R. Soc. London Ser. B 263:1251—1256. AND R. Korn. 1997. A CHDl gene is Z chromo- some linked in the chicken Gallus domesticus. Gene 197: 225-229. Longmire, J.L., R.E. Ambrose, N.C. Brovw, TJ. Cade, T. L. Maechtle, W.S. Seegar, F.P. Ward and C.M. White. 1991. Pages 217-229 inT. Burke, G. Dolf, A.J. Jefferys and W.R. Wolff [Eds.], DNA fingerprinting: approaches and applications. Birkhauser Verlag, Ba- sel, Switzerland. Maniatis, T., E.F. Fritch and K.J. Sambrook. 1982. Mo- lecular cloning: a laboratory manual. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY U. S.A. May, C.A., J.H. Whetton and D.T. Parkin. 1993. Poly- morphic sexspecific sequences in birds of prey. Proc. Royal Soc. London Ser. B 253:271-276. Mulus, K.B. AND F. Faloona. 1987. Specific synthesis of DNA in vitro via a polymerased catalyzed chain reac- tion. Methods ofEnzymology 155:335—350. Thomas, W.K. and S. Paabo. 1993. DNA sequences from old tissue remains. Methods of Enzymology 224::406-419. Received 30 January 1998; accepted 20 July 1998 J. Raptor Res. 32(4):281-285 © 1998 The Raptor Research Foundation, Inc. HEMATOLOGY AND HEMATOZOA OF ADULT AND NESTLING COOPER’S HAWKS IN ARIZONA Clint W. Boal^ School of Renewable Natural Resources, University of Arizona, Tucson, AZ 85721 U.S.A. K. Stormy Hudelson Raptor Resurgence, 4213 Texas Circle, Tucson, AZ 86711 U.S.A. R. William Mannan and Tracy S. Estabrook School of Renewable Natural Resources, University of Arizona, Tucson, AZ 85721 U.S.A. Abstract. — ^We determined age- and sex-specific packed cell volume (PCV) and total blood solid (TS) levels to detect diseases in Cooper’s Hawks {Accipiter cooperii) in southeast Arizona. We also identified hematozoa infecting Cooper’s Hawks, determined age- and sex-specific infection rates, and evaluated the influence of hematozoan infections on PCV and TS. Adult male Cooper’s Hawks had greater mean PCVs than adult females and nestlings (P < 0.05). Adult females also had a greater mean PCV than nestlings (P < 0.05). There was no difference in PCV between the sexes of nestlings and there was no difference in TS levels between the sexes of adults or nestlings, but TS levels were greater among adults {P < 0.05). Hematozoan infection rates did not differ between the sexes of adults (P = 0.553) but adults had a greater infection rate than nestlings (P = 0.022). Hematozoan infections did not appear to influence PCV or TS among adult Cooper’s Hawks. Key Words: Cooper’s Hawks', Accipiter cooperii; Arizona’, blood parasites', hematology, hematozoa. Hematologia y hematozoarios en pichones y adultos de Accipiter cooperii en Arizona Resumen. — Determinamos el volumen de celulas especificas compactadas de edad y sexo, y el total del nivel de solidos de sangre para detectar las enfermedades de Accipiter cooperii en el sudeste de Arizona. Tambien identificamos los hematozoarios que infestan a Accipiter cooperii, mediante la determinacion de las tasas de infestacion por sexo y edad. Evaluamos la influencia de los hematozoarios en las celulas compactadas y en el total de solidos de sangre. El macho adulto de Accipiter cooperii tuvo una media mayor de celulas compactadas que las hembras adultas y que los pichones (P < 0.005). No hubo diferencias de celulas compactadas entre sexos de pichones como tampoco en los niveles del total de solidos de sangre entre sexos de adultos o pichones, pero los niveles de solidos de sangre fueron mayores entre adultos (P < 0.05). Las tasas de infeccion de hematozoarios no difirieron entre sexos de adultos (P = 0.553), pero los adultos tuvieron una tasa de infestacion mayor que los pichones (P = 0.022). Las infestaciones por hematozoarios aparentemente no influenciaron las celulas compactadas o los solidos de sangre en los adultos de Accipiter cooperii. [Traduccion de Cesar Marquez] Two hematological variables often measured when evaluating the health of birds are packed cell volume (PCV) and total solids (TS) or the protein concentration in the plasma (Campbell 1988). Few studies have investigated these hematological pa- rameters for Cooper’s Hawks {Accipiter cooperii) ^ Present address: Minnesota Cooperative Fish and Wild- life Research Unit, University of Minnesota, 200 Hodson Hall, 1980 Folwell Avenue, St. Paul, MN 55108 U.S.A. (Smith and Bush 1978, Hunter and Powers 1980, Gessaman et al. 1986), nor have differences be- tween adults and nestlings or among birds with concomitant parasitic infections been investigated. Studies of the hematozoa of North American raptors have been primarily conducted in the east- ern and midwestern U.S. (Stabler and Holt 1965, Kocan et al. 1977, Kirkpatrick and Lauer 1985, Taft et al. 1994), but the occurrence of parasitic he- matozoa appears to vary regionally (Greiner et al. 281 282 Boal et al. VOL. 32, No. 4 1975) . Evaluation of hematozoa infection rates among Cooper’s Hawks has been hampered by the tendency of investigators to pool blood samples from all individuals regardless of age, season in which samples were taken, or whether they were free-ranging or captive. In a notable exception, Taft et al. (1994) evaluated infection rates of he- matozoa among Cooper’s Hawks on basis of sex and age during the breeding season. We obtained blood samples from adult, subadult and nestling Cooper’s Hawks while conducting a demographic study of the species in southeastern Arizona (Boal 1997). We analyzed blood samples to determine age- and sex-specific PCV and TS val- ues for Cooper’s Hawks, to identify hematozoa and hematozoan infection rates, to examine possible influences of hematozoan infections on PCV and TS, and to compare hematozoan infection rates be- tween our study and a similar study in Wisconsin (Taft et al. 1994). Materials and Methods We collected blood samples from breeding and nestling Cooper’s Hawks in southeastern Arizona, primarily in the vicinity of Tucson, Arizona (32°15'N, 111°55'W) from May-June 1995 (Boal 1997). We captured breeding hawks with dho-gaza and bal-chatri traps (Bloom 1987); nestiings were captured by hand at nests. The pronounced sexual size dimorphism in Cooper’s Hawks (Snyder and Wiley 1976) facilitated sexing of both adults and nestlings. We collected blood samples within 15 min of capture by draw- ing 0.25 ml of blood from the basilic vein with a 25-gauge nonheparinized needle and 3-ml syringe. Each sample was immediately transferred to an EDTA 0.3-ml tube and re- frigerated for transport from the field. We used the microhematocrit method to determine PCV. We centrifuged blood samples in nonheparinized mircrohematocrit tubes and determined the PCV by tak- ing the average value of two samples from each hawk. TS values were determined by analyzing plasma samples with a No. 33077 Schuco Clinical Refractometer. To examine the prevalence of hematozoa in Cooper’s Hawks, we made two thin smears of each blood sample on glass slides. The slides were air-dried, fixed in methanol, stained in Giemsa, and microscopically examined at lOOOX for hematazoa. The entire blood smear was examined for all samples. We also compared our results to data from Wis- consin (Taft et al. 1994) to examine age- and sex-specific hematozoa infection rates of Cooper’s Hawks from north- ern and southern parts of their breeding range. We used <-tests and one-way analysis of variance tests (Ramsey and Schafer 1997) to examine differences in PCV and TS between adult and nestling Cooper’s Hawks, be- tween males and females in each age class, and to examine the influence of hematozoa on PCV and TS. We report means and standard errors for PCV and TS levels. Sub- adult Cooper’s Hawks that were members of breeding pairs were pooled with adults for our analyses. When nec- essary, we logarithmically transformed data to meet as- Table 1 . Packed cell volume (PCV) and total solids (TS) for free-ranging adult and nestling Cooper’s Hawks in southeastern Arizona in 1995. Age/Sex N PCV SE TS SE Adult 9 9 35 50.7 0.64 4.13 0.10 Adult S S 26 53.7 0.51 4.02 0.06 Nestling 9 9 8 42.2 1.16 3.15 1.70 Nestling S 6 5 38.7 1.04 3.12 0.16 sumptions of normality and equal variance. If transfor- mations failed, we used Mann-Whitney rank sum tests and Kruskal-Wallis one-way analysis of variance on ranks (Ram- sey and Schafer 1997). We used chi-square contingency tables with Yates correction for continuity (Ramsey and Schafer 1997) to compare hematozoa infection rates be- tween sexes of adults, between adults and nestlings, and between regions. We used Fisher’s exact test (Ramsey and Schafer 1997) when small cell counts violated assumptions of a contingency table. Statistical analyses were conducted with the SigmaStat statistical package version 1 .0. Results We collected blood samples from 61 adult and 28 nestling Cooper’s Hawks. Data for PCV and TS of 15 of these nestlings were excluded due to Trich- omonas gallinae infections (Boal et al. 1998) that could have biased results. We found that PCV levels varied significantly among the ages and sexes of Cooper’s Hawks (E 3 70 = 46.7, P < 0.001; Table 1). A pairwise multiple comparison procedure indi- cated adult males (x = 53.7 ± 0.51) and adult fe- males {x = 50.7 ± 0.64) had greater mean PCVs than nestling males {x = 42.2 ± 1.16) or nestling females (x = 38.7 ± 1.04, P< 0.05; Table 1). Adult males also had a greater mean PCV than adult fe- males (P < 0.05) but there was no difference in mean PCV between nestling males and nestling fe- males (Table 1 ) . We found that TS levels also var- ied among the age and sex categories of Cooper’s Hawks = 24, P < 0.001; Table 1). A pairwise multiple comparison showed that age was the source of variability in TS levels. There was no dif- ference between adult males (x = 4.02 ± 0.06) and females (x = 4.13 ± 0.10) or between nestling males (x = 3.12 ± 0.16) and females (x = 3.15 ± 1.70), but adults had greater mean TS levels than nestlings (P < 0.05; Table 1). We examined blood smears of 44 breeding and 18 nestling Cooper’s Hawks for the presence of parasitic avian hematozoa. Infection rates were not different between the sexes of adult hawks (x^i = 0.351, P = 0.553) but rates were greater among December 1998 Hematology of Cooper’s Hawks 283 Table 2. Hematozoa infection rates of Cooper’s Hawks in southeastern Arizona in 1995 in relation to age and sex. Age/Sex N (%) Al (%) Ah (%) Ap (%) Adult S c? 17 8 (47) 1 (6) 8 (47) 1 (6) Adult ? 2 27 9 (33) 3 (11) 8 (30) 4 (15) Nestling S S 6 0 (0) 0 (0) 0 (0) 0 (0) Nestling 2 2 12 1 (8) 1 (8) 0 (0) 0 (0) Total 62 18 (29) 5 (8) 16 (26) 5 (8) Nj = number infected; Al = Leukocytozoan; = Haemoproteus-, Np = Plasmodium. adults (39%) than nestlings (5%) (x^i = 5.27, P = 0.022; Table 2). We identified Leucocytozoan toddi (as per Greiner and Kocan 1977), Haemoproteus spp., and Plasmodium spp. among the samples. All three hematozoa were found in two (4%) of the breeding Cooper’s Hawks (Table 2). There was no relationship between PCV and pres- ence of hematozoa among adult females (i ^5 = 0.862, P = 0.417) or males (fjg = 0.227, P = 0.823), nor was there a relationship between TS and presence of hematozoa among adult females {U = 114.0, P = 0.554) or males (ti^ = 0.434, P = 0.671). A low in- fection rate prevented us firom evaluating the influ- ences of hematozoa on PCV and TS of nestlings. Overall hematozoan infection rates were lower among breeding Cooper’s Hawks in Arizona (38.6%) than in Wisconsin (98.6%, Taft et al. 1994) (x^i = 5.55, P = 0.018). Cooper’s Hawks in Arizona had lower infection rates of Haemoproteus spp. (xS = 4.87, P = 0.027) and L. toddi (x^ = 58.5, P < 0.001) than in Wisconsin. Plasmodium spp. was not encountered in Wisconsin, but was detected in 11.3% of the Cooper’s Hawks sampled in Arizona (Table 2) . Hematozoan infection rates were low among nestling Cooper’s Hawks in both Arizona (5%) (Table 2) and Wisconsin (12%) (Taft et al. 1994) (Fisher’s exact test, P = 0.65). Discussion Smith and Bush (1978) suggested PCVs are con- sistent among raptors, but other studies indicate the parameter is highly variable (Balasch et al. 1976, Hunter and Powers 1980, Rehder et al. 1982, Rehder and Bird 1983, Redig 1993). This may be due in part to differences in hematology between free-ranging and captive raptors (Gessaman et al. 1986, Powers et al. 1994). Among free-ranging Ac- cipiter hawks, we found PCV levels for breeding Cooper’s Hawks were slightly higher than those for migrating Cooper’s Hawks and Sharp-shinned Hawks (A. striatus) (Gessaman et al. 1986, Powers et al. 1994) and similar to wintering Northern Gos- hawks {A. gentilis) (Hunter and Powers 1980). Breeding male Cooper’s Hawks had consistently higher PCVs than adult females. In contrast, there were no differences between the sexes of migrating Cooper’s Hawks and Sharp-shinned Hawks (Ges- saman et al. 1986, Powers et al. 1994). This maybe due to breeding males having higher androgen lev- els (Domm 1964, Rehder et al. 1982) which cause an increase in red blood cell production and thus PCV. Estrogen levels in female birds caring for young can be quite variable depending on the spe- cies. Estrogen causes bone marrow suppression in some animals and, if elevated in female Cooper’s Hawks during the nesting cycle, could cause a de- crease in their PCV. An elevated PCV and/or TS may be indicative of dehydration (Smith and Bush 1978) but all adult hawks in our study had an ap- parently unlimited access to water at riparian streams, ponds, bird baths, and other anthropo- genic sources of water (Boal 1997). Cooper’s Hawk nestlings had PCV levels 17% (females) and 28% (males) lower than adults. Sim- ilarly, the PCV of nestling Red-tailed Hawks {Buteo jamaicensis) is 26% lower than the PCV of adults (Redig 1993) . The lower PCV values of the nestling Cooper’s Hawks may represent a normal preadult hematological status as is documented in many an- imals (Jacobson and Kollias 1988). Lower preadult PCV levels may result when young hawks are under stress (e.g., sibling competition for food or nest crowding). Stress stimulates production of adre- nocorticotropic hormone, which in turn stimulates the adrenal gland to produce steroids such as cor- ticosterone and cortisol (Harvey et al. 1986) which may reduce PCV. Another possible explanation is that nestling Cooper’s Hawks may have smaller RBCs than adults, as is seen in some other avian species (Jacobson and Kollias 1988). Thus, nest- lings and adults may have similar RBC counts, but the smaller cell size in nestlings results in lower PCV. We did not determine red blood cell num- bers of either age group in our study. Age-specific levels of thyroid activity could also explain PCV differences among Cooper’s Hawks. Ronald and George (1988) demonstrated that in- creased thyroid activity in four races of Canada Geese {Branta canadensis) was correlated with high- er red blood cell counts and PCV. McNabb et al. 284 Boal et al. VoL. 32, No. 4 (1984) found thyroid activity in quail and doves did not reach adult levels until postfledging. Nest- ling Cooper’s Hawks may likewise have lower thy- roid hormone levels and, thus, lower PCV levels, Haemoproteus spp. has been identified as the most commonly detected avian hematozoan in infected wild birds (67%), with Plasmodium spp. (41.5%) and L. toddi (39%) occurring in similar frequencies (Bennett et al. 1982). We found all three of these hematozoan parasites in Cooper’s Hawks in south- ern Arizona, but they did not appear to affect PCV or TS. Prevalence of Haemoproteus spp. and L. toddi were lower in Arizona than in Wisconsin. This dif- ference may have been due to the life cycle of vec- tors. For example, black flies (Simuliidae) , the vec- tor of L. toddi, require running water to complete their life cycle. Running water is rare in the desert southwest, possibly decreasing the potential for spread of L. toddi. We did not quantify the severity of infections (i.e., percentage of infected red blood cells) but, subjectively, they appeared mild. The single excep- tion was a nestling that was heavily parasitized by L. toddi. Our data are from only one breeding sea- son, but it appears hematozoa infections among Cooper’s Hawks in southern Arizona are less prev- alent than in more northern parts of their range. ACKNOWI.EDGMENTS We are indebted to R.L. Spaulding for assisting in all as- pects of this study. A.E. Duerr and B.D. Bibles also assisted with capture of hawks and sample collection. We thank G.E. Duke, R.N. Rosenfield and S.J, Sweeney for providing thoughthil and constructive comments on the manuscript. This project was funded by Arizona Game and Fish Depart- ment Heritage Grant for Urban Wildlife No. U94010. Literature Cited Balasch, J., S. Musquera, L. Palacios, M. Jimenez and J. Palomeque. 1976. Comparative hematology of some Falconiforms. Condor 78:258-273. Bennett, G.E, A.D. Smith, W. Whitman and M. Camer- on. 1982. A host-parasite catalogue of the avian he- matozoa. Occasional Papers in Biology. Vol. 5, Me- morial Univ. Newfoundland, St. John’s, Newfoundland, Canada. Bloom, P.H. 1987. Capturing and handling raptors. Pag- es 99-123 in B.A. Millsap, K.W. Cline, B.G. Pendleton and D.A. Bird [Eds.], Raptor management techniques manual. Natl. Wildl. Fed., Washington, DC U.S.A. Boal, C.W. 1997. The urban environment as an ecolog- ical trap for Cooper’s Hawks. Ph.D. dissertation, Univ. Arizona, Tucson, AZ U.S.A. , R.W. Mannan and K.S. Hudelson. 1998. Tricho- moniasis in Cooper’s Hawks from Arizona. J. Wildl. Dis. 34:864-871. Campbell, TW. 1988. Avian hematology and cytology. Iowa State Univ. Press, Ames, lA U.S.A. Domm, L.V. 1964. Endocrine factors controlling erythro- cyte concentration in the blood of domestic fowl. Phy- siol. Tool. 19:258-281. Gessaman, J.A., J.A. Johnson and S.W. Hoffman. 1986. Hematocrits and erythrocyte numbers for Cooper’s and Sharp-shinned Hawks. Condor 88:95-96. Greiner, E.C. and A.A. Kogan. 1977. Leucocytozoan (Hae- mosporida; Leucocytozoidae) of the Falconiformes. Can. J. Zool. 55:761-770. , G.F. Bennett, E.M. White and R.F. Coombs. 1975. Distribution of the avian hematozoa of North America. Can.]. Zool. 53:1762-1787. Harvey, S., C.D. Scanes and K.I. Brown. 1986. Adrenals. Pages 479-493 in P.D. Sturkie [Ed.], Avian physiology, 4th Ed. Springer-Verlag, New York, NY U.S.A. Hunter, S.R. and L.R. Powers. 1980. Raptor hematocrit values. Cowrfor 82:226-227. Jacobson, E.R. and G. Kollias. 1988. Exotic animals. Churchill Livingston, New York, NY U.S.A. Kirkpatrick, C.E. and D.M. Lauer. 1985. Hematozoa of raptors from southern New Jersey and adjacent areas. J. Wildl. Dis. 21:1-6. Kocan, A.A., j. Snelling and E.C. Greiner. 1977. Some infectious and parasitic diseases of Oklahoma raptors. J. Wildl. Dis. 13:304-306. McNabb, F.M.A., F.W. Stanton and S.G. Dicken. 1984. Post-hatching thyroid development and body growth in precocial vs. altricial birds. J. Comp. Biochem. Physiol. 78A:629-635. Powers, L.V., M. Pokras and K. Rio. 1994. Hematology and occurrence of hemoparasites in migrating Sharp- shinned Hawks {Accipiter striatus) during fall migra- tion./. Raptor Res. 28:178-185. Ramsey, F.L. and D.W. Schafer. 1997. The statistical sleuth: a course in methods of data analysis. Duxbury Press, Belmont, CA U.S.A. Redig, P.T. 1993. Medical management of birds of prey: a collection of notes on selected topics, 3rd Ed., re- vised. The Raptor Center, Univ. Minnesota, St. Paul, MN U.S.A. Rehder, N.B. and D.M. Bird. 1983. Annual profiles of blood packed cell volumes of captive American Kes- trels. Can.]. Zool. 61:2550-2555. , D.M. Bird and PC. Lague. 1982. Variation in blood packed cell volume of captive American Kes- trels. /. Comp. Biochem. Physiol. 72A: 105-1 09. Ronald, K.M. andJ.C. George. 1988. Seasonal variation in certain hematological and respiratory properties of the blood of four races of Canada Geese, Branta can- adensis. Zool. Arizczger 220 (S.):71-78. Smith, E.E. and M. Bush. 1978. Haematologic parame- ters on various species of Strigiformes and Falconifor- mes. J. Wildl. Dis. 14:447—450. December 1998 Hematology of Cooper’s Hawks 285 Snyder, N.F.R. and J.W. Wiley, 1976. Sexual size dimor- phism in hawks and owls of North America. Ornithol. Monogr. 20. Stabler, R.M. and RA. Holt. 1965, Hematozoa from Colorado birds. II. Falconiformes and Strigiformes. /. Parasitol. 51:927-928. Taft, S.J., R.N. Rosenfield and J. Bielefeldt. 1994. Avi- an hematozoa of adult and nestling Cooper’s Hawks (Accipiter cooperii) in Wisconsin. J. Helminthol. Soc. Washington 61:146-148. Received 29 December 1997; accepted 20 July 1998 J. Raptor Res. 32(4);286-289 © 1998 The Raptor Research Foundation, Inc. EGESTION OF CHITIN IN PELLETS OF AMERICAN KESTRELS AND EASTERN SCREECH OWLS Chikako Aeaki and Gary E. Duke Department of Veterinary PathoBiology, University of Minnesota, St, Paul, MN 55108 US. A. Abstrac:t. — In studying the digestibility of chitin by American Kestrels (Falco sparverius) and Eastern Screech Owls {Otus asio), we found portions of ingested chitin not only occurred in excreta but also in pellets. When commercial chitin was fed with turkey or chicken meat, 23.8% (American Kestrel) and 29.6% (Eastern Screech Owl) of the ingested chitin was egested in pellets. In American Kestrels, 59.2% of the total amount of ingested chitin was found in excreta. The percent of chitin egested as pellets as compared to the amount ingested showed a negative correlation (r = —0.76, P< 0.001). Our results suggest that the lower gastrointestinal tract contributes to total chitin digestion in American Kestrels. Key Words: American Kestrel, Falco sparverius; Eastern Screech Owl; Otus asio; chitin; digestibility; pellet egestion. Residuos de queratina en egragopilas de Falco sparverius y Otus asio Resumen. — ^A1 estudiar la digestibilidad de la queratina en Falco sparverius y Otus asio, encontramos que las porciones de queratina ingerida no solo ocurren en las excretas si no que tambien en las egagropilas. Cuando la queratina de uso comercial fue suministrada con came de pavo o polio 23.8% {Falco sparv- erius) y 29.6% {Otus asio) este fue eliminado en las egagropilas. En Falco sparverius, 59.2% del total de queratina ingerida fue encontrada en las excretas. El porcentaje de queratina eliminada en las egagro- pilas comparado con el ingerido mostro una correlacion negativa (r = —0.76, P < 0.001). Nuestros resultados sugieren que el tracto gastrointestinal bajo contribuye a la digestion total de queratina en Falco sparverius. [Traduccion de Cesar Marquez] Insect exoskeletons are poorly digested by pred- ators (Kramer and Koga 1986). This is due to the indigestibility of chitin (poly [(3-(l-4)-2-acetamido- 2-deoxy-D-glucopyranose] ) which gives strength and structure to the exoskeleton (Roberts 1992). In spite of its indigestibility, insect chitin is consid- ered a possible dietary source of carbohydrate for predators (Jeuniaux and Cornelius 1978, Weiser et al. 1997). Eastern Screech Owls ( Otus asio) and American Kestrels {Falco sparverius) are partially or primarily insectivorous (Johnsgard 1988, 1990). When coarse chitin powder was fed, portions were not only found in excreta but also in egested pellets. Chitin egested in pellets is not exposed to digestive enzymes in the lower gastrointestinal (GI) tract where chitinolytic enzymes are found (Jeuniaux 1963). If the lower GI tract contributes to chitin digestion, chitin digestibility would be expected to be higher when all ingesta pass through the whole GI tract. In this study, we determined the proportion of ingested chitin that was egested in pellets by cap- tive Eastern Screech Owls and American Kestrels. We also determined the chitinolytic capacity of the lower GI tract in American Kestrels by comparing chitin digestibility in two d i f ferent cases with and without the egestion of chitin in pellets. Methods Four Eastern Screech Owls and three American Kes- trels were used. All individuals were permanently crip- pled but otherwise healthy. Birds were kept separately in wooden chambers (45 cm wide, 48 cm high and 45 cm deep) in an environmentally controlled room (20-22°C, 40-50% relative humidity and 12 hr of light per 24 hr). Between experiments, the birds were fed whole labora- tory mice {Mus musculus) daily totaling approximately 20% of each bird’s body weight at 1700 H for screech owls and at 1200 H for kestrels. The birds has access to mice until the cages were cleaned the next morning. Pellets consisting of coarse chitin powder were collect- ed in the process of determining chitin digestibility for kestrels or during the period of acclimating screech owls to a chitin-rich diet. For our experiments, we used com- mercially available chitin (from crab shell, practical grade. Sigma Chemical, St. Louis, MO, U.S.A.). Chitin 286 December 1998 Chitin in Pellets of Kestrels and Screech Owls 287 content in this product was determined by crude fiber determination (Helrich 1990) to be 68.5% of the weight of the product. After acclimation to a diet of chicken or turkey meat for 8 d, kestrels were fed an amount of chitin equivalent to 2% (by weight) of their total dried food (2% chitin diet) at the start of each experiment to determine chitin digestibilities. The day before chitin was fed, all excreta were collected and analyzed for chitin content as a con- trol. Chitin was packed in small pieces of meat. Each piece was fed by forceps to each bird to ensure that all the chitin was consumed. During the experiments, the birds were kept on a chicken or turkey meat diet which amounted to 18% of each bird’s body weight (wet weight) daily. The chicken and turkey meat each con- tained 27.7% dry matter. Following the feeding of chitin, all excreta and pellets, if egested, were collected from kestrels daily for 2 d on a polyethylene sheet set on a stainless steel pan in the bottom of each cage. Collected excreta and pellets were separately dried at 50°C for 2 d, weighed and finely ground with a pestle and mortar to pass through a 0.5 mm mesh. These ground samples were analyzed to de- termine their chitin contents. When we fed screech owls 144.5-170.1 mg of chitin with each feeding, they did not egest pellets. However, when we increased the amount of chitin to 300 mg, they egested pellets. Due to this, we fed each screech owl 300 mg of chitin either in turkey or chicken meat (chitin diet, total 15 g) each day for 6 wk to determine whether acclimation to chitin improved chi- tin digestibility. During this acclimation period, we also fed the birds mice at night to ensure a proper nutrient supply. The chitin diet was fed to screech owls in the afternoon after the birds egested pellets from mice con- sumed the night before. On many occasions, the owls did not eat the mice until they egested pellets from the chitin diet. These pellets, which consisted of only coarse chitin powder, were dried at 50°C for 2 d and weighed. Ten pellets were ground and prepared for the determination of their chitin content. No excreta were collected; there- fore, chitin digestibilities were not determined. Kestrels were acclimated the same way, but they tended to eat mice before they egested pellets from the chitin diet. As a result, kestrels egested a mixture of chitin pow- der and mouse fur as pellets. Since both chitin and hair are detected as crude fiber, determination of chitin con- tents was not possible by the crude fiber determination used when mouse fur contaminated the pellets. There- fore, no useful pellets were collected from kestrels during the acclimation period. Chitin content was estimated by using the method for crude fiber determination in animal feeds (Helrich 1990). This method was used to estimate chitin contents in arthropods by Jackson et al. (1992), Nicholson et al. (1996), and Weiser et al. (1997). Since the ground ex- creta and pellets of kestrels were mixed and analyzed to- gether to obtain their chitin contents in our previous study, six extra chitin pellets were collected from kestrels by feeding a 2% chitin diet to determine the chitin con- tent of pellets. A mean of 69% (by dry weight) of the pellet was chitin in kestrels. Similarly, 10 pellets from screech owls were analyzed and found to have a mean of 68% chitin (dry weight). These values were used to cal- culate the dry weight of chitin in chitin pellets. Chitin digestibilities of kestrels were determined by comparing the weight of chitin fed to the weight found in excreta and pellets (if egested). Because this method did not consider chitin retained in the GI tract (not im- mediately excreted), the chitin digestibilities obtained were referred to as “apparent” chitin digestibilities (Jackson et al. 1992). Chitin egested as pellets was not exposed to the possible chitinolytic enzymes in the lower GI tract. Therefore, we calculated means of chitin di- gestibilities separately in the two different cases (i.e., with or without egestion of pellets). Apparent chitin digest- ibilities were calculated based on the ratio of assimilation to ingestion and the ratio were converted to percentages of chitin assimilated to chitin ingested. Chitin ingestion and assimilation calculations were based on either the total dry weight of chitin ingested and excreted, or egest- ed. Similarly, the percent of chitin egested in pellets was based on the total dry weight of chitin in pellets. A pooled t-test (Devore and Peck 1993) was used for comparison of apparent chitin digestibilities with or with- out chitin pellets. An T-test was used to obtain a P value for correlation coefficients (Devore and Peck 1993). When P < 0.05, statistical comparisons were considered significantly different. Results and Discussion Fourteen pellets were collected from three kes- trels. No pellets were egested following three chitin feedings in two kestrels. The percent of chitin egested in a pellet relative to ingested chitin was 23.8% ± 11.0% (±SD) by weight (Table 1). Of to- tal ingested chitin, 59.2% — 9.9% was in excreta indicating that most of the ingested chitin was lost in excreta rather than egested in pellets or digested. A total of 49 pellets were collected from four screech owls. A total of 29.6% ± 9.1% of ingested chitin was egested in pellets when 300 mg of chitin was fed per day (Table 1). The percent of chitin egested in pellets relative to ingested chitin and apparent chitin digestibili- ties showed a strong negative correlation (r = —0.76, P < 0.001, Fig. 1) indicating that the more chitin egested in pellets, the less chitin was digest- ed. When pellets were egested (N= 14) in kestrels, apparent chitin digestibilities were determined to be 19.5% ± 5.3%. When no pellets were egested {N = 3) , digestibility was significantly higher at 28.9% ± 3.7% {P < 0.01). This suggested that the lower GI tract may contribute in the digestion of chitin in kestrels. Kestrels possess a relatively long colon compared to their body size although the cecum is extremely small (Duke et al. 1997). If the contribution to chitin digestion is due to bacterial enzymes, their large colon might support possible 288 Akaki and Duke VoL. 32, No. 4 Table 1. Mean weights of chitin in pellets and percents of chitin egested, excreted and digested in American Kestrels and Eastern Screech Owls. Results are expressed as x ± 1 SD. The number in parentheses is the number of samples. The samples of chitin pellets were collected during the chitin feeding trials (American Kestrel) or the acclimation to a chitin diet (Eastern Screech Owl). American Kestrel Eastern Screech Owl Dry weight of chitin in chitin pellet (mg) 28.4 ± 14.3 (14) 88.9 ± 27.3 (49) Percentage of chitin egested as pellet compared to total in- gested chitin (%)“* 23.8 ± 11.0 (14) 29.6 ± 9.1 (49) Percentage of chitin excreted in excreta compared to total ingested chitin (%)^ 59.2 ± 9.9 (17)* Apparent chitin digestibilities when chitin pellets were egested (%)*^ 19.5 ± 5.3 (14)** Apparent chitin digestibilities when no chitin pellets were egested (%)^ 28.9 ± 3.7 (3)** ® 100 (Chitin pellet/Chitin in). 100(Chitin out — Chitin pellet) /Chitin in. 100(Chitin in — Chitin out)/Chitin in. Chitin pellet = total dry weight of chitin in chitin pellet. Chitin in = total dry weight of ingested chitin. Chitin out = total dry weight of excreted or egested chitin. * Including three cases where no pellet was egested. ** Digestibilities when no pellets were egested were significantly higher than when pellets were egested (P < 0.01). chitinolytic bacterial populations. Screech owls have a pair of relatively large ceca with the poten- tial for bacterial fermentation indicating that en- teric bacteria probably contribute to chitin diges- tion (Akaki 1997). Chitin digestibilities determined using chitin powder are probably higher than digestibility of flakes or pieces of chitin obtained by eating insect prey. However, we felt that by feeding chitin with a uniform particle size and source our results Figure 1. Relationship between apparent chitin digest- ibilities and percentage of chitin egested in pellets in three American Kestrels. would be more consistent between experiments and species. We found variation in the size of pellets (0- 41.9% of ingested chitin by weight) egested by kes- trels. We found similar variation in the pellets of one screech owl which egested 10.5-46.3% of in- gested chitin in its pellets {N = 36), although the same amount of chitin was given to the bird every- day. The causes of this variation are unknown. Since pellets were collected under different con- ditions for kestrels and screech owls, it was impos- sible to compare the data obtained for the two spe- cies. Screech owls, however, appeared to egest chitin in pellets only when they were fed a relative- ly large amount of chitin (300 mg). In 80% of the feeding trials, kestrels egested chitin in pellets even when they were fed the 2% chitin diet (97.4-131.4 mg of chitin). Kestrels appear to be more sensitive to a small amount of undigested material remain- ing in the gizzard, but reasons are unknown. The oral egestion of coarse chitin powder in pel- lets of kestrels and screech owls suggests that chitin is difficult to degrade and tends to be eliminated by raptors with other undigestible material such as hair and bones. Both species egested chitin in pel- lets 6-12 hr and 6-10 hr, respectively, after the feeding of chitin. In spite of their retention of chi- tin in their stomachs, chitin powder was still rec- December 1998 Chitin in Pellets of Kestrels and Screech Owls 289 ognizable in the pellets and appeared macroscop- ically to be not significantiy different from the original size indicating that the digestion of chitin in the stomach of these two species is very limited. Although our results indicated that the lower GI tract contributed to chitin digestion in kestrels, chi- tin powder was still easily recognized in excreta in- dicating that chitin is difficult to digest even after exposure to digestive enzymes in the lower GI tract. It has not been determined why raptors digest chitin despite the difficulty of its degradation. One possible reason is that chitinous exoskeletons of prey need to be digested to expose soft tissue to digestive enzymes (Gooday 1990). Since mechani- cal digestion in the stomachs of raptors appears to be limited due to a less muscular gizzard as com- pared to fowl (Duke 1986), more chemical diges- tion may be required. It is possible that chitin itself is utilized as an energy source by raptors, although the final products of chitin hydrolysis are difficult to absorb in the intestine (Capps et al. 1966, Crane 1968, Jackson et al. 1992). Since the absorption and metabolism of digested chitin by screech owls and kestrels has not been studied, further investi- gation is required in order to determine the value of chitin as an energy source for these species. Acknowledgments We are very grateful to Len Soucy (The Wildlife Center of Virginia, Waynesboro, Virginia), Mark Pokras (The Wildlife Clinic, Tufts University, North Grafton, Massa- chusetts) , Adele Moore (Treehouse Wildlife Center, Brig- ton, Illinois) , and Lori Arent (The Gabbert Raptor Cen- ter, University of Minnesota, St. Paul, Minnesota) for providing Eastern Screech Owls and American Kestrels, Literature Cited Akaki, C. 1997. Chitin digestibilities in the Eastern Screech Owl {Otus asio) and the American Kestrel {Falco sparverius). M.S. thesis, Univ. Minnesota, St. Paul, MN U.S.A. Capps, J.C., M.R. Shetlar and R.H. Bradford. 1966. He- sosamine metabolism. I. The absorption and metab- olism, in vivo, of orally administered D-glucosamine and N-acetyl-glucosamine in the rat. Biochem. Biophys. Acta 127:194-204. Crane, R.K. 1968. Absorption of sugars. Page 1343 in C.F. Code and W. Heidel [Eds.], Handbook of physiology. section 6: alimentary canal. Vol. 3. Intestinal absorp- tion. American Physiological Society, Washington, DC U.S.A. Devore, J. And R. Peck. 1993. Statistics: the exploration and analysis of data, 2nd Ed. Wadsworth Inc., Bel- mont, CA U.S.A. Duke, G.E. 1986. Raptor physiology. Pages 370-376 m M.E. Fowler [Ed.], Zoo and wild animal medicine. W.B. Saunders Company, Philadelphia, PA U.S.A. , J. Reynhout, A.L. TerEick, A.E. Place and D.M. Bird. 1997. Gastrointestinal morphology and motility in American Kestrels receiving high or low fat diets. Con^ior 99:123-131. Gooday, G.W. 1990. The ecology of chitin degradation. Pages 387—430 in K.C. Marshall [Ed.], Advances in microbial ecology. Vol. 11. Plenum Press, New York, NY U.S.A. Helrich, K. 1990. Official methods of analysis of the As- sociation of Official Analytical Chemists, 15th Ed. Vol. 1. Association of Official Analytical Chemists, Arling- ton, VA U.S.A. Jackson, S., A.R. Place and LJ. Seiderer. 1992. Chitin digestion and assimilation by seabirds. Auk 109:758- 770. Jeuniaux, C. 1963. Chitin et chitinolyse, un chapitre de la biologie moleculaire. Masson, Paris, France. and C. Cornelius. 1978. Distribution and activity of chitinolytic enzymes in the digestive tract of birds and mammals. Pages 542-549 in R.A.A. Muzzarelli and E.R. Pariser [Eds.], Proceedings of the first inter- national conference on chitin/chitosan. MIT, Cam- bridge, MA U.S.A. JoHNSGARD, P.A. 1988. North American owls: biology and natural history. Smithsonian Institution, Washington, DC U.S.A. . 1990. Hawks, eagles and falcons of North Amer- ica: biology and natural history. Smithsonian Institu- tion, Washington, DC U.S.A. Kramer, K.J. and D. Koga. 1986. Insect chitin: physical state, synthesis, degradation and metabolic regula- tion. Insect Biochem. 16:851-877. Nicholson, J.W.G., R.E. McQueen, J.G. Allen and R.S. Bush. 1996. Composition, digestibility and rumen de- gradability of crab meal. Can. J. Anim. Sci. 76:89-94. Roberts, G.A.F. 1992. Chitin chemistry. Macmillan Press, London, U.K. Weiser, J.I., A. PoRTH, D. Mertens and W.H. Karasov. 1997. Digestion of chitin by Northern Bobwhites and American Robins. Condor 99:554—556. Received 31 December 1997; accepted 25 July 1998 J Raptor Res. 32(4):290-296 © 1998 The Raptor Research Foundation, Inc. AN INFRARED VIDEO CAMERA SYSTEM FOR MONITORING DIURNAL AND NOCTURNAL RAPTORS David K. Delaney^ and Teryl G. Grubb USD A Forest Service, Rocky Mountain Research Station, 2500 S. Pine Knoll Dr., Flagstaff, AZ 86001-6381 U.S.A. David K. Garcelon Institute for Wildlife Studies, P.O. Box 1104, Areata, CA 95518 U.S.A. Abstract. — A black and white, circuit-board video camera system with night vision was designed to monitor Mexican Spotted Owl (Strix occidentalis lucida) behavior. A 0.5-Lux infrared camera equipped with a 3.3 mm lens permitted vision up to 3 m in total darkness with the aid of six infrared light-emitting diodes (LEDs). To extend nighttime visibility at selected sites to approximately 6 m, we constructed a supplemental 9-LED infrared light source. Industrial-grade video recorders provided up to 24-hr coverage per VHS tape. Cameras averaged 6.9 m from nests (range 3.0-10.3 m). Mean camera installation time was 42 min (range 28-71 min). Between 25 April-3 July 1996, approximately 820 hr of video effort (76 hr for equipment assembly, 14 hr for camera placement, 230 hr for maintaining tapes and batteries, and 500 hr for subsequent video analysis) provided 2655 hr of usable video coverage (149 tapes) at 20 nest sites, a return ratio of nearly 3.2: 1 hr of coverage for each hour invested. Comparable detail, quality, or quantity of behavioral data would not have been possible through direct observation. This video system could have a wide application in other raptor behavior studies, especially for determining the effects of human activities. Key Words: behavior, diurnal activity, infrared photography, Mexican Spotted Owl] nocturnal activity; Strix occidentalis lucida; surveillance; video camera. Un sistema de video camara infrarojo para el monitoreo de aves rapaces diurnas y nocturnes Resumen. — Un sistema de video camara en bianco y negro con vision nocturna fue disenado para el monitoreo del comportamiento de Strix occidentalis lucida. Una camara de 0.5 Lux equipada con un lente de 3 mm permitio una vision de hasta 3 m en la obscuridad total con la ayuda de una luz infraroja de seis diodos. Con el fin de extender la visibilidad nocturna a 6 m en sitios seleccionados, construimos una fuente de luz infraroja suplementaria de 9 diodos. Con video grabadoras industriales cubrimos periodos de 24 horas en cintas de VHS. La distancia promedio de los nidos fue de 6.9 m (rango = 3.0- 10.3 m). La media del tiempo de instalacion de la camara fue de 34 min (rango = 28-71 min). Entre el 25 de abril-3 de Julio de 1996, 820 hr de video fueron registradas (76 hr para el ensamblaje del equipo, 14 hr para la ubicacion de la camara, 230 hr para el mantenimiento de cintas y baterias y 500 hr para el analisis de video) 2655 hr de cobertura de video (149 cintas) en 20 nidos, una tasa de retorno de cerca de 3.2:1 hr de cobertura por cada hora invertida. El detalle, la calidad o cantidad de datos de comportamiento no hubiera podido ser obtenida a traves de observaciones directas. Este sistema de video puede tener una aplicacion amplia en estudios de comportamiento de otras aves rapaces espe- cialmente con el fin de determiner los efectos de actividades humanas. [Traduccion de Cesar Marquez] Collecting baseline behavioral information on animals from field observations is an important prerequisite to determining and mitigating the ef- fects of human activities. To compare animal be- havior between manipulated and nonmanipulated ^ Present address: U.S. Army Construction Engineering Re- search Laboratories, P.O. Box 9005, Champaign, IL 61826 U.S.A. sites or periods, it is often necessary to make si- multaneous observations at more than one loca- tion and for extended periods of time. For study- ing owls, the ability to monitor nocturnal behavior is also critical. Recording wildlife activity with re- motely operated or automatic cameras has a long history (Dodge and Snyder 1960, Osterberg 1962, Cowardin and Ashe 1965, Patton et al. 1972). Tech- niques include time-lapse, super-8 movie cameras (Grubb 1983), conventional video cameras (Nye 290 December 1998 Infrared Video System 291 Figure 1. Miniature circuit-board video camera with weatherproof, plastic switch-box painted black (except for the lens and LED area) and wired for video and power connections. 1983, Kristan et al. 1996), miniature video-board cameras (Proudfoot 1996), 110 instamatic cameras (Jones and Raphael 1993), 35-mm infrared-aided cameras (Hernandez et al. 1997), and the most common approach, 35-mm, flash-aided photogra- phy (M^or 1991, Kucera and Barrett 1993, Brow- der et al. 1995, Danielson et al. 1996). During a recent study on the effects of helicop- ter and chain-saw noise on nesting Mexican Spot- ted Owls (Strix occidentalis ludda; Delaney et al. 1999a), we chose video surveillance as the primary means of recording owl behavior and responses to manipulations at nest sites because it did not re- quire capturing or handling owls for radioteleme- try, could be operated remotely with minimal dis- turbance to the owls, was silent with no moving parts, provided both diurnal and nocturnal record- ing capability, and facilitated real time, behavioral analyses a posteriori. However, to meet the unique requirements of unobtrusively recording continu- ous behavior of this primarily nocturnal species, we had to design a camera system that was small and easily mounted, functional in both daylight and darkness, and sufficient for monitoring owl nesting activity and prey deliveries. This paper describes the design, construction, and deployment of this essentially noninvasive, infrared video camera sys^ tern for monitoring 24-hr activity at Mexican Spot- ted Owl nest sites. Methods We used Marshall^ black and white, charge-coupled de- vice (CCD), circuit-board video cameras (Marshall Elec- tronics, Culver City, CA U.S.A.; Fig. 1). The solid state, 12-volt, circuit-board cameras came equipped with 3.3- mm lenses, which we replaced in most cases vdth an oj> tional 12.0-mm lens. A folly automatic electronic shutter compensated between bright daylight and nighttime con- ditions. The camera provided a minimum of 380 lines of resolution and with 0.5-Lux, permitted vision up to 3 m in total darkness with the aid of six infrared light-emitting diodes (LEDs; Figs. 1, 2A). To approximately double night vision capabilities (i.e., to monitor nests up to 6 m away) , we designed supplemental infrared, 9-LED (Tandy Corp., Ft. Worth, TX U.S.A.), light sources on 5-cm (2- inch) diameter circuit boards mounted in PVC-pipe end caps sealed with plexiglass (Fig. 2B) . Each of these lights was then attached to a 2-m piece of lightweight alumi- num screen molding that facilitated independent mount- ing in camera trees closer to the nests under observation. Cameras were mounted in waterproof, heavy-gauge plas- tic switch-boxes with transparent covers (11.5 X 6.4 X 5.5 cm; Newark Electronics, Chicago, IL U.S.A.) which, ex- ^ Use of trade names does not imply endorsement by the USDA Forest Service, Rocky Mountain Research Station, or Institute for Wildlife Studies to the exclusion of other po- tentially suitable products. VoL. 32, No. 4 292 Delaney et al. A A I f i § VI 4 V) T Front View End View Clear plastic window Wide angle lens Infrared LED Plastic weatherproof housing Lens mounted through plastic window Video and power connecting ports B Front View Side View ^5.0 cm Clear plastic window Full View (not to scale) Aluminum screen molding / Power cord 2.0 m Figure 2. Schematics of (A) the black and white, circuit-board infrared video camera and (B) the supplemental, inftared light source used to extend night recording capability to ~6 m. Table 1. Equipment and approximate costs for a night vision video surveillance system (based on 1996 prices associated with assembling 20 systems). Component Approximate Cost ($) Video cassette recorder 745.00 Miniature video camera 240.00 DC monitor ($110.00 per 4—5 systems)^ Rechargeable batteries ($55.00, 4 per sys- -25.00 tern) 220.00 Battery charger ($80.00 per 4—5 systems)^ Coaxial and power cables, connectors. -20.00 plugs 100.00 Protective bin 20.00 Tarpaulin and cord 30.00 Total $1400.00 ® Costs of DC monitors and battery chargers per system are pro- portionally reduced by the total number of systems deployed; we used 4 monitors (the same 10.5-cm DC monitors used to position the camera) and 4 chargers to operate 20 video systems. cept for the lens and LED area, were painted black (Fig. 1 ) . Two connecting ports were threaded into the protec- tive housing for the power supply and the video signal. Cover plates were drilled to accommodate lens barrels, which when the outer portion was attached through the plate, supported the entire circuit board. Panasonic Model AG-1070DC, industrial-grade VHS video recorders (Panasonic Corporation of America, Se- caucus, NJ U.S.A.), connected to cameras via coaxial ca- ble (RG-59), provided up to 24-hr coverage per tape. These 12-volt, DC-powered recorders were designed for law-enforcement surveillance applications. We obtained 24-hr coverage by recording approximately 5 frames per sec instead of the normal rate of 30 frames per sec. Cam- eras, supplemental lights, and video recorders were pow- ered by two 12-volt, 33.0-amp-hr, Power-Sonic Model PS- 12330, rechargeable batteries (Power Sonic, Redwood City, CA U.S.A.) connected in parallel because a 24-hr taping would draw a single battery below operational lim- its. These rugged, sealed “gel-cell” type batteries (weigh- ing 11.3 kg each) reduced the risk of battery damage, and eliminated the potential for spillage during backpack transport. The total cost per system was about $1400.00 (Table 1). Assembly time was approximately 4 hr per camera system. Cameras were attached to tree branches or trunks with adjustable. Jointed angle-brackets and screws (Fig. 3). Cameras were mounted at the same level or slightly above nest height in the nearest practical tree, which had to be large enough to climb to nest height and also far enough December 1998 Infrared Video System 293 Figure 3. Branch-mounted video camera showing jointed attachment bracket, acljustable in two planes. Power and video cables are attached through connectors on the rear of the unit (not visible in this view) and anchored to the supporting branch or tree trunk. from the nest tree so as not to disturb incubating owls. A 15-m combination power line and coaxial cable (or down line) was attached to a 10.5-cm DC-powered mon- itor and battery (Fig. 4), so camera placement during installation could be directed from the base of the cam- era tree. A minimum of two persons was required for camera placement, a climber to position the camera and a person on the ground to check the video signal and direct placement. Once the camera was positioned, the down line was taped to the tree and the system was left inoperative for up to a week. This allowed owls to habit- uate to camera presence prior to experiencing the visi- ble, dull red glow of the infrared LEDs once the system was powered. Visual sensitivity of Mexican Spotted Owls to infrared light is unknown; however, Konishi (1973) has shown that Barn Owls ( Tyto alba) are not sensitive to such light. A supplemental light source, when needed, was ex- tended toward the nest platform, then nailed, wired, or taped in place. Its power line was spliced to the camera’s with quick-connects. To make the system operational, a 60-m trunk line was attached at the base of the tree (cov- ered by 1.2-cm diameter hose for protection against ro- dents), permitting the power/ recording station to be placed away and out of sight from the nest tree to min- imize potential disturbance to the owls. We put the re- corder, two batteries, and all connectors inside a weath- erproof, rubberized storage bin (61 cm X 40 cm X 24 cm; Fig. 4) concealed under a camouflaged tarpaulin. Batteries and tapes were exchanged before and after each 24rhr recording period. Results During 10 field days between 9 April-27 May 1996, cameras were placed at 20 nest sites (1-4 sites per d depending on travel time between sites) in the Sacramento Mountains of southcentral New Mexico. Mean placement time from arrival to de- parture from the nest site was 42 min (range = 294 Delaney et al. VoL. 32, No. 4 Figure 4. Weatherproof, rubberized bin housing video recorder, batteries for powering entire system, and spare tapes, with a portable monitor used temporarily to check video image reception and quality. 28-71 min). Nest height averaged 15.3 m (range = 8.0-27.0 m) in 18 Douglas firs (Pseudotsuga men- ziesit) and one white fir {Abies concoUn). One nest tree was not measured. Cameras averaged 6.9 m from nests (range = 3.0-10.3 m). Because effective night vision was limited to approximately 6 m, we were only able to collect nocturnal information at eight nests. We mounted 18 cameras without flushing nest- ing owls. Two initial mounting efforts that caused a flush were immediately aborted, with the adults returning to their nests in <5 min. We were able to mount both cameras a week later with no fur- ther response. Aside from the two flushes in 22 mounting attempts, spotted owls appeared totally unaffected by the video systems once in place. Sev- eral owls that had done so previously, even contin- ued to perch in camera trees. There was no nest abandonment, and 18 of the 20 nests were suc- cessful. Neither nest failure was related to video camera presence (Delaney et al. 1999a) . Between 25 April-3 July 1996, our surveillance systems yielded 149 tapes and 2655 hr of taped cov- erage. Approximately 230 field hr were required for changing tapes and batteries or about 1.5 hr per change. In addition, over 500 office hours were required to analyze the tapes for related spotted owl behaviors such as nest attentiveness, number of prey deliveries, and number of female trips from the nest. A total of approximately 820 hr (includ- ing an additional 76 hr for equipment assembly and 14 hr for camera placement) were spent in obtaining the 2655 hr of usable video coverage, a return ratio of 3.2:1 of coverage for each hour in- vested. Discussion We developed this infrared camera system to fa- cilitate a study of helicopter noise effects on the threatened Mexican Spotted Owl (Delaney et al. 1999a). This conservative approach allowed us to observe natural behavior and spotted owl re- sponses to experimental manipulations with mini- mal risk to the owls. In addition, video coverage permitted the quantification and differentiation of several subtle, nonflushing behaviors that not only facilitated and strengthened our assessment of dis- turbance, but also provided new insight into spot- ted owl nesting and foraging activities (Delany et al. 1999b). Previous raptor responses to camera installation ranged from no apparent effect (i.e., successful fledging; Enderson et al. 1973) to extreme effects such as nest abandonment (Cain 1985, W. Bower- man pers. comm.). Responses may be affected by installation time, season, and camera placement, as December 1998 Infrared Video System 295 well as by animal temperament and prior experi- ence. Red-tailed Hawks {Buteo jamaicensis) and Northern Goshawks (Acdpiter gentilis) have been disturbed by the mere human presence associated with research activity (Olendorff 1975, Kennedy and Stahlecker 1993). Although our cameras were carefully installed after spotted owls had initiated nesting, we strongly recommend installation prior to nesting activity and before breeding adults are present. We would not have been able to collect the same level of detail, quality, or quantity of behavioral data through direct observation. Videotaping with the date and time on each frame provided a per- manent record that could be accurately measured and reviewed for additional information. In addi- tion, it provided uninterrupted 24-hr coverage and the capability of monitoring several nests simulta- neously, thus minimizing confounding factors re- lated to sample timing. To obtain comparable cov- erage via direct observation would have required 2-3 field assistants per site and tripled labor costs. Disruptive personnel shift changes and expensive night-vision equipment would also have been nec- essary. Additional advantages of this camera system are that cameras are unmanned and provide 24-hr, real-time assessment of the frequency, duration, timing, and type of behaviors, as opposed to the more limited sampling regimes inherent in com- mon forms of time-lapse or triggered photography. Infrared capability permits similar recording of nocturnal and diurnal activities without disruptive flashes. Remote placement allows observers to stay approximately 60 m from nests once cameras are installed, minimizing observer effects that might otherwise confound assessment of other human disturbances. The cameras are small, unobtrusive and quiet, and the cost per system is modest by comparison to other video systems. We also experienced several difficulties or limi- tations in operating this system. Installing the 60- m cables for power and video and protecting the system from moisture, loose connections, rodent damage, and vandalism required that all cables be encased in garden hose, which had to be hidden from view and located away from any game trails to reduce possible damage. A combination of this infrared video camera system and the solar-pow- ered transmitting system of Kristan et al. (1996) would eliminate these cumbersome cables and hos- es. Night vision attenuated rapidly with distance and was clearest when cameras and supplemental lights were <6 m from nest trees. Placing cameras 1-3 m above nests in the same tree would elimi- nate the supplemental light and maximize night recording clarity; however, this would have to be accomplished prior to occupancy to avoid distur- bance or abandonment. Typical of any video sys- tem, direct sunlight and reflection off nearby fo- liage distorted contrast and limited visibility into shaded areas. These factors must be considered and minimized during camera placement. Since our application, circuit-board video cam- eras have become less expensive while capabilities have increased to include color, sound, as well as small, factory-built weatherproof housings. In con- clusion, miniature circuit-board video systems are a reliable, relatively unobtrusive, and effective tool for monitoring behavior of raptors and other wild- life in a wide variety of applications. Based on our experience, this technique can particularly benefit research designed to assess the effects of human activities and land management practices on threatened or endangered species. Acknowledgments This camera system was developed as part of a study funded by the U.S. Air Force, Holloman AFB Legacy Fund. We thank P. Beier and T, Narahashi for assisting in camera development. H. Reiser, L. Pater, R. Baida and D. Patton reviewed the original manuscript. Literature Cited Browder, R.G., R.C. Browder and G.C. Garman. 1995. An inexpensive and automatic multiple-exposure photographic system./. Field Ornithol. 66:37-43. Cain, S.L. 1985. Nesting activity time budgets of Bald Ea- gles in southeast Alaska. M.S. thesis, Univ. Montana, Missoula, MT U.S.A. Cowardin, L.M. and J.E. Ashe. 1965. An automatic cam- era device for measuring waterfowl use. J . Wildl. Man- age. 29:636—640. Danielson, W.R., R.M. Degraff and T.K. Fuller. 1996. An inexpensive compact automatic camera system for wildlife research./. Field Ornithol. 67:414—421. Delaney, D.K., T.G. Grubb, P. Beier, L.L. Pater and M.H. Reiser. 1999a. Effects of helicopter noise on Mexican Spotted Owls./. Wildl. Manage. 63:60-76. , and . 1999b. Activity patterns of nesting Mexican Spotted Owls. Condor 101: in press. Dodge, W.E. and D.P. Snyder. 1960. An automatic cam- era device for recording wildlife activity. / Wildl. Man- age. 24:340-342. Enderson, J.H., S.A. Temple and L.G. Swartz. 1973. Time lapse photographic records of nesting Peregrine Falcons. Living Bird 111:113—128. 296 Delaney ex al. VoL. 32, No. 4 Grubb, T,G. 1983. Bald Eagle activity at an artificial nest structure in Arizona. Raptor Res. 17:114—121. Hernandez, R, D. Rollins and R. Cantu. 1997. An eval- uation of Trailmaster camera systems for identifying ground-nest predators. Wildl. Soc. Bull. 25:848-853. Jones, L.L.C. and M.G. Raphael. 1993. Inexpensive cam- era systems for detecting martens, fishers, and other animals: guidelines for use and standardization. Gen. Tech. Rep. PNW-GTR 306. USDA For. Serv., Pac. Northwest Res. Sta., Portland, OR U.S.A. Kennedy, P.L. and D.W. Stahlecker. 1993. Responsive- ness of nesting Northern Goshawks to taped broad- casts of three conspecific calls./. Raptor Res. 27:74—75. Konishi, M. 1973. How the owl tracks its prey. Am. Sd. 61:414-424. Kristan, D.M., R.T. Golightly, Jr. and S.M. Tomkiewicz, Jr. 1996. A solar-powered transmitting video camera for monitoring raptor nests. Wildl. Soc. Bull. 24:284- 290. Kucera, T.E. and R.H. Barrett. 1993. The Trailmaster camera system for detecting wildlife. Wildl. Soc. Bull. 21:505-508. Major, R.E. 1991. Identification of nest predators by pho- tography, dummy eggs, and adhesive tape. Auk 108. 190-195. Nye, P.E. 1983. A biological and economical review of the hacking process for restoration of Bald Eagles. Pages 127-135 in D.M. Bird, N.R. Seymour, and J.M. Ger- rard [Eds.], Biology and management of Bald Eagles and Ospreys. Harpell Press, Ste. Anne de Bellevue, Quebec, Canada. Olendorff, R.R. 1975. Population status of large raptors in northeastern Colorado, 1970-1972. Raptor Res. Rep 3:185-205. Osterberg, D.M. 1962. Activity of small mammals as re- corded by a photographic device./. Mammal. 43:219- 229. Patton, D.R., V.E. Scott and E.L. Boeker. 1972. Con- struction of an 8-mm time-lapse camera for biological research. Res. Pap. RM-88. USDA For. Serv., Rocky Mtn. For. and Rang. Exper. Sta., Ft. Collins, GO, U.S.A. Proudfoot, G.A. 1996. Miniature video-board camera used to inspect natural and artificial nest cavities. Wildl. Soc. Bull. 24:528-530. Received 6 March 1998; accepted 21 July 1998 /. Raptor Res. 32(4):297-305 © 1998 The Raptor Research Foundation, Inc, PREY OF BREEDING NORTHERN GOSHAWKS IN WASHINGTON James W. Watson, David W. Hays and Sean P. Finn^ Washington Department of Fish and Wildlife, 600 Capitol Way N., Olympia, WA 98501-1091 U.S.A. Paul Meehan-Martin^ Research Experiment Station, 3625 93rd Ave. 5.W, Olympia, WA 98502 U.S.A. Abstract. — ^We identified 936 prey from food remains and pellets collected at 82 Northern Goshawk (Accipiter gentilis) nest sites in Washington from 1986—96. Mammals and birds constituted half of the prey by frequency and biomass throughout Washington, although birds were more prevalent {P = 0.050) in the diet of goshawks nesting in the Olympic and Cascade mountains of western Washington (53%), than in the Cascades of eastern Washington (47%). Douglas’ squirrels {Tamiasciurus douglasii), grouse {Dendragapus obscurus and Bonasa umbellus), and snowshoe hares {Lepus americanus) were jointly the most frequently represented prey on the west side (41%) and east side (54%). Grouse and snowshoe hares accounted for the overwhelming majority of prey biomass in these respective areas (76% and 80%). Relative to other Northern Goshawk populations, goshawks in Washington appeared to prey on species from a similar number of genera, but they had a smaller food-niche breadth and they took larger-sized birds primarily due to their high consumption of grouse. Northern Goshawks in western Washington took prey in more equal numbers than those on the east side. Potential bias from examination of prey remains when compared to pellets reinforced the need for inclusion of observations on prey deliveries at nests when determining the diet of nesting Northern Goshawks. Key Words: Northern Goshawk, Accipiter gentilis; diet, food habits', grouse; hare, Washington. Presas del azor en reproduccion en Washington Resumen. — Identificamos 936 presas de restos de comida y egagropilas recolectadas en 82 nidos de Accipiter gentilis en Washington desde 1986—96. Los mamiferos y las aves constituyeron la mitad de las presas por frecuencia y biomasa en Washington, aunque las aves prevalecieron (P = 0.050) en la dieta de las montanas Olympic y Cascade del oeste de Washington (53%), al contrario de las Cascade del este Washington (47%). Tamiasciurus douglasii, Dendragapus obscurus, Bonasa umbellus y Lepus americanus fueron en conjunto las presas mas represen tadas en el oeste (41%) y este (54%). Dendragapus obscurus y Lepus americanus representaron la mayoria de la biomasa de presas en estas areas respectivas (76% y 80%). Con relacion a otras poblaciones de azores del norte, los azores de Washington aparentemente depredaron a especies de un numero similar de generos, pero tuvieron nichos de alimentacion de menor tamano y una media mayor en el peso de las aves, lo cual es el resultado del alto consume de Dendragrapus obscurus y Bonasa umbellus. Sin embargo, los azores del norte en el oeste de Washington tuvieron un uso mas equitativo de presas que los del este. El sesgo potencial del examen de los restos de presas comparado con las egagropilas refuerza la necesidad de incluir observaciones para la deter- minacion de la dieta de los azores del norte en anidacion. [Traduccion de Cesar Marquez] In the Pacific Northwest, the association of Northern Goshawks {Accipiter gentilis) with mature forests (Bull and Hohmann 1994, Hargis et al. ^ Present address: Raptor Research Center, Department of Biology, Boise State University, 1910 University Drive, Boise, ID 83725 U.S.A. ^ Present address: Snohomish County Public Works, 2930 Wetmore Ave., Suite 101, Everett, WA 98201 U.S.A. 1994, Woodbridge and Detrich 1994) may be re- lated to the structural characteristics of stands that optimize the availability of goshawk prey (Reynolds et al. 1992). Even where preferred prey are abun- dant, structural characteristics of habitat such as tree density and understory may reduce prey avail- ability thereby affecting habitat selection and dis- tribution of nests (Beier and Drennan 1997, De- Stefano and McCloskey 1997). 297 298 Watson et al. VoL. 32, No. 4 In Washington, nesting Northern Goshawks are distributed east and west of the Cascade Moun- tains, where there are different climates, forest communities and potentially different prey species and prey abundance. In western Washington, mar- itime influences at nest sites in the Olympic Moun- tains may further influence prey and diets of nest- ing Northern Goshawks. Diets in this area could be very different from that of goshawks nesting inland in the west Cascade Mountains. In the Coast Range of Oregon, for example, dense understory vegeta- tion and high rainfall are believed to contribute to low populations of nesting goshawks due to their negative effects on prey availability (Reynolds and Wight 1978, DeStefano and McCloskey 1997). There is also the potential for dietary differences in Northern Goshawks nesting in managed stands in national forests and private timberland, where timber harvest may influence prey availability, and in national parks, where there is no timber harvest (Crocker-Bedford 1990). Prey frequency, prey biomass, and food-niche breadth are commonly used to quantify raptor di- ets (Marti 1987). Methods of identifying raptor prey, including direct observation, examination of prey remains, and pellet examination provide data on diet, but each is subject to potential biases (Marti 1987). Here, we examine prey species iden- tified in prey remains and pellets of nesting North- ern Goshawks throughout Washington, with specif- ic objectives to contrast prey frequency, biomass and food-niche breadth for populations of North- ern Goshawks east and west of the Cascade Moun- tain crest; contrast major prey groups among sub- regions of these populations, and in areas potentially subject to timber harvest and those without harvest; identify differences in prey species or food-niche breadth peculiar to Washington Northern Goshawks relative to other areas in North America; and identify biases associated with identification of prey from remains or pellets. Study Area and Methods Prey remains and pellets were collected at 38 Northern Goshawk nest sites in western Washington (16 in the Olympic Mountains, 22 in the Cascade Mountains) from 1986-96, and at 44 nest sites in the Cascades of eastern Washington (17 in the central Cascades, 27 in northern Cascades) from 1992-96 (Fig. 1). Prey and pellets were collected from nests, under nest trees, and at plucking posts. Most remains were collected incidentally during breeding surveys from the nestling stage through post- fledging, and nests were not sampled equally among years (65% sampled 1 yr, 24% sampled 2 yr, and 11% sampled >2 yr). Most nest trees were in late successional forests and were located in national forests {N = 58), national parks (N =11), private timberland (N= 9), and state land {N = 4). In ownerships other than national parks, landscapes surrounding nests and within nesting territories were potentially subject to forest management. The actual degree of timber harvest within these terri- tories was unknown. The climate in western Washington is characterized by mild, wet winters and warm, dry summers. Forests are predominantly Douglas-fir {Pseudotsuga raewzieiM) , western hemlock ( Tsuga heterophylla) , and western redcedar ( Thu- ja plicata) . Sitka spruce {Picea sitchensis) is present at a few lower elevation nest sites on the west side of the Olympic Peninsula. Forests in the Cascades of eastern Washing- ton, a region with cool winters and hot, dry summers, are dominated by stands of Douglas-fir, ponderosa pine {Pi- nus ponderosa) , and western hemlock. For each collection of prey remains, we attempted to identify the minimum number of individuals represented to species level from pooled occurrences in food remains and pellets. Matched hair and feather samples from prey and pellets were considered to represent the same indi- vidual, whereas counts of pooled bones and flight feath- ers allowed for identification of >1 individual. When we found skeletal remains of snowshoe hares (Lepus ameri- canus) and grouse (Dendragapus obscurus and Bonasa um- bellus), we estimated the age of individuals through size comparisons with museum specimens and the degree of bone fusion at joints. Ages of these species were used to estimate their respective contributions to prey biomass. Solid remains (e.g., skeletal remains, beaks) were iden- tified from museum specimens (University of Washing- ton, Seattle, or University of Wisconsin, Madison) or identification keys (Olsen 1964, 1972). Fur and feathers were matched to museum specimens or descriptions in field guides (Peterson 1947, Burt and Grossenheider 1976). Arthropods were excluded from data analyses. Our suspicion was that many insects found in prey re- mains, particularly beetles and ants, were consumed in- directly when small mammals and grouse were eaten. Presence of ants was correlated (r^ = 0.18, P = 0.001) with the occurrence of Douglas’ squirrels (Tamiasciurus douglasii) and chipmunks {Tamias spp.) in prey remains, and stomach contents of three whole carcasses of Doug- las’ squirrels and chipmunks contained numerous beetle shell fragments. Several pellets contained insect frag- ments mixed with fir needles, seeds, and grouse remains. We reported mammalian and avian prey by frequency and biomass. Biomass estimates were derived from aver- age weights of species from Reynolds and Meslow (1984) and other published sources (Table 1). Weights were de- rived for juvenile and adult age classes of snowshoe hares and grouse. For prey for which we could estimate bio- mass (i.e., not including unidentified birds or mammals), we calculated the mean weight of avian prey (MWAP), mean weight of mammalian prey (MWMP) and mean weight of total prey (MWTP). Food-niche breadth was calculated for prey genera using the following equation (Levins 1968); 1 December 1998 Goshawk Prey in Washington 299 Whstcom Snohomish | SEAUU Wahkiokum Cowtiti Klickitat Okanogan / _ Clallam \ Jemson cP ° ^ o ° O • - Harbor\^ Kittitas Thurston — Lems Pacific : Yakima SYMBOLS Wect of CMcade Mountain Drvide Eact of Caacada Mountain Ovtde Figure 1. Locations of Northern Goshawk nest sites in Washington State where prey were collected from 1986-96. where F- was the proportion of prey in each taxon. In order to compare food-niche breadth with other north- ern goshawk research, breadth was standardized (Reyn- olds and Meslow 1984) using; B,= {B- l)/(n- 1) where n = the total number of taxons. Values approach- ing 1 were indicative of relatively more equitable use of prey, with lower values indicative of narrower diet breadth. We used chi-square contingency tests at the P = 0.05 signiRcance level for frequency comparisons of prey spe- cies and classes by region (east side and west side, and four study areas) and collection type (prey remains or pellet), ages of major prey species (adult or juvenile) by region, and mcyor prey species by forest management sta- tus (managed or unmanaged). Unidentihed mammalian and avian prey were excluded from analyses involving prey species, and prey with combined frequencies ^1 were pooled into a miscellaneous species category. Results We identified 936 prey at 82 Northern Goshawk nest sites. West side prey collections {N = 38 sites) accounted for 57% of identified prey, and east side collections (AT = 44 sites) accounted for 43% of prey. An average of 11,0 (SD = 10.5, range = 1- 53) individual prey items were identified per nest site. Prey remains were not identified beyond class for 11% of 465 mammalian remains and 17% of 471 avian remains. These remains typically consist- 300 Watson et al. VoL. 32, No. 4 Table 1. Northern Goshawk prey assessed from prey remains and pellets at 44 nest sites in the Olympic and Cascade mountains of western Washington, and at 38 nest sites in the Cascade mountains of eastern Washington from 1986-96. Western Eastern Washington Washington Weight % Bio- % Bio- Species Common Name (g)" No. MASS" No. %»> MASS" Mammals Tamiasciurus douglasii Douglas’ squirrel 201.2 80 15.1 9.6 78 19.2 10.0 Lepus americanus snowshoe hare d 47 8.9 32.6 57 14.1 40.6 Tamias spp. Unidentified chipmunk 80.5 31 5.8 1.5 26 6.4 1.3 Unidentified mammal n/ a 27 5.1 n/ a 19 4.7 n/ a Glaucomys sabrinus northern flying squirrel 167.0 28 5.3 2.8 12 3.0 1.3 Clethrionomys gapperi red-backed vole 27.0^ 7 1.3 0.1 9 2.2 0.2 Unidentified vole 25.0 13 2.5 0.2 1 0.3 <0.1 Peromyscus spp. Unidentified mouse 19.5f 6 1.1 <0.1 6 1.5 <0.1 Thomomys mamma Mazama pocket gopher 103.0^^ 5 0.9 0.3 0 0.0 0.0 Unidentified small mammal n/a 2 0.4 n/a 3 0.7 n/ a Scapanus townsendii Townsend’s mole 140.0" 1 0.2 <0.1 1 0.3 <0.1 Thomomys talpoides northern pocket gopher 104.0" 0 0.0 0.0 2 0.5 0.1 Ochotona princeps pika 146.5" 1 0.2 <0.1 0 0.0 0.0 Sorex cinereus masked shrew 4.5" 1 0.2 <0.1 0 0.0 0.0 Neotoma cinerea bushytail woodrat 396.0" 0 0.0 0.0 1 0.3 0.3 Maries americana marten g 0 0.0 n/a 1 0.3 n/a Subtotal 249 47.0 47.1 216 53.5 53.8 Birds Unidentified grouse h 73 13.8 35.1 74 18.3 35.8 Unidentified bird n/a 49 9.2 n/a 32 7.9 n/a Cyanocitta stelleri Steller’s Jay 106.6 46 8.7 2.9 16 4.0 1.1 Colaptes auratus Northern Flicker 148.8 26 4.9 2.3 23 5.7 2.2 Ixoreus naevius Varied Thrush 79.3 25 4.7 1.2 4 1.0 0.2 Turdus migratorius American Robin 81.2 18 3.4 0.9 1 0.3 <0.1 Dendragapus obscurus Blue grouse i 11 2.1 7.1 5 1.2 2.7 Picoides villosus Hairy Woodpecker 48.3 3 0.6 <0.1 8 2.0 0.2 Unidentified woodpecker 165.2J 7 1.3 0.7 3 0.7 0.3 Perisoreus canadensis Gray Jay 89.4*^ 9 1.7 0.5 0 0.0 0.0 Unidentified passerine 168.7* 3 0.6 0.3 6 1.5 0.6 Bonasa umbellus Ruffed Grouse 550.0“ 3 0.6 1.0 3 0.7 1.1 Varied Thrush or American 80.0 1 0.2 <0.1 3 0.7 0.2 Robin Spinus pinus Pine Siskin 13.0 1 0.2 <0.1 3 0.7 <0.1 Corvus spp. Northwestern or American Crow 460.0f 2 0.4 0.6 1 0.3 0.3 Unidentified owl 259.0" 0 0.0 0.0 3 0.7 0.5 Bombycilla cedrorum Cedar Waxwing 33.5 1 0.2 <0.1 1 0.3 <0.1 Glaucidium gnoma Northern Pygmy Owl 42.8° 1 0.2 <0.1 0 0.0 0.0 Junco hyemalis Dark-eyed Junco 17.6 1 0.2 <0.1 0 0.0 0.0 Loxia leucoptera White-winged Crossbill 24.1P 1 0.2 <0.1 0 0.0 0.0 Sturnus vulgaris European Starling 74.5 1 0.2 <0.1 0 0.0 0.0 Dryocopus pileatus Pileated Woodpecker 282.0 0 0.0 0.0 1 0.3 0.2 Sphyrapicus varius Red-breasted Sapsucker 48.3^ 0 0.0 0.0 1 0.3 <0.1 Anas platyrhynchos Mallard 1185.0f 0 0.0 0.0 1 0.3 0.8 Subtotal 282 53.4 52.6 189 46.9 46.2 December 1998 Goshawk Prey in Washington 301 ed of hair samples and feather shafts, but no skel- etal remains. At least 13 species of mammals and 18 species of birds were identified in prey remains (Table 1 ) , Douglas’ squirrels, grouse (unidentified grouse, Blue Grouse [Dendragapus obscurus] and Ruffed Grouse [Bonasa umbellus]), and snowshoe hares were the most common prey species, and together accounted for 54% of all prey in eastern Washing- ton and 41% in western Washington. They were also the most widely distributed prey, with Douglas’ squirrels identified at 69% of the 82 nest sites state- wide, grouse identified at 57% of nest sites, and snowshoe hares identified at 61% of all nest sites. Other species that accounted for >3% of prey by frequency in both eastern and western Washington included chipmunks {Tamias spp.), northern flying squirrels (Glaucomys sabrinus), Steller’s Jays {Cyan- ocitta stellen) and Northern Flickers {Colaptes aura- tus). Passerines accounted for 28% of west side prey and 18% of east side prey. Mammals and birds composed equal propor- tions (50%) of goshawk prey throughout Washing- ton by frequency. However, proportions of mam- mals and birds in prey remains differed between western and eastern Washington (x^ = 3.81, df = 1, P = 0.050). Birds were more prevalent than mammals in prey remains of west side goshawks (53% vs. 47%), while mammals more prevalent than birds on the east side (53% vs. 47%). Relative to other birds, proportions of grouse, Steller’s Jays, Varied Thrush (Ixoreus naevius), American Robins {Tardus migratorius) , and Gray Jays (Perisoreus cana- densis) were greater in west side than east side avian remains (x^ = 38.89, df = 5, P = 0.001). Converse- ly, relative to other mammals combined, propor- tions of Douglas’ squirrels and snowshoe hares in east side remains were greater than in western Washington (x^ — 6.96, df = 2, P = 0.031). Mammals and birds accounted for similar pro- portions of prey biomass throughout Washington (51% and 49%, respectively). While Douglas’ squir- rels were the most prevalent species in prey re- mains, they accounted for only 10% of prey bio- mass on both east and west sides (Table 1). Snowshoe hares and combined grouse species were the most important to overall biomass. These tax- ons accounted for 80% of all prey biomass in east- ern Washington, and 76% of all biomass in western Washington. Adult specimens accounted for much of the biomass; adult snowshoe hares composed 87% of 67 hares that were aged, and adult grouse composed 75% of 113 grouse remains that were aged. There was no difference in age of captured snowshoe hares (P = 0.458) or grouse (P = 0.410) between eastern and western Washington. Other prey species contributed <3% of overall biomass throughout Washington (Table 1 ) . Mean weight of mammalian (N = 399), avian (N = 390) and total prey was 411, 415, and 413 g, <- ® Weight of individual prey item used in biomass estimation. From Reynolds and Meslow (1984) unless noted otherwise. ^ Percent of prey in overall diet. Percent of prey biomass to overall biomass. Weight of juvenile (150 g) and adult L. americanus (1500 g) from Forsman et al. (1984); mean weight of adult and juvenile used to estimate weight of unaged specimens. Remains included 27 adults, 3 juveniles and 16 unaged specimens. Burt and Grossenheider (1976). ^Steenhof (1983). g Mass for this prey not used in estimate of biomass due to the inherent bias; guard hairs found in pellets likely from a scavenged carcass. ^Average weight of adult (1053 g) and juvenile (909 g) D. obscurus (Zwickel et al. 1966) and adult (575 g) and juvenile (550 g) B. umbellus (Bump et al. 1947); mean weight of adults and juveniles used to estimate weight of unaged specimens. Remains included 37 adults, 9 juveniles and 30 unaged specimens. ‘ Average weight of adult and juvenile D. obscurus (Zwickel et al. 1966) ; mean weight of adult and juvenile used to estimate weight of unaged specimens. Remains included 4 adults, 1 juvenile and 7 unaged specimens, j Average weight of P. villosus and D. pileatus. ‘‘Average weight of unidentified jay from Reynolds and Meslow (1984). ‘ Average weight of passerines identified to species. ™ Average weight of juvenile B. umbellus (Bump et al. 1947). Remains were of 1 juvenile. " Used weight of medium-sized owl {Asio otus) from Karalus and Eckert (1974). ° Karalus and Eckert (1974). P Average weight of White-crowned Sparrow ( Zonotrichia leucophrys) from Reynolds and Meslow ( 1984) . ‘1 Used weight of P. villosus from Reynolds and Meslow (1984). 302 Watson et al. VoL. 32, No. 4 respectively. The standardized food-niche breadth (FNB) was 0.27, based on frequencies of prey among 20 genera. However, goshawks in western Washington had a more equitable use of prey (FNB = 0.44, 18 genera) than those in eastern Washington (FNB = 0.31, 16 genera). Proportions of mammals and birds in the diet were different (x^ = 17.67, df = 3, P = 0.001) among prey of goshawks nesting in the Olympic Range, western Cascade Range, the central/ south- ern east Cascades, and northern Cascades in east- ern Washington (N= 16, 22, 27, and 17 territories, respectively). Goshawks in the central and south- ern Cascades of eastern Washington ate the high- est proportion of mammals (57%), with fewer mammals eaten in the Olympic Range (54%), northern Cascades in eastern Washington (44%), and west Cascade Range (41%). Proportions of Douglas’ squirrels in prey remains differed (x^ = 14.79, df = 3, P = 0.002) among goshawks in the central and southern region of the east Cascades (22%), Olympic Range (20%), northern Cascades in eastern Washington (15%), and west Cascades (11%). Proportions of snowshoe hares also dif- fered (x^ = 11.73, df = 3, P = 0.008) in the central and southern region of the east Cascades (16%), Olympic Range (10%), northern Cascades in east- ern Washihgton (10%), and west Cascades (7%). Proportions of grouse were different (x^ = 22.43, df = 3, P = 0.001) in the northern Cascades in eastern Washington (32%), west Cascades (20%), central and southern region of the east Cascades (17%), and Olympic Range (12%). We found no difference (P = 0.853) among fre- quencies of Douglas’ squirrels, snowshoe hares and grouse relative to each other on land ownerships with potential timber harvest (i.e., national forest, state, and private land) and without harvest (i.e., national park). We collected pellets 17% less often (x^ = 5.34, df = 1, P = 0.021) when sampling nests on the west side {N = 47 visits) compared to the east side (N = 76 visits). We suspected that some skeletal remains on the west side were misclassified as com- ing from prey remains rather than pellets due to the rapid breakdown of pellets in the moist cli- mate. Twenty-eight percent more birds than mam- mals were identified in prey remains when com- pared to pellets (x^ = 81.59, df = 1, P = 0.001). Remains of snowshoe hares were 24% more prev- alent among prey than pellets when compared to all mammals of smaller size (x^ = 19.81, df = 1, P = 0.001). Remains of grouse were 15% more prev- alent among prey than pellets when compared to other birds (x^ = 15.82, df = 1, P = 0.001). Discussion Raptor diets are most accurately described through the combination of observations of prey deliveries at nests and prey collections (Marti 1987). We identified biases associated with the identification of only Northern Goshawk prey re- mains that overemphasized snowshoe hares and grouse, and believe that by including pellets in the analysis a more complete representation of the ac- tual diet results, particularly in regard to the im- portance of small mammals. In western Washing- ton, the predominance of collected prey remains compared to pellets may have partiy accounted for the greater occurrence of avian prey, particularly grouse, on the west side. We were unable to iden- tify biases that may have resulted from a lack of observations at nests. This may have underestimat- ed the consumption of arthropods and reptiles as was found for Accipiters in Oregon (Reynolds and Meslow 1984), and overemphasized avian prey in the diet as determined in several studies (Ziesemer 1981, Reynolds and Meslow 1984, Boal and Man- nan 1994). We concluded that most arthropods were eaten by goshawks incidental to the consump- tion of other prey. Although we identified no rep- tiles as prey, reptiles, notably garter snakes {Tham- nophis spp.) , were common in all forests we studied throughout Washington (K. McCallister pers. coram.). Other studies have not identified these same biases from prey sampling methodologies. For example, prey and pellet analysis of nesting Northern Goshawks in northeast Spain over-rep- resented Leporids, and under-represented thrushes and small birds (Manosa 1994). The rank of prey taxons assessed from prey remains, pellets and ob- servations did not differ for breeding goshawks in New Mexico (Kennedy 1991). These differences reemphasize the importance of observations of prey deliveries for determining diets of specific populations of nesting goshawks. Variation in the seasonal and annual timing of prey collections among nest sites introduced other potential biases in diet assessment. Seasonal changes in diet composition of Northern Gos- hawks may include a shift to fledgling passerines and increased diet diversity as nesting progresses (Squires and Reynolds 1997). Thus, prey constitu- tion may change from the nestling to fledgling pe- December 1998 Goshawk Prey in Washington 303 riods of the nesting phenology. Our geographical comparisons of Northern Goshawk prey in Wash- ington were based on irregular prey collections over the 10-yr period and at different times of the nesting period; westside prey were collected throughout the entire 10-yr period, whereas east- side prey were collected over a 5-yr period. These collections were a composite of several studies, and each nest site was not sampled equally. It was not known how, or if, cyclic changes of major prey spe- cies throughout the state may have biased our an- alyses because we did not monitor their spatial or temporal variability. In the northern boreal forest, snowshoe hare and Ruffed Grouse undergo re- gion-wide cyclic population fluctuations approxi- mately every 10 yr (Keith and Rusch 1986, Doyle and Smith 1994, Hik 1994). Populations of other potential prey, particularly Douglas’ squirrels, may also be subject to periodic cycles depending on the annual production of cones by conifer forests (Buchanan et al. 1990). However, Douglas’ squir- rels accounted for little biomass relative to other frequently eaten prey of goshawks in Washington suggesting a lesser importance of this species in the diet overall. Reduced hare numbers in southwest Yukon resulted in dietary shifts to smaller mam- malian prey and increased avian consumption (Doyle and Smith 1994). A sudden decline in Eu- ropean hare ( Oryctolagus cuniculus) in northeastern Spain resulted in a reduction in rabbit consump- tion by nesting goshawks and increased predation on Red-legged Partridge {Alectoris rufa) (Mahosa 1994) . Consequently, if cyclic population phenom- ena are similar for hare and grouse in Washington, our regional comparison of prey could, at best, be interpreted to reflect actual differences in state- wide prey selection; or, at worst, to be merely the identification of prey species eaten by breeding goshawks in eastern and western Washington. The same prey species eaten by goshawks in east- ern and western Washington accounted for the greatest biomass and frequency of prey in these areas (i.e., snowshoe hares, grouse, and to a lesser degree, Douglas’ squirrels, chipmunks, Steller’s Jays, and Northern Flickers). These same species have been found to be important prey throughout the goshawk’s North American range (Reynolds et al. 1992, Squires and Reynolds 1997). Compared to goshawk diets in other Pacific Coast states, the most pronounced latitudinal differences appear to be the prominence of grouse in diets of Northern Goshawks in Washington relative to southern pop- ulations in California (Bloom et al. 1986, Wood- bridge et al. 1988) and a greater consumption of snowshoe hares relative to northern populations in southeast Alaska where hares are evidently uncom- mon (Titus et al. 1994). In California, primary prey species were Douglas’ squirrels, Steller’s Jays, and Northern Flickers; lagomorphs and sciurids com- prise 66% of the total biomass (Bloom et al. 1986). In the southern Cascades of northern California, Steller’s Jays and four species of woodpeckers are the principal birds taken and sciurids account for over half of the total biomass (Woodbridge et al. 1988). In Washington, we found grouse accounted for 42% of total biomass and lagomorphs and sciurids composed an additional 46% of total bio- mass. Even assuming unidentified grouse were the smallest juvenile grouse and unaged hares were all smaller juveniles, these taxons still accounted for 42% and 44% of total biomass, respectively. In southeast Alaska, goshawks eat high numbers of Blue Grouse which were identified at 73% of 25 nest sites, but snowshoe hare were found at only one nest (Titus et al. 1994). Additionally, Steller’s Jays, Varied Thrush, and red squirrels {Tamiasciu- rus hudsonicus) have been found at >47% of the southeast Alaskan territories. Comparatively few small mammals are available as prey, which may limit populations (Titus et al. 1994). Queen Char- lotte Goshawks on Vancouver Island eat species similar to those eaten by goshawks in Washington including Steller’s Jays, Varied Thrush, and North- western Crows {Corvus caurinus) (Beebe 1974). Shorebirds and seabirds are also common prey, but we did not record them as prey in Washington, most likely because no nests in our study were lo- cated near seacoasts. Even though regional and study area prey class proportions in Washington were statistically differ- ent (e.g., regional variation of 46-54%, study area variation of 41-59%), dietary class proportions were more similar to goshawk diets in New Mexico, Arizona and Oregon than to diets in New Jersey and California (Table 2). Goshawks in New Jersey and California eat 10-15% fewer mammals and 10-15% more birds compared to goshawks in Washington. More recent prey collections at gos- hawk nests in three different areas of eastern Oregon found frequencies of mammalian prey var- ied from 38-66% (Bull and Hohmann 1994, De- Stefano et al. 1994). These results indicate that there can be as much variation in proportions of major prey species and classes of prey between 304 Watson et al. VoL. 32, No. 4 Table 2. Comparative food-niche breadths (standardized) and prey class ratios of Northern Goshawks in North America. Diet parameters are based on prey remains and pellets collected at nests unless indicated otherwise. Location Nests Mammal : Bird Ratio Food-Niche Breadth (Number Genera) Source New Jersey 16 30:70 0.26 (22) Bosakowski et al. (1992) Arizona 20 53:47 0.29 (18) Boal and Mannan (1994)^ Eastern Washington 44 53:47 0.31 (16) this study New Mexico 8 49:51 0.36 (22) Kennedy (1991)’’’*^ California 114 32:68 0.41 (21) Bloom et al. (1986)^'^ Western Washington 38 47:53 0.44 (18) this study Oregon 59 45:55 0.45 (30) Reynolds and Meslow (1984)*^ ® Analysis of prey remains. Pellet analysis. Standardized food-niche breadth calculated by Boal and Mannan (1994). Study areas separated by <100 km, as there can be in nests separated by several hundred kilometers. Dietary proportions of mammals and birds are re- flective of the abundance and availability of poten- tial prey species throughout the range of the Northern Goshawk (Reynolds et al. 1992), suggest- ing there was considerable variation in local abun- dance or availability of key prey in Washington. We did not find a relationship in the occurrence of mzyor prey types among managed and unmanaged forests, which we hypothesized might be a factor influencing local prey abundance or availability. Relative to five other breeding populations throughout the U.S., goshawks nesting in eastern Washington had a low food-niche breadth while those in western Washington had a high food- niche breadth. While similar species were eaten, east side goshawks tended to eat large, cyclic prey such as hares and grouse more frequently. The high consumption of grouse throughout the state resulted in a mean avian prey weight (415 g) that was higher than that reported in New Jersey (332 g) and Connecticut (337 g) (Bosakowski et al. 1992), and Oregon (195 g) (Reynolds and Meslow 1984). The mean weight of mammalian prey (411 g) in Washington was more similar to the range of the average mammalian prey in these same studies (423-445 g) . The variety of species we identified as prey suggested that nest occupancy and productiv- ity of goshawks in Washington is not dependent on cyclic fluctuations in the populations of grouse and hare alone, although east side goshawks were more specialized feeders during this study. While the species is an opportunistic feeder (Doyle and Smith 1994), without a variety of prey species to buffer the effects of specialized feeding, goshawk productivity may mirror the changes in cyclic prey populations (Reynolds et al. 1992, Doyle and Smith 1994). Monitoring temporal changes in hare and grouse populations to assess their cyclic tendencies, and simultaneous collection of prey at the same goshawk nest sites over several years, both in eastern and western Washington, would provide an informative contrast as to the importance of cy- clic prey to nest site occupancy and productivity. Acknowledgments J. Begley, J. Fackler, S.P. Finn, C.J. Flatten, XL. Fleming, B. Gaussoin, R.E. Lowell, D. Mueller, M.L. Nixon, andj. Swingle collected prey remains. B. Bicknell, I. Otto, B.L. Cunningham, and C. Fletcher identified prey. We thank L.F. Ruggiero for logistical assistance. C.W. Boal, T. Bo- sakowski, A.B. Carey, E.D. Forsman, S. DeStefano, and R.N. Rosenfield commented on earlier drafts. The proj- ect was supported by the Pacific Northwest Research Sta- tion and Randall Ranger District of the U.S. Forest Ser- vice, in cooperation with the Wildlife Research and Diversity Divisions, Washington Department of Fish and Wildlife. 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Pages 144-151 in R.E. Kenward and I.M, Lindsay [Eds.], Understanding the goshawk. Int. Assoc. Fal- conry Conserv. Birds Prey, Fleury en Biere, France. ZwiCKEL, F.C., J.H. Brighan and I.O. Buss. 1966. Autumn weights of Blue Grouse in northcentral-Washington, 1954-1963. Conrfor 68:488-496. Received 6 March 1998; accepted 24 July 1998 J. Raptor Res. 32(4) :306-311 © 1998 The Raptor Research Foundation, Inc. FOOD HABITS OF THE GREAT HORNED OWL {BUBO VIRGINIANUS) IN A PATAGONIAN STEPPE IN ARGENTINA Ana Trejo and Dora Grigera Centro Regional Universitario Bariloche, Universidad Nacional del Comahue, Unidad Postal Universidad, 8400 Bariloche, Argentina Abstract. — ^We studied seasonal variation in the diet of the Great Horned Owl (Bubo virginianus) through pellet analysis. Pellets were collected every month during 1995—96 from a steppe area in north- west Patagonia, Argentina. We identified 1216 prey items in 522 pellets. Rodents accounted for 98.5% of the diet while the remainder consisted of a variety of birds and insects. Rodents most frequently found in pellets were Eligmodontia morgani, Abrothrix longipilis, A. xanthorhinus, Oligoryzomys longicaudatus, Reithrodon auritus, and Ctenomys haigi. In terms of biomass, the most important species were R. auritus, A. longipilis, C. haigi, and E. morgani. Food-niche breadth was greatest in winter. Within the study area, the Great Horned Owl should be considered to be a rodent specialist all year round. Key Words: Great Horned Owl; Bubo virginianus; diet, rodents; Patagonia. Habitos alimentarios del Bubo virginianus en un area esteparia del noroeste de la Patagonia Argentina Resumen. — Se estudio estacionalmente la dieta de Bubo virginianus mediante el analisis de egagropilas recolectadas mensualmente durante los anos 1995 y 1996, en un area esteparia del noroeste de la Patagonia Argentina. Fueron analizadas 522 egagropilas que contenian 1216 presas. El 98.5% de las presas eran roedores, mientras qe el 1.5% restante eran principalmente aves e insectos. Entre los roe- dores consumidos se encontraron en mayor numero ejemplares de Eligmodontia morgani, Abrothrix lon- gipilis, A. xanthorhinus, Oligoryzomys longicaudatus, Reithrodon auritus y Ctenomys haigi. En terminos de biomasa, las mayores contribuciones corresponden a R. auritus, A. longipilis, C. haigi y E. morgani. La amplitud trofica alcanza el valor maximo en el invierno. En el area estudiada B. virginianus puede considerarse un especialista en roedores durante todo el ano. [Traduccion de Autores] The Great Horned Owl (Bubo virginianus) is dis- tributed widely throughout the Americas and it lives in a variety of different habitats (Burton 1992). Its food habits have been studied at many different sites in North America. In South America, several quantitative studies have been carried out in Chile (Jaksic et al. 1978, Yahez et al. 1978,Jaksic and Yahez 1980, Jaksic and Marti 1984, Jaksic et al. 1986, Iriarte et al. 1990) and Argentina (Don^ar et al. 1997). Marti et al. (1983) reviewed studies of the owl’s diet in North and South America. Most of these studies reported Great Horned Owls main- ly preying on rodents and lagomorphs, although there were regional, seasonal, yearly and long-term differences in diet. Our study analyzed the food habits of the Great Horned Owl in a steppe area in northwest Pata- gonia, Argentina, and described the seasonal changes in diet composition and food-niche breadth over two years (1995-96). Study Area and Methods Our study was conducted in northwest Patagonia, east of the city of Bariloche, Argentina (41°08'-41°08'45"S, 7l°12'-7l°13'20"W). The study site was located in a steppe area of the transition zone between the subant- arctic forests and the Patagonian steppe. The area is dominated by bunchgrasses such as Stipa speciosa and Acaena splendens and scattered bushes (Senedo filaginoides, Baccharis linearis, Colletia hytstrix and the exotic species Rosa ruhiginosa). A road lined by exotic conifers (Pinus spp. and Cupressus spp.) ran through the area. These trees provide roosts for the Great Horned Owl. The small mammal community in the area has been studied by Guthmann (1996) and Guthmann et al. (1997). According to them, the fauna consists of repre- sentatives of forest and steppe species dominated by Elig- modontia morgani, Reithrodon auritus and Abrothrix xanthor- hinus, which are typical of semiarid steppe. A. longipilis 306 December 1998 Great Horned Owl Diet in Argentina 307 inhabits areas of dense forest to bushy steppe, and Oli- goryzomys longicaudatus is abundant in brush areas and the edges of forests (Pearson 1995). Smaller numbers of Lox- odontomys micropus inhabit humid or mesic brushy habi- tats, and Ctenomys haigi inhabits open areas with sandy soils (Pearson 1995). There were so far no records of other nocturnal raptor species within the study site, al- though Barn Owls ( Tyto alba) were probably in the area. Owl roosts were located hy observing areas of white- wash or recording places where pellets were found. Pel- lets were collected monthly from February 1995-Novem- ber 1996 at six known roost sites. Pellets were air dried and their length and width was measured with an elec- tronic caliper to the nearest 0.01 mm. The pellets were dissected using standard techniques (Yalden 1990). Var- iations in measurements were related to the number of prey contained in the pellets by means of a one-way AN- OVA. Prey biomass was calculated only for rodents. Mass estimates for each prey taxon were either determined from individuals captured in the study area or taken from literature. Prey were identified to the finest possible taxonomic level. Mammalian prey were identified and quantified on the basis of skulls and dentary pairs using reference col- lections and keys (Pearson 1995). Insects were quantified by counting head capsules and mandibles. For other prey items, reference collections were used and they were quantified by assuming minimum number of individuals (e.g., feathers or scales of a given species were deemed to represent only one individual) . Diet composition was compared between seasons and years with chi-square and G tests. The contribution of each rodent species to the biomass of the owls’ diet was calculated by multiplying mean body mass of individuals by number of individuals in the pel- lets. Values were expressed as a percentage of total ro- dent biomass consumed. Food-niche breadth (FNB) was estimated using Levins’ (1968) index; FNB = 1/ (S pi^), where pi is the propor- tion of prey taxon / in the diet. A standardized-niche breadth value (FNBst) was calculated, which ranged from 0 to 1; FNBst ~ (FNB — l)/(n — 1), where n is the total number of prey categories (Colwell and Futuyma 1971). Evenness of prey numbers was measured using the Shan- non-Wiener function J' (Krebs 1989): J' = H'/log n, where H' is the Shannon-Wiener formula and n is the total number of prey categories. Results A total of 1216 prey items was identified from 522 pellets. The mean number of prey/pellet was 2.3 (SD = 1.1; range = 1-7). Pellet measurements ranged from 2. 3-8. 8 cm long (x = 4.5; SD = 1.1; N = 516) and from 1.4- 4.3 cm wide (x = 2.7; SD = 0.4; N = 516). Significant differences (P< 0.05) were found for both length (F = 17.365, df = 4,507) and width (F = 20.365, df = 4,506) and they appeared to be related to the number of prey in each pellet. Rodents accounted for 98.5% of the prey (Table 1). The remaining 1.5% consisted of birds, insects, one lizard, and one lagomorph (a young Lepus about 0-6 months old according to cranial sutures described by Gonzalez [1993]). We found one in- dividual each of the following birds in the diet: Tachycineta leucopyga, Troglodytes aedon, Sicalis luteola, Zonotrichia capensis, Anthus sp., and one unidenti- fied Furnariidae. Insects that could be identified were Coleopterans (one of them Scarabaeidae) and Lepidopterans. Great Horned Owls preyed mainly on Eligmodon- tia morgani over both years of the study, followed by Abrotkrix longipilis, A. xanthorhinus, Oligoryzomys longicaudatus, Reithrodon auritus, Ctenomys haigi, and Loxodontomys micropus. The number of rodents con- sumed varied seasonally and was lower during win- ter. There were significant differences between the number of prey of different species eaten in 1995 and 1996 (x^ = 14, df = 6, P < 0.05) . The greatest difference between the two years was the lower than expected consumption of L. micropus and O. longicaudatus in 1996. There were no significant differences in the number of different species con- sumed between winters (x^ == 10,01, df = 6, P < 0.05), but consumption of prey did differ signifi- cantly between summers (x^ = 35.93, df = 6, P < 0.05), autumns (G = 29.64, df = 6, P < 0.05) and springs (x^ = 33.74, df = 6, P < 0.05). The mean weight of rodent prey ranged from 15.3 g for A. xanthorhinus to 146.2 g for C. haigi (Table 2). R. auritus, C. haigi and E. morgani con- tributed most to the prey biomass and all three were consumed in a greater proportion in 1996 than in 1995. In the pellets collected during 1995, the proportion of R. auritus in the diet fell consid- erably in spring, while that of A. longipilis and C. haigi rose. Food-niche breadth was greatest in winter and smallest in spring during both 1995 and 1996. Al- though the number of prey types was highest in spring, evenness was lower than in winter (Table 1). The standardized-niche breadth calculated for the two years (FNBgt = 0.202) was slightly lower than for breeding seasons (spring and summer) for both years (FNE^t = 0.218, N = 4). Discussion Because of their small size. Great Horned Owls that occur in southern South America have been placed in their own subspecies {B. v. magellanicus, Traylor 1958) and it has even been suggested that they in fact belong to their own species {Bubo ma- 308 Trejo and Grigera VoL. 32, No. 4 Table 1. Seasonal diet of Great Horned Owls in northwestern Patagonia, Argentina. N = number of prey in each taxon; % calculated over the total number of prey for each. 1995 Summer Autumn Winter Spring Prey Type N % N % N % N % MAMMALS Rodents Muridae Abrothrix longipilis 7 5.8 10 11.1 40 14.5 97 35.9 Abrothrix xanthorhinus 7 5.8 1 1.1 32 11.6 12 4.4 Eligodontia morgani 39 32.5 19 21.1 70 25.5 58 21.5 Loxodontomys micropus 2 1.7 10 11.1 12 4.4 10 3.7 Chelemys macronyx — — — — — — 1 0.4 Reithrodon auritus 25 20.8 24 26.7 60 21.8 9 3.3 Oligoryzomys 27 22.5 18 20.0 25 9.1 43 15.9 Geoxus valdivianus — — — — — — — — Irenomys tarsalis — — — — — — — — Unidentified Ctenomyidae 7 5.8 5 5.6 30 10.9 21 7.8 Ctenomys haigi 3 2.5 4 4.4 6 2.2 15 5.6 Lagomorphs Lepus europaeus — — — — — — — 0.0 BIRDS Passeriformes 1 0.8 — — — — 2 0.8 REPTILES Liolaemus sp. — — — — — — — — INSECTS 2 1.7 — — — — 2 0.7 SPIDERS Total prey Total pellets FNBst J' 120 42 0.446 0.773 90 37 0.667 0.880 275 130 0.672 0.892 270 114 0.308 0.700 FNBst = food-niche breadth measured with standardized Levins’ index (see text for explanations). J' = preys number evenness by Shannon-Wiener function. gellanicus, Konig et al. 1996). Owing to their small size, the average length and width of their pellets are among the smallest reported for Great Horned Owls. Yahez et al. (1978) studied Great Horned Owl pellets from two regions in Chile, and found that those that contained remains of rodents were significantly wider than those containing arthro- pods. We could not verify this relationship in our study because the pellets contained almost exclu- sively rodents. Nevertheless, we did find that, in terms of the number of prey contained in pellets, there was less variation in pellet width than length. This could have been related to the fact that the gape of the owls limited the size of the pellets they regurgitated. The low correlation between biomass and size of pellets could be a consequence of es- timating biomass as average prey weight, without considering that the predator might select the size of its prey. Studies in Chile (Yanez et al. 1978, Jaksic et al. 1986, Iriarte et al. 1990) have found that, in some seasons, Great Horned Owls eat birds, insects, arachnids, and lagomorphs (up to 17% in Torres del Paine National Park [Iriarte et al. 1990]). In our study, these prey made up a negligible part of the diet. Near Junin de los Andes, Argentina, Don- December 1998 Great Horned Owl Diet in Argentina 309 Table 1. Extended. 1996 Summer Autumn Winter Spring Total N % N % N % N % N % 49 25.0 12 14.5 11 15.7 31 27.4 257 49.2 25 12.8 3 3.6 11 15.7 7 6.2 98 18.8 59 30.1 31 37.2 16 22.9 23 20.4 315 60.3 3 1.5 — — — — 4 3.5 41 7.9 — — — — — — — — 1 0.2 19 9.7 6 7.2 10 14.3 21 18.6 174 33.3 17 8.7 9 10.8 7 10.0 7 6.2 153 29.3 — — 1 1.2 — — — — 1 0.2 — — — — — — 1 0.9 1 0.2 12 6.1 16 19.3 8 11.4 10 8.8 109 20.9 6 3.1 5 6.0 5 7.1 3 2.7 47 9.0 — — — — 1 1.4 — — 1 0.2 2 1 — — 1 1.4 — — 6 1.2 — — — — — — 1 0.9 1 0.2 2 1.0 — — — — 4 3.6 10 2.0 96 73 0.394 0.746 83 33 0.429 0.794 70 39 0.672 0.885 1 113 54 0.376 0.764 0.9 1 1216 522 0.202 0.597 0.2 azar et al. (1997) found the diet of Great Horned Owls consisted of 11.9% Lepus europaeus and 27.3% arthropods but, in terms of biomass, the two main prey items (55.2% of total prey) were juveniles of introduced lagomorphs (L. europaeus and Oryctola- gus cuniculus). Lagomorphs are considered to be the best prey for horned owls because their large body mass best suits the daily energy requirements of owls (Don- azar et al. 1989). In our study, the number of lago- morphs in the diet was remarkably low despite the apparent abundance of L. europaeus in the area (7- 12 individuals/ha, Novaro et al. 1992). According to Jaksic (1986), this situation is common for small mammal predation in shrublands and grasslands of southern South America, with predators hunt- ing mainly the most abundant native rodents, sometimes “ignoring” dense populations of intro- duced lagomorphs. The proportion of lagomorphs we found in the diet did not support the generalization by Donazar et al. (1997) that lagomorphs represent 15% by number of the diet of Great Horned Owls in Ar- gentine Patagonia. However, our results reinforce their explanation for the low frequency of lago- morphs in the diet of Patagonian Great Horned Owls as compared to horned owls at similar lati- tudes in the northern hemisphere, where they 310 Trejo and Grigera VoL. 32, No. 4 Table 2. Biomass of rodents in Great Horned Owl diets in Argentina expressed as a percent of the total biomass of rodents consumed in each season. Mean prey weights were obtained from Pearson (1983) for C. macronyx, G. valdi- vianus and /. tarsalis] from Pearson (pers. comm.) for C. haigi, and from Trejo (unpubl. data) for the remaining species. Prey ABL ABX ELI LOX CHE REI OLI GEO IRE CTE 1995 Summer 5.2 2.8 17.1 3.0 — 42.2 18.1 — — 11.6 Autumn 7.5 0.4 8.4 15.0 — 40.9 12.2 — — 15.6 Winter 12.8 5.6 13.2 7.7 — 43.5 7.2 — — 10.0 Spring 32.6 2.2 11.5 6.7 0.8 6.9 13.1 — — 26.2 1996 Summer 25.4 7.0 18.0 3.1 — 22.3 8.0 — — 16.2 Autumn 14.9 2.0 22.7 — — 16.9 10.1 1.2 — 32.2 Winter 13.5 7.3 11.6 — — 27.9 7.8 — — 31.9 Spring 24.3 3.0 10.7 6.3 — 37.4 5.0 — 1.2 12.2 TOTAL % 18.9 3.9 13.7 6.0 0.2 29.0 10.2 0.1 0.1 18.0 Prey mean 28.1 15.3 16.6 56.2 66.8 63.8 25.4 27.8 41.3 146.2 ABL, Abrothrix hngipilis\ ABX, Abrothrix xanthorhinus; ELI, Eligmodontia morgani; LOX, Loxodontomys micropusr, CHE, Chelemys macronyx; REI, Reithrodon auritus; OLI, Oligoryzomys longicaudatus-, GEO, Geoxus valdivianus, IRE, Irenomys tarsalis; CTE, Ctenomys haigi. weigh on average 30—40% more. Don^ar et al. (1997) suggested that the large size of adult lago- morphs could constrain Patagonian horned owls from preying on them, while large rodents and young lagomorphs may be more easily handled. E. morgani, the mouse consumed most frequently numerically and whose biomass had least seasonal variation, would not seem to be a profitable prey due to its low weight (20 g). The energetic cost of capturing and handling these mice may exceed the actual gains (Jaksic and Marti 1984). Nevertheless, E. morgani was abundant in the area (Guthmann 1996) and vulnerable, the two conditions that Jak- sic and Marti (1984) consider appropriate for such small prey to be included in the diet of Bubo owls. It is easy to catch because it inhabits sites with little plant cover or bare ground and it runs in the open for prolonged periods (Trejo pers. obs.). The prey that supplied the greatest biomass in our study was Reithrodon spp. According to Pearson (1988), its nocturnality, long hours of feeding, open habitat, and unwary behavior seem to expose it to preda- tion by owls and other nocturnal predators. Cteno- mys haigi, the largest rodent in the area, was eaten in low numbers likely due to its fossorial habits. O. longicaudatus and L. micropus, which inhabit areas covered by bushy vegetation, are scansorial (Pear- son 1983, 1995), which could facilitate their detec- tion and capture by owls. Although only one specimen each of Irenomys tar- salis, Chelemys macronyx and Geoxus valdivianus were found in the pellets, their occurrence was note- worthy because none of them were captured dur- ing the three years over which Guthmann (1996) systematically trapped rodents at the same site where we collected pellets. All three species are typical of the forest and environments with high plant coverage (Pearson 1983, 1995). Their occur- rence in the diet indicated that they may have been present in the area in low numbers, or perhaps the fossorial habits of G. valdivianus and C. macronyx made them difficult to capture. There was seasonal variation in food-niche breadth. Both the overall food-niche and breeding season (spring and summer) food-niche breadths were similar to those calculated by Donazar et al. (1997) in their study in Junin de los Andes. They estimated a standardized food-niche breadth of 0.20 for the breeding season. Jaksic et al. (1986) found that the horned owl diet breadth in Chile declined from north to south based on standard- ized food-niche breadth measurements obtained for three Chilean locations at different latitudes: La Dehesa, 33°2LS (FNBgj = 0.66), Puerto Ibanez, 46°18'S (FNB,t = 0.62) and Torres del Paine, 51°S (FNBst = 0.24). However, the FNB^t = 0.20 ob- tained both for Junin de los Andes (39°30'- 40°20'S, 70°30'-7l°30'W, Donazar et al. 1997) and for Bariloche (41°08'S, present study) does not fit within the latitudinal trends proposed for Chile. December 1998 Great Horned Owl Diet in Argentina 311 The FNBst = 0.60 obtained by Iriarte et al. (1990) for Torres del Paine is also at odds with the pro- posed latitudinal trend. Considering the seasonal fluctuations in the composition of the diet, com- parisons between different locations should prob- ably be done using data from the same time of year. In our study, the five species most consumed by horned owls had minimum population levels in winter, while in other seasons they reached peak numbers (Guthmann et al. 1997). This would ex- plain the increase of the food-niche breadth in winter caused by the greater evenness, since the availability of all prey species. Acknowledgments We are grateful to J. Noriega for the identification of birds in the pellets and to L. De Santis, M. Run, F. Cres- po, H. Planas, N. Ibarguengoytia, D. Anon Suarez, and J. Puntieri for their help at different stages of this study. We would also like to thank the referees who revised the orig- inal manuscript for their valuable contributions and sug- gestions. Literature Cited Burton, J.A. [Ed.]. 1992. Owls of the world. Peter Lowe, Eurobook, Italy. Colwell, R.K. and D.J. Futuyma. 1971. On the measure- ment of niche breadth and overlap. Ecology 52:567- 576. Donazar, J.A., F. Hiraldo, M. Delibes and R.R. Estrel- la. 1989. Comparative food habits of the Eagle Owl Bubo bubo and the Great Horned Owl Bubo vir^nianus in six Palearctic and Nearctic biomes. Ornis Scand. 20: 298-306. , A. Travaini, O. Ceballos, M. Delibes and F. Hir- aldo. 1997. Food habits of the Great Horned Owl in northwestern Argentine Patagonia: the role of intro- duced lagomorphs. / Raptor Res. 31:364-369. GonzAlez, S. 1993. Estudio craneometrico de la liebre {Lepus sp.) introducida en el Uruguay (Lagomorpha: Leporidae). Bol. Soc. Zool. Umgwoy 8:304— 312. Guthmann, N. 1996. Estudio de un ensamble de roe- dores en la estepa ecotonal patagonica. Tesis Doctor- al, Universidad Nacional del Comahue, Centro Re- gional Universitario Bariloche, S. C. de Bariloche, Argentina. , M. Lozada, J. Monjeau and K. Heinemann. 1997. Population dynamics of five sigmodontine rodents of northwestern Patagonia. Acta Theriologica 42:143-152. Iriarte, J.A., W.L. Franklin and W.E. Johnson. 1990. Di- ets of sympatric raptors in Southern Chile. J. Raptor Res. 24:41-46. Jaksic, E 1986. Predation upon small mammals in shrub- lands and grasslands of southern South America: eco- logical correlates and presumable consequences. Rev. Chil. Hist. Nat. 59:209-221. andJ. Yanez. 1980. Differential utilization of prey resources by Great Horned Owls and Barn Owls in Central Chile. Auk 97:895-896. and C.D. Marti. 1984. Comparative food habits of Bubo owls in Mediterranean-type ecosystems. Condor 86:288-296. , J.R. Rau and j. Yanez. 1978. Oferta de presas y predacion por Bubo virginianus (Strigidae) en el Parque Nacional “Torres del Paine.” Ans. Inst. Pat 9: 199-202. , J.L. YAnez and J.R. Rau. 1986. Prey and trophic ecology of Great Horned Owls in western South America: an indication of latitudinal trends. Raptor Res. 20:113-116. Konig, C., P. Heidrich and M. Wink. 1996. Zur Taxon- omic der Uhus (Strigidae: Bubo spp.) im siidlichen Sudamerika. Stuttgarter Beitr. Naturk. Ser. A 540. Krebs, C.J. 1989. Ecological methodology. Harper and Row, New York, NY U.S.A. Levins, R. 1968. Evolution in changing environments, some theoretical explorations. Princeton Univ. Press, Princeton, NJ U.S.A. Marti, C.D., E. KorpimAki and EM. Jaksic. 1983. Trophic structure of raptor communities: a three-continent comparison and synthesis. Pages 47-137 in D.M. Pow- er [Ed.], Current Ornithology. Vol. 1. Plenum Press, New York, NY U.S.A. Novaro, A., A. Capurro, A. Travaini, M. Fines and J Rabinovich. 1992. Pellet-count sampling based on spatial distribution: a case study of the European hare in Patagonia. Ecol. Aust. 2:11-18. Pearson, O.P. 1983. Characteristics of a mammalian fau- na from forests in Patagonia, Southern Argentina. J. Mammal. 64:476-492. . 1988. Biology and feeding dynamics of a South American herbivorous rodent, Reithrodon. Stud. Neo- trop. Eauna Environ. 23:25-39. . 1995. Annotated keys for identifying small mam- mals living in or near Nahuel Huapi National Park or Lanin National Park, Southern Argentina. Mastozool- ogia Neotrop. 2:99-148. Travlor, M.A. 1958. Variation in South American Great Horned Owls. Auk 75:143-148. Yalden, D.W. 1990. The analysis of owl pellets. Occas Publ. Mammal. Soc. No. 13, London, U.K. YAnez, j., J.R. Rau and F. Jaksic. 1978. Estudio compar- ativo de la alimentacion de Bubo virginianus (Strigi- dae) en dos regiones de Chile. An. Mus. Hist. Nat. IT 97-104. Received 21 November 1997; accepted 27 July 1998 Short Communications /. Raptor Res. 32(4):312-314 © 1998 The Raptor Research Foundation, Inc. Habitat Use of Crowned Eagles (Harpyhauaetus coronatus) in the Southern Limits OF THE Species’ Range M. Isabel Bellocq, Stella M. Bonaventura, Favio N, Marcelino and Maria Sabatini Departamento de Ciencias Biold^cas, FCEN-Universidad de Buenos Aires, Ciudad Universitaria Pab. 2 Piso 4, Buenos Aires 1428, Argentina Key Words: Crowned Eagle, Harpyhaliaetus coronatus; habitat use, Argentina. The breeding range of the Crowned Eagle {Harpyhal- laetus coronatus) is limited to semi-open woodlands in low- lands and moderate altitude mountain ranges of Argen- tina, Bolivia, Brazil, Paraguay, and Uruguay). It is a large-sized, open country raptor that eats a variety of ver- tebrate prey species. There are over 112 sight records for the species, most of them from Argentina over the past 50 years, including relatively recent encounters in Lihue Calel (province of La Pampa) in the southern limit of the species’ range (Collar et al. 1992, De Lucca 1992 and 1993). Based on this, it appears that the Crowned Eagle mainly occurs in the northcentral part of the country, in open woodlands and savannas. Three nests have been described in Argentina. All contained a single egg (Giai 1952, de la Pena 1992). The Crowned Eagle has been protected in Argentina since 1954 and in Brazil it is listed as a Threatened Species (Chebez 1994). Litde is known, however, about its ecology and behavior (Collar et al. 1992, Salvador and Eroles 1994, Gil et al. 1995). Here, we provide new information on the Crowned Eagle’s habitat requirements by describing the habitats it uses for roosting and nesting in the southerrl limits of its range. Materials and Methods Our study was conducted during 1996—97 in an area covering approximately 5000 km^ centered in Lihue Cal- el National Park (37°54'S, 65°39'W), province of La Pam- pa, Argentina. The area is situated at the ecotone be- tween savanna dominated by Prosopis caldenia and shrubland dominated by Larrea spp. Since the 19th cen- tury, the natural landscape has been gradually modified by tifforestation followed by extensive ranching. Current- ly, natural woodlands occur primarily in depressions and ravines, and shrublands with isolated P. caldenia or small woodlots characterize the landscape. Fire is a common natural disturbance and it is often prescribed to improve grass productivity. The clime is semiarid; mean temper- ature of the warmest and coolest months is 25°C and 9°C, respectively, and the mean annual precipitation is 414 mm. Because we expected the Crowned Eagle to be difficult to see, we conducted both road surveys and interviews with local farmers to locate eagle roosting areas. Addi- tionally, staff at the Lihue Calel National Park was in- structed to look for and report any encounter with Crowned Eagles. Road surveys were conducted along six 50-km transects, completing one observation stop of 5 min every 0.8 km (Fuller and Mosher 1987). Surveys were performed by the same observers, during 18-24 No- vember 1996 from 600-1300 H. A total of 20 farmers were interviewed. We asked them whether they had seen Crowned Eagles. If the answer was yes, we asked for a description of the animal. If the description fit a Crowned Eagle, we proceeded to fill out a questionnaire asking the following questions: (1) When did you see the eagle?; (2) Where did you see it?; (3) In what type of habitat?; (4) From where did you see the eagle?; (5) Was the eagle dead or alive?; and (6) What was the eagle do- ing? After completing the questionnaire, we asked farm- ers to bring us to the exact locations where eagles were observed. The following variables were recorded in 1-ha square plots centered on the points where eagles were seen: habitat type, number of vegetation strata, canopy cover, canopy height, dominant tree species, shrub cover, shrub height, dominant shrub species, understory cover, understory height, and dominant herbaceous plants. Results and Discussion Three new records for the Crowned Eagle were re- ported by staff of the National Park of Lihue Calel in 1996—97. On 18 November 1996, an eagle was observed perched in a tree approximately 20 km east of the Lihue Calel National Park. A second sighting was made on 22 November 1996 approximately 40 km southeast of the park. The third sighting was of a subadult Crowned Eagle on 21 September 1997 perched in a Prosopis tree in the park. No Crowned Eagles were recorded during road sur- veys. Of the 20 farmers interviewed, 10 said they had seen Crowned Eagles and their descriptions fit the eagle’s fea- tures. All of the farmers referred to the large size and head feathers, and most of them recalled the eagle’s 312 December 1998 Short Communications 313 characteristic whistle and reluctance to fly off when ap- proached. Eagles were encountered while farmers were walking (40%), driving (30%) or riding horses (30%). Most eagles were observed in natural woodlands (50%) or near tajamares (40%, artificial ponds surrounded by trees that provide water for cattle). Eagles were seen perched (80%), flying (10%) or perched and eating. Four encounters were not considered in the analysis, one of them because it had occurred about six years prior to the interview (all other sightings were in 1996—97). The remaining three cases were not used because farmers were unable to determine the exact location where they saw eagles. No farmer recalled the encounter date and no dead eagles were reported. Vegetation in all roosting habitats consisted of three strata. The dominant tree species was P. caldenia. Canopy cover was 37 ± 18% (x ± 1 SD) and canopy height was 6.2 ± 2.6 m. Dominant shrub species were Larrea nitida (present in 67% of the described sites), Lycium chilense (17%) and Prosopis flexuosa. Other shrub species included Larrea divaricata (in 67% of the sites), Condalia microphylla (67%), Chuquiraga erinacea (50%), followed by Geoffroea decorticans, Schinus fasdculatus, Prosopidastrum globosum and Lycium gilliessianum. Shrub cover and height were 1 7 ± 16% and 1.6 ± 0.2 m, respectively. The understory was dominated by grasses {Stipa gynerioides and S. tenuissima) m five of the described sites, and by Verbena aspera in the remaining site. Sites where Crowned Eagles were seen roosting or nesting appeared to be similar to the typical tajamar or woodlots in the area, but different from the matrix of the shrubland landscape. One nest site was found as a result of our interviews. The nest had been partially destroyed in the summer of 1996 and it did not show any sign of activity on our visit in February 1997. It was located approximately 12 km east of the National Park in a natural 2X4 km forest of P. caldenia crossed by a stream. Habitat surrounding the nest tree had 45% canopy cover and a canopy height of 7 m. The middle stratum was dominated by seedlings of P. caldenia and by shrub species such as L. chilense, P. flex- uosa, G. decorticans, S. fasdculatus, and C. microphylla. Mean shrub cover was 25% and mean height was 1.5 m. The understory was dominated by Stipa gynerioides, S. ten- uissima, and Bacchari ulidna. Percent cover of herbaceous plants was 25% and height was 0.4 m. The nest was a large platform of sticks placed 6 m high in a 1 2 m Prosopis tree. It was supported by two branches and was built with Prosopis branches that measured 0.6— 2.2 cm in diameter. Previously, Giai (1952) described two Crowned Eagle nests built on communal nests of Monk Parakeets {Myiop- sitta monachus) and De la Pena (1992) described a large platform nest 5 m up in an Eucalyptus tree. Our results show that Crowned Eagles may build nests in shorter and less conspicuous trees than those dominating northern savannas. Our sightings were consistent in that Crowned Eagles were observed using primarily P. caldenia for roosting and habitats that provide for tree, shrub and grass cover. The southern limit of the species’ range appears to be at the ecotone between the phytogeographic provinces of Espin- al and del Monte, that occur through the NE— SW gradient of decreasing mean annual precipitation in Argentina. The Espinal is a savanna dominated by Prosopis sp. and del Monte is characterized by shrublands dominated by Larrea sp. with isolated Prosopis and isolated woodlots occurring mainly in depressions and ravines. Crowned Eagles seem to depend on the presence of trees because they do not occur south in the Patagonian steppe. In the southern limit of its range, the Crowned Eagle occurs in a fairly transformed landscape character- ized by shrublands with isolated groups of native trees providing nesting and roosting habitats. This finding has conservation implications for Crowned Eagles. Current land management in the area includes afforestation fol- lowed by ranching. Creation of extensive areas lacking trees or having isolated trees may result in the reduction of the eagle’s range. Conservation efforts should include the provision of native woodlots due to their importance for Crowned Eagles. Resumen. — En este estudio aportamos nueva informa- cion acerca de los requerimientos de habitat del aguila coronada {Harpyhaliaetus coronatus), a traves de la des- cripcion de los sitios usados como posadero en el limite sur del area de distribucion de la especie. Adicional- mente, aportamos tres nuevos registros y describimos un nido. Los sitios donde las aguilas fueron vistas eran sim- ilares a un tipico tajamar (laguna artificial redeada de arboles) o a un monte, pero diferentes a la matriz del paisaje de tipo arbustiva. La vegetacion presentaba tres estratos, donde Prosopis caldenia (calden) era la especie arborea dominante. La cobertura de la canopia era de 37 ± 18% (promedio ± 1 DE) y la altura de 6.2 ± 2.6 m. Las especies arbustivas dominantes eran Larrea nitida, Lycium chilense y Prosopis flexuosa. La cobertura y altura de arbustos era de 17 ± 16% and 1.6 ± 0.2 m, respectiva- mente. El estrato bajo estaba dominado por pastos. La creacion de areas extensas sin arboles o con arboles ais- lados podria resultar en la reduccion del area de distri- bucion de la especie. Esfuerzos de conservacion requer- iran de un manejo del habitat que provea grupos de arboles natives. [Traduccion de Autores] Acknowledgments We deeply thank the logistic support provided by Ad- ministracion Parques Nacionales of Argentina through A. Balabusic, R. Milne, and M. Romero. Local farmers took the time to guide us to the roosting spots, and kindly encouraged us to conduct research on their properties. Suggestions made by G.R. Bortolotti and J.A. Donazar improved the manuscript. The work was funded by the American Bird Conservancy, the Universidad de Buenos Aires, and the Consejo Nacional de Investigaciones Cien- tificas y Tecnicas of Argentina. 314 Short Communications VoL. 32, No. 4 Literature Cited Chebez, J.C. 1994. Los que se van. Especies argentinas en peligro. Editorial Albatros. Collar, N.J, L.P. Gonzaga, N. Krabbe, A. Madrono, L.G. Naraujo, T.A. Parker and D.C. Wege. 1992. Threat- ened birds of the Americas. The ICBP/IUCN red data book. Smithsonian Institution Press, Washington, DC U.S.A. De la Pena, R.M. 1992. Las aves argentina. Editorial L.O.L.A. De Lucca, E.R. 1992. El aguila coronada, Harpyhaliaetus coronatus, en San Juan. Nuestras Aves 26:25. . 1993. Rapaces Amenazadas. El aguila coronada. Nuestras Aves 29:14—17. Fuller, M.R. and J.A. Mosher. 1987. Raptor survey tech- niques. Pages 37-65 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline and D.M. Bird [Eds.], Raptor management techniques manual. Natl. Wildl. Fed., Washington, DC U.S.A. Giai, a. 1952- Diccionario ilustrado de las aves argenti- nas. 1. Aves Continentales. Revista Mundo Agrario, Editorial Haynes, Buenos vMres, Argentina. Gil, G., E. Haene and J.C. Chebez. 1995. Notas sobre la avifauna de Sierras de las Ouijadas. Nuestras Aves 31: 26-28. Salvador, S.A. and P.G. Erodes. 1994. Notas sobre aves de Santiago del Estero. Nuestras Aves 30:24—25. Received 30 January 1998; accepted 10 August 1998 /. Raptor Res. 32(4):314-318 © 1998 The Raptor Research Foundation, Inc. A Comparison of Methods to Evaluate the Diet of Golden Eagles in Corsica Jean-Francois Seguin Parc Naturel Regional de Corse, B.R 417, F-20184 Ajaccio, Corsica and Ecole Pratique des Hautes Etudes, Laboratoire de Biogeographie et Ecologie des Vertebres, Place Eugene Bataillon, F-34095 Montpellier Cedex 05, France Patrick Bayle 15 rue Bravet, F-13005 Marseille, France Jean-Claude Thibault and Jose Torre Parc Naturel Regional de Corse, B.P 417, F-20184 Ajaccio, Corsica Jean-Denis Vigne CNRS, URA 1415, Museum National d’Histoire Naturelle, Laboratoire dAnatomie Comparee, 55 rue Buffon, F-75005 Paris, France Key Words: Golden Eagle, Aquila chrysaetos; diet, Corsica. Identification of prey remains, pellet analysis and di- rect observation of prey deliveries are the principal meth- ods used to study the diets of nesting raptors (Marti 1987). Although it is often best to observe or film nests for long periods to quantify prey deliveries, this is not always possible due to time and logistical constraints. To assess the validity of using prey remains and pellets as a means of determining diet, several authors have com- pared data from collections of nest contents with data obtained from direct observation for various raptor spe- cies (Collopy 1983, Simmons et al. 1991, Mersmann et al 1992, Manosa 1994, Real 1996). Overall, they have found that by combining remains and pellets, collected with the same level of effort, it is possible to determine diet. Previous studies of the diet of Golden Eagles {Aquila chrysaetos) in the Mediterranean area have been based on the collection of prey remains, without taking into ac- count any possible biases in the data collected using only this technique (Handrinos 1987, Cheylan 1983, Fasce and Fasce 1984, Fernandez 1991, Grubac 1987, Huboux 1984). Considering that the variety of food resources on Mediterranean islands is limited (Seguin and Thibault 1996) with a moderate spectrum of potential prey, we conducted this study to determine the best methods for monitoring the diet of Golden Eagles on Corsica. Study Area and Methods Corsica (42°N, 9°E) is one of the major islands in the western Mediterranean covering an area of 8750 km^. It supports a breeding population of 32-37 pairs of Golden Eagles (Torre 1995). Our study area, in the Verghello December 1998 Short Communications 315 Table 1. Minimal Number of Individuals (MNI), percentage of different prey according to different diet analysis methods and correction factors (c.f.) for a Golden Eagle nest in Verghello Valley (Corsica), 1992, 1994, and 1995 Delivered Prey Remains Pellets Remains + Pellets iV = 79 N= 52 N= 50 N = 72 N % N % c.f. MNI % c.f. MNI % c.f. Mammals Large mammals 31 39.2 30 57.7 Small mammals 6 7.6 1 1.9* Birds Corvidae 10 12.7 11 21.2 Alectoris rufa 3 3.8 6 11.5* Others 2 2.5 1 1.9 Reptiles Coluber viridiflavus 27 34.2 3 5.8* + 1.47 25 50.0 + 1.28 32 44.4 + 1.13 -4.00 3 6.0 -1.27 4 5.6 -1.36 + 1.67 2 4.0* -3.37 11 15.3 + 1.20 +3.03 2 4.0 + 1.05 6 8.3* +2.18 -1.32 3 6.0* +2.4 4 5.6* +2.24 -5.9 15 30.0 -1.14 15 20.8 -1.64 Significantly different from the frequencies of delivered prey. Valley, included one breeding pair that had been moni- tored by the Parc Naturel Regional de Corse since 1981. We observed prey brought to this nest by adult eagles from mid-May to late July in 1992, 1994, and 1995. Dur- ing the three years, hatching occurred between 15—24 May and fledging occurred between 28 July-4 August. We made observations using a 20-60 X spotting scope from a blind located 200-250 m from the nest. Observers came to and left from the blind at night in order not to disturb the adults. Observations were made for 1 d every 2.5 d with observation days evenly distributed between hatch- ing and fledging for a total of 1271 observation hr spread over 82 d (1992—27 d, 1994—23 d, and 1995—32 d). Whenever possible, prey items were identified to species and the identification was relatively easy because the number of mammalian species likely to be taken by Gold- en Eagles was low (15 taxa included eight domestic, Saint-Girons 1989, Raveneau 1993). However, not all prey could be identified due to poor visibility during obser- vation periods caused by heat, haze, and aggressive be- havior of the young as they took prey from adults. Do- mestic goat {Capra hircus) and sheep {Ovis aries) could not be differentiated in any cases, so they were grouped as Caprini. In each of the three years, remains were carefully col- lected in and under the nest in late August after fledging. Pellets were dissected and separated into bone frag- ments, feathers, reptile scales, and hair. Bones collected in the nest or extracted from pellets were identified by comparison with osteological collections (Museum Na- tional d’Histoire Naturelle, Paris, France) following methods of Payne (1985), Barone (1986), and Vigne (1995). Feathers (both from the nest or extracted from pellets) were identified by comparison with a reference collection. Hair was identified by comparison with Spill- mann (1991). Because adults spent most of the time away from the nest after the young were 4-wk old, we assumed that most pellets we collected from the nest were from the young. Each species identified in a pellet was counted as an individual. Quantification of food remains was based on minimum number of individual estimates (MNI) (Poplin 1976, Vig- ne 1991) based on the number of the most frequent an- atomical part in food remains or the pairing of anatom- ical parts (e.g., jaws). The drawback of this method is that it is impossible to be totally objective in the pairing of bone pairs. Also, the most frequent species are underes- timated in comparison to rare species (Poplin 1976). Prey were separated into six categories: large mammals (Caprini, boar [5 m5 scrofa] and red fox [Vulpes vulpes]), small mammals (weasel [Mustela nivalis], European hedgehog [Erinaceus europaeus] , and black rat [Rattus rat- tus]), birds (Corvidae, Red-legged Partridge [Alectoris ru- fal] and other birds), and snakes. Differences between taxa, years or prey categories obtained by both methods were tested with Chi-square contingency tables. Results and Discussion Of the prey delivered to the nest, 86% (N = 79, Table 1) were whole. The remainder consisted of portions of large mammals (Caprini, boar and unidentified mam- mals). Altogether, 39% of the prey delivered to the nest was large mammals, 8% was small mammals, 19% was birds including Red-legged Partridges, Common Kestrels {Falco tinnunculus), an unidentified raptor nesding, pi- geons {Columba spp.). Common Raven {Corvus corax), and Eurasian Jay {Garrulus glandarius), and 34% was snakes (western whip snake [ Coluber viridiflavus] ) . No sig- nificant difference appeared among the three years in the amount of these different prey that was delivered to the nest (x^ = 3.23, df = 6, P = 0.78). Analysis of prey remains collected at the nest showed the diet consisted of 44% large mammals, 6% small mammals, 29% birds, and 21% snakes. Again, no significant difference was found in the diet among the three years (x^ = 4.44, df = 6, P= 0.67). Bones contributed most data for the quantitative as- 316 Short Communications VoL. 32, No. 4 Table 2. Minimal Number of Individuals and number of species (in parentheses) obtained from bone identifi- cation and complementary data by pellet and feather ex- amination from material collected in a Golden Eagle nest m Verghello Valley (Corsica), 1992, 1994, and 1995. Bones Pellets Feathers Large mammals 30 (4) 3 (0) — Small mammals 1 (1) 3 (1) — Large birds 10 (2) 0 (0) 4 (1) Small birds 0 (0) 1 (1) 9 (3) Reptiles 3 (1) 12 (0) — sessment of MNI for large mammals and large birds (Ta- ble 2). Pellets provided little additional information for large mammals, but added additional data for estimating MNI for small mammals and snakes. Feathers provided supplementary data on bird numbers, especially on smaller species. Analysis of bones yielded the most infor- mation on the number of species while pellet analysis better predicted occurrence of small mammals and birds (Table 2). Feathers provided the best estimate for small bird species. Comparison of data obtained for prey delivered to the nest with that of prey remains showed a significant dif- ference between the six categories of prey (x^ = 19.43, df = 5, P = 0.002). The number of mammals and reptiles m the diet was underestimated, while birds are overesti- mated in samples of prey remains. In fact, the frequency of small mammals was four times lower in remains than in prey delivered. Red-legged Partridge, in contrast, were three times more frequent and western whip snakes were SIX times less frequent. The small mammals, the Red-leg- ged Partridge and the western whip snake contributed to the significant difference between prey delivery and re- mains. The comparison between prey delivered and pel- lets was not significant among the six prey categories (x^ = 4.51, df = 5, P = 0.48). Nevertheless, the Corvidae were three times less frequent in pellets than in prey de- liveries. On the other hand, the frequency of birds (ex- cept the Corvidae and the Red-legged Partridge) in pel- lets was 2.4 times greater than in prey deliveries. The comparison between prey delivered and remains plus pel- lets was not significant among the six prey categories (X^ = 5.03, df = 5, P = 0.41). Nevertheless, the Red- legged Partridge and other birds were two times more frequent than in the prey delivered. Using all methods, 15 species of prey were identified (Table 3) . Here also, there was no significant difference in the species composition of the diet estimated by direct observation or by analysis of remains and pellets (x^ = 6.51, df = 2, P = 0.99). One might expect that food habits data collected once at the end of the nesting season would be biased in favor of large prey species. However, when adult Golden Eagles clean nests, females often eliminate the larger remains which could result in an underestimation of large prey species (Mathieu and Choisy 1982, Tjernberg 1981). This bias has been noted for other species (Real 1996). Several sources of bias exist in the results of prey anal- ysis based on remains only that are related to prey size and factors affecting fragmentation of remains such as removal when remains are taken out of nests by females, difhculties in identification owing to wear, differences in the size of prey, and destruction of osteological remains. These factors probably explain the differences we ob- served between the prey delivery and prey remains meth- ods. One of the more important biases we found in the collection of prey remains of Golden Eagles was the un- derestimation of the small prey items, in particular small mammals and reptiles, because most of the time they were completely eaten. This bias has been previously ob- served in Golden Eagle dietary studies (Delibes et al. 1975, Mathieu and Choisy 1982, Tjernberg 1981), and of other raptors (Simmons et al. 1991, Mersmann et al. 1992, Maiiosa 1994, Real 1996). Birds such as Red-legged Partridges are overestimated because of the abundance of sterna and feathers. Pellets overestimated birds other than corvids and Red-legged Partridges in the diet be- cause they were eaten entirely. Assuming that the occur- rence of a prey species in a pellet corresponds to an in- dividual can also overestimate the number of large mammals in the diet since several pellets could contain the remains of the same individual of a prey taxon eaten Table 3. Overall number and percentage of species identified by the different diet analysis methods (prey delivered, remains, pellets, and remains -f pellets), at the Golden Eagle nest in Verghello Valley (Corsica), 1992, 1994, and 1995. Deuvered Prey Remains Pellets Remains + Pellets N % N % N % N % Mammals {N = 6 species) 5 83.3 6 100.0 4 66.7 6 100.0 Birds {N = S species) 5 62.5 6 75.0 5 62.5 7 87.5 Reptiles (N = 1 species) 1 100.00 1 100.0 1 100.0 1 100.0 Total {N = 15 species) 11 73.3 13 86.7 10 66.7 14 93.3 December 1998 Short Communications 317 over several days. No method gives a perfect estimate of the nesting diet but combining remains and pellets seems to be the least biased estimator of diet available if deliveries cannot be recorded. The complementary na- ture between these two types of prey analysis has been shown in previous studies on raptor diet (Simmons et al. 1991, Mersmann et al. 1992, Mahosa 1994, Oro and Telia 1995, Real 1996). The comparison of direct observations and collection of prey remains to determine the diet of Golden Eagles was studied by Collopy (1983), but in a region where the largest prey was jackrabbits {Lepus californicus) . Our study was the first to compare the different analytical methods in an area where prey are larger than Leporidae. While either method gave similar results for the percent fre- quency of prey in the diet of Golden Eagles, periodic observations of food delivered to nests are necessary if the main objective is estimate prey biomass (Collopy 1983), or to obtain information on selection of prey (Real 1996). Our data indicate that the combination of prey remains plus pellets collected on only one visit after the breeding season would enable the study of several pairs of eagles over a large area and a short period of time. Resumen. — Numerosos estudios sobre el regimen alimen- ticio del polio de Aguila real {Aquila chrysaetos) estan bas- ados en el analisis de los restos oseos o de las egagropilas. Pero, dado que dichos restos sufren una degradacion di- ferencial, los resultados pueden quedar sesgados. Desde esta optica hemos comparado durante cuatro periodos de reproduccion, en una isle mediterranea, los restos de huesos, de egagropilas y de plumas encontrados en un nido a los datos obtenidos por observacion directa. Que- da comprobado que los diferentes tipos de restos se com- plementan, y que por consiguiente su recogida y analisis con el mismo esfuerzo son necesarios pare que la des- cripcion del regimen alimenticio del polio de Aguila real se acerque en lo posible de la realidad. [Traduccion de Pedro Arrizabalaga] Acknowledgments This study was financed by the Office de TEnviro- nnement de la Corse and the DIREN, Ministere charge de 1 ’Environnement. Gary Bortolotti, Geoff Holroyd, Ron Jackman, and Mike Marquiss improved an earlier draft of the manuscript with dieir comments and criti- cism. Literature Cited Barone, R. 1986. Anatomic comparee des mammiferes domestiques. Tome 1. Osteologie. Vigot, Paris, France. Cheylan, G. 1983. Note sur I’alimentation de I’Aigle roy- al Aquila chrysaetos en Basse Provence. Bull. Centre de Recherches Ornithologiques de Provence 5:56—57. Collopy, M.W. 1983. A comparison of direct observa- tions and collections of prey remains in determining the diet of Golden Eagles. J. Wildl. Manage. 47:360- 368. Delibes, M., J. Calderon and F. Hiraldo. 1975. Selec- cion de presa y alimentacion en Espaha del Aguila real {Aquila chrysaetos). Ardeola 21:285-303. Fasce, P. and L. Fasce. 1984. L’Aquila reale in Italia. Lega Italiana Protezione Uccelli, Parma, Italy. Fernandez, C. 1991. Variation clinale du regime alimen- taire et de la reproduction chez I’Aigle royal {Aquila chrysaetos) sur le versant sud des Pyrenees. Rev. Ecol. {Terre Vie) 46:363-371. Grubac, R. 1987. L’Aigle royal en Macedoine. Actes du premier colloque international sur I’vMgle royal en Europe, Arvieux 1986. Maison de la Nature, Brian- fon, France. Handrinos, G.I. 1987. L’Aigle royal en Grece. Actes du premier colloque international sur I’Aigle royal en Europe, Arvieux 1986. Maison de la Nature, Brian- fon, France. Huboux, R. 1984. Contribution a une meilleure con- naissance du regime alimentaire de I’Aigle royal en periode de reproduction pour les Alpes du Sud et la Provence. Bull. Centre de Recherches Ornithologiques de Provence 6:30-34. Manosa, S. 1994. Goshawk diet in a Mediterranean area of northeastern Spain. J. Raptor Res. 28:84-92- Marti, C.D. 1987. Raptor food habit studies. Pages 67- 80 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline and D.M. Bird [Eds.], Raptor management tech- niques manual. Natl. Wild. Fed. Washington, DC U.S.A. Mathieu, R. and J.-P. Choisy. 1982. L’Aigle royal dans les Alpes meridionales frangaises de 1964 a 1980. Le Bie- vre 4:1-32. Mersmann, T.J., D.A. Buehler, J.D. Fraser and J.KD Seegar. 1992. Assessing bias in studies of Bald Eagle food habits./. Wildl. Manage. 56:73-78. Oro, D. and J.L. Tella. 1995. A comparison of two meth- ods for studying the diet of the Peregrine Falcon. J Raptor Res. 29:207-210. Payne, S. 1985. Morphological distinctions between the mandibular teeth of young sheep, Ovis, and goats, Capra./. Archeol. Sd. 12:139-147. Poplin, F. 1976. A propos du nombre de restes et du nombre d’individus dans les echantillons d’ossements. Cahier du Centre de Recherches Prehistoriques { Univ. Pans I) 5:61-74. Raveneau, a. 1993. Inventaire des animaux domestiques en France. Nathan, Paris, France. Real, J. 1996. Biases in diet study methods in the Bo- nelli’s Eagle./. Wildl. Manage. 60:632-638. Seguin, J.-F. and J.-C. Thibault. 1996. j^ustement de I’alimentation de I’Aigle royal {Aquila chrysaetos) a la disponibilite saisonniere des proies pendant la peri- ode de reproduction en Corse. Rev. Ecol. {Terre Vie) 51:329-339. 318 Short Communications VoL. 32, No. 4 Saint-Girons, M.-C. 1989. Les mammiferes en France. Sang de la Terre et La Manufacture, Paris, France. Simmons, R.E., D.M. Avery and G. Avery. 1991. Biaises in diets determined from pellets and remains: correc- tion factors for a mammal and bird-eating raptor. J. Raptor Res. 25:63-67. Spillmann, P.-L. 1991. Atlas des pois des mammiferes sau- vages terrestres de Gorse. Mem. Maitrise Sci. Tech., Universite de Corse, Corte, Corsica. Tjernberg, M. 1981. Diet of the Golden Eagle Aquila chry- saetos during the breeding season in Sweden. Holarct. Ecol. 4:12-19. Torre, J. 1995. L’Aigle royal {Aquila chrysaetos) en Corse: repartition et biologie de la reproduction. Trav. Sc. Parc Nat. Reg. Res. Nat. Com 51:87— 90. ViGNE, J.-D. 1991. The meat and offal weight (MOW) method and the relative proportion of ovicaprines in some ancient meat diets of the north-western Medi- terranean. Rivista di Studi Liguri 57:21-47. . 1995. Criteres de determination des onglons d’artiodactyles de Corse pour une contribution a la connaissance du regime alimentaire du Gypaete. Rev. Ecol. {Terre Vie) 50:85-92. Received 12 October 1997; accepted 27 July 1998 J. Raptor Res. 32(4):318-321 © 1998 The Raptor Research Foundation, Inc. A Record of a Harpy Eagle from Eastern Paraguay Thomas M. Brooks^ Department of Ecology and Evolutionary Biology, 569 Dabney Hall, University of Tennessee, Knoxville, TN 37996-1610 U.S.A. Key Words: Harpy Eagle] Harpia harpyja; Paraguay; sight record. On 2 August 1995, I recorded an immature Harpy Ea- gle {Harpia harpyja) in rainforest at Reserva Privada Itabo (24°20'S, 54°35'W), Departamento Canindeyu, Paraguay. The Harpy Eagle is poorly known in Paraguay and has not been previously recorded at this site. I first sighted the perched eagle in an emergent tree beside the main road through the reserve. It had been forced into the tree by a flock of seven White-eyed Par- akeets {Aratinga leucopthalmus) . After 10 min, the bird was again mobbed by the parakeet flock, causing it to fly off into the adjacent forest canopy. There was no question that the bird was a Harpy Eagle. Its most obvious feature was its large, completely creamy- white facial disc. Its bill was dark grey and its eyes large and black. Several completely white feathers formed a crest on its head. Its breast and belly were a uniform creamy white except for a pale grey area across its breast. The undertail appeared dark brown and the underwings appeared pale with some dark barring. I hardly saw the upperparts but they appeared to be largely grey, at least ^ Present address: Department of Biological Sciences and Center for Advanced Spatial Technologies, 12 Ozark Hall, University of Arkansas, Fayetteville, AR 72701 U.S.A. on the back, scapulars and wing coverts, with black lower on the wings. I did not see the upperwings or uppertail in flight. Not all of the salient characters, notably the enormous tarsi and the divided crest could be seen due to the angle of observation. However, nothing about the bird indicat- ed that it was a Crested Eagle {Morphnus guianensis) . Im- mature Crested Eagles are distinguished from immature Harpy Eagles by their slimmer bodies, long tails, smaller bills, dark lores, black-tipped crests and long, relatively small tarsi. Light phase Crested Eagles also have white underwing coverts contrasting with barred remiges (Hilty and Brown 1986). Crested Eagles have not been record- ed in Paraguay (Hayes 1995), although they have been historically recorded in Misiones Province, Argentina (Narosky and Yzurieta 1987). I excluded other large raptors such as Mantled Hawk {Leucoptemis polionota) , Black-and-white Hawk-Eagle {Spi- zastur melanoleucus) , Black Hawk-Eagle {Spizaetus tyrannus) and Ornate Hawk-Eagle {S. ornatus) based on the size and bulk of the bird alone and the plumage of the bird I observed did not match the plumages of any of these species (Narosky and Yzurieta 1987) . The latter three spe- cies are known from Reserva Privada Itabo (Lowen et al. 1996). The Harpy Eagle is rare throughout its range from Mexico to Argentina. It was considered Globally Threat- December 1998 Short Communications 319 Figure 1 . Forest cover and some recent records of Harpy Eagles in the Atlantic forests. Forest cover is shaded dark following Brown and Brown (1992). Recent records of Harpy Eagles are as follows: Brazil (1) Esta^;ao Experimental Pau-Brasil, Porto Seguro, Bahia, 1991 (Forrester 1993, Galetti et al. 1997), (2) probable at Sooretama Federal Bio- logical Reserve, Espirito Santo, 1993 (Forrester 1993), (3) Compania Vale do Rio Doce Reserve, Linhares, Espirito Santo, 1992 and 1995 (Forrester 1993, Galetti et al. 1997), (4) probable at Nova Lombardia Federal Biological Reserve, Espirito Santo, 1993 (Forrester 1993), (5) reported without details from Rio Doce State Park and Fazenda Montes Claros, Minas Gerais (Forrester 1993), (6) reported without details from Serra do Mar, Itatiaia National Park and Serra dos Orgaos, Rio de Janeiro (Forrester 1993), (7) Cananeia, Sao Paulo, 1989, 1990, 1991 and 1993 (Galetti et al. 1997), (8) Parque Estadual da Serra do Tabuleiro, Santa Catarina, 1989 (Albuquerque 1995), (9) Turvo, Parana, 1984—85 (Bornschein and Straube 1991), (10) Cascavel, Parana, 1982-83 (Bornschein and Straube 1991); Argentina (11) Misiones, 1980-90s (Chebez et al. 1990, Chebez 1992, De Lucca et al. 1993, De Lucca 1996); Paraguay (12) Itaipu Biological Reserves, Alto Parana, 1990s (Gill Morlis et al. 1995), (13) Reserva Privada Itabo, Canindeyu, 1995 (this record), (14) Reserva Natural del Bosque Mbaracayu, Canindeyu, 1994 (Madroho-Nieto and Esquivel 1995), and (15) Caaguazu, 1993 (Lowen et al. 1996). ened (Collar and Andrew 1988) but it has now been downgraded to Near Threatened (Collar et al. 1992) due to the large amounts of habitat for the species in the Amazonian portion of its range. In southeastern Brazil, It is very rare (Scott and Brooke 1985) and recent records from this region (Fig. 1) range from Bahia (Galetti et al. 1997) south to Santa Catarina (Albuquerque 1995, do Rosario 1996), with scattered sightings in between (Bornschein and Straube 1991, Forrester 1993, Tobias et al. 1993, Sick 1993, Scherer-Neto and Straube 1995, do Rosario 1996, Galetti et al. 1997). The extensive deforestation of Parana State (Albu- querque 1995) has probably now permanently separated these coastal populations of Harpy Eagles from the in- land Paranaense forest of Iguazu National Park, Parana State (Brazil), Misiones Province (Argentina) and eastern Paraguay. Forrester (1993) did not list any records for Iguafu National Park, Parana State, Brazil and Saibene et al. (1996) did not list the species for Iguazu National Park, Misiones Province (Argentina) . However, Harpy Ea- gles have recently been found nesting at higher altitude sites elsewhere in the province, in Departamentos San Pedro, Eldorado and Iguazu (Chebez et al. 1990, Chebez 1992, De Lucca et al. 1993, De Lucca 1996). Hayes (1995) lists seven records of Harpy Eagles from a wide range of locations in Paraguay, although none of these are supported by published descriptions or speci- mens. In addition, there is a recent sight record from the Itaipu Biological Reserves in Departamento Alto Parana (Gill Morlis et al. 1995, Scherer-Neto and Straube 1995). Madrono-Nieto and Esquivel (1995) recorded an imma- ture Harpy Eagle at Lagunita in the Reserva Natural del Bosque Mbaracayu, Departamento Canindeyu in 1994 and an eagle was reported in Caaguazu in 1993 (Lowen 320 Short Communications VoL. 32, No. 4 et al. 1996). The species is considered Endangered in Paraguay (CDC 1990). The Reserva Privada Itabo covers 3000 ha of forest which is sustainably harvested for palmito hearts of palm (Brooks et al. 1993). The concentration of fruiting palms at the site attracts large numbers of frugivorous birds and mammals, which in turn support high densities of car- nivores (Lowen et al. 1995). Presence of an immature Harpy Eagle potentially indicates that the species breeds at Itabo. However, the lack of other records at the site (Lowen et al. 1996) suggests that this bird was more prob- ably a wandering individual attracted to the site by the abundance of food. Albuquerque (1995) similarly felt that individual Harpy Eagles move between Araucaria groves with the seasonal abundance of prey, and until 1958 “migrant individuals” occurred in summer in Rio Grande do Sul State, Brazil (Sick 1993). Whatever the explanation for the presence of the individual at Itabo, this record supports the conclusion that Reserva Privada Itabo is of key importance for bird conservation in Par- aguay (Lowen et al, 1995). Resumen. — El 2 de agosto de 1995 registre un ejemplar juvenil del aguila harpia {Harpia harpyja) en la selva de la Reserva Privada Itabo (24°20'S, 54°35'W), Departa- mento Canindeyu, Paraguay, [Traduccion de Autor] Acknowledgments This observation was made during Project YACUTIN- GA ’95 (Lowen et al. 1996). My thanks go to that team, to the Fundacion Moises Bertoni, and to everyone at Re- serva Privada Itabo for their support, and to the Harvard Traveller’s Club Permanent Fund for supporting my par- ticipation in the project. Thanks to D. Vazquez for trans- lations, J.M. Barnett, W. Belton, L.A. do Rosario, F. Fer- nandez Campon, P. Scherer-Neto, F.C. Straube andJ.A. Tobias for providing information and literature, and two anonymous reviewers for helpful comments. Literature Cited Albuquerque, J.L.B. 1995. Observations of rare raptors in southern Atlantic rainforest of Brazil. J. Field Orni- thol 66:363-369. Bornschein, M.R. and F.C. Straube. 1991. Novos regis- tros de alguns Accipitridae nos estados do Parana e Santa Catarina (Sul do Brasil) . Page 38 in Resumenes, encuentro de ornitologia de Paraguay, Brasil y Argen- tina, 8-11 Mayo 1991. Ciudad del Este, Paraguay. Brooks, T.M., R. Barnes, L. Bartrina, S.H.M. Butchart, R.P. Clay, E.Z. Esquivel, N.I. Etcheverry, J.C. Lowen AND J. Vincent. 1993. Bird surveys and conservation in the Paraguayan Atlantic Forest. Project CANOPY ’92: hnal report. BirdLife International Study Report No. 57, BirdLife International, Cambridge, U.K, Brown, K.S., Jr. and G.G. Brown. 1992. Habitat alter- ation and species loss in Brazilian forests. Pages 119- 142 in TC. Whitmore andJ.A. Sayer [Eds.], Tropical deforestation and species extinction. Chapman and Hall, London, U.K. CDC. 1990. Areas prioritarias para la conservacion en la Region Oriental del Paraguay. Centro de Datos para la Conservacion, Asuncion, Paraguay. Chebez, J.C. 1992. Notas sobre algunas aves poco cono- cidas o amenazadas de Misiones (Argentina). Aprona Bol. dent. 21:12-29. , M. Silva Croome, A. Serret and A. Taborda. 1990. La nidificacion de la harpia {Harpia harpyja) en Argentina. Hornero 13:155-158. Collar, NJ. and P. Andrew. 1988. Birds to watch. The ICBP World Check-list of Threatened Birds. Interna- tional Council for Bird Preservation, Cambridge, U.K , L.P. Gonzaga, N. Krabbe, A. Madrono-Nieto, L.G. Naranjo, T.A. Parker III and D.C. Wege. 1992. Threatened birds of the Americas. The ICBP/IUCN Red Data Book. International Council for Bird Pres- ervation, Cambridge, U.K. De Lucca, E.R. 1996. A successful nest of Harpy Eagles in Argentina. Hornero 14:70—72. , A. Blanchard and E. Coconier. 1993. Programa Argentino para la conservacion de la harpia. Inform 1991-1993. Page 15 in Resumenes, primera reunion de ornitologia de la Cuenca del Plata, 20-25 Septiem- bre, 1993. Puerto Iguazu, Argentina. do RosArio, L.A. 1996. As aves em Santa Catarina. Dis- tribuiiicao geografica e meio ambiente. Fundayao do Meio Ambiente — FATMA, Florianopolis, Brazil. Forrester, B.C. 1993. Birding Brazil. A check-list and site guide. John Geddes, Irvine, U.K. Galetti, M., P. Martuscelli, M.A. Pizo and I. Simao. 1997. Records of Harpy and Crested Eagles in the Bra- zilian Atlantic forest. Bull. Brit. Ornithol. Club 117:27- 31. Gill Morlis, W., A. Dure Rodas, N. Perez Villamayor, A. Golman Jara, j. Van Humbeck B. and W. Silvera Avalos. 1995. Vertebrados del area de Itaipu. Biota 2. 1-64. Hayes, F.E. 1995. Status, distribution and biogeography of the birds of Paraguay. Monog. Field Ornithol. No 1., American Birding Association, Colorado Springs, CO U.S.A. Hilty, S.L. and W.L. Brown. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, NJ U.S.A. Lowen, J.C., R.P, Clay, T.M. Brooks, E.Z. Esquivel, L. Bartrina, R. Barnes, S.H.M. Butchart and N.I. Etcheverry. 1995. Bird conservation in the Paraguay- an Atlantic forest. Cotinga 4:58—64. , L. Bartrina, R.P. Clay and J.A. Tobias. 1996 Biological surveys and conservation priorities in east- ern Paraguay. CSB Publications, Cambridge, U.K. Madrono-Nieto, A. and E.Z. Esquivel. 1995. Reserva natural del Bosque Mbaracayu: su importancia en la conservacion de aves amenazadas, cuasi-amenazadas y endemicas del Bosque Atlantico. Cotinga 4:52—57. December 1998 Short Communications 321 Narosky, T. and D. Yzurieta. 1987. Birds of Argentina and Uruguay, a field guide. Vazquez Mazzini Editores, Buenos Aires, Argentina. Saibene, C.A., M.A. Castelino, N.R. Rey,J. Herrera and J. Calo. 1996. Inventario de las aves del Parque Na- cional “Iguazu,” Misiones, Argentina. Editorial L.O.L.A. Monografia No. 9, Buenos Aires, Argentina. Scherer-Neto, P. and EC. Straube. 1995. Aves do Para- na. Historia, lista anotada e bibliografia. Logos Press, Curitiba, Brazil. Scott, D.A. and M. de L. Brooke. 1985. The endangered avifauna of southeastern Brazil: a report on the BOU/ WWF expeditions of 1980/81 and 1981/82. Pages 115-139 in A.W. Diamond and T.E. Lovejoy [Eds.], Conservation of tropical forest birds. ICBP Tech. Publ. No. 4., International Council for Bird Preser- vation, Cambridge, U.K. Sick, H. 1993. Birds in Brazil. Princeton University Press, Princeton, NJ, U.S.A. Received 12 October 1997; accepted 25 July 1998 Letters J. Raptor Res. 32(4):322 © 1998 The Raptor Research Foundation, Inc. Dust Bathing in the Bearded Vulture ( Gypaetus barbatus) The source of the rufous coloration of adult Bearded Vultures {Gypaetus barbatus) has been a point of debate. In some cases, variations in this coloration have been used as a systematic character to establish new subspecies (Fatio 1899, Faune des Vertebres de la Suisse., Vol. 2; Fischer 1963, Die eier. Neue Brehm-Bucherei, Wittenberg. Several studies have in fact confirmed that the rusty coloration of underparts and the neck and head of adult birds is due to iron oxides derived from weathered dolomitic limestone (Volker 1960, Fortschr. Chem. org. NatStoffe 18:107-110; Berthold 1967, Zool. Jb. Syst.; Brown and Bruton 1991,/. ZooL Lond. 223:627-640; Houston et al. 1993, Aull. B.O.C. 113(4):260-263) Apparently, Bearded Vultures acquire the red-orange coloration passively as they roost at night on their bellies on rock ledges rich in iron compound (Berthold 1967, Zool. Jb. Syst.] Siegfried and Frost 1973, Bonn. Zool. Beitr. 24:387- 393). Such staining of breast and neck feathers has been argued by Clancey 1968 {Bokmakierie 20:36-37) since no bird has ever been recorded dusting in the wild. In fact, radio-tagged vultures in South Africa and released birds in the Alps have not shown such feather staining (Brown 1988, Ph.D. thesis, Univ. of Natal; Houston et al. 1993, Aull. BO.C. 113(4):260-263). In captivity. Bearded Vultures develop pure white feathers and are attracted to red soils often dusting or mud bathing (Berthold 1967, Zool. Jb. Syst. 93:507-595; Brown and Bruton 1991,/. Zool. Lond. 223:627-640). Bathing in water has been reported to be a rather common phenomenon in South Africa but no iron oxides have been found in the pools used by vultures for bathing (Steyn 1982, Birds of prey of Southern Africa. Cape Town: David Philip). Although an adult Bearded Vulture was recently reported bathing in the Pyrenees beneath a spring rich in iron oxides (Caussimont et al. 1995, Bearded vulture annual report.53), no field observations of birds using dust or mud wallows containing iron deposits have been reported. This may be due to the fact that Bearded Vultures are secretive when visiting such places (Houston et al. 1993, Aull. B.O.C. 113(4) :260-263) . On 23 March 1997, I observed an adult Bearded Vulture at the Northern slopes of Dikti massif (Eastern Crete, Greece) dust bathing. I had observed it using this location for roosting and sleeping for several months during the winter. The elevation of the roost site was 300 m and the roost itself was located on a 1.5 m shelf on an east-facing cliff of eroded limestone rocks (terra rosa). While observing the bird with a 30X spotting scope from a distance of 300 m, I saw it rubbing its head, neck and chest on the bottom of the ledge. After that, it started pecking and biting and rubbing its head and neck on the rock. This behavior lasted about 8-12 min and finally the vulture laid its belly on the ledge where it spent the rest of the night. It is quite possible that in arid areas, such as the mountains of Crete where upland streams are scarce and muddy places are completely lacking, Bearded Vultures have no easy access to damp red soils. To acquire their orange coloration, they may rub and peck on rocks to produce dust for dust bathing. They do not appear to eat these dust particles (Brown and Plug 1991, S. Afr. Zool. 25(3):169-177) and they do not suffer from calcium deficiency like other scavenging birds (e.g., Gyps, Houston 1978,/. Zool. Lond. 186:175-184). If this kind of behavior is indeed the source of pigmentation for feathers of the Bearded Vulture, it is surprising that it has not been recorded more often. The fact that the reddish tones of feathers of Bearded Vultures vary from location to location indicates that feather coloration is passively acquired (Berthold 1967, Bull. Br. Ornithol. Club 87: 89-90) . On Crete, the intensity of rufous coloration among pairs of Bearded Vultures ranges from dark orange to pure white. In areas with limestone rocks that are resistant to erosion or low annual precipitation (60-80 cm/yr), dirty white or completely white vultures predominate perhaps because dust from dust bathing does not stain the feathers as effectively as does mud and water rich in iron oxides. — Stavros Xirouchakis, Natural History Museum of Crete, University of Crete, Knossou Ave., Heraklion 71409, Crete, Greece. 322 Commentary Edited by Daniel E. Varland J. Raptor Res. 32(4):323-329 © 1998 The Raptor Research Foundation, Inc. On the Evidence Needed for Listing Northern Goshawks {Accipiter gentilis) Under the Endangered Species Act: A Reply to Kennedy K. Shawn Smallwood Consulting in the Public Interest, 109 Luz Place, Davis, CA 95616 US. A. Kennedy (1997) assessed whether the available scien- tific evidence supports the claims of declining Northern Goshawk {Accipiter gentilis) abundance, which were made in recent petitions (Anonymous 1997) to list the North- ern Goshawk as a Threatened Species under the Endan- gered Species Act (ESA). She analyzed scientific data from published research reports for evidence of a decline in goshawk abundance across North America, including declines in geographic range, population density, nest oc- cupancy, fecundity and survival, and rates of population change. Based on analyses of these variables, she con- cluded that the available evidence did not support the listing petitioners’ claims of declining goshawk abun- dance across North America. Congress intended for ESA listings to be based on the best scientific and commercial data available, although the types of data and those qualifying as the best were left up to environmental scientists (Bogert 1994). Lack- ing internal statutory guidance as to what are the best scientific and commercial data applicable to listing deci- sions, Carroll et al. (1996) proposed the following stan- dards for prioritizing listing of candidate species: (1) the number of additional species that can benefit from the listing; (2) the species’ ecological role; (3) the species’ recovery potential; and (4) the species’ taxonomic or evolutionary distinctiveness. However, these standards ap- pear to be intended for increasing collateral benefits to the ecosystem and for balancing costs, although the latter would be contrary to the intent of the ESA. None of these standards bear directly on reducing the species’ jeopardy of extinction and increasing its chances for sur- vival and recovery in the wild (i.e., conserving the spe- cies) . Kennedy chose declining abundance of the taxon as her standard, which was a decision warranted by the intent of the ESA. The purpose of my reply to Kennedy is to question both the appropriateness of her choice of variables and her analyses of them when testing for evi- dence of declining Northern Goshawk abundance. Geographic Range Contraction A contracting geographic range would indeed signal a likely decline in goshawk abundance. However, the se- quence of range maps used for concluding such a trend need to be examined carefully for possible biases due to several influential factors. First, as Kennedy speculated, an apparent range expansion in the eastern U.S. could be due to greater efforts at locating goshawks during modern times. A temporal trend in the size of the geo- graphic range cannot be justified as an indicator of gos- hawk abundance without considering trends in the level of search effort within this range. Second, natural, mul- tiannual shifts in geographic range due to climate or oth- er factors (MacArthur 1972) can appear as unidirectional contractions or expansions when examined over too few years. Third, habitat typically grows more patchy and sparse near a species’ range boundary, as does species’ abundance (MacArthur 1972, Taylor 1993, Krebs 1994). Accordingly, a number of methods have been used for deciding where to delineate range boundaries (Krebs 1994). Should the range boundary circumvent all breed- ing populations? All individuals? All habitat patches? Or, should it include only high-quality habitat patches? Per- ceived temporal trends in range boundary could be due to inconsistent application of multiple range delineation methods. Kennedy (1997) provided no rigorous account- ing of these aforementioned methodological problems in comparing geographic range maps through time. Probably the most useful indicator variable for detect- ing range contraction is the fraction of area used by the species, which can be measured as the cumulative area either of all occupied habitat patches or of all occupied grid cells overlaid on a distribution map (Gaston 1991, Hanski et al. 1993). However, because species abundance patterns tend to consist of population clusters that shift locations every generation or so (Taylor and Taylor 1977, 1979, den Boer 1981, Hanski 1994), as well as large areas with little or no ecological value to the species (Gaston 1991, Hanski et al. 1993), the fraction of area providing environmental conditions known to serve as high-quality habitat also would be useful for assessing range contrac- tion of Northern Goshawk (Ward et al. 1992, Iverson et al. 1996). Maguire (1993) found that habitat loss contrib- 323 324 Commentary VoL. 32, No. 4 Table 1. Published estimates of nesting density for Northern Goshawks in North America. Authors Location Year Study Area (km^) No. OF Prs of Active Nests Nesting Density (Pairs/ km^) McGowan (1975) near Fairbanks, AK 1971 372.0 7.0 0.0188 McGowan (1975) near Fairbanks, AK 1971 372.0 9.0 0.0242 McGowan (1975) near Fairbanks, AK 1973 372.0 8.0 0.0215 McGowan (1975) near Fairbanks, AK 1974 372.0 1.0 0.0027 Shuster (1976) northern CO, Rocky Mts. 1974 81.0 6.0 0.0741 Shuster (1976) northern CO, Rocky Mts. 1975 81.0 6.0 0.0741 Bartelt (1977)"^ Black Hills, SD 1975 448.5 8.0 0.0178 Reynolds and Wight (1978) western OR 1970 92.8 0.0 0.0000 Reynolds and Wight (1978) western OR 1971 92.8 0.0 0.0000 Reynolds and Wight (1978) western OR 1974 117.4 4.0 0.0341 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 8.5 0.9 0.1059 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 12.0 1.2 0.1000 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 22.0 3.0 0.1364 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 27.5 4.0 0.1455 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 29.0 2.1 0.0724 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 36.0 2.4 0.0667 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 44.5 3.3 0.0742 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 50.5 5.1 0.1010 Crocker-Bedford and Chaney (1988) Kaibab Plateau, AZ 1985 230.0 24.0 0.1043 Kennedy (1989) Jemez Mts., NM 1986 121.0 7.7 0.0636 Kennedy (1989) Jemez Mts., NM 1986 273.5 7.7 0.0282 Austin (1993) Cascades of CA 1989 473.7 9.0 0.0190 DeStefano et al. (1994) Paisley, east OR 1992 87.8 4.0 0.0456 DeStefano et al. (1994) Paisley, east OR 1993 129.6 8.0 0.0617 DeStefano et al. (1994) east Bear Valley, east OR 1992 90.5 8.0 0.0884 DeStefano et al. (1994) east Bear Valley, east OR 1993 90.5 6.0 0.0663 DeStefano et al. (1994) west Bear Valley, east OR 1993 105.2 9.0 0.0856 DeStefano et al. (1994) Spring Creek, east OR 1992 114.0 8.0 0.0702 DeStefano et al. (1994) Spring Creek, east OR 1993 114.0 3.0 0.0263 DeStefano et al. (1994) Bly, east OR 1993 106.3 4.0 0.0376 Doyle and Smith (1994)'^ southwest Yukon 1990 100.0 10.0 0.1000 Woodbridge and Detrich (1994) Sierran Montane, CA 1989 102.3 11.0 0.1075 Woodbridge and Detrich (1994) Upper Montane, CA 1989 104.4 6.0 0.0575 ^ Reported density estimates from two immediately adjacent areas, which I combined into one area and one estimate. Assumed that the 5 pr they observed comprised only half the population. uted substantially to a decline in goshawk population vi- ability on the Kaibab Plateau, Arizona. Maguire’s popu- lation viability analysis (PVA) simulated a declining trend m habitat carrying capacity of 1%/yr and produced cer- tain extinction in goshawk populations, even those with stable or increasing growth rates. Concluding whether the fraction of area used or potentially used by goshawks has changed through time must include knowledge of goshawk habitat and habitat fragmentation, which I will discuss further. Nesting Density To evaluate the appropriateness of nesting density for detecting a range-wide abundance trend, I compared 33 nesting density estimates made from 24 study sites span- ning the years 1970-93 (Table 1). Estimates of nesting density averaged 0.062 pair per km^ (range = 0-0.145, SD = 0,039). The nesting populations studied averaged only 6 pairs of nesting goshawks (range = 0-24, SD = 4.4) on study areas that averaged 148 km^ in size (range = 8.5-474, SD = 134). As noted by Kennedy, estimates of goshawk density have been highly variable. However, her comparison of these density estimates was unlikely to reveal any tem- poral trends because half the variation in goshawk nest- ing densities can be explained by the size of the study areas used to make the density estimates (Fig. 1). Similar December 1998 Commentary 325 Nesting density (pairs + 1 per km^) Figure 1. Relationship between nesting density (log of nesting pairs per km^) and study area size (log km^ of study area) for Northern Goshawks across North America (see Table 1). to other species, such as Swainson’s Hawks {Buteo swain- soni; Smallwood 1995), European Kestrels {Falco tinnun- culusr. Village 1984, Kostrzewa 1988), mammalian primary consumers (Blackburn and Gaston 1996) and mamma- lian carnivores (Smallwood and Schonewald 1996), pub- lished estimates of goshawk nesting density were inversely proportional to the study area (r^ = 0.53, Root MSE = 0.27, P< 0.0001): log Density = 0.072 — 0.658 log^w^ study area, where density was calculated as the number of nesting pairs plus one, so as to avoid log-transforming 0-values. The y-intercept of the regression slope predicted 0.18 pair of Northern Goshawks on the average 1 km^ of hab- itat area included within the collective study boundaries. This predicted density is about three times as large as the average of reported densities, which is already higher than will be found on the majority of North American forest land units the size of 1 km^. My model prediction was absnrd. After all, nesting home ranges of 73 adult goshawks averaged 59 km^ in size and ranged up to 879 km^ (Bartelt 1977, Kennedy 1989, Austin 1993, Doyle and Smith 1994, Hargis et al. 1994, Keane and Morrison 1994, Iverson et al. 1996). Foraging areas of 50 goshawks averaged 894 km^ in size and were as large as 2321 km^ (Hargis et al. 1994, Keane and Morrison 1994, Iverson et al. 1996). The most likely explanation for the excessive density predicted both by the regression model at 1 km^ (see Smallwood and Schonewald 1996) and by the aver- age among reported estimates was that most investigators selected study sites known in advance to support breed- ing populations of Northern Goshawk. In fact, the loca- tions of four of the 10 studies summarized in Table 1 were reportedly selected based on historical records of goshawk nesting or on the distribution of high-quality habitat. At least most of the remaining sites were likely also chosen in one of these ways, rather than randomly Therefore, estimates of nesting density were made for only one aspect of the population: the high-density clus- ter. Without long-term sampling across large geographic areas, including the majority of the forest landscapes where goshawks are much rarer, comparisons of nesting density are unlikely to reveal any temporal trend in gos- hawk abundance across North America. Further adding to the unsuitability of available density estimates for detecting temporal trends in range-wide goshawk abundance, high-density clusters typically shift locations every generation or so (Taylor and Taylor 1977, 1979, den Boer 1981). A stndy originally designed around a high density cluster might detect a sudden drop in abundance after a few years. Such a reduction in local density would likely be misinterpreted as a population decline rather than a spatial shift, unless the sampling was of sufficient duration and spatial extent to detect the shift. All but two density estimates included <11 nesting pairs, which in my opinion is barely enough to qualify as a population cluster. The studies generating these esti- mates have lasted <9 yr, which is less than a goshawk lifespan and therefore is insufficient for judging persis- tence (Connell and Sousa 1983). The studies designed to estimate density were not intended to detect popula- tion trends across large areas, let alone North America Reproductive Patterns Fecundity and survival, estimated from local, autono- mous studies, also have no necessary relationship with goshawk abundance at the scale of North America. Such estimates represent populations, and have no document- ed relationship with geographic range size (Gaston 1990) or range-wide abundance. Habitat fragmentation has been proposed as the most likely cause for declines in Northern Goshawk abundance across North America (Crocker-Bedford 1990, Keane and Morrison 1994). However, habitat fragmentation might reduce nest-site occupancy and availability (Crocker-Bedford 1990, Ward et al. 1992, Woodbridge and Detrich 1994), and not fe- cundity (Woodbridge and Detrich 1994) and survival. Ex- trapolating Crocker-Bedford ’s (1990) observed rates of timber harvest and impacts on goshawk nesting on the Kaibab Plateau, habitat loss could conceivably reduce gos- hawk abundance across North America by 75% during the 75-yr lifetime of a scientific investigator. However, the remaining 25% might reprodnce and survive at levels comparable to pre-harvest conditions (Woodbridge and Detrich 1994). The relationships between habitat frag- mentation and reproductive success remain unknown ex- cept for what has been learned from the stand-thinning studies of Crocker-Bedford (1990) and Ward et al (1992). Like geographic range contraction, widespread 326 Commentary VoL. 32, No, 4 reductions in fecundity or survival across North America would be of concern, but local, autonomous estimates are inappropriate for extrapolation to range-wide esti- mates of productivity. Temporal Abundance Trend Kirk and Hyslop (1998) recently assessed the status of Canadian raptors by analyzing data from migratory hawk counts, Christmas Bird Counts (CBC), and the Breeding Bird Surveys (BBS) across North America. They found significant declines in the annual number of migrating Northern Goshawks at the majority of migratory hawk count sites in the U.S., although the CBC and BBS showed no such declines. Kirk and Hyslop (1998) ac- knowledged the hazards of relying on counts of migrat- ing raptors, such as possibly misinterpreting change over several counting years as a trend rather than just as part of a multiannual population cycle. However, changing counts of migrating Northern Goshawks are more likely to be indicative of continent-scale change in abundance through time than would be the rate of population change assessed by Kennedy, because populations are lo- cal and may shift locations through time as described previously (Taylor and Taylor 1977, 1979, den Boer 1981). Kennedy dismissed counts of migrating goshawks be- cause no direct relationship has been established be- tween counts of migrants and the abundance of goshawks across North America. This rationale was not applied to geographic range, population density estimates, nor fe- cundity and survival, although there was every reason to do so. Her (1997) use of these variables for assessing ev- idence of a goshawk decline in North America lacks sci- entific foundation, but serves as a first step in the needed scientific debate on the evidence needed to conclude whether a species is declining across its geographic range. Habitat Fragmentation The relationships between goshawk nesting patterns and forest landscape conditions were not assessed by Kennedy. These relationships also bear on critical habitat designation, which is one of the major steps called for in the ESA listing process, and was originally intended to precede listing decisions (National Research Council 1995). Critical habitat was not defined explicitly in the ESA, but Hall et al. (1997) defined this habitat as the geographic areas providing the resources necessary for breeding and population persistence, consistent with the concept of high-quality habitat. Although critical habitat has yet to be designated for the Northern Goshawk, the available research reports indicate that “mature,” “closed-canopy,” or “old-growth” forest will likely com- prise a good part of the critical habitat designation (Crocker-Bedford and Chaney 1988, Ward et al. 1992, Graham et al. 1994, Iverson et al, 1996, Beier and Dren- nan 1997). Fragmentation of mature forest may be the greatest threat to Northern Goshawks (Keane and Morrison 1994, Woodbridge and Detrich 1994, Iverson et al. 1996). Hab- itat fragmentation is the reduction in and increased iso- lation of available habitat (Wilcox and Murphy 1985). In general, habitat fragmentation has been widely acknowl- edged as the greatest threat to the survival of many spe- cies (Wilcox and Murphy 1985). Habitat fragmentation should be given the greatest scrutiny in making listing decisions, and its possible impact on the goshawk is mea- surable indirectly using historical and recent maps of ma- ture forests (Ward et al. 1992). However, habitat fragmentation must be defined clear- ly so that it can be made operational with respect to im- pacts on Northern Goshawks. Hansen and Urban (1992) rated goshawks as highly sensitive to old-growth forest fragmentation based on reproductive effort, nest type, and territory size, but they lacked information on gos- hawk responses to edge and patch size. Nest-site occu- pancy was later found positively related to mature forest patch size (Woodbridge and Detrich 1994) and percent canopy closure (Ward et al. 1992), and nesting areas con- tained less edge between forest and nonforest vegetation types (Iverson et al. 1996). Goshawk habitat must be de- scribed carefully using multiscale studies such as con- ducted and advocated by Keane and Morrison (1994) and Beier and Drennan (1997). Specific resource and habitat patch sizes and their configurations on the land- scape must be related to abundance patterns of the spe- cies (Kotlier and Wiens 1990, Hanski 1994). The condi- tion of goshawk habitat can then serve to indicate the abundance of goshawks in North America, although pre- dictions of abundance based on the indicator (s) need verification with an extensive sampling and monitoring program (Green 1979). A metaanalysis, as recommended by Kennedy, probably would not suffice for assessing goshawk abundance trends in North America in lieu of proper sampling (also see Keane and Morrison 1994). I conducted a similar type of analysis for puma (Puma concolor californica) den- sity, and found that the autonomy of each population study rendered the collection of studies incapable of pro- viding much insight (Smallwood 1997). Smallwood and Schonewald (1998) since compared all published carni- vore population estimates and associated study attributes, but we found the same result: surprisingly little insight into the factors that influence carnivore density, except for the influence of study area on density. Most popula- tion studies are not sampling programs per se, but rather measurements of population attributes at particular sites and during brief periods of time (relative to the ecolog- ical time scale of the species) . Comparison of these attri- butes for temporal trends is inappropriate without con- trolling for a variety of environmental and study conditions. Such comparison is one form of pseudorep- lication (Hurlbert 1984). An appropriate sampling program would start with a December 1998 Commentary 327 protocol for selecting multiple sampling sites from vari- ous environmental conditions, from which variation in population attributes could be effectively interpreted (Green 1979). The entire geographic range of the taxon IS the appropriate spatial scale for sampling that is in- tended to test for abundance trends and to make taxo- nomically-based listing decisions. The appropriate sam- pling protocol for drawing inferences on trends in abundance would involve random or systematic selection of sites throughout the range. Intensive studies of re- source requirements at a subset of the sampling sites would need to be linked to the more extensive sampling program so that evolutionary and ecological questions of ‘why’ and ‘how’ can be answered, and meaningful con- servation strategies put to practice (Keane and Morrison 1994). Such a sampling program may seem daunting, but the case needs to be made that the Northern Goshawk and other species in the U.S. deserve allocation of the necessary funding for sampling at a scale and level of rigor sufficient to achieve the objectives of the ESA. Conclusions Kennedy’s decision to pursue evidence of declining Northern Goshawk abundance was more appropriate to the intent of the ESA than were those of Carroll et al. (1996). However, a listing decision for the Northern Gos- hawk should not rely on the data and analysis she used. Population density, fecundity, survival, and rate of pop- ulation change all lack scientifically defensible relation- ships with range-wide abundance, as does the size of the geographic range within a single species (Gaston 1990). The population parameters can be related to local pop- ulation trends, but their relationships to the trend in range-wide abundance can only be inferred by multiscale study at sites chosen randomly or systematically from across the geographic range. In lieu of appropriate sam- pling, and in lieu of agreement among scientists for ad- ditional variables that should be analyzed, evidence for a Northern Goshawk decline across its range should be based on changes in the availability and contiguity of hab- itat and migratory counts. According to Kennedy, the petitioners for the goshawk listing were motivated by their concern for over-harvest of old-growth forest. Regardless of the motivation behind the listing petitions, the listing decision should be based on analysis of the variables that most likely represent a threat to the survival of Northern Goshawks in the wild: the extent of its critical habitat and level of recent habitat fragmentation. Kennedy did not rigorously assess habitat fragmentation as a possible indicator of declining gos- hawk abundance. Assessing inappropriate variables for making a listing decision threatens the credibility of the ESA more so than does an ulterior motivation for a listing petition, because the former is an action that can reduce the like- lihood of survival and recovery of the species in the wild, whereas the latter is a request that poses no threat to the goshawk population. That is, applying less than the best scientific data to a listing decision risks committing a Type II error which can have severe conservation rami- fications and would be the less ethical choice (Shrader- Frechette and McCoy 1992). Committing a Type I error and inappropriately listing a species as threatened will not reduce the likelihood of its survival, although a de- listing in the future can also be time-consuming and damaging to the integrity of the ESA (if listing was un- warranted in the first place). Of course, using the best available scientific data (appropriate variables) would also reduce the chance of committing a Type I error. Environmental scientists need to develop standards for qualifying scientific data as the best available when mak- ing listing decisions, as called for in the ESA. Perhaps Kennedy’s paper and my reply can help initiate the need- ed scientific debate on the methods and variables that are most appropriate for assessing whether a species has declined significantly enough across its range to warrant listing under the ESA. Acknowledgments I thank Robert Rosenfield, Kim Titus, Stephen De- Stefano, and an anonymous reviewer for their comments on an earlier draft of this manuscript. I also thank Cole- man Crocker-Bedford for sharing his knowledge of gos- hawks and for his assistance in locating unpublished re- ports. Literature Cited Anonymous. 1997. 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The Value of Demographic and Habitat Studies in Determining the Status of Northern Goshawks {Accipiter gentilis atricapillus) with Special Reeerence to Crocker-Bedford ( 1990 ) and Kennedy ( 1997 ) D. Coleman Crocker-Bedford 243 Wood Road, Ketchikan, AK 99901 U.S.A. Northern Goshawks {Accipiter gentilis atricapillus) have long been associated with mature forests, an attribute that has brought them into recent debates over forest management practices. Bent (1937) associated goshawks with extensive forests and large stands of big trees, and more recent research on their nesting habitat found an association with relatively large trees and relatively dense canopies (Shuster 1980, Reynolds et al. 1982, Moore and Henny 1983, Speiser and Bosakowski 1987, Crocker-Bed- ford and Chaney 1988, Hayward and Escano 1989). Reyn- olds (1989) described the foraging habitat during the breeding season as older, tall forest where goshawks can maneuver in and below the canopy while foraging. Most of the investigators cited above deduced that timber har- vesting could impact goshawks, while others concluded that timber harvest actually had reduced goshawk abun- dance in portions of some states (Reynolds and Meslow 1984, Mannan and Meslow 1984, Bloom et al. 1985, Ken- nedy 1988). I (Crocker-Bedford 1990) reported that the rate of nest reoccupancy in logged areas was 20-25% the reoccupan- cy rate in areas not logged, despite nest buffers having been left intact in the logged areas. This finding, along with deductions on the effects of timber harvest on the size of the local population, catalyzed additional research (Squires and Reynolds 1997) and debate. Many scientists (seemingly including Kennedy 1997) and forest manag- ers were left confused over the methods and results of my research. Herein, I assess the strengths and weak- nesses of my 1990 paper in order to move the debate on methodologies toward implementation of more produc- tive resource management practices. Kennedy (1997) emphasized the use of demographic studies in determining whether goshawks warrant Threat- ened or Endangered status under the United States En- dangered Species Act (ESA; United States Government 1988); however, I assert that demographic statistics are unlikely to ever provide sufficient information to deter- mine goshawk status under the ESA. In light of limita- tions in technology, funding and other problems, this pa- per suggests an alternative approach to status assessment Finally, hypotheses are presented on landscape-level hab- itat needs of goshawks, for use in goshawk status assess- ment, and as suggestions for further study. Review of Croc:ker-Bedford (1990) My study area was the North Kaibab Ranger District of northern Arizona. I started nest monitoring in 1982 un- der a study plan having the objective of comparing the efficacy of different-sized no-cut nest buffers for goshawk 330 Commentary VoL. 32, No. 4 habitat protection. During 1973-84, U.S. Forest Service personnel located at least one goshawk nest within each territory discussed in my 1990 paper. I reported on reoc- cupancy during 1985-87 of individual nest trees and ter- ritories. 1 defined a territory as the area associated with a cluster of nests and reoccupancy as a nesting attempt. In most cases reoccupancy was proven by seeing a gos- hawk in a nest, but in some cases reoccupancy was in- ferred by detection of new greenery in the nest along with seeing goshawks nearby, or by finding recent gos- hawk feathers or egg fragments at the nest. Despite spec- ulation (Kennedy 1997) that some of the located terri- tories might originally have been occupied by other species, goshawks were seen on nests in 97% of the stud- ied territories, while the single remaining nest cluster was presumed to belong to goshawks due to nest and stand characteristics plus goshawk activity near the nest. Nests were located within timber sale assessment areas chosen by foresters; areas which I termed “locales.” Tim- ber sale preparation involved assessing every individual tree over roughly 83% of each locale, including all trees in nearly 100% of the stands suitable for goshawk nesting (described by Crocker-Bedford and Chaney 1988), so there was a high likelihood of finding at least one of the nests of a territory. Once a nest was located, the vicinity was extensively searched for alternate nests. Harvests of dead and dying trees occurred almost ev- erywhere in my study area from 1945-70. Control locales (N = 9; the smallest contiguous block was 4700 ha) did not incur timber sale harvest from 1970 until after nest monitoring was completed in 1987. Treatment locales (N = 6; the smallest contiguous block was 1000 ha) were harvested after treatment territories were located but be- fore 1985. Nineteen control territories (nest clusters) were located within the control locales, while 12 treat- ment territories were located within the treatment lo- cales. I did not include 40 other goshawk territories known by 1987 because they did not fit the above criteria. Partial harvests and selection harvests, not clearcuts, re- moved about one-third (range = 15-50%) of the sawtim- ber volume from about 79% (range = 73-86%) of the hectares in treatment locales. No-cut biiffers were left around goshawk nests (small buffers were 1-3 ha; large buffers were 16-200 ha). One strength of my study was that I demonstrated long-term nest-tree hdelity in the absence of habitat deg- radation. For individual nest trees in control locales, reoccupancy at least once in 1985-87 was equal between nests foimd in 1973-78 (67%) and those found in 1981- 84 (65%). Despite no-cut nest buffers, I found that the average reoccupancy rate from 1985-87 in treatment lo- cales was only 20-25% the rate in control locales. In 1987, the two nests occupied after treatment (occupied treatment nests) had zero and one nestling, while the 12 occupied control nests averaged 2.1 nestlings. No-cut nest buffers were similarly ineffective, whether small or large. Prior to the publication of my results, goshawk management recommendations concentrated on nesting habitat (Reynolds et al. 1982, Crocker-Bedford and Cha- ney 1988, Kennedy 1988). After my paper was published, the critical importance of hunting habitat throughout the home range was recognized (Crocker-Bedford 1990, Warren et al. 1990, Reynolds et al. 1992). The differences in breeding and reproduction between treatment and control locales were consistent with the extent of the tim- ber harvests as well as literature showing that mature for- est with denser than average canopy is the most selected foraging habitat (Widen 1989, Austin 1993, Bright-Smith and Mannan 1994, Hargis et al. 1994, Iverson et al. 1996, Beier and Drennan 1997). These results were consistent with results I reported for the same study area (Crocker-Bedford 1987, Crocker- Bedford 1995). In the 1987 paper, I considered only nests known to be occupied in 1982-83, and compared their reoccupancy in 1984-85 according to whether logging occurred after they were occupied in 1982 or 1983. In the 1995 paper, I analyzed 1987 reoccupancy and repro- duction from a larger number of territories (N = 53) in relation to the amount of timber harvest during 1973-86 within circles of 2.7-km radius around the center of each nest cluster. Breeding population projections, based on results from my studies, were consistent with a nearly complete census of the study area made by Reynolds and Joy (1998). Given the reduced reoccupancy in logged lo- cales, along with the amount of habitat logged, I (Crock- er-Bedford 1990) estimated that by 1988 nesting pairs were probably reduced to half the 1972 breeding popu- lation. In the 1990 paper, I only considered breeding density surveys through 1985 because they had already been published (Crocker-Bedford and Chaney 1988) However, by 1987 I had goshawk survey data from six tracts totaling 270 km^ which had not been harvested since 1970, and which averaged a breeding pair density of 12 or 13 pair per 100 km^ (Crocker-Bedford unpubl data). Given 1200 km^ within the breeding range of gos- hawks on the North Kaibab Ranger District, about 150 pairs may have existed circa 1972. If half were lost by 1988, the remaining breeding population would have been about 75 pairs. Data presented by Reynolds and Joy (1998) demonstrate that the comparable figure was somewhere between 49 and 73 pr during 1991-96. From a census ol 95% of the goshawk habitat on North Kaibab Ranger District, Reynolds and Joy (1998) reported that 95 territories were occupied at least once between 1991- 96, so about 100 territories remained on the District. Their mean annual rate of occupancy (defined as at least one goshawk seen at least twice within a territory; not necessarily a nest attempt as in my studies) was 73% Whereas 100% of my occiipied control territories pro- duced young, only 67% (range = 44-92%) of the occu- pied territories produced young in 1991-96 or, in other words, an average of only 49 pairs were successful from 1991-96. December 1998 Commentary 331 My results also showed changes in the raptor commu- nity associated with treatment territories. While I never found another raptor nesting within 1 km of any control nest, other raptor species used nests or nesting stands formerly occupied by goshawks in seven of 12 treatment territories. Comparisons of my 1990 paper involved the same years, and control and treatment locales were well dis- tributed over the study area. As a result, comparisons were less likely to be confounded by factors such as weather conditions (Penteriani 1997), prey cycles (Doyle and Smith 1994), and inherent site prodixctivity; these can confound correlations between demographic statis- tics and habitat differences over time. My study was not biased by an inappropriate or inad- equate nest search effort. The number of nest trees known per territory was the same for reoccupied controls (2.33), unoccupied controls (2.25), reoccupied treat- ments (2.33), and unoccupied treatments (2.44), which demonstrates that search effort was appropriately bal- anced. Furthermore, I reported the largest number of goshawk territories (71) and nest trees (157) of any pub- lished paper through 1990. Thirty-one of the territories, including 73 known nest trees, met the criteria for inclu- sion in my analyses, yielding the largest sample size of any study by 1990 on A.g. atricapillus. The differences be- tween treatment and control locales were highly signifi- cant in terms of goshawk reoccupancy {P = 0.001, 0.003 and 0.01), number of nestlings {P = 0.003 and 0.001), and use by other raptor species (P < 0.001). Despite its strengths, there were also several weakness- es in my 1990 paper. The difference between the number of nestlings found in occupied treatment and control ter- ritories may have been due to sample size. Few nests were occupied in treatment locales. As in almost all raptor re- search, my studied territories were neither randomly se- lected nor randomly assigned as treatments or controls. Therefore, the results should be considered correlative and not a true hypothesis test for cause and effect rela- tionships. Perhaps most importantly, the study was not designed to assess effects at the population level. In 1982, I was directed to compare the efficacy of small and large no- cut nest buffers for maintaining goshawk nest site use- fulness. The 1990 paper should have explicitly stated im- plicit assumptions regarding estimates of population change. Despite no-cut nest buffers, some goshawks which had been nesting in the treatment locales before logging might have moved to unlogged areas for nesting. If so, the total nesting population may have been stable. Also, if breeders packed into unlogged areas, then sur- veys of pair density prior to treatment may have been artificially high. Moreover, the estimate of the size of the breeding population prior to any significant logging (cir- ca 1945) was likely flawed, in that it was an extrapolation based on densities in the two locales harvested the least prior to goshawk surveys. The locales were too few and too small (1000 ha and 2750 ha) to provide a reliable estimate. Some of my study’s results may have been temporary The 1990 paper discussed how forest birds and tree squir- rels (Sciurus aberti and Tamiasciurus hudsonicus) were re- duced in numbers by selection harvests. However, I did not con.sider that other species might eventually increase in the more open forest, so that prey composition might shift (Boat and Mannan 1994). Comments on Kennedy (1997) A species may be listed as Threatened or Endangered under the ESA due to any one of five criteria (United States Government 1988). Kennedy (1997) only dealt with the range contraction portion of one of these cri- teria, the present or threatened destruction, modifica- tion, or curtailment of its habitat or range (United States Government 1988). Kennedy provided a literature review that, for the east- ern U.S., showed that goshawks there were reduced in abundance during the 19th century and, since 1950, gos- hawk abundance has increased and the species’ range has apparendy expanded, logically due to reoccupancy as forested landscapes have increased and matured follow- ing the extensive deforestation of the 19th century. Per- haps she thought it obvious, but she should have explic- itly stated that goshawks can be reduced in number and apparently even extirpated in landscapes where timber harvesting is too great, and that for most of western North America extensive timber harvesting did not begin until the 20th century. Kennedy (1997) went to great lengths to present de- mographic statistics related to the rate of population change (X.). However, except in situations where the rate of population change is far different from neutral (X = 1.0), it is usually impossible to calculate a meaningful X for a sparsely distributed species. The number of sam- ples, needed by each age class to calculate rates of pair- ing, natality, survival, emigration, and immigration, are typically so few from a sparsely distributed species that the calculated X shows a confidence interval ranging from population increase to population decrease. Demographic statistics generated from goshawk studies have additional problems. Some results vary with prey cycles (Doyle and Smith 1994) and weather (Penteriani 1997). Immigration and emigration may also vary (Squires and Reynolds 1997) and are affected by the de- gree of population isolation. DeStefano et al. (1994) de- scribe problems associated with marking and resightmg goshawks at nests, such as potentially underestimating survival. Maguire and Call (1993) determined that a X based on data from existing goshawk nest sites can be biased high, so that a declining trend in habitat carrying capacity, where 1 % is lost each year, produces certain ex- tinction in populations whose growth rates are otherwise stable or increasing. Reynolds and Joy (1998) could not determine X, 332 Commentary VoL. 32, No. 4 though their study is so far the most intensive in North America on goshawk demography. Also, they held the advantage of starting with a large number of territories (known from the work of Crocker-Bedford 1990 and Zmn and Tibbitts 1990). In addition, because the study was conducted in one of the most isolated tracts of gos- hawk habitat, it should have been less affected by immi- gration and emigration. Since Reynolds and Joy’s (1998) intensive and exacting demographic study could not de- termine X for a relatively discrete and small study area, It is unlikely that sufficient technology and funding exist to determine whether regional populations are increas- ing, stable, or decreasing. Moreover, due to effects of weather and prey cycles, demographic data collected during one time period might have little relevance to another. Kennedy proposed overcoming sample-size problems by pooling published and unpublished goshawk data into a metaanalysis. However, even a metaanalysis is unlikely to overcome the problems described above to a degree that would yield a rate of population change meaningful for a status review (i.e,, a X with a small confidence in- terval which is applicable over the long-term and an en- tire region). Furthermore, demographic data are not col- lected or stored by a consistent protocol. Finally, because the areas where goshawks have been studied have not been randomly selected and because some landscapes are probably population sources while others are likely population sinks, combining studies will not likely rep- resent the true mean of a region. These problems may explain why the U.S. Congress did not include a documented population decline as a criterion for listing a species under the ESA (United States Government 1988). Some scientists (e.g., Braun et al 1996, Kennedy 1997) seem to believe that results from demographic studies should prove that goshawks are de- creasing over a large portion of their range before the species is entitled to special management. However, I sug- gest that some scientists may be so involved with demo- graphic data and statistical analyses as to occasionally overlook the importance of deductive reasoning in man- agement. Kennedy also used unpublished demographic data from her goshawk studies, an approach which was incon- sistent with her determination to not include results from non-peer-reviewed literature. Given her standard for oth- ers, I would have expected to see her studies peer- reviewed and published separately before appearing as summaries in her 1997 paper. Her presentation of un- published studies was so brief that the quality of the methods, data and analyses, and appropriateness of the conclusions and inferences, could not be evaluated. For example, the increase in the number of territories found over the first five years of the Ashley study likely was meaningless with respect to population change. More- over, three of the marked populations described by Ken- nedy have had little or no habitat modifications within about 90% of individual goshawk territories since the in- dividual demographic studies began (Desimone 1997); therefore, it is not surprising that the studies did not pro- vide evidence of population decline. Kennedy did not cite several agency reports that indicated reduced nest occupancy or reproduction, even though these had un- dergone more peer review than her demographic analy- ses (Bloom et al. 1985, Patla 1991, Ward et al. 1992, Ar- izona Game and Fish Department 1993, Maguire and Call 1993, Patla and Trost 1995). She also neglected the extensive literature on the hab- itat relationships of goshawks, even though such litera- ture is critical for evaluating the amount of habitat de- struction or modification, a key listing criterion of the ESA (United States Government 1988). Goshawks appar- ently prefer stands of relatively large trees with relatively dense canopies for nesting and foraging (Moore and Henny 1983, Speiser and Bosakowski 1987, Crocker-Bed- ford and Chaney 1988, Widen 1989, Austin 1993, Bright- Smith and Mannan 1994, Hargis et al. 1994, Iverson et al. 1996, Beier and Drennan 1997). Typically, they select larger stands or less-fragmented landscapes (Bent 1937, Widen 1989, Speiser and Bosakowski 1987, Falk 1990, Bo- sakowski and Speiser 1994, Bright-Smith and Mannan 1994, Woodbridge and Detrich 1994), though some nest- ing stands are surrounded by areas that are naturally tree- less (Swem and Adams 1992, Younk and Bechard 1994). One purpose of the ESA is to provide a means whereby the ecosystems upon which Threatened and Endangered Species depend may be conserved (United States Gov- ernment 1988, Sec. 2[b]). Ecosystem conservation may be one reason why any species, or any distinct population segment of any species (United States Government 1988, Sec. 3 [15]), needs to be likely to become an Endangered Species within the foreseeable future in only a significant portion of its range (United States Government 1988, Sec. 3 [19]) in order for the entire species or segment to be listed. What constitutes a significant portion of its range is debatable for the Northern Goshawk or the pop- ulation segment west of the Great Plains, Because the goshawk is an indicator of ecosystem health (a predator of forest birds and medium-sized mammals) , I would be concerned if its abundance was seriously declining in ar- eas far smaller than during the 19th century in the east- ern U.S. For the Northern Goshawk, I suggest that 100 000 km^ is significant where forest cover once dom- inated the landscape, while a disjunct forest as small as 1000 km^ might also be significant under the concepts of the ESA. Kennedy concluded, “Although the concerns about overharvest of forested communities is certainly justifi- able, listing a species for which there is no evidence of a population decline would be a misuse of [ESA] legisla- tion.” The ESA does not require evidence of population decline. Moreover, if concerns about overharvest of for- ested communities are justifiable, then this assertion by Kennedy supports one of her alternative conclusions that December 1998 Commentary 333 “it is possible the goshawk is declining and the decline IS going undetected because of the paucity of data on temporal trends in mortality and abundance.” If forests in some regions are being harvested faster than goshawk habitat is developing, then goshawks in those regions will be impacted long before demographic analyses indicate problems such as those described by Widen (1997). Kennedy did not fully report the data from my publi- cations. The correct figure from Crocker-Bedford and Chaney (1988) for the number of nests studied was 74. Kennedy shows a question mark instead of the data. It appears that she might have intended the N in her Table 1 to be number of occupied nests. If so, then the correct figure for Crocker-Bedford and Chaney (1988) was 24 because the average occupancy rate of nests was 33%. She defined nest success as the proportion of occu- pied territories that produce at least one young of band- able age. She reported the figure as unavailable in Crock- er-Bedford (1990). In fact, I reported 1.00 for occupied control territories and 0.50 for occupied treatment ter- ritories. A Habitat-based Status Review Kennedy concluded that a detailed analysis of 20th century deforestation and reforestation rates throughout North America would provide additional indirect infor- mation on potential temporal changes in the goshawk’s range. I strongly support this recommendation. However, because reforestation generally refers to development of seedlings and saplings, I recommend analyzing forest maturation rates in order to emphasize habitat useful to goshawks. In addition, for each North American region and for- est type, goshawk habitat requirements should be esti- mated at three scales: the amounts of important habitats necessary to support a productive breeding pair; the composition within a landscape for a stable or increasing local population; and the composition within a region for a stable or increasing regional population. To estimate the habitat requirements, a committee of goshawk ex- perts should be convened. These experts should repre- sent diverse views and different regions. The committee should be chaired by a scientist who has not been influ- enced by the North American goshawk debates. Al- though the chairperson should be a strong facilitator of group consensus, the committee report should present alternative hypotheses. Goshawks tend to hunt in mature forests, especially larger stands with relatively dense canopies, and gos- hawks are more likely to kill prey in mature forests. Nev- ertheless, goshawks may successfully forage in some open habitats (Kenward 1982, Reynolds et al. 1992, Swem and Adams 1992, Younk and Bechard 1994). This dichotomy is part of the current philosophical debate over whether management of publicly-owned forests should emphasize timber production, or emphasize pristine conditions in- cluding many stands of old trees and large tracts left to nature. Even if a silviculture system can produce both timber and goshawks, some people question whether it is appropriate for wildlife on publicly-owned wildlands Managers of public forests address such questions as they implement laws passed by elected politicians. To provide information for both philosophies, the committee of di- verse goshawk experts should address management by sil- viculture to develop adequate habitat within a forest scheduled for logging, as well as management by habitat reserves including the sizes, shapes, structures, and spac- ings of old stands and large tracts to be left unharvested in perpetuity. I hypothesize that home ranges are larger and terri- tories are more widely spaced in landscapes where less area exists in stands useful for foraging. Kenward (1982) reported that home range size of goshawks varied to en- compass a sufficient amount of prime foraging habitat. Breeding season home ranges typically vary from 6 to 35 km^ (Squires and Reynolds 1997), although one adult in California ranged over 69 km^ (Austin 1993) and two in Alaska each covered more than 600 km^ (Iverson et al. 1996). Breeding pair density varies by an order of mag- nitude (Squires and Reynolds 1997). Breeding pair density may depend on the amount of habitat where suitable prey is more abundant than some threshold and is accessible enough (forest structure) that the chance of prey capture in the habitat is worth the time and energy expended. This hypothesis is based on evidence from studies of habitat selection and home range sizes (Kenward 1982, Widen 1989, Falk 1990, Aus- tin 1993, Bosakowski and Speiser 1994, Bright-Smith and Mannan 1994, Hargis et al. 1994, Iverson et al. 1996, Beier and Drennan 1997), as well as deductive logic. Gos- hawk home ranges would be smaller if goshawks were able to benefit from the total biomass of all the prey spe- cies within most habitats. The time for hunting is likely inadequate for goshawks to directly assess prey abun- dance and accessibility in every hectare of their large home ranges, so goshawks need search images for habi- tats that are likely to be useful. Furthermore, selection harvesting 10-39% of the area within home ranges had no apparent effect on reproduction in half the cases, while in the other half goshawk nesting seemed to be eliminated (Crocker-Bedford 1995), and I suspect this difference was due to whether harvesting occurred in im- portant foraging habitats. Finally, even selection harvest- ing has the potential to degrade habitat below some threshold of usefulness, and it can reduce forest prey populations (Crocker-Bedford 1990). I hypothesize that most forest structures and most area within the typical home range provide little or no benefit to goshawks. Consequently, timber operations that miss important habitats may have little or no effect on home range size or breeding density. However, timber harvests in important foraging habitat likely have effects dispro- portionate to their sizes. 334 Commentary VoL. 32, No. 4 Conclusions Goshawk demographic trend studies typically require decades of data collection to be useful for population status assessment (Widen 1997). Even then, anyone who wishes to doubt the long-term results could assert that any trends found were really due to weather, prey cycles, inconsistent techniques, or inadequate sampling. Rates of population change (X) for goshawks are also open to question owing to wide confidence intervals, inherently biased field techniques, and data representing few years and a small number of nonrandom study sites. Environ- mental degradation could continue for many years or de- cades while demographic data are collected, and habitat degradation might continue as litigants and their con- sultants debate whether the trend data or X statistic are meaningful. Studies comparing goshawk parameters in relation to forest management practices are unlikely to ever achieve all criteria of ideal experimental designs for hypothesis testing. No landowner will ever dedicate to goshawk re- search multiple large tracts of forest (>1000 km^), nor is there likely to be adequate financing and enough time to locate most goshawks before the experimental treat- ment, gather pretreatment data, perform manipulations in randomly selected home ranges, wait for the manip- ulations to have their habitat effects, and then gather the comparison data. Still, comparison studies that fall short of the perfect experimental design will typically have few- er problems with confounding factors than will long-term trend studies of forest management effects. Goshawk research that is funded to gather information for management purposes should compare goshawk pa- rameters (e.g., demographic data, home range sizes, spacing of territories, habitat selection, diets) between replicates of similar landscapes under different manage- ment treatments. Whenever possible, data should be col- lected before treatment to demonstrate the pretreatment similarity of the landscapes with respect to the parame- ters studied. Retrospective studies allow more rapid in- sights into management questions at lower costs, and ae- rial photos can suggest pretreatment similarity (Ward et al 1992). Because replicates of management treatments and con- trols are unlikely to ever be randomly assigned to areas large enough to fully encompass home ranges, scientists should explicitly recognize that goshawk field studies are correlative, and should not interpret their results as ab- solute proofs. Nevertheless, they should not be dissuaded from providing logical deductions based on data and lit- erature, although they should also explicitly state their assumptions. Goshawk experts from different regions, including proponents of divergent theories, should be brought to- gether to consider landscape-level habitat requirements. After gathering information from forest inventory ex- perts on forest-landscape changes, the team could assess whether goshawks in portions of the U.S. deserve protec- tion under the ESA, which does not require habitat threats to be range-wide before listing a species or pop- ulation segment. I hypothesize that goshawks are sup- ported by only a portion of the habitats present, and that typically most of a home range (especially where trees are small or sparse) provides little or no sustenance to individuals. Acknowledgments I am grateful to Joseph Buchanan, Stephen DeStefano, Scott Horton, and Daniel Varland, whose substantive comments on an earlier version of this paper induced many improvements. Dan Varland edited several drafts to improve the readability. Of course, the opinions ex- pressed herein are my own and do not necessarily rep- resent those of the reviewers. Literature Cited Arizona Game and Eish Department. 1993. Review of U.S. Forest Service strategy for managing Northern Goshawk habitat in the southwestern United States Arizona Game and Fish Department, Phoenix, AZ U.S.A. Austin, K.F. 1993. Habitat use and home range size of breeding goshawks in the southern Cascades. M.S thesis, Oregon State Univ., Corvallis, OR U.S.A. Beier, P. and J.E. Drennan. 1997. Forest structure and prey abundance in foraging areas of Northern Gos- hawks. Ecol. Appl. 7:564-571. Bent, A.C. 1937. Life histories of North American birds of prey. Part 1. Dover Publ., New York, NY U.S.A. Bloom, P.H., G.R. 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The Academy of Natural Sciences, Philadelphia, PA U.S.A. Swem, T. and M. Adams. 1992. A Northern Goshawk nest in the tundra biome./. Raptor Res. 26:102. United States Government. 1988. Endangered species act of 1973 as amended through the 100th Congress. USDI Fish and Wildl. Serv., Washington, DC U.S.A. Ward, L.Z., D.K. Ward and T.J. Tibbitts. 1992. Canopy density analysis at goshawk nesting territories on the North Kaibab Ranger District, Kaibab National Forest. Nongame and Endangered Wildlife Program, Ariz Game and Eish Dept., Phoenix, AZ U.S.A. Warren, N., G.D. Hayward, T. Holland, R. Escano, D.C 336 Commentary VoL. 32, No. 4 Crocker-Bedford, T. Komberec, D. Sasse, L. Saun- ders-Ogg and W.C. Shuster. 1990. Goshawk habitat relationships. Pages 19-27 mN.M. Warren [Ed.], Old- growth habitats and associated wildlife species in the northern Rocky Mountains. USDA For. Ser, North. Reg. Rl-90-42, Missoula, MT U.S.A. Widen, P. 1989. The hunting habitats of Goshawks {Ac- cipiter gentilis) in boreal forests of central Sweden. Ibis. 131:205-231. . 1997. How, and why, is the Goshawk {Accipiter gentilis) affected by modern forest management in Fennoscandia? J. Raptor Res. 31:107-113. WOODBRIDGE, B. AND P.J. Detrich. 1994. Territory occu- pancy and habitat patch size of Northern Goshawks in the southern Cascades of California. Stud. Avian Biol. 16:83-87, Younk, J.V. AND M.J. Bechard. 1994. Breeding ecology of the Northern Goshawk in high-elevation aspen forests of northern Nevada. Stud. Avian Biol. 16:119-121. Zinn, L.J. and T.J. Ttbbitts. 1990. Goshawk nesting survey 1990. North Kaibab Ranger District, Kaibab National Forest, Ariz. Game and Fish Dept., Phoenix, AZ U.S.A. Received 30 January 1998; accepted 22 July 1998. J Raptor Res. 32(4):336-342 © 1998 The Raptor Research Foundation, Inc. Evaluating Northern Goshawk {Accipiter gentilis atricapillus) Population Status: A Reply to Smallwood and Crocker-Bedford Patricia L. Kennedy Department of Fishery and Wildlife Biology and Graduate Degree Program in Ecolosy, Colorado State University, Ft. Collins, CO 80523 U.S.A. Shawn Smallwood and Cole Crocker-Bedford present thought-provoking reviews of my recent paper on North- ern Goshawk {Accipiter gentilis atricapillus) population trends (Kennedy 1997). In addition, Crocker-Bedford provides a detailed review of his controversial 1990 paper on forest management and its impact on goshawk repro- duction (Crocker-Bedford 1990). Finally, both authors present their ideas on alternative approaches that might be used to evaluate the status of the goshawk. Here is my reply to their comments. Objective of Kennedy (1997) Smallwood and Crocker-Bedford find fault with my pa- per because I did not include habitat analyses. They rightly claim that evaluating habitat loss is a key listing criterion of the Endangered Species Act (ESA) . I do not disagree with them and think a thorough analysis of gos- hawk habitat data is an important component of a status review. But the aim of my paper was not to conduct a status evaluation for the listing proposal, which was clear- ly misunderstood by the two authors. A status review is the purview of the U.S. Fish & Wildlife Service (USFWS) and they just finished such an evaluation (Clark 1998). I merely evaluated the petitioners’ claim “that goshawk populations have suffered significant declines.” I wanted to see if the statements presented by the petitioners as fact indeed had empirical basis. I treated their statement as an hypothesis, proceeded to test this hypothesis, and found no support for their statements. The goal of my paper was to conduct the first step in a status assessment and determine, in a scientifically thor- ough manner, if there is evidence of a population de- cline. I did not continue to the next step, that of deter- mining reasons for a decline, because, as I stated in my paper, “Diagnosing a cause of decline is irrelevant if there is no evidence that a decline has occurred.” Once some evidence of a decline has been documented then the cause (s) of the decline can be determined and ap- propriate conservation plans developed and implement- ed (Caughley and Gunn 1995). If there is no evidence of a demographic decline, how can we Justify spending taxpayer dollars to develop and implement expensive re- covery programs? Without demographic data, how does the recovery team establish achievable, quantifiable re- covery goals as delisting criteria (see Pagel et al. 1996, Cade et al. 1997, and Pagel and Bell 1997 on the debate about recovery goals for American Peregrine Falcons \Falco peregrinus anatum])? The USFWS used a similar ap- proach in their recent status evaluation where they ex- amined evidence that goshawk populations were declin- ing and then proceeded to evaluate the potential loss of goshawk habitat. They concluded that listing the goshawk as Endangered or Threatened west of the 100th meridian is not warranted (Clark 1998). What Response Variables Are Appropriate to Evaiuate Goshawk Population Trends? Evaluating Goshawk Trends Using Demographic Vari- ables. There are two general approaches that can be used December 1998 Commentary 337 to monitor population trends: the survey method and the demographic method (Taylor and Gerrodette 1993). Us- ing a survey method would entail attempting to estimate population size (or some index of population size) di- rectly over several years and determine whether or not the estimates indicate a decline over time. Because it is not feasible to census the entire population of most bird species (including raptors), population monitoring is al- most always based upon surveys of a sample of the pop- ulation. The demographic method involves monitoring trends in vital rates (survival, fecundity, immigration, and emigration) and then using these data to calculate finite population growth rate (X). X can be calculated by fol- lowing reproduction and survival of individual cohorts (age classes), or it can be estimated through simulation based on annual variation in cohort survivorship and re- production (Gotelli 1998). In my paper, I examined available data that could be used to monitor goshawk population trends, using either the survey or demographic approach. Surprisingly, nei- ther author thought any of the demographic response variables I chose to evaluate trends was useful for deter- mining goshawk population status! In his conclusions, Smallwood states: “Population density, fecundity, survival and rate of population change all lack scientifically de- fensible relationships with range-wide abundance. ...” I disagree and still adhere to the basic tenets of population biology that I describe here. Attaining accurate measure- ments of these parameters that are appropriate for the scale of inference, however, is problematic but not im- possible. Population Abundance. Abundance refers to the num- ber of individuals within a population (or population size) (Krebs 1994). If the population is so large that a study cannot encompass the whole of it (e.g., range-wide goshawk population) , then abundance must be present- ed in terms of densities rather than absolute numbers. Thus samples are taken and abundance is expressed as number of animals per unit area (Begon and Mortimer 1986). Density is thus the spatial expression of abun- dance (Krebs 1994). Temporal trends of density would reflect temporal trends in abundance. As indicated by Smallwood, simple tallies of nests to estimate breeding density in a study area is fraught with problems and pro- duces biased estimates of population size (Gould and Ful- ler 1995) . Rather than rejecting density as an appropriate response variable, this problem could be solved by esti- mating population size using Jolly-Seber models. The Jol- ly-Seber model is a capture-recapture model allowing for an open population in which additions and/ or deletions occur. The model produces population density estimates for each sampling period (e.g., year). This method has been described extensively in the literature and the ap- plication of this approach to raptors is described in an excellent paper by Gould and Fuller (1995). Another potential approach for monitoring abun- dance of goshawks is the area-occupied technique (Iver- son and Fuller 1991). This approach employs repeatedly broadcasting calls from the same locations, and using the pattern of responses to estimate the probability of de- tecting an animal given that one is present. Probability of detection — area occupied techniques have been used successfully on another woodland raptor, the Red-shoul- dered Hawk {Buteo lineatus, McLeod and Andersen in press), and are particularly promising for monitoring species in landscapes where proportion of area occupied is high, and birds have a high probability of responding to a call. To date, little work with this technique has been conducted with goshawks. However, goshawks respond to call broadcasts (Kennedy and Stahlecker 1993); thus, this approach may be useful in monitoring their populations. Before this technique could be applied widely, it would need to be validated in areas where goshawk density has been estimated independently. Currently, the relation- ship between estimates of area occupied and breeding density have not been clearly established; so, before this technique could be used to monitor breeding density, such a relationship would have to be evaluated. Bart and Robson (1995) describe a double-sampling procedure that could be used to calibrate this technique. Density could be estimated on quadrats using foot (Rosenfield et al. 1998) or aerial surveys for occupied nests (aerial sur- veys could only be used before leaf-out in deciduous hab- itat [see Cook and Anderson 1990 for an example]). These estimates would be compared to the estimates ob- tained from the area-occupied technique and the area- occupied estimates would be adjusted accordingly. Vital Rates. The population attributes (or vital rates) influencing changes in abundance are immigration and birth, which increase abundance, and emigration and death which reduce it (Begon and Mortimer 1986, Krebs 1994). The combined effect of these four processes pro- vides an accurate indication of how abundance changes. X potentially can be estimated with a high degree of pre- cision and accuracy. Both authors criticize the use of these demographic variables because of sampling diffi- culties. Crocker-Bedford states that “. . . it is usually im- possible to calculate a meaningful X for a sparsely distrib- uted species.” This is not true. Meaningful Xs have been calculated for several species of management concern in- cluding the Northern Spotted Owl {Strix ocddentalis caur- ina, Burnham et al. 1996) and Ashy Storm-petrel {Ocean- odroma homochroa, Sydeman et al. 1998). I agree with Crocker-Bedford that this parameter is difficult to esti- mate particularly when using capture-recapture data to estimate survival. However, survival rates can be deter- mined using other methods such as radiotelemetry (Iver- son et al. 1996, Ward and Kennedy 1996, Ganey et al. 1998). The estimation procedure is less complex than for banding data (see White and Garrott 1990) and I hy- pothesize that smaller sample sizes would be required than with capture-recapture data, although I have not conducted a power analysis to test that hypothesis. Contrary to the criticisms of both authors, I still think 338 Commentary VoL. 32, No. 4 a metaanalysis would be useful to estimate goshawk fe- cundity and survival from currently available vital rate data collected at individual study areas. This approach was used successfully to analyze Northern Spotted Owl datasets (Burnham et al. 1996) so there is no reason why this approach could not be used for the goshawk which is a species that is more widely distributed and probably more abundant than the Northern Spotted Owl. This me- taanalysis would be an inexpensive next step to deter- mine what types of data are needed and how many study areas would be required to obtain sufficient data. For example, using this approach, the datasets of Reynolds and Joy (1998) referred to by Crocker-Bedford could be pooled with the survival data presented in my paper and in DeStefano et al. (1994). Because sampling protocols were similar in all three study areas, survival estimates could be analyzed for the years in which the studies over- lapped (1991-92 for all three studies and 1991-95 for New Mexico and Arizona). This should be done before more resources are committed to collecting vital rate data and the results of the analyses could be used to assist the design of future long-term studies. 1 agree with Small- wood that a metaanalysis should not be used in lieu of proper sampling. However, it is an underutilized tool that can be used to analyze data from multiple, well-designed, coordinated studies which are unlikely to estimate pop- ulation trends individually due to the rarity of the species. Evaluating Goshawk Trends Using Migration Counts. Smallwood suggests that goshawk abundance should be evaluated based on changes in migratory counts. The utility of migration counts for monitoring population trends has been much debated (see Bildstein 1998 for a detailed discussion of the strengths and weaknesses of migration counts as an index to population size). To track population change, a constant proportion of the index (e.g., migration counts of goshawks) to the true population size must be maintained. If this does not oc- cur then the proportion must be estimated. These vali- dation studies bave not been conducted on the goshawk for a local area or range wide, so the trends in the cur- rent migration count data are difficult to interpret. Also, trends in migration counts could reflect distri- butional changes or changes in residency patterns rather than changes in population size. For example, recent an- alyses of Christmas Bird Count data suggest that Sharp- shinned Hawks {A. striatus) are increasing. Several au- thors have suggested that more Sharp-shinned Hawks are overwintering in northern North America because of warmer winter climates and/or the abundance of bird feeders which provide a stable overwinter food source (see review in Bildstein 1998). This could be the reason that counts of Sharp-shinned Hawks at northern migra- tion stations have been lower in recent years. Since gos- hawk migrations are characterized by irruptive invasions, migration counts of this species are more likely to reflect residency patterns than changes in abundance (Bednarz et al. 1990, Titus and Fuller 1990). So, in response to Smallwood, to replace demographic variables that are known to represent abundance or influence abundance with an uncalibrated index is inappropriate. However, mi- gration counts could be continued and used as an ad- dendum to demographic studies to determine if the counts reflect demographic changes in goshawk popula- tions. Evaluating Goshawk Status by Monitoring Habitat Var- iables. What is the role of monitoring habitat variables in determining tbe status of goshawks? I agree with Small- wood, Crocker-Bedford, and DeStefano that habitat var- iables should be included in a goshawk-monitoring pro- gram. However, as noted by Crocker-Bedford and DeStefano, habitat monitoring should augment demo- graphic studies, not replace them. Evaluating goshawk status purely from migratory counts and information on habitat availability and contiguity as suggested by Small- wood assumes that goshawk habitat can be defined and that the relationship between these variables and gos- hawk abundance is well-documented. Currently, these re- lationships are not well-defined. In the recent status evaluation the USFWS concluded, “The information presented in the petition relies largely on the contention that the Northern Goshawk is depen- dent on large, unbroken tracts of ‘old-growth’ and mature forest. However, the Service has found no evidence to sup- port this claim. The Service found that while the goshawk typically does use mature forest or larger trees for nesting habitat, it appears to be a forest generalist in terms of the types and ages of forests it will use to meet its life history requirement. Goshawks can use small patches of mature habitat to meet their nesting requirements within a mosaic of habitats of different age classes ...” (Clark 1998). I con- cur with their findings and suggest that more habitat stud- ies are needed that are designed to determine the range of habitats used by the goshawk. I agree with Smallwood, Crocker-Bedford, and DeStefano that these studies need to be conducted at multiple spatial scales to be meaning- ful. I would add that habitat studies should be conducted year-round and not just focused on nesting habitat. Our knowledge of goshawk winter ecology is appallingly scant (Squires and Reynolds 1997). Finally, 1 concur with De- Stefano that trends in forest habitat availability should also be documented to determine trends in availability of gos- hawk habitat. Once goshawk habitat is well-defined and demograph- ic data are available from several study areas for an anal- ysis of population trends (see DeStefano for further dis- cussion of the value of long-term studies at multiple study areas) , I’d recommend we begin development of a model (or models) that predicts the relationships between suit- able nesting and winter habitat and population trends and/or performance. This predictive model will need to be refined and tested to examine relationships between habitat data and population size or other relevant de- mographic parameter. If a habitat model can predict gos- hawk population performance, then monitoring pro- December 1998 Commentary 339 grams can switch emphasis from population-based monitoring to habitat-based monitoring. If habitat mod- els do not adequately predict population performance, population-based monitoring will need to be continued and the habitat relationship information will need to be reevaluated. This approach is based on ideas presented by recent monitoring plans for the Marbled Murrelet {Brachyram- phus marmoratus, Madsen et al. in press) and Northern Spotted Owl (Lint et al., in press) in the Pacific North- west, and monitoring plans for the goshawk in the west- ern Great Lakes region (Kennedy and Anderson unpubl. data) . The emphasis is to use the demographic and hab- itat data collected in the initial phases (Phase I) of a monitoring program and to develop habitat-based mod- els that use habitat features to predict goshawk occur- rence and demographic performance in the latter phases (Phase II) of a monitoring program. If reliable habitat models can be developed to predict population status and trend at a landscape scale, monitoring can switch from intensive and costly population-based monitoring to a less expensive habitat-based monitoring approach. The habitat-based monitoring would emphasize monitoring the habitat features that predict goshawk performance and/or status, with less emphasis on monitoring popu- lation parameters. However, presence/absence of breed- ing goshawks in suitable habitat (as identified by the hab- itat models) would need to continue in Phase II to ensure that this habitat remains occupied. I emphasize that the switch from Phase I to Phase II can only occur if the habitat models are demonstrated to reliably predict goshawk population performance. Models that are not validated are essentially equivalent to untested hypothe- ses, so population-based monitoring would have to con- tinue until validated models are developed. In addition to the model development, I strongly sup- port DeStefano’s suggestion that on-site experiments de- signed to measure goshawk responses to silvicultural treatments be initiated. These quasi-experiments are be- ing implemented continuously in the form of timber har- vest near goshawk nests; most sale areas are identified years before the sale allowing for the collection of ade- quate pretreatment data. Monitoring pre- and posttreat- ment movements of even a few pairs of birds would pro- vide us with fascinating qualitative insights into goshawk responses to harvest and could be the basis for designing additional experiments. Crocker-Bedford does not think field experiments like this are possible and states, “Scientists should explicidy recognize that goshawk field studies are correlative. . . .” I disagree with this statement because these types of land- scape-level, quasi-experiments have been conducted on passerine communities (Bierregaard and Lovejoy 1989, Schmiegelow et al. 1997) and goshawks have been suc- cessfully used as experimental units in field experiments (Kenward et al. 1993, Ward and Kennedy 1996, Dewey 1998). Thus, we are not restricted to correlative studies. Although correlative studies are valuable in identifying patterns, they do not imply cause and effect (Romesburg 1981, 1989, Krebs 1994). For example, trends in popu- lation or habitat availability do not imply causes of pop- ulation change; experimental data are needed for such an evaluation. Raptor biology can move beyond its de- pendence on the correlative approach and toward more field experimentation with creative thinking about how to test hypotheses and a willingness to try new approach- es. Romesburg (1981) claimed nearly two decades ago that much wildlife science was compromised with respect to providing the reliable knowledge required to make management decisions. He argued that management should be based on “good science,” which is the scien- tific evidence best able to provide reliable knowledge. Re- liable knowledge is based on the hypothetico-deductive (H-D) method. The H-D method employs three steps, observation/induction, hypothesis formation and exper- imentation (Romesburg 1981, 1989). Crocker-Bedford is arguing that we approach goshawk management by only completing the first two steps. What typically happens when this is done in management is hypotheses advanced to account for observations gradually evolve into expla- nations for them through a process Romesburg (1981) called retroduction. The petitioners’ statements about goshawk declines are examples of retroduction. Comments on Crocker-Bedford (1990) In addition to providing a thoughtful critique of my paper, Crocker-Bedford dedicates a considerable seg- ment of his rebuttal detailing methodologies and strengths and weaknesses of his controversial 1990 paper. He is providing these details to rebut recent scientific evaluations of his 1990 paper (Kennedy 1997, White and Kiff 1998). Crocker-Bedford’s identification of the strengths and weaknesses of his 1990 paper adds a valu- able component to this scientific debate and an appro- priate addendum to his 1990 paper. However, I disagree with several points he makes. As I mentioned in my paper (Kennedy 1997), one of the major strengths of Crocker-Bedford’s 1990 paper was that it was the first published paper to suggest that gos- hawk populations were declining due to overharvest of their forested nesting habitat. This idea was important and it fueled this stimulating debate on goshawks and forest management. However, his paper has some serious flaws. Crocker-Bedford implies that his study was criti- cized because he had conclusions that were politically sensitive. It is likely that some of the unpublished criti- cisms he received over the years were politically motivat- ed, yet the aforementioned published critiques were based on scientific merit. Crocker-Bedford claims that one of the strengths of his paper is that he “. . . demonstrated long-term nest tree fidelity in the absence of habitat degradation.” Whether or not he demonstrated this depended on his methods for estimating locale reoccupancy, which have still not 340 Commentary VoL. 32, No. 4 been adequately explained. Comparisons of occupancy rates need to be done cautiously because occupancy rate is a subjective parameter that is probably correlated with the amount of effort expended to determine territory status (White et al. 1995, Kennedy 1997). We still do not know if Crocker-Bedford (1990) used standard search ef- fort techniques for treatment and control locales. He states that his study was not biased by an inappropriate nest search effort and justifies this based on his large sample size. However, sample size is not the major factor influencing estimation of occupancy rates, it is search ef- fort. He states “. . . the vicinity was extensively searched for alternate nests.” Was each nest site searched with equal effort and was an equal-sized area searched prior to determining a site was unoccupied? This is important because there is a high probability of missing alternative nests in goshawk territories due to large inter-alternative distances. In California, mean distance between alterna- tive nests was 273 m and the range was 30-2066 m (Woodbridge and Detrich 1994). In Arizona, mean inter- alternative nest distance was 489 m and the range was 21-3410 m. Approximately 89% of alternative nests in Arizona were within 900 m and 95% were within 1400 m of one another (Reynolds and Joy 1998). Clearly, the po- tential for misclassifying an occupied territory as unoc- cupied is great if nest site searches are restricted to the immediate vicinity (50-100 m) of the most recently used nest. So small search areas, even if they are consistently applied to treatment and control locales, might result in more false negatives in treatment locales because harvest might influence inter-alternative distances rather than occupancy rates. The most controversial statement in Crocker-Bedford (1990) was his claim in his summary that the goshawk population on the North Kaibab Ranger District de- clined, “. . . from an estimated 260 nesting pairs in 1972 to approximately 60 pairs by 1988.” He claims that his breeding population projections are one of the strengths of his paper. I strongly disagree because 1 think this state- ment is an example of inappropriate inference given his dataset. He did not provide an analysis of the limitations of his calculations nor did he provide alternative expla- nations for his results. He based his estimation of rate of population change solely on published breeding density estimates of the areas harvested in the 1950s and 1960s (Crocker-Bedford and Chaney 1988) and his estimates of reoccupancy rates (Crocker-Bedford 1990). He cites un- published data in this rebuttal that were apparently used m these calculations. However, the methods he used for estimating these densities are unknown and should have been presented in the 1990 paper. In addition, he did not estimate a variance of any of his density estimates, which influences one’s interpretation, as I will demon- strate below. Crocker-Bedford argues that his breeding population projections are corroborated by recent population size estimates of the same area by Reynolds and Joy (1998). In contrast, I suggest that the Reynolds and Joy (1998) results provide an excellent example of why his projec- tions were an example of inappropriate inference. Reyn- olds and Joy (1998) estimate that approximately 100 ter- ritories currently remain on the District (they have located 95 occupied territories in surveys of 95% of the District). Crocker-Bedford estimated the population size in 1988 to be 60 pairs. If we take a conservative approach and assume the population size has not increased be- tween 1988-96, this suggests that Crocker-Bedford’s esti- mate of 60 pairs could vary by 66% (20-100 pairs). If we extend this simple estimate of variance to his historical estimates they could have varied from 86-432. We cannot compare these ranges statistically because we do not know his estimate of variance, but these calculations sug- gest that one plausible breeding projection would be that the number of pairs varied between 86-100 between 1972-88, respectively. This is equally as plausible an in- terpretation as the one provided by Crocker-Bedford (1990). Crocker-Bedford (1990) used two estimates of density that may or may not be comparable, depending on the estimation procedures, did not provide an estimate of the precision and bias of his estimator, drew a line through these two points, made a single interpretation of the trends and ignored any plausible alternative explana- tions. This is considered inappropriate inference within the scientific community. Crocker-Bedford (1990) should have concluded that it was not possible to determine if the North Kaibab goshawk population was increasing, de- creasing, or stable because of wide variation in demo- graphic estimates. Maguire and Call (1992) reached sim- ilar conclusions in their population viability analysis (PVA) for the same goshawk population. They found, “. . . the range of variability in parameter estimates, par- ticularly for mortality rates, was so great that our simu- lation results produced populations that ranged from rapidly increasing to rapidly declining. We are unable to conclude from these results whether the North Kaibab Ranger District is stable, increasing or decreasing.” Smallwood incorrectly interpreted their study (cited as Maguire 1993) by focusing on the potential for popula- tion declines as a result of habitat loss. However, this was not the major conclusion of the Maguire and Call PVA. Conclusions Although neither Crocker-Bedford nor Smallwood can provide empirical results to refute my conclusions or the conclusions of the USFWS status review, their papers pro- vide thoughtful and insightful comments that have stim- ulated an interesting discussion about approaches for evaluating population trends in goshawks. The disagree- ment and controversy described by Smallwood and Crocker-Bedford and expanded by DeStefano are char- acteristics of intellectual ferment driven by the best cre- ative effort of ecologists and are among the reasons why conservation biology and wildlife management are such December 1998 Commentary 341 exciting fields. I hope these discussions continue and they result in improved approaches to evaluating popu- lation trends of rare and uncommon species. Acknowledgments I thank S. DeStefano, J. Marzluff, S. Skagen and an anonymous reviewer for their thoughtful and construc- tive reviews of this manuscript. My special thanks to D. Varland for patiently waiting for drafts of this manuscript and for providing me with the opportunity to participate in this dialogue. Many of the ideas presented in this pa- per resulted from numerous in-depth discussions with D.E. Andersen that occurred while I was on sabbatical leave at the University of Minnesota. 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Schmiegelow, F.K.A., C.S. Machtans and SJ. Hannon. 1997. Are boreal birds resilient to forest fragmenta- tion? An experimental study of short-term community responses. Ecology 78:1914-1932. Squires, J.R. and R.T. Reynolds. 1997. Northern Gos- hawk {Accipiter gentilis) . In A. Poole and F. Gill [Eds.], The birds of North America, No. 298. The Academy of Natural Sciences, Philadelphia, PA U.S.A. Sydeman, W.J., N. Nur, E.B. McLaren and GJ. Mc- Chesney. 1998. Status and trends of the Ashy Storm- petrel on southeast Farallon Island, California, based upon capture-recapture analyses. Cont/or 100:438-447. Taylor, B.L. and T. Gerrodette. 1993. The uses of sta- tistical power in conservation biology: the Vaquita and Northern Spotted Owl. Conserv. Biol. 7:489-500. Titus, K. and M.R. Fuller. 1990. Recent trends in counts of migrant hawks from northeastern North America. /. Wildl. Manage. 54:463-470. Ward, J.M. and P.L. Kennedy. 1996. Effects of supple- mental food on size and survival of juvenile Northern Goshawks. Auk 113:200—208, White, C.M. and L.F. Kiff. 1998. Language use and mis- applied, selective “science”; their roles in swaying public opinion and policy as shown with two North American raptors. Pages 547-560 in Chancellor, R.D., B.-U. Meyburg andJ.J. Ferrero [Eds.]. Holarctic birds of prey. Adenex and World Working Group of Birds of Prey, Merida, Spain. White, G.C. and R.A. Garrott. 1990. Analysis of wildlife radio-tracking data. Academic Press, New York, NY U.S.A. , A.B. Franklin and J.P. Ward. 1995. Population biology. Pages 1-25 in USDI Fish and Wildlife Service, Recovery plan for the Mexican Spotted Owl, Chap. 2. Vol. II. Albuquerque, NM U.S.A. Woodbridge, B. and PJ- Detrich. 1994. Territory occu- pancy and habitat patch size of Northern Goshawks in the southern Cascades of California. Stud. Avian Biol. 16:83-87. Received 1 August 1998; accepted 24 August 1998 / Raptor Res. 32(4) : 342-348 © 1998 The Raptor Research Foundation, Inc. Determining the Status oe Northern Goshawks in the West: Is Our Conceptual Model Correct? Stephen DeStefano U.S. Geological Survey, Arizona Cooperative Fish and Wildlife Research Unit, 104 Biological Sciences East, University of Arizona, Tucson, AZ 85721 U.S. A. In federal district court in Tucson, Arizona recently, a case was heard regarding the status of the Endangered Cactus Ferruginous Pygmy-owl {Glaucidium brasilianum cactorum) and development in the Tucson basin (Defend- ers of Wildlife vs. Amphitheater School District). The western population (Arizona) of the Cactus Ferruginous Pygmy-owl had been listed in 1997 under the Endan- gered Species Act (ESA) , and a local school district want- ed to build on an area allegedly used by one or more owls. Defenders of Wildlife, as the plaintiff, was suing to stop the development. Owls had been seen just north and south of the boundary of the property in question, and the attorney for the defense built part of her case on the fact that an owl had not actually been seen inside the property boundary. She used this “uncertainty” about the owls’ use of the property, as well as other as- pects of its little-known ecology in Arizona, to her advan- tage and stated in court “there comes a point where the December 1998 Commentary 343 best evidence available isn’t good enough” (Nintzel 1998). That statement is a big problem for biologists in court, and one that could always be used against us. The “best evidence available” will always involve uncertainty be- cause our best data are usually sample data, which, by definition, contain uncertainty (Ramsey and Schafer 1997), and we will rarely have all the data we need. “Un- certainty” is not a negative concept in science, but part of the process (Murphy and Noon 1991, Williams et al. 1996) . The courts, however, view uncertainty as equiva- lent to “a shadow of doubt.” If conservationists are al- ways charged with the burden of proof, we will more of- ten than not lose in court, which is where conservation and resource management decisions are made with in- creasing frequency. The status of the Cactus Ferruginous Pygmy-owl has implications for a small part of the world — the few par- cels of undeveloped land in the unplanned and overde- veloped Tucson basin of southern Arizona. The status of another raptor, the Northern Goshawk (Accipiter gentilis atricapillus) has much broader implications. The goshawk IS distributed in forested areas throughout much of North America, and the implications of listing this spe- cies as Threatened or Endangered under the ESA are far- reaching and important, perhaps even more so than the listing of the Northern Spotted Owl {Strix occidentalis caur- ina) as a Threatened Species in 1990. Like the Northern Spotted Owl, the goshawk is a forest raptor dependent, at least partially, on older forest, and thus millions of dollars worth of timber are involved. This certainly heightens the interest of the public, the Congress, and the courts. In addition, the goshawk occurs over a much broader geographic area than the Northern Spotted Owl. Regardless of the final decision to list or not list the gos- hawk, court is likely where we are headed. This paper represents some thoughts on the status of goshawks in the West, including a review of recent events that helped shape the debate over Endangered Species management, a summary of available data on goshawk ecology, some suggestions for additional data that could or should be collected, and some questions on how pro- fessional biologists, environmental groups, and society in general invoke and use the ESA. It is also a forum for me to air some of my own uncertainties regarding the status of this species and some suggestions for courses of action for its management and conservation. I hope that any or all of this fosters additional discussion. I focus on goshawks west of the 100th meridian, and refer to this as the West, because that has been the geographic scope of recent listing petitions (U.S. Fish and Wildlife Service 1998b) and includes the area where most of the recent ecological and demographic research has occurred (Block et al. 1994, Kennedy 1997, Squires and Reynolds 1997) . Finally, I make liberal use of the pronoun “we” throughout the paper to emphasize the idea that conser- vation issues are the concern and responsibility of all cit- izens, and to deemphasize the concept of “us” vs. “them” that so often plagues conservation debates. A Recent Historical Perspective Northern Spotted Owl as Conservation Model. It would be a mistake to evaluate the status of any candidate species for listing under the ESA, and particularly any forest raptor, without first considering the history and implications of the Northern Spotted Owl issue in the Pacific Northwest. Yaffee (1994) called the spotted owl controversy a “watershed event” in resource and envi- ronmental policy. In many ways we entered a new era m conservation, with myriad implications in policy, politics, and public relations. Important among them was a stron- ger focus on ecosystems as the public, through the me- dia, saw the extent of the destruction of old-growth forest (i.e., native forest unaltered by human activities with nat- ural processes [e.g., hydrology, succession, wind-throw, fire] intact) . The alteration of ecosystems in North Amer- ica was not new — consider, for example, wetlands, prai- ries, and deserts — but the focus and level of attention was something different. Equally important was a demonstra- tion of the power and reach of the ESA. This law became a potent tool for environmentalists; any citizen could pe- tition for a listing (Rohlf 1989), and if listing occurred, there was legal power to alter the rate of resource ex- traction. Bridging concerns over the loss of old-growth forests and the power of the ESA to change that trend was per- haps an ideal species: a somewhat mysterious but easily photographed (and thus newsworthy) owl that was an old-growth obligate (Forsman et al. 1984). The listing of the Northern Spotted Owl under the ESA as a Threat- ened Species brought harvest of old-growth timber in the region to a standstill, an environmental issue to the at- tention of the nation, and a president to Portland, Oregon for a national meeting. The old growth-Northern Spotted Owl model of controversy, confrontation, and conservation became a template for protection of nature. A Parallel Course? During the latter stages of the spot- ted owl issue, Crocker-Bedford (1990) published a paper on goshawk reproduction and forest management in Ar- izona, citing a correlation between excessive timber har- vest and loss of goshawk breeding territories. Petitions to list the goshawk soon followed (Kennedy 1997). At issue again was not only concern for the continued existence of a species, but a desire to stop logging in old-growth forest: not just the mesic forests of Douglas-fir {Pseudo- tsuga menziesii) , western hemlock ( Tsuga heterophylla) , and firs {Abies spp.) west of the Cascade Range, but the much more widespread drier forests of Ponderosa pine {Pinus ponderosa), lodgepole pine {P. contorta), and mixed coni- fers of the interior West. We had just seen a demonstra- tion of the power of the ESA to slow the pace of timber harvest to the benefit of Northern Spotted Owls; perhaps this was the best course for the goshawk. 344 Commentary VoL. 32, No. 4 4 \ Available forest cover Increasing mean Decreasing variance Forest structure Figure 1. Theoretical graphs comparing Northern Spotted Owl and Northern Goshawk use (e.g., for nest or roost sites) of old-growth forest structure (e.g., density of large trees, high overstory canopy closure) to forest structure available on the landscape. Preponderance of old-growth characteristics increases to the right of the x-axis. Northern Goshawks use a wider range of forest structural stages than Northern Spotted Owls, but use older forest more than it is available on the landscape. See text for additional discussion. Goshawks and Old-growth Forest Early petitions to list the goshawk prompted a thor- ough examination of past studies and a host of new stud- ies by independent researchers in several western states (Squires and Reynolds 1997, Daw et al. 1998). Most of these studies focused on nesting habitat, partly because of the importance of breeding biology to the ecology and management of goshawks, but also because it was difficult to approach research on this elusive species in any other way. These studies may be criticized as a duplication of effort, but when one examines them as a group, an in- teresting and important pattern emerges: goshawks, re- gardless of region or forest type, tend to select stands with large trees (e.g., >53 cm dbh; Daw et al. 1998) and relatively high canopy closure (e.g., >50-60%; Ward et al. 1992, Daw et al. 1998) for nesting (see Daw et al. 1998 for a summary of research). I believe it was a combination of our recent experience with Northern Spotted Owls and the pattern of goshawks nesting in forest stands with old-growth characteristics that led many to believe that the goshawk was an “old- growth species.” Reynolds et al. (1992) described what might be optimal goshawk habitat in the southwestern U S.: it included not only a large percentage of the land- scape in older forest, but also a mix of stand types and ages that provides for a variety of prey and takes into account forest stand dynamics (Graham et al. 1994). Im- portantly, the southwestern management guidelines in- corporated timber harvest as a mechanism to achieve the desired mix and distribution of forest structural stages. Fig. 1 illustrates, in a very general way, one idea of how Northern Spotted Owls, goshawks, and forest cover may relate to one another over a broad geographic scale. The x-axis can be any forest structure variable or combination of variables that characterize old-growth forest (increas- ing size of trees, density of large trees, and/or overstory canopy closure); the further right one goes on the x-axis the more prevalent are those characteristics. The y-axis represents increasing frequency of occurrence; for owls or goshawks it could be number of nest or roosting sites; for available forest cover it is the frequency of occurrence for a particular structural stage on the landscape. Al- though these graphs are theoretical, data exists to sup- port them (Ripple et al. 1991, Siders and Kennedy 1996, McGrath 1997). The top graph shows that Northern Spotted Owls are found mostly in older forest, with lim- ited variation around the mean, indicating the impor- tance of older forest to their existence. The second graph shows goshawks as being found in a wider variety of forest structural stages compared to spotted owls. Older forest is important to goshawks, but goshawks are more of a forest generalist than are spotted owls. Finally, the third graph illustrates general forest structure across much of the West, based on measurements taken at random points as an index of “availability” (Manly et al. 1993). Compared to the graph for goshawks, the mean is cen- December 1998 Commentary 345 tered over younger forest and there is wider variance. The relative positions of these three graphs probably would be expected even for pristine forests. Today, how- ever, forests in the West have clearly been forced to ear- lier structural stages (i.e., forest structure has been “pushed” to the left side of the graph). The changing structural stage of forests is a trend that should and does concern us. Setting forest succession back through clearcutting old-growth forest west of the Cascade Range has had important implications for Northern Spotted Owls— enough to list the species as Threatened. The effect that multiple entry selective cut- ting on Ponderosa pine and other dry forest tree species has had on goshawks is also of concern, but the impli- cations are less clear. Given that forest management prac- tices are likely affecting even this relatively versatile forest raptor, the question becomes how to respond to that con- cern. One possible response is to list the goshawk as an Endangered Species, which would likely stop or at least slow the cutting, as it did for the Northern Spotted Owl. Based on this logic, a series of petitions by environmental groups to list various segments of the goshawk popula- tion in the West began in the early 1990s and has contin- ued unsuccessfully well into the decade (U.S. Fish and Wildlife Service 1998b). The Data We Have Demography. In response to the petitions to list, Ken- nedy (1997) reviewed the available published literature on the subspecies A. g. atricapillus in North America and conducted analyses on demographic data from two pop- ulations in New Mexico and Utah. She evaluated the claim that goshawk populations were declining in North America, stating that evidence of a decline would include range contractions, decreases in density, or decreases in fecundity or survival, which might translate into a nega- tive rate of population change (X). Based on this ap- proach, she concluded that there was no evidence to sup- port the contention that goshawk populations were declining. Importantly, she stated that this result could be interpreted in two ways: goshawk populations are not declining, or goshawk populations are declining but the decline has not been detected. The latter interpretation would be a Type II error and, as such, is of concern to conservation biologists (Steidl et al. 1997). Kennedy’s (1997) review was an important and neces- sary step in examining the status of goshawks. Cole Crocker-Bedford and Shawn Smallwood have taken issue with Kennedy’s approach and have pointed out problems that can arise in collecting and interpreting demographic data. However, demographic information, as difficult as it is to collect, is vital to understanding population dy- namics: the available demographic data on any species considered for listing must first be assessed {sensu Ken- nedy 1997) before collection of additional demographic data can be improved {sensu Smallwood 1998). Habitat. Goshawks can be found in a variety of forest cover types throughout the West (Squires and Reynolds 1997), and in that sense can be viewed as forest gener- alists. For any given forest cover type, however, goshawks tend to nest in stands with large trees and high canopy closure; their choice of nest sites could relate to micro- climate, protection from predation, or something else, but the pattern is well-documented (Daw et al. 1998) Older forest may also be important in the postfledging family area (PFA) (Kennedy et al. 1994, Daw 1997). As one looks at forest cover at increasing distances from the nest, however, older forest becomes less prevalent (Daw 1997, Desimone 1997), and possibly less important (McGrath 1997). While older forest may be less prevalent on the landscape in general because of past timber man- agement activities, older forest away from the nest may be less important to breeding goshawks than older forest immediately around the nest. Prey. Goshawks hunt in older forest and may even pre- fer it if it is available (Bright-Smith and Mannan 1994, Beier and Drennan 1997), but they also hunt in a variety of vegetative cover. For example, in eastern Oregon it was not uncommon to see goshawks hunting in open sage- brush {Artemisia spp.), and we often found ground-squir- rels {Spermophilus spp.) in prey remains (Cutler et al. 1996). In addition, some of the most important prey of goshawks are lagomorphs and grouse, particularly snow- shoe hares {Lepus americanus) and Ruffed Grouse {Bonasa umbellus) . These species provide more biomass than most other prey, and reproductive output in goshawks may be negatively affected when large-biomass prey are not avail- able (Doyle and Smith 1994, Iverson et al. 1996). Snow- shoe hares and Ruffed Grouse inhabit early successional stage forest and are key species in the ten-year cycle in northern North America (Doyle and Smith 1994). There are also very important relationships between prey abun- dance and availability for foraging goshawks, and forest structure plays an important role in goshawk foraging habitat (Beier and Drennan 1997, DeStefano and Mc- Closkey 1997) . The Data We Need Demography. Demographic data are vital, but studies must be properly designed and be long-term or the re- sults are difficult, if not impossible, to interpret (De- Stefano et al. 1994) . A study of goshawk demography and habitat use on the Kaibab Plateau, which is probably the longest running study on the species to date, is approach- ing a long-term basis. However, funding waxes and wanes as the threat of listing the goshawk comes and goes (R.T. Reynolds pers. comm.). Unreliable funding for needed long-term studies is short-sighted and counter-produc- tive. The U.S. Forest Service and other federal agencies must commit to studies that run greater than 10 years, as the answers we need cannot be determined in two to three years. Estimating the rate of population change (X) for a species such as the goshawk may simply be too dif- ficult and take too long for the listing process. Nonethe- 346 Commentary VoL. 32, No. 4 less, data on reproductive rates and survival are critical to understanding the ecology of goshawks and their likely response at a population level to changes in their habitat. It is worth considering if and how one can design and implement good demographic studies on goshawks be- fore we dismiss them altogether. Related to this, listing decisions based on migratory counts of goshawks would also be problematic, given the importance and influence of cyclic prey in the boreal forest and the capability of goshawks for long-range movements in response to declining prey. It would be difficult to assess trends in goshawk numbers based on migratory count data alone, even over a long period of time. However, migratory counts combined with other demographic data could provide important additional in- formation on goshawks (Bildstein 1998). Habitat. With some exceptions (e.g., A. g. laingi in southeast Alaska, A. g. apache in the Southwest) , another study on nesting habitat of goshawks in the West may not be necessary. However, there remains plenty to learn re- garding how juvenile goshawks use habitat within PFAs and how adults use habitat to forage. Also, very few hab- itat studies have been conducted in winter. Documenting the distribution of all forest structural stages, including mature or old-growth forest, across the West would be an important step in the status review pro- cess. Such documentation will be important for a number of wildlife species, including goshawks, and has been sug- gested by Crocker-Bedford (1998) and Smallwood (1998). Recent efforts of the U.S. Fish and Wildlife Ser- vice in the latest review of the status of goshawks in the West showed how poorly information on forest stand structure is documented and/ or available in a usable for- mat (U.S. Fish and Wildlife Service 1998a). Low response rates on questionnaires sent to land management agen- cies and a wide variety of documentation, both in quality of information and methods used, make decisions on goshawk status based on habitat availability problematic. Although methods to gather and compile data on cur- rent forest conditions across the West need to be im- proved, future decisions on the status of goshawks ought not to be made based on the availability of old-growth forest alone. Concurrent data on demography and dis- tribution of goshawks are also needed. Prey. Because prey resources are so important to the population dynamics and distribution of goshawks, ad- ditional information on prey use, and the influence and interaction of prey abundance, availability, and habitat structure on goshawk populations, is needed. A multi- species approach, which includes predators, prey, and competitors, also moves us away from single-species man- agement and more toward community and ecosystem ap- proaches (Squires et al. 1998). Discussion and Conclusions There is little doubt that we have destroyed, fragment- ed, and otherwise altered old-growth forest in North America (Norse 1990). In frustration to conserve rem- nant patches of old-growth, or any native ecosystem, the strongest tools of persuasion are going to be the ones most used. One such tool is the ESA. In the case of the Northern Spotted Owl and the temperate old-growth rainforest of the Pacific Northwest, this approach was prudent and necessary; listing the owl was the right course of action. However, before we take this action for the goshawk and list it as Threatened or Endangered, we need to ask if it is in the best interest of the species and the ESA itself. Listing decisions should be made regard- less of politics (Sidle 1998), but politics are surely a part of the process, and political opposition to the ESA is real and strong. I am not advocating a weak stance on pro- tecting species, just a reasoned one that considers our credibility as scientists and a judicious use of the ES/l. So, am I concerned about the status of goshawks in North America? Yes. Am I concerned about the loss of old-growth forest? Definitely. Should we list the goshawk to protect it and old-growth forest habitat? Probably not. This position may sound contradictory, given the case made for goshawks’ use of old-growth forest, but it hinges on several considerations, such as the variety of structural stages that goshawks use, the importance of some early successional stage forest prey, the overwhelming pressure to list many species in the U.S. — several of which are truly threatened with extinction — that taxes our limited re- sources, and a concern that we invoke the ESA judicious- ly- I recommend a different approach. I think there is time and opportunity to manage for goshawks in the West without listing. However, goshawks may currently be in the same position that spotted owls were in one to two decades ago. That is, some options remain, but if action is not taken now, far fewer options will be available later. To exercise some of our options now, I suggest the fol- lowing: ( 1 ) provide funding and support to maintain cur- rent research similar to that on the Kaibab Plateau, and perhaps two or three additional and coordinated studies in other regions; (2) continue coordinated efforts to identify and map areas of remaining older forests across the West; (3) support the testing and evaluation of em- pirical habitat models that have been developed in the Southwest (Reynolds et al. 1992) and Northwest (Mc- Grath 1997); (4) conduct on-site experiments to measure goshawk responses to silvicultural treatments; and (5) de- fer listing the goshawk under the ESA in favor of a co- ordinated national effort to assess habitat conditions, monitor populations, and evaluate habitat models and silvicultural treatment experiments (see Marzluff and Sal- labanks 1998, Squires et al. 1998). Federal and state land management agencies as well as the timber industry should be involved in this process. We should keep in mind, however, that listing remains an option and per- haps a necessity, but one that should be based more on coordinated scientific efforts than political agendas from either side of the issue. Resource agencies need to make December 1998 Commentary 347 firm commitments now to avoid listing the goshawk later. It would also be beneficial to avoid court, where “truth” IS not always based on the best science, but rather the most forceful argument. There is growing dissatisfaction with single species ap- proaches to conservation and management. We need to pursue research and management at all levels of orga- nization: populations, communities, and ecosystems. The goshawk is a good candidate for this multilevel approach. However, if we were to base our plans for the conserva- tion and management of old-growth forest solely on the goshawk, we may not like what we get. It is true that mature forest is important around nest sites and as a component of foraging habitat, but ideal goshawk habitat may include a sizeable portion of the landscape in early serai stage forest to encourage high populations of im- portant prey such as lagomorphs and Ruffed Grouse. The distribution of serai stages that may be good for gos- hawks, however, may actually include less old-growth than some other species require (possibly Pileated Woodpeck- ers [Dryocopus pileatus] and American marten [Martes americana ] ) . Implementing the above recommendations would take our collective will and effort, and it would mean that the land management agencies most involved with goshawks would need to be proactive and support research, adap- tive management, and monitoring for more than a few years. Terms like “proactive” and “adaptive manage- ment” are often used, but these concepts would need to be translated into action on the ground (Marzluff and Sallabanks 1998). Such actions, of course, will take quite a bit of money, but I couldn’t agree with Smallwood (1998) more when he states that adequate funding should be made available to ensure the viability of wildlife populations. Acknowledgments I thank D.C. Crocker-Bedford, T. Bosakowski, M.H. Henning, P.L. Kennedy, J.M. Marzluff, and K.S. Small- wood for their thoughtful and constructive reviews. My special thanks to D.E. Varland for providing me the op- portunity to air my views. Research on goshawks in Oregon was funded by the Nongame Program of the Oregon Department of Fish and Wildlife, U.S. Forest Ser- vice, U.S. Fish and Wildlife Service, Boise-Cascade Cor- poration, National Council for Air and Stream Improve- ment, and Center for Analysis of Environmental Change at Oregon State University. I appreciate the logistic sup- port of the Oregon and Arizona Cooperative Research Units. This paper is dedicated to S.K. Daw, S.M. Desi- mone, and M.T. McGrath, the diligent graduate students who did all the work. Literature Cited Beier, P. and J.E. Drennan. 1997. Forest structure and prey abundance in foraging areas of Northern Gos- hawks. Fcol. Appl. 7:564-571. Bildstein, K.L. 1998. Long-term counts of migrating rap- tors: a role for volunteers in wildlife research./. Wildl. Manage. 62:435—445. Block, W.M., M.L. Morrison and M.H. Reiser [Eds.]. 1994. The Northern Goshawk: ecology and manage- ment. Stud. Avian Biol. 16. Bright-Smith, D.J. and R.W. Mannan. 1994. Habitat use by breeding male Northern Goshawks in northern Ar- izona. Stud. Avian Biol. 16:58-65. Crocker-Bedford, D.C. 1990. Goshawk reproduction and forest management. Wildl. Soc. Bull. 18:262—269. Cutler, T.L., R.J. Steidl and S. DeStefano. 1996, Diets of Northern Goshawks in Oregon. USDA For. Serv, Portland, OR U.S.A. Daw, S.K. 1997. Northern Goshawk nest site selection and habitat associations at the post-fledging family area scale in Oregon. M.S. thesis, Oregon State Univ , Corvallis, OR U.S.A. , S. DeStefano and R.J. Steidl. 1998. Does search method bias the description of Northern Goshawk nest-site selection? J. Wildl. Manage. 62:1378-1383. Desimone, S.M. 1997. Occupancy rates and habitat rela- tionships of Northern Goshawks in historic nesting areas in Oregon, M.S. thesis, Oregon State Univ., Cor- vallis, OR U.S.A. DeStefano, S. andJ. McCloskey. 1997. Does forest struc- ture limit the distribution of Northern Goshawks in the Coast Ranges of Oregon? J. Raptor Res. 31:34—39 , B. Woodbridge and P.J. Detrich. 1994. Survival of Northern Goshawks in the southern Cascades of California. Stud. Avian Biol. 16:133-136. Doyle, F.I. and J.M.N. Smith. 1994. Popnlation responses of Northern Goshawks to the 10-year cycle in num- bers of snowshoe hares. Stud. Avian Biol. 16:122—129. Forsman, E.D., E.C. Meslow and H.M. Wight. 1984. Dis- tribution and biology of the Spotted Owl in Oregon. Wildl. Monogr. 87. Graham, R.T., R.T. Reynolds, M.H. Reiser, R.L. Bassett and D.A. Boyce. 1994. Sustaining forest habitat for the Northern Goshawk: a question of scale. Stud. Avi- an Biol. 16:12-17. Iverson, G.C., G.D. Hayward, K. Titus, E. DeGayner, R.E. Lowell, D.C. Crocker-Bedford, P.F. Schempf andJ. Lindell. 1996. Conservation assessment for the Northern Goshawk in southeast Alaska. USDA For Serv. Gen. Tech. Rep. PNW-GTR-387, Portland, OR U.S.A. Kennedy, P.L. 1997. The Northern Goshawk {Accipiter gen- tilis atricapillus) : is there evidence of a population de- cline? J. Raptor Res. 31:95-106. ,J M. Ward, G.A. Rinker andJ.A. Gessaman. 1994. Post-Hedging areas in Northern Goshawk home rang- es. Stud. Avian Biol. 16:75—82. Manly, B., L. McDonald and D. Thomas. 1993. Resource selection by animals. Chapman and Hall, London, U.K. Marzluff, J.M. and R. Sallabanks. 1998. Past approach- es and future directions for avian conservation biol- 348 Commentary VoL. 32, No. 4 ogy. Pages 5-14 in J.M. Marzluff and R. Sallabanks [Eds.], Avian conservation, research and manage- ment. Island Press, Washington, DC U.S.A. McGrath, M.T. 1997. Northern Goshawk habitat analysis on managed landscapes. M.S. thesis, Oregon State Univ., Corvallis, OR U.S.A. Murphy, D.D. and B.D. Noon. 1991. Coping with uncer- tainty in wildlife biology. /. Wildl. Manage. 55:773-782. Nintzel, J. 1998. Owl play — legal eagles square off over one troublesome bird. Tucson Weekly 15(10) :20. Norse, E.A. 1990. Ancient forests of the Pacific North- west. Island Press, Washington, DC U.S.A. Ramsey, E.L. and D.W. Schafer. 1997. The statistical sleuth. Duxbury Press, Belmont, CA U.S.A. Reynolds, R.T., R.T. Graham, M.H. Reiser, R.L. Bassett, P.L. Kennedy, D.A. Boyce, Jr., G. Goodwin, R. Smith and E.L. Fisher. 1992. Management recommenda- tions for the Northern Goshawk in the southwestern United States. USDA For. Ser. Gen. Tech. Rep. RM- 217, Fort Collins, CO U.S.A. Ripple, W.J., D.H. Johnson, K.T. Hersheyand E.C. Mes- LOW. 1991. Old-growth and mature forests near spot- ted owl nests in western Oregon. J. Wildl. Manage. 55: 316-318. Rohlf, DJ. 1989. The Endangered Species Act: a guide to its protections and implementation. Stanford En- vironmental Law Society, Stanford, CA U.S.A. SiDERS, M.S. and P.L. Kennedy. 1996. Eorest structural characteristics of accipiter nesting habitat: is there an allometric relationship. Cowrfor 98:123-132. Sidle, J.G. 1998. Arbitrary and capricious species conser- vation. Cons. Biol. 12:248-249. Squires, J.R., G.D. Hayward and J.F. Gore. 1998. The role of sensitive species in avian conservation. Pages 155-176 m J.M. Marzluff and R. Sallabanks [Eds.], Avian conservation, research and management. Is- land Press, Washington, DC U.S.A. AND R.T. Reynolds. 1997. Northern Goshawk {Ac- cipiter gentilis) . In A. Poole and F. Gill [Eds.], The birds of North America, No. 298. The Academy of Natural Sciences, Philadelphia, PA U.S.A. Steidl, RJ.,J.P. Hayes and E. Schauber. 1997. Statistical power analysis in wildlife research. J. Wildl. Manaee. 61:270-279. U.S. Fish and Wildlife Service. 1998a. Northern Gos- hawk status review. U.S. Fish and Wildlife Service, Portland, OR U.S.A. , 1998b. Notice of 12-month finding on a petition to list the Northern Goshawk in the contiguous Unit- ed States west of the 100th meridian. Federal Register 63(124):35183-35184. Williams, B.K., FA. Johnson and K. Wilkins. 1996. Un- certainty and the adaptive management of waterfowl harvests./. Wildl. Manage. 60:223-232. Ward, L.Z., D.K. Ward and TJ. Tibbits. 1992. Canopy density analysis at goshawk nesting territories on the North Kaibab Ranger District, Kaibab National Forest Arizona Game and Fish Dept., Phoenix, AZ U.S.A. Yaffee, S.L. 1994. The wisdom of the spotted owl. Island Press, Washington, DC U.S.A. Received 10 February 1998; accepted 25 August 1998 BOOK REVIEWS Edited by Jeffrey S. Marks J Raptor Res. 32(4):349 © 1998 The Raptor Research Foundation, Inc. The Raptors of Arizona. Edited by Richard L. Glin- ski. 1998. University of Arizona Press, Tucson, AZ. xv + 220 pp., 42 color plates by Richard Sloan, 42 range maps, 1 table, 1 appendix. ISBN 0-8165-1322-8. Cloth, $75.00. — ^This is a handsome, well-written, and beau- tifully illustrated volume on the raptors of Arizona by people who obviously had their heart and soul in it. In terms of format, the book is a blend between pop- ular and scientific literature. Twenty-seven contribu- tors present the known information on each of 42 species of birds of prey. Each member of the 26 fal- coniforms, 13 strigiforms, and raptor-like 3 ciconi- iforms are given two to five pages including descrip- tion, distribution, habitat, life history, and status in Arizona. The authors often add their own personal observations and interesting notes on the ecology of each species. According to the editor, Arizona is matched only by Texas in terms of raptor species diversity. This book is a superb compilation of that group. The 42 color plates by Richard Sloan are exquisite and in my mind reminiscent of the beautiful early paint- ings of Allan Brooks. The birds are presented in natural habitat settings in a characteristic behavior or attitude. Each painting nicely captures the es- sence of the species as viewed in Arizona habitats. The introductory chapter provides a complete, yet succinct summary of what is to be expected. Included is a helpful map of the major Arizona river systems, mountain ranges, and important cit- ies. The next chapter, entided “Conservation of Arizona Raptors,” provides the reader with an his- toric perspective about habitat change, raptor pop- ulation changes, and how little we really know about even the recent past. The editor provides an excellent overview of the various ways that man- kind has negatively affected (habitat loss, contam- inants, electrocution, shooting) raptor popula- tions, but in my opinion he could have developed a more positive assessment for at least some of their futures. For instance, the use by many raptor species of man-made nest structures and use of ur- ban environments could have been highlighted in this chapter. Table 1, the only table in the book, provides handy information on habitat and season- al occurrence. The next chapter, “Habitats of Arizona Raptors” by D.E. Brown, provides concise and informative descriptions of 19 habitats. These descriptions un- doubtedly will be helpful to people not familiar with the diversity of Arizona’s habitats and topog- raphy. Each habitat receives a description of vege- tation, elevation, and weather conditions. The end of this chapter includes a discussion of factors in- fluencing raptor distribution. An informative chapter on the details of where to find raptors is presented by S.W. Hoffman. Included are all the known raptor hot spots whether they be breeding areas, migratory flyways, or wintering areas. J.W. Dawson and B.D. Taubert provide a good over- view of contemporary falconry in Arizona in the fol- lowing chapter, and A.M. Rea provides a short intro- duction to the New World Vultures. A central goal of this book is to “enhance public awareness of these species, enticing readers to go out and discover these birds in the wild and help ensure their presence in Arizona skies.” To this end the ed- itor, artist, and authors have easily succeeded. A plea- sure to read and to look at, this book will fill out your “raptors of the southwestern United States” in- terests. Apparently very much a collaborative effort by the editor, authors, Arizona Wildlife Foundation, Arizona Game and Fish Department, and University of Arizona Press, this book could serve as the stan- dard for what I would hope will be future efforts in other states to promote the appreciation of raptors. For those of you interested in natural history, orni- thology, and birds of prey, this book is a must for your library. — ^Peter H. Bloom, Western Foundation of Vertebrate Zoology, 439 Calle San Pablo, Cama- riUo, CA 93010 U.SA. 349 350 Book Reviews VoL. 32, No. 4 /. Raptor Res. 32(4):350 © 1998 The Raptor Research Foundation, Inc. The Long-eared Owl. By Derick Scott. 1997. The Hawk and Owl Trust, London, xv + 128 pp., 29 color photographs, 2 range maps, 2 appendices, numerous black-and-white illustrations. ISBN 0- 9503187-7-9. Cloth, £17.95 (U.K.).— Derick Scott has studied Long-eared Owls {Asio otus) in Britain for 45 years and perhaps has spent more time ob- serving this species than anyone else on earth. His work is mentioned in Stanley Cramp’s The Birds of the Western Palearctic and in David Glue’s papers on Long-eared Owls, but little of Scott’s research has appeared in the refereed literature. Here, Scott distills his observations into the first book devoted to this interesting and somewhat enigmatic species. Focusing on Long-eared Owls in Britain, 10 chapters present general information on appear- ance, population status, distribution, food habits, habitat and home range, breeding biology, behav- ior, vocalizations, mortality and conservation. The book concludes with an appendix that catalogues diseases and parasites that have been documented in Long-eared Owls and another that lists scientific names of species mentioned in the text. The color photographs by Scott are excellent, as are Dan Powell’s black-and-white illustrations. Because the book is written for the layperson, almost no hard data are presented. Instead, the book consists of a free-flowing narrative, some of which is based on published work or personal com- munications from others, and some taken from Scott’s own experiences. A “Selected Bibliogra- phy” lists 36 books and 98 journal references, most of which are not cited in the text. Moreover, no fewer than 19 of the articles that are cited in the text are not included in the list of references! This informal style makes for easy reading, but the lack of detail regarding methods of study and docu- mentation of results leaves many questions unan- swered. Most important, nowhere is it mentioned that Scott has ever banded a Long-eared Owl. At the very least, it would seem that most of his ob- servations were of unbanded individuals. Scott states that males sometimes incubate eggs and brood young, behaviors that have not been docu- mented in studies of marked owls. Similarly, he be- lieves that mate and site fidelity are the rule in British Long-eared Owls, which is quite the oppo- site from the situation in North America and Eu- rope. He also states that incubation typically does not begin until the clutch is complete. Again, this has never been seen elsewhere. Finally, Scott pre- sents some largely unconvincing evidence that Long-eared Owls sometimes move eggs and young among nests (similar reports have been published for nigh^ars and later found to be untrue). Are Long-eared Owls in Britain really that different from those elsewhere? Perhaps so, but one won- ders why so many of these seemingly fantastic ob- servations have not appeared in the refereed lit- erature. The main problem is that these behaviors can only be documented with marked individuals (aside from the issue of when incubation begins) ; without such evidence, the behaviors in question must be considered hypothetical. Because of these potential problems, I am at a loss to identify a readership who will benefit from this book. The text will be of interest to nonpro- fessionals, who unfortunately are likely to accept at face value the undocumented statements therein. The lack of documentation of the results makes the book unsuitable for professionals. Having said this, I must admit that I enjoyed the book because I identified with many of the experiences that Scott describes. Clearly, he is a keen observer with a strong dedication to conservation. Read the book if you must, but do not hesitate to question some of its conclusions. — Jeff Marks, Montana Cooper- ative Wildlife Research Unit, University of Mon- tana, Missoula, MT 59812 U.S.A. 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EH Original and three copies of manuscript and illustra- tions. EH Diskette containing a text file of the manuscript text and tables (if the manuscript was prepared using a word processor) . 354 Information for Contributors VoL. 32, No. 4 I I Submit to: Marc J. Bechard, Editor Department of Biology Boise State University Boise, Idaho 83725 U.S.A. More information? Telephone: 208 426-3530 FAX: 208 426-4267 E-mail: MBECHARD@BOISESTATE.EDU J. Raptor Res. 32(4):355-360 © 1998 The Raptor Research Foundation, Inc. Index to Volume 32 By Elise Vernon Schmidt The index includes references to general, species, common names, key words and authors. Reference is also made to book reviews, dissertation and thesis abstracts, letters, and reviewers. Taxa other than raptors are included where referenced by authors. A Accipiter cooperii, 281—285 gentilis, 189-194, 297-305 Aegypius monachus, 202-207 Africa, 151-158 east, 28-39 Akaki, Ghikako, and Gary E. Duke, Egestion of chitin in pellets of American Kestrels and Eastern Screech Owls, 286-289 Alaska, 261-264 Amadon, Dean, A review of Rotmilan-Sonderheft, Edited by K. Richarz, B.-U. Meyburg, and M. Horsman, 1995, 186 Anderson, Raymond K., see Stout, William E. Aquila chrysaetos, 314—318 Argentina, 306-311, 312-314 Arizona, 281-285 Arrowood, Patricia C., see Botelho, Eugene S. Arroyo, Beatriz, Alain Leroux, and Vincent Bretagnolle, Patterns of egg and clutch size variation in the Mon- tagu’s Harrier, 136-142 Artificial burrows, 233—240 Asia flammeus, 111-115, 116—119 otus, 170—174 Athene cunicularia, 241-245 Augspurger, Tom, and Allen Boynton, Organochlorines and mercury in Peregrine Falcon eggs from western North Carolina, 251—254 Australia, 64-73 B Balen, van, S. (Bas), Tropical forest raptors in Indonesia: Recent information on distribution, status, and con- servation, 56-63 Bayle, Patrick, see Sequin, Jean-Francois Bechard, Marc J., see Kaltenecker, Gregory S. Behavior, 290-296 Bellocq, M. Isabel, Stella M. Bonaventura, Favio N. Mar- celino, and Maria Sabatini, Habitat use of Crowned Eagles (Harpyhaliaetus coronatus) in the southern lim- its of the species range, 312-314 Benn, Grant A., see Jenkins, Andrew R. Bennetts, Robert E., see Valentine-Darby, Patricia L. Bielefeldt, John, see Rosenfield, Robert N. Bildstein, Keith L., Conservation status of tropical rap- tors, 3—18 Birerregaard, Richard O., Jr., Conservation status of birds of prey in the South American tropics, 19-27 Black-Hawk, Great, 175-177 Blanco, Guillermo, see Fargallo, Juan A Blood, 159-162 Blood parasites, 281-285 Bloom, Peter H., A review of: The Raptors of Arizona, Ed. by Richard L. Glinski, 1998, 349-350 Boal, Clint W., K. Stormy Hudelson, R. William Mannan, and Tracy S. Estabrook, Hematology and hematozoa of adult and nestling Cooper’s Hawks in Arizona, 281-285 Bonaventura, Stella M., see Bellocq, M. Isabel Book reviews, 74-75, 185-187, 349-350 Botelho, Eugene S., and Patricia C. Arrowood, The effect of burrow site use on the reproductive success of a partially migratory population of western Burrowing Owls {Speotyto cunicularia hypugaea), 233-240. Boynton, Allen, see Augspurger, Tom Breeding biology, 175-177 range, 189-194 season, 98-103 Bretagnolle, Vincent, see Arroyo, Beatriz Brooks, Thomas M., A record of a Harpy Eagle from east- ern Paraguay, 318-321 Bruggers, Richard L., see Keith, James O. Buteo buteo, 82—89 jamaicensis, 163-169, 178-180, 221-228 lagopus, 178-180 lineatus, 257—260 Buteogallus urubitinga, 175—177 C California, northwestern, 104—110 Calvo, Jose E, see Sanchez-Zapata, Jose A. Cape Peninsula, 90-97 Caracara, Crested, 159-162 Caracara plancus audubonii, 159-162 Chapman, Brian R., see Howell, Doug L. Chavez-Leon, Gilberto, see Gutierrez, R. J. CHD gene, 278-280 Chile, 111-115 Chitin, 286-289 355 356 Index to Volume 32 VoL. 32, No. 4 Circus cyaneus, 116—119, 178-180 pygargus, 136-142, 254-256, 269-277 Clarke, Ralph T., see Hodder, Kathy H. Cluster analysis, incremental, 82-89 Clutch size, 136-142 Codina, Jordi, see Manosa, Santi Commentary, Ed. by Daniel E. Varland, 323-348 Communal roosts, 116-119 Conservation, 19-27, 28-39, 40-55, 56-63, 64-73, 126- 135, 208-214, 233-240 status, 3-18 Copulation, 269-277 Copulation refusal, 269-277 Corsica, 314—318 Crocker-Bedford, D. Coleman, The value of demograph- ic and habitat studies in determining the status of Northern Goshawks (Accipiter gentilis atricapillus) with special reference to Crocker-Bedford (1990) and Kennedy (1997), 329-336 D Dams, 215-220 Delaney, David K., Teryl G. Grubb, and David K. Garce- lon, An infrared video camera system for monitoring diurnal and nocturnal raptors, 290-296. DeStefano, Stephen, Determining the status of Northern Goshawks in the west: Is our conceptual model cor- rect?, 342-348 Diet, 116-119, 175-177, 241-245, 254-256, 297-305, 314-318 Digestibility, 286-289 Distribution, 40-55, 56-63, 126-135 Disturbance, 261-264 Diurnal activity, 290-296 Dominican Republic, 241-245 Doolittle, Thomas C. J., see Rosenfield, Robert N. Doyle, Terry J., see Ritchie, Robert J. Dudin, R L, see Henny, C. J. Duke, Gary E., see Akaki, Chikako E Eagle, Bald, 120-125, 215-220 Bonelli’s, 208-214 Crowned, 312-314 Golden, 314-318 Harpy, 318-321 Eagles, 143-150 Ecology, 28-39, 241-245 Egg size, 136-142 Elliott, James D., Jr., see Norris-Caneda, Kim H. Ellis, David H., and Richard L. Bunn, Caribou antlers as nest materials for Golden Eagles in northwestern Alaska, 268 Ellis, Susie, see Bildstein, Keith L. Endangered species, 19-27 Endemics, 3-18 Energy intake, 195—201 Estabrook, Tracy S., see Boal, Clint W. Estades, Cristian F., Stanley A.Temple, and Alvaro F. Ga- jardo, Unusual nesting of the Rufousdegged Owl?, 183 Extra-pair copulation, 269-277 F Falco peregrinus, 90-97, 143-150, 251-254, 261-264 sparverius, 163-169, 178-180, 286-289 Falcon, Peregrine, 90-97, 143-150, 251-254, 261-264 Falconiformes, 19-27 Falcons, 143-150 Fargallo, Juan A., Guillermo Blanco, and Eduardo Soto- Largo, Forest management effects on nesting habitat selected by Eurasian Black Vultures {Aegypius mona- chus) in central Spain, 202-207 Figueroa, Ricardo A., see Martinez, David R. Finn, Sean P., see Watson, James W. Florida, 98-103 Food habits, 257-260, 297-305, 306-311 Foraging ecology, 215-220 habitat, 246-247 success, 246-247 Forest, old-growth, 104-110 Forest management, 202-207 Forrester, Donald J., see Foster, Garry W. Foster, Garry W., Joan L. Morrison, Christine S. Hartless, and Donald J. Forrester, Haemoproteus tinnunculi in Crested Caracaras ( Caracara plancus audubonii) from southcentral Florida, 159-162 Fry, D. Michael, see Stein, Robert W. G G^ardo, Alvaro F., see Estades, Cristian F. Galushin, V. M., see Henny, C. J. Gamauf, Anita, see Preleuthner, Monika Garcelon, David K., see Delaney, David K. Georgia, 257-260 Gerhardt, Richard R, see Seavy, Nathaniel E. Gilson, Lauren N., Evaluation of neck-mounted radio transmitters for use with juvenile Ospreys, 247-250 Goshawk, Northern, 189-194, 297-305 Pale Chanting, 195-201 Grigera, Dora, see Trejo, A Grouse, 297-305 Grubb, Teryl G., see Delaney, David K. Guatemala, 175-177 Gutierrez, R. J.,John E. Hunter, Gilberto Chavez-Leon, and John Price, Characteristics of Spotted Owl hab- itat in landscapes disturbed by timber harvest in northwestern California, 104-110 H Haak, Bruce, Review of The Prairie Falcon, by Stanley H. Anderson and John R Squires, 1997, 74—75 December 1998 Index to Volume 32 357 Habitat loss, 19-27 selection, 104-110, 208-214 use, 77-81, 90-97, 98-103, 312-314 Haemoproteus tinnunculi, 159-162 Haliaeetus leucocephalus, 120-125, 215-220 Hare, 297-305 Harpia harpyja, 318-321 Harpy haliaetus coronatus, 312-314 Harrier, Montagu’s, 136-142, 254-256, 269-277 Northern, 116-119, 178-180 Hartless, Christine S., see Foster, Garry W. Hawk, Cooper’s, 281-285 Red-shouldered, 257-260 Red-tailed, 163-169, 178-180, 221-228 Rough-legged, 178-180 Hawk-eagle, Philippine, 126-135 Hawks, 143-150 Hays, David W., see Watson, James W. Hayward, Gregory D., see Wright Anthony L. Hematology, 163-169, 281-285 Hematozoa, 163-169, 281-285 Henny, C. J., V. M. Galushin, P. 1. Dudin, A. V. Khrustov, A. L. Mischenko, V. N. Moseikin, V. S. Sarychev, and V. G. Turchin, Organochlorine pesticides, PCBs and mercury in hawk, falcon, eagle, and owl eggs from the Lipetsk, Voronezh, Novgorod, and Saratov re- gions, Russia, 1992-1993, 143-150 Hieraaetus fasdatus, 208-214 Highway mortality, 229-232 Hodder, Kathy H., Robert E. Kenward, Sean S. Walls, and Ralph T. Clarke, Estimating core ranges: A compar- ison of techniques using the Common Buzzard {Bu- teo buteo), 82-89 Howell, Doug L., and Brian R. Chapman, Prey brought to Red-shouldered Hawk nests in the Georgia Pied- mont, 257-260. Hudelson, K. Stormy, see Boal, Clint W. Hungary, 264-266 Hunter, John E., see Gutierrez, R. J. Hunting range, 111-115 1 Ictinia mississippiensis, 246-247 Idaho, 215-220 Indian Ocean, western, 28-39 Indonesia, 56-63 Infrared photography, 290-296 Injured raptors, 264-266 Islands, 28-39 J Jaksic, Fabian M., see Martinez, David R. Jenkins, Andrew R., and Grant A. Benn, Home range size and habitat requirements of Peregrine Falcons on the Cape Peninsula, South Africa, 90-97 Johnson, Charles L., and Richard T. Reynolds, A new trap design for capturing Spotted Owls, 181-182 Juvenile dispersal, 208-214 survival, 195-201 K Kaltenecker, Gregory S., Karen Steenhof, Marc J. Be- chard, and James C. Munger, Winter foraging ecol- ogy of Bald Eagles on a regulated river in southwest Idaho, 215-220 Keith, James O., and Richard L, Bruggers, Review of haz- ards to raptors from pest control in Sahelian Africa, 151-158 Kennedy, Patricia L., Evaluating Northern Goshawk (Ac- dpiter gentilis atricapillus) population status: a reply to Smallwood and Crocker-Bedford, 336—342 Kenward, Robert E., see Hodder, Kathy H. Kestrel, American, 163-169, 178-180, 286-289 Kitchens, Wiley M., see Valentine-Darby, Patricia L. Kite, Mississippi, 246-247 Snail, 98-103 Khrustov, A. V., see Henny, C. J. L Landscape, 104—110 Leroux, Alain, see Arroyo, Beatriz. Letters, 183-184, 267-268, 322 Locust control, 151-158 Londei, Tiziano, Evidence of Spotted Kestrel {Falco mol- uccensis) nesting in the roofs of Sumba’s traditional houses, 267 Louse infestations, 264—266 M Malan, Gerard, Solitary and social hunting in Pale Chant- ing Goshawk {Melierax canorus) families: Why use both Strategies?, 195-201 Mannan, R. William, see Boal, Clint W. Manosa, Santi, Joan Real, and Jordi Codina, Selection of settlement areas by juvenile Bonelli’s Eagle in Cata- lonia, 208-214 Manuscript referees, 76 Marcelino, Favio N., see Bellocq, M. Isabel Marks, Jeffrey S., Ed., Book Reviews, 74-75, 185-187, 349-350 Marks, Jeffrey S., A review of: A Field Guide to Birds of The Gambia and Senegal. By Clive Barlow and Tim Wacher, 1997, 186-187 Marks, Jeffrey S., A review of: The Long-eared Owl, by Derick Scott, 1997, 349-350 Martinez, David R., Ricardo A. Figueroa, Carmen L. Ocampo, and Fabian M. Jaksic, Food habits and hunting ranges of Short-eared Owls (Asia flammeus) in agricultural landscapes of southern Chile, 111- 115 358 Index to Volume 32 VoL. 32, No. 4 Massemin, Sylvie and Thierry Zorn, Highway mortality of Barn Owls in northeastern France, 229-232 McClelland, B. Riley, David S. Shea, Patricia T. Mc- Clelland, and David A. Patterson, Size variation of migrant Bald Eagles at Glacier National Park, Mon- tana, 120-125 McClelland, Patricia T, see McClelland, B. Riley Measurements, 120-125 Mediterranean, 254—256 Meehan-Martin, Paul, see Watson, James W. Meherax canorus, 195-201 Mercury, 143-150, 251-254 Migration, 3-18, 120-125 Mischenko, A. L., see Henny, C. J. Mooney, Nick, Status and conservation of raptors in Aus- tralia’s tropics, 64-73 Morphology, 120-125, 126-135 Morrison, Joan L., see Foster, Garry W. Moseikin, V. N., see Henny, C. J. Movement, 77-81 Munger, James C., see Kaltenecker, Gregory S. N Necklace, 247-250 Nests, 257-260 artificial, 261-264 Nest-site habitat, 189-194, 202-207 Nesting, 261—264 activity, 170—174 density, 221-228 distribution, 189-194 habitat, 221-228 type use, 233—240 Nocturnal activity, 290-296 Norris-Caneda, Kim H., and James D. Elliott, Jr., Sex identification in raptors using PCR, 278-280 North Carolina, 251-254 O Ocampo, Carmen L., see Martinez, David R. Olivetti, Giancarlo, see Pandolfi, Massimo Organochlorine pesticides, 143-150, 251-254 Osprey, 247-250 Otus asio, 286-289 Owl, Barn, 229-232 Barred, 77-81 Burrowing, 233-240, 241-245 Eastern Screech, 286-289 Great Horned, 306-311 Long-eared, 170—174 Mexican Spotted, 290-296 Northern Spotted, 104—110 Spotted, 181-182 Short-eared, 111-115, 116-119 Owls, 143-150 P Pagliarani, Roberto, see Pandolfi, Massimo Pandion haliaetus, 247-250 Pandolfi, Massimo, Roberto Pagliarani, and Giancarlo Olivetti, Intra- and extra-pair copulations and female refusal of mating in Montagu’s Harriers, 269-277 Papp, Joseph M., see Stout, William E. Paraguay, 318-321 Parasite, 159-162 Patterson, David A., see McClelland, B. Riley. PCBs, 143-150 PCR, 278-280 Pellet egestion, 286-289 Pennsylvania, 178-180 Pesticides, 151-158 Peten, 175-177 Phenotypic plasticity, 136-142 Philippines, 126-135 Phthiraptera, 264—266 Piedmont, 257-260 Plasma biochemistry, 163—169 Population density, 208-214 Preleuthner, Monika and Anita Gamauf, A possible new subspecies of the Philippine Hawk-eagle {Spizaetus philippensis) and its future prospects, 126-135 Prey, 257-260 selection, 111-115 size, 195-201 Price, John, see Gutierrez, R. J. Priorities, 28-39 Q Quelea control, 151-158 R Radiotelemetry, 82-89, 98-103 Range expansion, 77-81 core, 82-89 home, 82-89, 90—97 Raptor populations, 40—55 Raptors, 28-39, 151-158, 278-280 tropical, 64—73 Real, Joan, see Manosa, Santi Recapture, 181-182 Reclaimed surface mine, 178-180 Redig, Patrick T., see Tordoff, Harrison B. Rehabilitation centers, 264-266 Research, 28-39 Retention, 247-250 Reynolds, Richard T., see Johnson, Charles L. Ritchie, Robert J., Terry J. Doyle, and John M. Wright, Peregrine Falcons {Falco peregrinus) nest in a quarry and on highway cutbanks in Alaska, 261-264 Rivers, 215-220 Rodent control, 151-158 December 1998 Index to Volume 32 359 Rohrbaugh, Ronald W., Jr., see Yahner, Richard H. Roost habitat, 116-119 Rosenfield, Robert N., John Bielefeldt, Dale R. Trexel, and Thomas C. J. Doolittle, Breeding distribution and nest-site habitat of Northern Goshawks in Wis- consin, 189-194 Rostrhamus sodabilis, 98-103 Rural, 221-228 Russia, 143-150 S Sabatini, Maria, see Bellocq, M. Isabel Sanchez-Zapata, Jose A., and Jose F. Calvo, Importance of birds and potential bias in food habit studies of Montagu’s Harriers {Circus pygargus) in southeastern Spain, 254-256 Sarychev, V. S., see Henny, C. J. Schelsky, Wendy, see Bildstein, K. L. Seasonal shifts, 98—103 Seavy, Nathaniel E. and Richard R Gerhardt, Breeding biology and nestling diet of the Great Black-Hawk, 175-177 Sequin, Jean-Francois, Patrick Bayle, Jean-Claude Thi- bault, Jose Torre, and Jean-Denis Vigne, A compar- ison of methods to evaluate the diet of Golden Ea- gles in Corsica, 314-318 Sex identification, 278-280 Shea, David S., see McClelland, B. Riley Sight record, 318-321 Smallwood, K. Shawn, On the evidence needed for listing Northern Goshawks {Accipiter gentilis) under the en- dangered species act: a reply to Kennedy, 323-329 Social hunting, 195-201 Solt, Szabolcs, Lice (Phthiraptera: Amblycera, Ischno- cera) of raptors in Hungarian zoos and rehabilita- tion centers, 264—266 Soto-Largo, Eduardo, see Fargallo, Juan A. South America, 19-27 South Asia, 40-55 Spain, 208-214 Speotyto cunicularia hypugaea, 233-240 Spizaetus philippensis, 126-135 Status, 64-73 diurnal birds of prey, 56-63 Steenhof, Karen, see Kaltenecker, Gregory S. Stein, Robert W., Julie T. Yamamoto, D. Michael Fry, and Barry W. Wilson, Comparative hematology and plas- ma biochemistry of Red-tailed Hawks and American Kestrels wintering in California, 163—169 Stout, William E., Raymond K. Anderson, and Joseph M. Papp, Urban, suburban and rural Red-tailed Hawk nesting habitat and populations in southeast Wiscon- sin, 221-228 Strigiformes, 19-27 Strix occidentalis, 181-182 occidentalis caurina, 104-110 occidentalis lucida, 290—296 varia, 77-81 Subspecies, new, 126-135 Suburban, 221-228 Surveillance, 290-296 T Temperate agroecosystems, 111-115 Temple, Stanley A., see Estades, Cristian F. Thibault, Jean-Claude, see Sequin, Jean-Francois Thiollay, Jean-Marc, Current status and conservation of Falconiformes in tropical Asia, 40-55 Tome, Davorin, Activity of incubating female Long-eared Owls as measured by fluctuations in nest tempera- tures, 170-174 Tordoff, Harrison B., and Patrick T. Redig, Apparent sib- licide in Peregrine Falcons, 184 Torre, Jose, see Sequin, Jean-Francois Transmitters, 247-250 Trap, 181-182 Trejo, Ana and Dora Grigera, Food habits of the Great Horned Owl {Bubo virginianus) in a patagonian steppe in Argentina, 306-311. Trexel, Dale R., see Rosenfield, Robert N. Tropical forest, 19-27 Tropical raptors, 3-18 Tropics, 3-18 Turchin, V. G., see Henny, C. J. Tyto alba, 229-232 U Urban, 221-228 V Valentine-Darby, Patricia L., Robert E. Bennetts, and Wi- ley M. Kitchens, Seasonal patterns of habitat use by Snail Kites in Florida, 98-103 Video camera, 290-296 Vigne, Jean-Denis, see Sequin, Jean-Francois Virani, Munir and Richard T. Watson, Raptors in the east African tropics and western Indian Ocean Islands: State of ecological knowledge and conservation sta- tus, 28-39 Vulture, Eurasian Black, 202-207 W W-chromosome, 278-280 Walk, Jeffery W., Winter roost sites of Northern Harriers and Short-eared Owls on Illinois grasslands, 116-119 Walls, Sean S., see Hodder, Kathy H. Washington, 297—305 Watson, James W, David W. Hays, Sean P. Finn, and Paul Meehan-Martin, Prey of Northern Goshawks breed- ing in Washington, 297-305 360 Index to Volume 32 VoL. 32, No. 4 Watson, Richard T, Preface: Conservation and Ecology of Raptors in the Tropics, 1-2 Watson, Richard T., see Virani, M. White, Clayton M., A review of: A Fascination with Fal- cons: A Biologist’s Adventures from Greenland to the Tropics. By Bill Burnham, 1997, 185-186 Wilderness, 77-81 Wiley, James W., Breeding-season food habits of Burrow- ing Owls {Athene cunicularia) in southwestern Do- minican Republic, 241-245 Wilson, Barry W., see Stein, Robert W. Wintering ecology, 215-220 Wischusen, E. William, Rates of open-field foraging by the Mississippi Kite {Ictinia mississipppiensis) , 246-247 Wright, Anthony L., and Gregory D. Hayward, Barred owl range expansion into the central Idaho wilderness, 77-81 Wright, John M., see Ritchie, Robert J. X Xirouchakis, Stavros, Dust bathing in the Bearded Vul- ture ( Gypaetus barbatus ) , 322 Y Yahner, Richard H., and Ronald W. Rohrbaugh, Jr., A comparison of raptor use of reclaimed surface mines and agricultural habitats in Pennsylvania, 178-180 Yamamoto, Julie T., see Stein, Robert W. Z Zalles, Jorje, see Bildstein, K. L. Zorn, Thierry, see Massemin, Sylvie. THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBUCATION OF THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966 ) EDITOR IN CHIEF MarcJ. Bechard ASSOCIATE EDITORS Gary R. Bortolotti Fabian Jaksic Allen M. Fish Daniel E. Varland Charles J. Henny BOOK REVIEW EDITOR Jeffrey S. Marks CONTENTS FOR VOLUME 32, 1998 Number 1 Preface: Conservation and Ecology of Raptors in the Tropics. Richard t. Watson 1 Conservation Status of Tropical Raptors. Keith l. Biidstein, Wendy Scheisky, jorje Zalles and Susie Ellis 3 Conservation Status of Birds of Prey in the South American Tropics. Richard O. Bierregaard, Jr. 19 Raptors in the East African Tropics and Western Indian Ocean Islands: State of Ecological Knowledge and Conservation Status. Munir virani and Richard T. Watson 28 Current Status and Conservation of Falconiformes in Tropical Asia, jean- Marc Thiollay 40 Tropical Forest Raptors in Indonesia: Recent Information on Distribution, Status, and Conservation, s. (Bas) van Baien 56 Status and Conservation of Raptors in Australia’s Tropics. Nick Mooney 64 Book Review. Edited by Jeffrey S. Marks 74 Manuscript Referees 76 Number 2 Barred Owl Range Expansion into the Central Idaho Wilderness. Anthony L. Wright and Gregory D. Hayward 77 Estimating Core Ranges: A Comparison of Techniques Using the Common Buzzard {BUTEO BUTEO). Kathy H. Hodder, Robert E. Kenward, Sean S. Walls and Ralph T. Clarke 82 Home Range Size and Habitat Requirements of Peregrine Falcons on the Cape Peninsula, South Africa. Andrew R. Jenkins and Grant a. Benn 90 Seasonal Patterns of Habitat Use by Snail Kites in Florida. Patricia l. Valentine-Darby, Robert E. Bennetts and Wiley M. Kitchens 98 Characteristics of Spotted Owl Habitat in Landscapes Disturbed by Timber Harvest in Northwestern California, rj. Gutierrez, John E. Hunter, Gilberto Chavez-Leon and John Price 104 Food Habits and Hunting Ranges of Short-eared Owls (Asio flammeus) in Agricultural Landscapes of Southern Chile. David r. Martinez, Ricardo a. Figueroa, Carmen L. Ocampo and Fabian M. Jaksic Ill Winter Roost Sites of Northern Harriers and Short-eared Owls on Illinois Grasslands. Jeffery w. Walk 116 Size Variation of Migrant Bald Eagles at Glacier National Park, Montana. B. Riley McClelland, David S. Shea, Patricia T. McClelland and David A. Patterson 120 A Possible New Subspecies of the Philippine Hawk-Eagle {Spizaetus PHIUPPENSIS) AND ITS FUTURE PROSPECTS. Monika Preleuthner and Anita Gamauf 126 Patterns of Egg and Clutch Size Variation in the Montagu’s Harrier. Beatriz Arroyo, Alain Leroux and Vincent Bretagnolle 136 Organochlorine Pesticides, PCBs and Mercury in Hawk, Falcon, Eagle AND Owl Eggs from the Lipetsk, Voronezh, Novgorod and Saratov Regions, Russia, 1992—1993. C.J. Henny, V.M. Galushin, P.l. Dudin, A.V. Khrustov, A.L. Mischenko, VN. Moseikin, V.S. Sarychev and V.G. Turchin 143 Review of Hazards to Raptors from Pest Control in Sahelian Africa. James O. Keith and Richard L. Bruggers 151 HAEMOPROTEUS TINNUNCUU IN CRESTED CaRACARAS {CARACARA PLANCUS AUDUBONII) from Southcentral Florida. Garry W. Foster, Joan L. Morrison, Christine S. Hartless and Donald J. Forrester 159 Comparative Hematology and Plasma Biochemistry of Red-tailed Hawks AND American Kestrels Wintering in California. Robert w. stein, juiie x Yamamoto, D. Michael Fry and Barry W. Wilson 163 Activity of Incubating Female Long-eared Owls as Measured by Fluctuations in Nest Temperatures. Davorin Tome 170 Short Communications Breeding Biology and Nestling Diet of the Great Black-Hawk. Nathaniel e. Seavy and Richard P. Gerhardt 175 A Comparison of Raptor Use of Reclaimed Surface Mines and Agricultural Habitats in Pennsylvania. Richard h. Yahner and Ronald w. Rohrbaugh, Jr. 178 A New Trap Design for Capturing Spotted Owls. Charles l. Johnson and Richard T. Reynolds 181 Letters 183 Book Reviews Edited by Jeffrey S. Marks 185 Number 3 Breeding Distribution and Nest-Site Habitat of Northern Goshawks in Wisconsin. Robert N. Rosenfield, John Bielefeldt, Dale R. Trexel and Thomas CJ. Doolittle.. 189 Solitary and Social Hunting in Pale Chanting Goshawk {Meuerax canorus) Families: Why Use Both Strategies? Gerard Maian 195 I Forest Management Effects on Nesting Habitat Selected by Eurasian Black Vultures {Aegypius monachus) in Central Spain, juan a. Fargaiio, Guillermo Blanco and Eduardo Soto-Largo 202 Selection of Settlement Areas by Juvenile Bonelli’s Eagle in Catalonia. Santi Manosa, Joan Real and Jordi Godina 208 Winter Foraging Ecology of Bald Eagles on a Regulated River in Southwest Idaho. Gregory S. Kaltenecker, Karen Steenhof, Marc J. Bechard and James C. Munger 215 Urban, Suburban and Rural Red-tailed Hawk Nesting Habitat and Populations in Southeast Wisconsin. William e. stout, Raymond k. Anderson and Joseph M. Papp 221 Highway Mortality of Barn Owls in Northeastern France. Syivie Massemin and Thierry Zorn 229 The Effect of Burrow Site Use on the Reproductive Success of a Partially Migratory Population of Western Burrowing Owls (Speotyto CUNICULARIA HYPUGAEA ) . Eugene S. Botelho and Patricia C. Arrowood 233 Breeding-Season Food Habits of Burrowing Owls {Athene cunicularia) in Southwestern Dominican Republic. James w. Wiiey 241 Short Communications Rates of Open-Field Foraging by the Mississippi Kite {Ictinia mississippiensis) . E. William Wischusen 246 Evaluation of Neck-Mounted Radio Transmitters for Use with Juvenile Ospreys. Lauren N. Gilson 247 Organochlorines and Mercury in Peregrine Falcon Eggs from Western North Carolina. Tom Augspurger and Allen Boynton 251 Importance of Birds and Potential Bias in Food Habit Studies of Montagu’s Harriers {Circus pygargus) in Southeastern Spain. Jose a. Sanchez-Zapata and Jose F, Calvo 254 Prey Brought to Red-shouldered Hawk Nests in the Georgia Piedmont. Doug L. Howell and Brian R. Chapman 257 Peregrine Falcons {Falco peregrinus) Nest in a Quarry and on Highway CUTBANKS IN AlASKA. Robert J. Ritchie, Terry J. Doyle and John M. Wright 261 Lice (Phthiraptera: Amblycera, Ischnocera) of Raptors in Hungarian Zoos AND Rehabilitation Centers. Szabolcs Soit 264 Letters 267 Number 4 In MeMORIAM: Frances HAMERSTROM. Dale E. GawUk and Raymond K. Anderson ii Intra- and Extra-pair Copulations and Female Refusal of Mating in Montagu’s Harriers. Massimo Pandolfi, Roberto Pagliarani and Giancarlo Olivetti 269 Sex Identification in Raptors Using PCR. Kim h. Norris-Caneda and James d. Elliott, Jr. 278 Hematology and Hematozoa of Adult and Nestling Cooper’s Hawks in Arizona. CUnt W. Boal, K. stormy Hudelson, R, William Mannan and Tracy S. Estabrook 281 Egestion of Chitin in Pellets of American Kestrels and Eastern Screech Owls. Chikako Akaki and Gary E. Duke 286 An Infrared Video Camera System for Monitoring Diurnal and Nocturnal Raptors. David K. Delaney, Teryl G. Grubb and David K. Garcelon 290 Prey of Breeding Northern Goshawks in Washington. James w. Watson, David W. Hays, Sean P. Finn and Paul Meehan-Martin 297 Food Habits of the Great Horned Owl {Bubo virginianus) in a Patagonian Steppe in Argentina. Ana Trejo and Dora Grigera 306 Short Communications Habitat Use of Crowned Eagles {Harpyhauaetus coronatus) in the Southern Limits of the Species’ Range. M. Isabel Bellocq, Stella M. Bonaventura, Favio N. Marcelino and Maria Sabatini 312 A Comparison of Methods to Evaluate the Diet of Golden Eagles in Corsica. Jean- Franyois Seguin, Patrick Bayle, Jean-Claude Thibault, Jose Torre and Jean-Denis Vigne 314 A Record of a Harpy Eagle from Eastern Paraguay. Thomas M. Brooks 318 Letters 322 Commentary. Edited by Daniel E. Varland On the Evidence Needed for Listing Northern Goshawks (Accipiter gentius) Under the Endangered Species Act; A Reply to Kennedy. K. Shawn Smallwood 323 The Value of Demographic and Habitat Studies in Determining the Status of Northern Goshawks {Accipiter gentius atricapillus) with Special Reference to Crocker-Bedford (1990) AND Kennedy (1997). D. Coleman Crocker-Bedford 329 Evaluating Northern Goshawk {Accipiter gentius atricapillus) Population Status: A Reply to Smallwood and Crocker-Bedford. Patricia L. Kennedy 336 Determining the Status of Northern Goshawks in the West: Is Our Conceptual Model Correct? Stephen DeStefano 342 Book Reviews. Edited by Jeffrey S. Marks 349 Information for Contributors 351 Index to Volume 32 355 BUTEO BOOKS The following Birds of North America Species Accounts are available through Buteo Books, 3130 Laurel Road, Shipman, VA 22971. TOLL-FREE ORDERING: 1-800-722-2460; FAX: (804) 263-4842. Barn Owl (1), Carl D. Marti. 1992. 16 pp. Boreal Owl (63). G.D. Hayward and RH. Hayward. 1993. 20 pp. Broad-winged Hawk. (218). L.J. Goodrich, S.C. Crocoll and S.E. Senner. 1996. 28 pp. Burrowing Owl (61). E.A. Haug, B.A. Millsap and M.S. Martell. 1993. 20 pp. Common Black-hawk (122). Jay H. Schnell. 1994, 20 pp. Cooper’s Hawk (75). R.N. Rosenfield and J. Bielefeldt. 1993. 24 pp. Crested Caracara (249). Joan L. Morrison. 1996. 28 pp. Eastern Screech-owl (165). Frederick R. Gehlbach. 1995. 24 pp. Ferruginous Hawk (172). MarcJ. Bechard and Josef K. Schmutz. 1995. 20 pp, Flammulated Owl (93). D. Archibald McCallum. 1994. 24 pp. Great Gray Owl (41). Evelyn L. Bull and James R. Duncan. 1993. 16 pp. Gyrfalcon (114). Nancy J. Clum and Tom J. Cade. 1994. 28 pp. Harris’ Hawk (146). James C. Bednarz. 1995. 24 pp. Long-eared Owl (133). J.S. Marks, D.L. Evans and D.W. Holt. 1994. 24 pp. Merlin (44). N.S. Sodhi, L. Oliphant, R James and I. Warkentin. 1993. 20 pp. Northern Saw-whet Owl (42). ^chard J. Cannings. 1993. 20 pp. Northern Goshawk (298). John R. Squires and Richard T. Reynolds. 1997. 32 pp. Northern Harrier (210). R. Bruce MacWhirter and Keith L. Bildstein. 1996. 32 pp. Red-shouldered Hawk (107). Scott T. Crocoll. 1994. 20 pp. Red-tailed Hawk (52). C.R. Preston and R.D. Beane. 1993, 24 pp. Short-eared Owl (62). D.W. Holt and S.M. Leasure. 1993. 24 pp. Snail Kite (171). RW. Sykes, Jr., J. A. Rodgers, Jr. and R.E. Bennetts. 1995. 32 pp. Snowy Owl (10). David F. Parmelee. 1992. 20 pp. Spotted Owl (179). R.J. Gutierrez, A.B. Franklin and W.S. Lahaye. 1995. 28 pp. Swainson’s Hawk (265). A. Sidney England, MarcJ. Bechard and C. Stuart Houston. 1997. 28 pp. Swallow-tailed Kite (138). Kenneth D. Meyer. 1995. 24 pp. White-tailed Hawk (30). C. Craig Farquhar. 1992. 20 pp. White-tailed Kite (178). Jeffrey R. Dunk. 1995. 16 pp. THE RAPTOR RESEARCH FOUNDATION, INC. (Founded 1966 ) OFFICERS PRESIDENT; Michael N. Kochert SECRETARY: Patricia A. Hall VICE-PRESIDENT: David E. Andersen TREASURER: Jim Fitzpatrick BOARD OF DIRECTORS NORTH AMERICAN DIRECTOR #1: Brian A. Millsap NORTH AMERICAN DIRECTOR #2: Petra Bohall Wood NORTH AMERICAN DIRECTOR #3: Karen Steenhof INTERNATIONAL DIRECTOR #1: Massimo Pandolfi INTERNATIONAL DIRECTOR #2: Reuven Yosef INTERNATIONAL DIRECTOR #3: Michael McGrady DIRECTOR AT LARGE #1: Patricia L. Kennedy DIRECTOR AT LARGE #2: John A. Smallwood DIRECTOR AT LARGE #3: James C. Bednarz DIRECTOR AT LARGE #4: Cesar MArquez Reyes DIRECTOR AT LARGE #5: Lloyd Kiff DIRECTOR AT LARGE #6: Robert Kenward EDITORIAL STAFF EDITOR: Marc J. Bechard, Department of Biology, Boise State University, Boise, ID 83725 U.S.A. ASSOCIATE EDITORS Allen M. Fish Fabian Jaksic Gary R. Bortolotti Daniel E. Varland Charles J. Henny BOOK REVIEW EDITOR; Jeffrey S. Marks, Montana Cooperative Research Unit, University of Montana, Missoula, MT 59812 U.S.A. SPECIAL PUBLICATIONS EDITOR; Daniel E. Varland, Rayonier, 3033 Ingram Street, Hoquiam, WA 98550 SPANISH EDITOR: Cesar Marquez Reyes, Institute Humbolist Colombia, AA. 094766, Bogota 8, Colombia The Journal of Raptor Research is distributed quarterly to all current members. Original manuscripts dealing with the biology and conservation of diurnal and nocturnal birds of prey are welcomed from throughout the world, but must be written in English. Submissions can be in the form of research articles, letters to the editor, thesis abstracts and book reviews. Contributors should submit a typewritten original and three copies to the Editor. All submissions must be typewritten and double-spaced on one side of 216 X 278 mm (8V^ X 11 in.) or standard international, white, bond paper, with 25 mm (1 in.) margins. The cover page should contain a title, the author’s full name(s) and address (es). Name and address should be centered on the cover page. If the current address is different, indicate this via a footnote. A short version of the title, not exceeding 35 characters, should be provided for a running head. An abstract of about 250 words should accompany all research articles on a separate page. Tables, one to a page, should be double-spaced throughout and be assigned consecutive Arabic numer- als. Collect all figure legends on a separate page. Each illustration should be centered on a single page and be no smaller than final size and no larger than twice final size. The name of the author (s) and figure number, assigned consecutively using Arabic numerals, should be pencilled on the back of each figure. Names for birds should follow the A.O.U. Checklist of North American Birds (6th ed., 1983) or another authoritative source for other regions. Subspecific identification should be cited only when pertinent to the material presented. Metric units should be used for all measurements. Use the 24-hour clock (e.g., 0830 H and 2030 H) and “continental” dating (e.g., 1 January 1990). Refer to a recent issue of the Journal for details in format. Explicit instructions and publication policy are outlined in “Information for contributors,”/. Raptor Res., Vol. 27(4), and are available from the editor. 1999 ANNUAL MEETING The Raptor Research Eoundation, Inc. 1999 annual meeting will be held on 3-7 November in Las Pas, Mexico. Eor information about the meeting contact Ricardo Rodriguez Estrella, Centro de Investigaciones Biologicas del Noreste, Division de Biologica Terrestrie, KM 1 Carretera, San Juan de LaCosta, La Paz 23000, Mexico. Telephone 112-536-33, FAX 112-553-43, E-mail estrella@cibnor. mex. Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Send requests for information concerning membership, subscriptions, special publications, or change of address to OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A. The Journal of Raptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $33.00 per year and to libraries and institutions for $50.00 per year from The Raptor Research Foundation, Inc., 14377 117th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental United States.) Periodicals postage paid at Hastings, Minnesota, and additional mailing offices. POSTMASTER: Send address changes to The Journal of Raptor Research, OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A. Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A. Copyright 1998 by The Raptor Research Foundation, Inc. Printed in U.S.A. 0 This paper meets the requirements of ANSI/NiSO Z39.48-1992 (Permanence of Paper). Raptor Research Foundation, Inc., Awards Recognition for Significant Contributions^ The Dean Amadon Award recognizes an individual who has made significant contributions in the field of systematics or distribution of raptors. Contact: Dr. Clayton White, 161 WIDE, Department of Zoology, Brigham Young University, Provo, UT 84602 U.SA. Deadline August 15. The Tom Cade Award recognizes an individual who has made significant advances in the area of captive propagation and reintroduction of raptors. Contact: Dr. Brian Walton, Predatory Bird Research Group, Lower Quarry, University of California, Santa Cruz, CA 95064 U.SjV. Deadline: August 15. The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significantly to the understanding of raptor ecology and natural history. Contact: Dr. David E. Andersen, Department of Fisheries and Wildlife, 200 Hodson HaU, 1980 Folwell Avenue, University of Minnesota, St. Paul, MN 55108 U.SA. Deadline: August 15. Recognition and Travel Assistance The James R. Koplin Travel Award is given to a student who is the senior author of the paper to be presented at the meeting for which travel funds are requested. Contact; Dr. Petra Wood, West Virginia Cooperative Fish and Wildlife Research Unit, P.O. Box 6125^ Percival Hall, Room 333, Morgantown, WV 26506-6125 U.SA. Deadline: established for conference paper abstracts. The William C. Andersen Memorial Award is given to the student who presents the best paper at the annual Raptor Research Foundation Meeting. Contact: Ms. Laurie Goodrich, Hawk Mountain Sanctuary, Rural Route 2, Box 191, Kempton, PA 19529-9449 U.SA. Deadline; Deadline established for meeting paper abstracts. Grants^ The Stephen R. TuUy Memorial Grant for $500 is given to support research, management and conservation of raptors, especially to students and amateurs with limited access to alternative funding. Contact: Dr. Kimberly Titus, Alaska Division of Wildhfe Conservation, P.O. Box 20, Douglas, AK 99824 U.SA. Dead- line: September 10. The Leslie Brown Memorial Grant for $500-$l,000 is given to support research and/or the dissemination of information on raptors, especially to individuals carrying out work in Africa. Contact: Dr. Jeffrey L. Lincer, 1220 Rosecrans St. #315, San Diego, CA 92106 U.SA. Deadline: September 15. ' Nominations should include: (1) the name, title and address of both nominee and nominator, (2) the names of three persons qualified to evaluate the nominee’s scientific contribution, (3) a brief (one page) summary of the scientific contribution of the nominee. Send 5 copies of a proposal (^5 pages) describing the applicant’s background, study goals and methods, anticipated budget, and other funding.