Cooper's Hawks Research Articles

Prevalence of Blood Parasites in Migrating and Wintering California Hawks

Abstract Infectious diseases can potentially affect the seasonal migration of hawks. We tested three species of California hawks from autumn 2004 to spring 2006 for haemosporidian blood parasites (Plasmodium, Haemoproteus, and Leucocytozoon spp.). We screened 323 Red-tailed Hawks (Buteo jamaicensis), 100 Cooper's Hawks (Accipiter cooperii), and 21 Red-shouldered Hawks (B. lineatus) for blood parasites using polymerase chain reaction (PCR). Among these hawks, 221 (50%) were infected with Haemoproteus, 134 (30%) with Leucocytozoon, and none with Plasmodium species. We compared blood parasite prevalence results to identify infection patterns in two populations (birds captured during autumn at a migration watchsite in the Marin Headlands [Golden Gate Raptor Observatory] vs. birds captured during winter in the Central Valley) and between years, seasonal periods, and sex and age classes. In 2004, Marin Red-tailed Hawks were more likely to test positive for blood parasites if sampled late in the migration; howev...

Estimation of Species Identification Error: Implications for Raptor Migration Counts and Trend Estimation

Abstract:One of the primary assumptions associated with many wildlife and population trend studies is that target species are correctly identified. This assumption may not always be valid, particularly for species similar in appearance to co‐occurring species. We examined size overlap and identification error rates among Cooper's (Accipiter cooperii) and sharp‐shinned (A. striatus) hawks specific to a raptor migration count station along the Pacific Coast of North America. Illustrating the difficulty of distinguishing between these 2 species, we found overlap in 7 metrics among species‐sex groups and in 2 metrics between species, and a principal components analysis revealed a continuum of discrete clusters for each species‐sex combination in morphospace. Among juvenile hawks (n= 940), we found the greatest misidentification rate for male Cooper's hawks (23% of the 156 males were identified as sharp‐shinned), lesser error rates for female Cooper's (8%,n= 339) and female sharp‐shinned (6%,n= 246), and the lowest misidentification rate for male sharp‐shinned hawks (0%,n= 199). We observed a similar pattern of misidentification among adult hawks (n= 48). We attempted to use conditional probabilities (identification rates) from calibration data to calculate the true number of adult and juvenile Cooper's hawks and sharp‐shinned hawks. Discrepancies between total number of observed accipiters and estimated number using calibration data suggest that daily observer misclassification rates are higher than misclassification rates estimated from calibration data and prevent correction of the raw data. Our results illustrate the importance of testing for and quantifying observer error in species identification in wildlife census and population trend studies particularly when target species may be easily confused with other nontarget species.

Estimation of Species Identification Error: Implications for Raptor Migration Counts and Trend Estimation

One of the primary assumptions associated with many wildlife and population trend studies is that target species are correctly identified. This assumption may not always be valid, particularly for species similar in appearance to co-occurring species. We examined size overlap and identification error rates among Cooper's (Accipiter cooperii) and sharp-shinned (A. striatus) hawks specific to a raptor migration count station along the Pacific Coast of North America. Illustrating the difficulty of distinguishing between these 2 species, we found overlap in 7 metrics among species–sex groups and in 2 metrics between species, and a principal components analysis revealed a continuum of discrete clusters for each species–sex combination in morphospace. Among juvenile hawks (n = 940), we found the greatest misidentification rate for male Cooper's hawks (23% of the 156 males were identified as sharp-shinned), lesser error rates for female Cooper's (8%, n = 339) and female sharp-shinned (6%, n = 246), and the lowest misidentification rate for male sharp-shinned hawks (0%, n = 199). We observed a similar pattern of misidentification among adult hawks (n = 48). We attempted to use conditional probabilities (identification rates) from calibration data to calculate the true number of adult and juvenile Cooper's hawks and sharp-shinned hawks. Discrepancies between total number of observed accipiters and estimated number using calibration data suggest that daily observer misclassification rates are higher than misclassification rates estimated from calibration data and prevent correction of the raw data. Our results illustrate the importance of testing for and quantifying observer error in species identification in wildlife census and population trend studies particularly when target species may be easily confused with other nontarget species.

The Adrenocortical Stress Response in Three North American Accipiters During Fall Migration

Abstract The associations among corticosterone levels, energy stores, and stress are highly relevant to bird migration physiology. Many birds maintain elevated baseline corticosterone levels during migration, yet they frequently modulate additional glucocorticoid secretion, probably to protect their flight muscles from catabolism. We report on the adrenocortical response to capture and handling stress in three Accipiter species, the Sharp-shinned Hawk (Accipiter striatus), the Cooper's Hawk (A. cooperii), and the Northern Goshawk (A. gentilis) during fall migration. We found mean baseline corticosterone levels to be similar in Sharp-shinned Hawks and Northern Goshawks, but significantly higher in Cooper's Hawks. Likewise, mean baseline levels of corticosterone did not differ in hatch-year and after-hatch-year male and female Sharp-shinned Hawks and Northern Goshawks, but they were higher in adult male Cooper's Hawks than adult females. Mean corticosterone levels did not increase significantly after 30 min...

Reports of Cooper's Hawks (Accipiter cooperii), Swainson's Hawks (Buteo swainsoni), and Short-tailed Hawks (Buteo brachyurus) in Cuba

REGISTRO DE ACCIPITER COOPERII, BUTEO SWAINSONI Y BUTEO BRACHYURUS EN CUBA Reporto informacion sobre la migracion otonal de Accipiter cooperii, Buteo swainsoni y Buteo brachyurus hacia Cuba. Las observaciones las realice entre el 21 de julio y el 1 de octubre del 2007 en el Cabo de San Antonio, extremo occidental de Cuba. No obtuve evidencias de que las tres especies cruzaran el Estrecho del Yucatan, y todos los individuos que llegaron al Cabo de San Antonio revirtieron su ruta migratoria hacia el este. Los avistamientos realizados sugieren que las especies A. cooperii, B. swainsoni y B. brachyurus son visitantes invernales casuales en Cuba. [Traduccion del equipo editorial]

Relationship of Temporary Settling Areas to First Nesting Sites in Cooper's Hawks

RELACION ENTRE LOS SITIOS DE ASENTAMIENTO TEMPORALES Y LOS SITIOS DE LA PRIMERA ANIDACION EN ACCIPITER COOPERII En las aves territoriales, los transeuntes son individuos no reproductivos que se encuentran en fase de dispersion y pueden entrar en una poblacion reproductiva cuando un territorio de cria se hace disponible. Existe poca informacion sobre el movimiento de estos individuos transeuntes con relacion al sitio donde eventualmente anidan por primera vez. Examine la relacion espacial entre las areas de vida de individuos de Accipiter cooperii no reproductivos en su primer ano de vida y las areas en que anidaron mas tarde. De nueve halcones que establecieron areas de vida en su primer invierno, seis adquirieron sitios de cria (y uno fue encontrado muerto) entre 2 a 8 anos despues, los cuales se localizaron en o cerca de las areas de vida que establecieron durante su primer invierno. [Traduccion del equipo editorial]

Predator Vocalizations Affect Foraging Trade-offs of Northern Cardinals

We investigated the roles of food quality and predator avoidance in shaping foraging behavior of Northern Cardinals (Cardinalis cardinalis). Cardinals visited feeders near cover and feeders with sunflower seed significantly more than they visited those in the open and those with commercial wild bird seed mix. Cardinals with a choice between their preferred food and preferred location visited the sunflower seed feeder in the open significantly more than the mixed seed feeder near cover, despite their prior preference for feeding near cover. We recorded visits to these feeders over a 2-day period during which we played Cooper's Hawk (Accipiter cooperi) calls every 2 hrs. The overall visitation rate did not decrease significantly, nor did the visitation rate to feeders near cover increase significantly. However, the decrease in the visitation rate to feeders in the open approached significance. Overall, we observed a significant shift in the proportion of visits to feeders near cover (containing less preferred seed). We conclude Northern Cardinals are sensitive to both food quality and predation risk, and adjust foraging to prevailing perceptions of risk.

Comparative Morphology of Northern Populations of Breeding Cooper's Hawks

Abstract. Few studies at a broad geographical scale have characterized intraspecific variation in morphology of woodland hawks in the genus Accipiter. From 1999 to 2007 we investigated morphological variation in large samples of live Cooper's Hawks (A. cooperii) nesting in four study areas: coniferous woodland around Victoria, British Columbia, Canada, isolated deciduous woodlands in short-grass prairies of northwestern North Dakota, towns and rural deciduous woodlands along the border of North Dakota and Minnesota, and urban and rural mixed deciduous and coniferous landscapes of Wisconsin. These sites span 2660 km across the northern part of the species' breeding range. We measured body mass (i.e., size), wing chord, tail length, tarsus diameter, hallux length, and culmen length of breeding adults, finding significant and clinal variation in body mass (or size). The smallest and most similar-sized birds occurred in British Columbia and western North Dakota, larger birds along the border between North Dak...

Why are American Kestrel (Falco sparverius) Populations Declining in North America? Evidence from Nest-Box Programs

Abstract Declines in American Kestrel (Falco sparverius) populations are widely reported, and Breeding Bird Survey (BBS) data suggest that the North American population declined significantly from 1984 to 2007. Potential causes include the spread of West Nile virus (WNV), increases in populations of Cooper's Hawks (Accipiter cooperii), and loss of suitable habitat. We examined trends in the numbers of both migratory and resident kestrel populations that use nest boxes in eight study areas in Florida, Georgia, Virginia and Maryland, New Jersey, Massachusetts, Pennsylvania, Saskatchewan, and the Yukon Territory, 1984–2007. All eight populations underwent significant declines; the mean annual decline in nest-box occupancy rate was 3.0% and ranged from 0.6% in Pennsylvania to 4.7% in New Jersey. Except for the most recent nest-box program, established in 1995 and declining since 2002, all nest-box populations began to experience declines before WNV arrived in North America in 1999. To test whether changes in ...

Notes on Breeding Sharp-shinned Hawks and Cooper's Hawks in Barnwell County, South Carolina

Breeding records of Accipiter striatus (Sharp-shinned Hawks) in the southeastern US are scattered and isolated. We documented a Sharp-shinned Hawk and Accipiter cooperii (Cooper's Hawk) nest while conducting a telemetry study on Melanerpes erythrocephalus (Red-headed Woodpeckers) in Barnwell County, SC in 2006 and 2007. We report the first known nest of a Sharp-shinned Hawk in Barnwell County, SC and the first report of Sharp-shinned Hawks preying upon Red-headed Woodpeckers. Thirteen of 93 (13.9 %) woodpeckers were killed by accipiters in the summers of 2006 and 2007. Large, contiguous forests managed for Picoides borealis (Red-cockaded Woodpeckers) may be used by breeding Sharp-shinned Hawks. The bright plumage, loud calls, and behavior of Red-headed Woodpeckers, particularly during the nestling stage, may make them conspicuous prey for accipiters.

Human-Related Threats to Urban Raptors

Abstract Annual bird mortality in the United States from anthropogenic sources is estimated at one billion. Urban raptors are affected by many of these factors; however, little is known about the relative frequency and magnitude of sources within and among species. I reviewed 86 published sources on mortality and urban use for the raptors of the United States and Canada. Within the Falconiformes (28 urban species), vehicle collisions and electrocutions were reported for most species (73% and 48%, respectively), and vehicular and window strikes were the leading sources of mortality for 39% and 12% of species, respectively. For the Strigiformes (14 urban species), vehicular (63%) and window (47%) collisions affected most species, and the primary sources of mortality were from vehicles (32%) and electrocution (5%). Window-strike mortality was reported for 45% of urban raptors and represented the leading source of mortality for Sharp-shinned Hawks (Accipiter striatus), Cooper's Hawks (A. cooperii), Merlins (F...

Low Prevalence of Trichomonas gallinae in Urban and Migratory Cooper's Hawks in Northcentral North America

Trichomoniasis is a digestive tract disease caused by ingestion of the protozoan Trichomonas gallinae. This disease can be a significant source of mortality. No deaths of nestlings could be attributed to trichomoniasis in Cooper's Hawks (Accipiter cooperii) breeding in urban and rural environs in Wisconsin, North Dakota, and British Columbia. We detected T. gallinae in four (5.2%) of 77 nestling Cooper's Hawks during 2006 and 2007 among 42 urban nests on new study areas in southeast Wisconsin and eastern North Dakota/western Minnesota. All four infected young fledged. We did not detect T. gallinae in 52 breeding adult Cooper's Hawks on two urban study sites, nor in 28 migrant hatching year (n = 24) and adult (n = 4) Cooper's Hawks at Hawk Ridge Nature Reserve, Duluth, Minnesota in 2006–2007. Overall, we detected T. gallinae in only 2.5% of 157 Cooper's Hawks in northcentral North America. These results suggest a low prevalence of T. gallinae in Cooper's Hawks in the northern part of this hawk's breeding range.

Survival Rates and Lifetime Reproduction of Breeding Male Cooper's Hawks in Wisconsin, 1980–2005

There are few published data on annual survival and no reports of lifetime reproduction for breeding Cooper's Hawks (Accipiter cooperii). Breeding males (n = 105) in central and southeastern Wisconsin had an annual mortality rate of 19%, or a survival rate of 81% for birds ≤10 years of age. We did not detect significant differences in mortality rates between urban and rural habitats, nor between the earlier 13 years and later 13 years of this study. Male Cooper's Hawks produced from zero to 32 nestlings during their lifetimes. Body mass or size appeared unrelated to annual survivorship and lifetime reproduction, although lifetime reproduction was correlated strongly with longevity of breeding males. Fifteen of 66 males (23%) produced most (53%) of the nestlings. Our studies occurred in an area where breeding populations may be increasing with some of the highest reported productivity indices and nesting densities for this species. Habitat used for nesting on our Wisconsin study areas may be less important for survivorship and lifetime reproduction than acquisition of a nesting area in which a male will breed throughout his life.

GOLDEN-CHEEKED WARBLER NEST MORTALITY AND PREDATORS IN URBAN AND RURAL LANDSCAPES

Abstract Predation is a major cause of nest failure for songbirds, yet information is lacking on the relative importance of predator species in different landscapes. We identified nest predators of Golden-cheeked Warblers (Dendroica chrysoparia) in an urban landscape, compared cause-specific mortality rates between urban and rural landscapes, and evaluated whether monitoring nests with cameras affected nest survival. We monitored 68 nests with cameras in Austin, Texas, during 2005, 2006, and 2008 to identify causes of mortality, including predators, in an urban landscape. The period mortality and predation rates were 0.60 (95% CI: 0.42–0.73) and 0.52 (95% CI: 0.37–0.68), respectively. We identified predators at 20 nests: Texas rat snakes (Elaphe obsoleta lindheimerii) depredated eight nests (40%), Western Scrub-Jays (Aphelocoma californica) depredated six (30%), Cooper's Hawks (Accipter cooperii) depredated two (10%), fox squirrels (Sciurus niger) depredated three (15%), and fire ants (Solenopsis sp.) dep...

COLUMBID HERPESVIRUS-1 IN TWO COOPER'S HAWKS (ACCIPITER COOPERII) WITH FATAL INCLUSION BODY DISEASE

We report two separate naturally occurring cases of fatal herpesviral disease in Cooper's Hawks (Accipiter cooperii). Gross lesions included splenomegaly and hepatomegaly, with diffuse pale mottling or scattered small white foci. Histologic lesions included splenic and hepatic necrosis associated with eosinophilic intranuclear inclusion bodies characteristic of herpesvirus. In one case, necrosis and inclusions were also noted in bone marrow, thymus, bursa of Fabricius, thyroid gland, parathyroid gland, ceca, and the enteric system. Transmission electron microscopy demonstrated viral particles typical of herpesvirus within hepatocyte nuclei and budding from the nuclear membrane. Herpesviral DNA was amplified via polymerase chain reaction (PCR) of paraffin-embedded liver and spleen, and sequence data were consistent with columbid herpesvirus-1, an alphaherpesvirus of Rock Pigeons (Columba livia). PCR results provide evidence that this disease is transmitted to raptors via Rock Pigeons, most likely through ingestion of Rock Pigeons as prey.

SPATIAL ECOLOGY OF WINTINGACCIPITERHAWKS: HOME RANGE, HABITAT USE, AND THE INFLUENCE OF BIRD FEEDERS

Abstract Despite their likely ecological importance, the basic biology of Cooper's (Accipiter cooperii) and Sharp-shinned (A. striatus) Hawks remains poorly understood. This is particularly true during the winter, when even basic information on the spatial ecology of these species is largely unknown. Thus, we characterized the home range size and habitat chosen by these species as part of a larger study on wintering Accipiter hawks. We also compared our findings of bird feeder use by Cooper's Hawks to our previously published study on Sharp-shinned Hawks. During the winters of 1999–2004, we intensively radio-tracked 21 Sharp-shinned Hawks and six Cooper's Hawks in rural areas, and eight Cooper's Hawks in urban areas. We found that Sharp-shinned Hawks and Cooper's Hawks in rural areas used significantly larger areas than did Cooper's Hawks in urban areas, and that adult hawks generally used smaller areas than immature individuals. Habitat use by Cooper's Hawks and Sharp-shinned Hawks in rural areas was nea...

Sex determination of three raptor species using morphology and molecular techniques

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Nesting with an enemy: The abundance and distribution of preferred and secondary prey near nesting Cooper's hawks, Accipiter cooperii

By nesting near their predators, birds may gain safe nest sites because predators defend a region around their own nests. For some species, this benefit comes at the potential cost of increased predation risk due to the predators. We hypothesized that birds less vulnerable to predation were more likely to associate with predatory birds. We surveyed different bird species near active Cooper's hawk, Accipiter cooperii, nests, 200 m from each hawk nest, and at control sites that did not contain Cooper's hawk nests. The birds surveyed were categorized by weight, foraging height, and nest type. Canopy foraging birds were found in relatively higher densities near the Cooper's hawk nests than at other sites, whereas ground and mid-level foragers were more common away from Cooper's hawk nests. The association with Cooper's hawks was most pronounced for those canopy foraging birds that were small and built cup nests. Birds less vulnerable to predation by Cooper's hawks are more likely to nest in association with these hawks than are more vulnerable birds.

Ophthalmologic and oculopathologic findings in red-tailed hawks and Cooper's hawks with naturally acquired West Nile virus infection

To assess ophthalmologic features and ocular lesions in red-tailed hawks and Cooper's hawks naturally infected with West Nile virus (WNV). Original study. 13 hawks. All hawks underwent complete ophthalmic examinations including slit lamp biomicroscopy and binocular indirect ophthalmoscopy. Eleven hawks were euthanized because of a grave prognosis; complete necropsies were performed. Eyes, brain, heart, and kidneys were processed for histologic and immunohistochemical examinations. Pooled tissue homogenates and aqueous humor samples were assessed for WNV nucleic acid via PCR assay, and anti-WNV antibody titers in aqueous humor and plasma were determined. All birds had similar funduscopic abnormalities including exudative chorioretinal lesions and chorioretinal scarring in a geographic or linear pattern. Eleven birds were euthanized, and 2 birds were released. Plasma from both released hawks and plasma and aqueous humor of all euthanized hawks that were evaluated contained anti-WNV antibodies. Except for 1 hawk, all euthanized hawks had WNV-associated disease (determined via detection of WNV antigen or nucleic acid in at least 1 organ). Histopathologic ocular abnormalities, most commonly pectenitis, were detected in all euthanized birds; several birds had segmental choroiditis, often with corresponding segmental retinal atrophy. West Nile virus antigen was detected in the retinas of 9 of the euthanized birds. In 2 hawks, WNV antigen was detected in the retina only. Results indicated that funduscopically detectable chorioretinal lesions appear to be associated with WNV disease in hawks. Detection of ocular lesions may aid in antemortem or postmortem diagnosis of this condition.

Frequency of Injuries in Three Raptor Species Wintering in Northeastern Arkansas

It may be reasonable to assume that raptors would likely perish as the result of an injury that potentially impaired their ability to capture prey. We present results from 98 wild-caught raptors that support the converse claim: raptors can and do survive with many types of injuries. We report a conservative injury estimate of 14% for wintering populations of Red-tailed Hawks (Buteo jamaicensis), American Kestrels (Falco sparverius), and Cooper's Hawks (Accipiter cooperii) in northeastern Arkansas. Injuries in these species included broken or missing talons, ulcerative pododermatitis (bumblefoot), missing toes, healed wing fractures, and iris damage.