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Numerous studies have demonstrated earlier timing of spring migration and egg-laying in small passerines, but documentation of such responses to recent climate change in the life histories of higher trophic feeding birds such as raptors is relatively scarce. Raptors may be particularly susceptible to possible adverse effects of climate change due to their longer generation turnover times and lower reproductive capacity, which could lead to population declines because of an inability to match reproductive timing with optimal brood rearing conditions. Conversely adaptively favorable outcomes due to the influence of changing climate may occur. In general, birds that seasonally nest earlier typically have higher reproductive output compared to conspecifics that nest later in the season. Given the strong seasonal decline in reproductive output, and the heritability of nesting phenology, it is possible that nesting seasons would (adaptively) advance over time. Recent climate warming may release prior ecological constraints on birds that depend on food availability at the time of egg production, as do various raptors including Cooper's Hawks ( Accipiter cooperii). Under this scenario, productivity, especially clutch size, might increase because it is likely that this reproductive demographic may be the most immediate response to the earlier seasonal presence of food resources. We demonstrated a statistically significant shift of about 4-5 days to an earlier timing of egg-hatching in spring across 36 years during 1980-2015 for a partially migratory population of Cooper's Hawks in Wisconsin, United States, which is consistent with a recent study that showed that Cooper's Hawks had advanced their timing of spring migration during 1979-2012. Both studies occurred in the Great Lakes region, an area that compared to global averages is experiencing earlier and increased warming particularly in the spring in Wisconsin. The nesting period did not lengthen. We suggest that the gradual shift of six consecutive generations of hawks was likely in response to recent climate change or warming. We did not detect any long-term temporal change in average clutch or brood sizes. However, such indices of reproduction are among the highest known for the species and thus may be at their physio-ecological maximum for this population. Our study population appears to show resilience to and does not appear to be adversely influenced by the recent rate of changing climate at this time. [ABSTRACT FROM AUTHOR]

Capturamos, marcamos individualmente y pesamos 271 hembras reproductoras de segundo año de Accipiter cooperii durante la época de cría en dos áreas de estudio principales en Wisconsin durante el periodo comprendido entre 1980 y 2007. Luego recapturamos o volvimos a avistar a algunas de las aves utilizando prismáticos o telescopios y las identificamos a través del color de sus anillas. Para analizar la relación de la longevidad de la hembra con el tamaño, examinamos la masa corporal de adultos reproductores recapturados o avistados nuevamente por categoría de edad relativa durante el último año de detección. Encontramos que la masa corporal (o tamaño) en esta especie no estuvo relacionada con la longevidad ni con la dispersión reproductiva entre, o la fidelidad con, las áreas de nidificación en Wisconsin. Aunque previamente demostramos que la masa corporal tanto en machos como en hembras estuvo relacionada significativa y positivamente con la tasa reproductiva anual y con el número de reclutamientos (o la eficacia biológica), pero inversamente relacionada con el tiempo de la reproducción (i.e., las aves de mayor tamaño se reprodujeron antes en la temporada), parece que, para los machos, el tamaño corporal en A. cooperii está subordinado a otros factores no relacionados con el hábitat que influyen en la longevidad y la re-ocupación de las áreas de nidificación en Wisconsin. Los factores biológicos que influyen tanto sobre la dispersión interanual a un área de nidificación diferente por parte de una hembra experimentada, como sobre la fidelidad año tras año a un sitio se puede basar en comportamientos sociales complejos previos a la incubación en A. cooperii. Sugerimos que nuestro conocimiento de la dispersión reproductiva de aves rapaces mejoraría si se documentaran detalladamente las interacciones sociales entre individuos durante la adquisición de lugares de cría. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

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The article focuses on a study that compares morphological data on breeding Cooper's Hawks caught in southern Vancouver Island, British Columbia, central and southeastern Wisconsin, and northwestern and north-central North Dakota from 1999 to 2003. It measures the woodland hawks' body mass, tail length, wing chord, hallux length, and culmen length. Results show differences in breeding Cooper's Hawks' body mass and body structure. It adds that geographic segregation affect regional variations.

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. [ABSTRACT FROM AUTHOR]

We investigated several reproductive attributes among three spatially and morphometrically separable northern populations of breeding Cooper's Hawks (Accipiter cooperii) in differing ecological settings in British Columbia, North Dakota, and Wisconsin during 1995-2001. We did not detect significant inter-year variation in reproduction within any of our study areas. Cumulative clutch and brood sizes were significantly higher in British Columbia (mean = 4.41 and 3,60, respectively) and Wisconsin (4.26 and 3.73) than in North Dakota (3.5 and 3.0), but not significantly different between British Columbia and Wisconsin. Total nest success rates (91 and 82% in British Columbia and Wisconsin, respectively) varied significantly among all three study sites, but were lowest in North Dakota (68%). We hypothesize that smaller clutch and consequentially lower brood sizes in North Dakota may be the result of the comparatively later nesting phenology in this highly migratory population. Our results underscore the significance of clutch size data, and the need for further research on regional and other large-scale variation in avian demographic parameters to help decide if, when, and where population demographics may warrant a management response. [ABSTRACT FROM AUTHOR]

Studies the nesting ecology of Cooper's Hawks in Wisconsin. Assessment of quality of nesting areas; Determination of hatching dates by backdating; Investigation of the possibility of nonrandom mating; Analysis of adult mass; Results and discussion.

Studies the sex ratios at hatching in nests where complete clutch sizes were known, all eggs hatched and all young survived to an age at which sex could be determined. Sex ratio among Cooper's hawk fledglings following banding and sexing of nestlings; Temporal analyses of offspring sex ratios; Time of clutch completion.