Search

From an analysis of nest site habitat data at 24 Sharp-shinned Hawk (Accipiter striatus) and 52 Cooper's Hawk (A. cooperii) nests in Wisconsin, we conclude that Cooper's Hawks tend to nest in stands with lower densities of taller and larger trees than do Sharp-shinned Hawks, and that Cooper's Hawks also tend to nest in sites with a greater proportion of hardwood cover than Sharp-shinned Hawks. Significant interspecific differences were found in combined habitat types (hardwoods, mixed conifer-hardwoods, and conifer plantations) for nest tree height and nest tree DBH (diameter at breast height); nest height; nest height relative to tree height: canopy height: canopy cover; tall shrub density: tree density; and mean DBH. Nest sites of the two species were similar in terms of understory canopy cover, ground cover, low shrub index, understory tree density, basal area, distance to nearest forest opening, and distance to water. We detected few significant intraspecific differences in nest site habitat, and these only in the Cooper's Hawk., Although the Sharp-shinned Hawk (Accipiter striatus) and the Cooper's Hawk (A. cooperii) breed sympatrically in many parts of the United States and southern Canada, their nest site habitats have been [...]

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]

Life-history theory suggests that delayed maturation is beneficial to birds when costs of breeding early in life are high. We compared selected aspects of the biology of male Cooper's Hawks (Accipiter cooperii) that began breeding at 1 year of age (SY males) vs. males that began breeding ≥2 years of age (ASY males) in an effort to elucidate what renders breeding of SY males rare. Of the 732 males of known age whose breeding we studied over 32 years (1980-2011) 13 (2%) were SY and 719 (98%) were ASY. During this period, the incidence of breeding of SY males changed markedly, as 12 of the instances of breeding of SY males were recorded in the first half of our study, only 1 in the latter half. We suggest that SY males could acquire nest sites more readily in the first half of the study when the breeding population of ASY males was apparently lower. Males breeding in their second year were on average similar in size to ASY males but were molting more extensively than were ASY males. ASY males lived longer than males breeding in their second year, and maximum lifetime production of young was greater, so SY males may have sacrificed greater longevity for breeding early. A strategy of facultative breeding in response to the constraints of higher numbers of older breeding males and restraints of trade-offs in energy allocation may explain why SY male Cooper's Hawks rarely breed. [ABSTRACT FROM AUTHOR]

The article discusses the results of a study that examines the genetic structure and gene flow of Cooper's Hawk or Accipiter cooperii and compares the divergence at morphological traits and genetic markers. Cooper's Hawks conform to the genetic pattern of an east-west divide and the British Columbia populations are genetically differentiated from north-central populations. It concludes that prey mass and migratory behavior vary among populations.

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.