An Urban Cooper’s Hawk Nesting Study in the Metropolitan Milwaukee Area

William E. Stout

Oconomowoc, WI,

The objectives of this study are to gather baseline data on the reproductive success of Cooper’s hawks (Accipiter cooperii) in the urban metropolitan Milwaukee area, to describe urban nesting habitat, and to compare these data with other Cooper’s hawk studies in Wisconsin. Long-term objectives are to determine Cooper’s hawk nest site fidelity, breeding population mortality and recruitment, population growth trends, immigration and emigration patterns, and natal dispersal patterns for the same urban population. In 2015, Cooper’s hawks at 18 of 32 sites that I monitored laid eggs. Fifteen of these 18 laying pairs produced 54 young to a bandable age (ca. 18 days; 3.00 young/laying pair, 3.60 young/successful pair, 83.3% nesting success). All nestlings (32 males, 22 females) were banded. Fourteen additional occupied sites were monitored but no nesting attempts were found. Eighteen adult (i.e., breeding) Cooper’s hawks (9 males, 9 females) were trapped, banded, measured, colormarked, and processed for additional analyses at 11 different nest sites. All nine males were in adult plumage; seven of the nine females were in adult plumage, and two were in juvenile plumage. Two of the adult males were natal dispersals, and one of the adult females was a natal dispersal. The adult males dispersed 7.34 and 9.48 km from their natal sites, and the female dispersed 12.03 km from her natal site. No nesting attempt was found in Downer woods for either great horned owls or Cooper’s hawks. One juvenile Cooper’s hawk was observed in Downer Woods on 3 May 2015.