Are There Differences in Select Ecological Attributes and Reproductive Output of Yearling Female Cooper's Hawks (Accipiter cooperii) Breeding in Urban vs. Rural Landscapes in Wisconsin?

Abstract. Cooper's Hawks (Accipiter cooperii) nest commonly in various habitats throughout North America, but there are few comparative studies of the ecology of urban vs. rural nesting birds, especially regarding 1 y olds whose inexperience is purported to place them under different selective pressures than more commonly nesting hawks ≥ 2 y of age. Notably, selective pressures of cities have prompted recent changes in the life histories and phenotypes of urban birds, and some of these pressures may be age dependent. We investigated select intrinsic properties of individuals and reproductive output of breeding yearling females and their mates for potential differences in the ecology of urban vs. rural birds in Wisconsin, 1980–2017. We found no differences in mean body mass of yearling females, their male mates, nesting phenology, nor in average clutch or brood counts in urban vs. rural Cooper's Hawks. Excluding one instance, yearling females were mated to older males, ≥ 2 y of age, and within 33 pairs birds mated by like sizes (small/small, etc.). Sums of masses for paired birds were not correlated with their brood sizes, in contrast to our earlier findings on the same study areas where brood size was positively and significantly correlated with summed masses of paired birds ≥ 2 y old who also mated by similar size. We call for more comparative studies of Cooper's Hawks in cities < 100,000 people as studied herein, as most research on urban nesting Cooper's Hawks stem from large, metropolitan cities with about 1 million people, which are less prevalent than smaller cities as we investigated. Indeed, there is growing evidence worldwide that the types and strength of selective pressures on urban wildlife is greater in larger cities, yet less is known about small cities.