Comparative breeding ecology of Cooper's hawks in urban and exurban areas of southeastern Arizona

One step in assessing the quality of an urban environment as habitat for a species is to compare its breeding ecology and productivity in urban and exurban (i.e., undeveloped, natural) areas. We studied Cooper's hawks (Accipiter cooperii) in Tucson, Arizona, and in exurban areas in southeastern Arizona, 1994-96. Urban pairs nested earlier (P < 0.001) and had larger clutches (P = 0.085) than exurban pairs. Nestling mortality was greater among urban nests (50.3%) than exurban nests (4.9%). The primary cause of death among urban nestlings was trichomoniasis (79.9%), which was a consistent mortality factor among years (P = 0.402). An overall failure rate among urban nests (52.6%) was greater than at exurban nests (20.5%; P < 0.001). Although the role of bird feeding in the spread of trichomoniasis remains unclear, promoting 'dove-proof' feeders or abstinence from bird feeding may minimize the spread of the disease among prey species, thereby reducing mortality of nestling Cooper's hawks. The greatest cause of mortality among free-ranging Cooper's hawks in the urban area was collisions (69.8%), primarily with windows. Techniques to decrease window collisions should be promoted to reduce window-strike mortalities among both Cooper's hawks and their prey. Cooper's hawks also are occasionally aggressive when defending their nests from perceived threats, which may lead to fear and persecution by city residents. Hence, environmental education may be an important component of managing this species in urban settings.