Productivity and nest-site characteristics of Gray Hawks in southern Arizona

We studied Gray Hawks (Asturina nitida) nesting along the upper San Pedro River in southeastern Arizona from 1995-97. We identified 27 nesting areas with a mean of 24.3 nesting areas occupied per year. Productivity averaged 1.32 young per occupied nest. Number of successful nests and number of young produced per nest did not differ among years. Mean size of home range (N = 10 males), based on the 90% adaptive kernel method, was 59.2 ha (range = 21.4-91.2). Almost all Gray Hawk nests were located in large, dominant cottonwood trees (Populus fremontii). However, we doubt that Gray Hawks inherently prefer cottonwood trees over other species, but rather speculate that they use them because they are the only tall nest substrate currently available. The increase in Gray Hawks in southern Arizona during the past 30 yr was probably due to an increase in habitat. In the future, groundwater depletion may represent a risk to maintenance of Gray Hawk populations in southern Arizona.