Breeding Biology and Prey Selection of Ferruginous Hawks in Northwestern South Dakota

A study of the breeding biology and prey selection of ferruginous hawks (Buteo regalis) was conducted in northwestern South Dakota during 1976 and 1977. Twenty four pairs were located in 1976 and 18 pairs attempted to nest; 17 pairs located in 1977 attempted to nest. The ecological density of breeding pairs was approximately one per 100 km2. Young fledged per nesting attempt averaged 1.89 in 1976 and 2.29 in 1977. All but one nest were located in unbroken, lightly grazed prairie and all were situated on hills, buttes, or river cutbanks. General nest orientation was toward the south and west. Six hundred ninety food items were identified identified from regurgitated pellets and prey remains collected at the nest sites. Mammals composed 94 percent, birds 5 percent, and reptiles 1 percent of prey biomass; white-tailed jackrabbits (Lepus townsendi) and thirteen-lined ground squirrels (Citellus tridecemlincatus) were the most important items. Movements of six radio-tagged juveniles were monitored from the time of fledging until departure from the study area. The juveniles usually expanded the size of their utilized areas during each successive week after fledging. Most ferruginous hawks had left the study area by mid-September