| Abstract: | Several species of raptors winter at Rocky Mountain Arsenal National Wildlife Refuge (Refuge) including the Bald Eagle ( Haliaeetus leucocephalus ), Ferruginous Hawk ( Buteo regalis ), Red-tailed Hawk ( Buteo jamaicensis ), and Rough-legged Hawk ( Buteo lagopus ). Raptors were monitored each winter from 1988-89 to 1996-97 using a standardized road survey. Black-tailed prairie dogs ( Cynomys ludovicianus ) form a major component of the prey base for wintering raptors on the Refuge, with 1850 ha of active prairie dog towns mapped in 1988. Prairie dog town areas and population data were determined by mapping active towns and conducting visual counts on study plots to determine population density on an annual basis from 1988 to 1996. Large-scale plague epizootics were documented on the Refuge in 1988-89 and 1994-95, reducing prairie dog towns by 95% and 99%, respectively. A significant relationship was found in the numeric response of Ferruginous Hawks to changes in prairie dog town area ( r 2 = 0.96, P r 2 = 0.97, P r 2 = 0.07, P = 0.486). This contrasted sharply with the responses to prairie dog town area found for Red-tailed ( r 2 = 0.11, P = 0.377) and Roughlegged Hawks ( r 2 = 0.04, P = 0.612). |
