SCALING SWAINSONS-HAWK POPULATION-DENSITY FOR ASSESSING HABITAT USE ACROSS AN AGRICULTURAL LANDSCAPE

By integrating population density estimates of Swainson's hawk (Buteo swainsoni) from other studies, I found that the areas within study bou ndaries consistently support much higher densities of Swainson's hawk than do the surrounding areas, and most of the variation in density wa s explained by the spatial extent of study. Therefore, I designed a sa mpling program to express habitat use across multiple potential cluste rs of home ranges, thereby representing the population-level interacti on with the agricultural landscape of the Sacramento Valley, CA. I map ped 162 observations of Swainson's hawks in 5 yr of surveys (110 surve ys) along a 204-km road transect from a car traveling at 80-88 kph. Ba sed on use and availability of landscape elements along the transect, Swainson's hawks ''preferred'' riparian habitat, grassland, alfalfa st ands >2 yr old during irrigation and mowing, and annual field crops du ring harvest. Hawks ''avoided'' most other crops, tilled fields, and b uilt-up areas.