Effects of Urbanization and Habitat on the Diet and Reproduction of Red-shouldered Hawks in Central California

Urbanization alters biological community interactions and trophic structures compared to natural habitats; these changes may be reflected in the diets of apex predators such as raptors. The red-shouldered hawk (Buteo lineatus) is a dietary generalist that is expanding from natural and rural habitats into urbanized areas. In this study, direct observation was used to quantify the diet and reproductive success of red-shouldered hawks in Santa Clara County, California during the 2019 breeding season. GIS methods were used to quantify the nesting habitat and level of urbanization at each nest. Hawk diet consisted of mammals (50.4% by frequency and 77.7% by biomass) and reptiles (20.9% by frequency and 11.1% by biomass), along with limited birds, frogs, and crayfish. The number of chicks fledged did not differ among urban, suburban, and rural nests, but the mean number of chicks fledged from successful nests was greater for rural nests than for suburban or urban nests. Nests were subject to high levels of external activity, with 93% from anthropogenic sources, but hawks responded to only 3.5% of nearby activity. Road length, developed landcover, and tree canopy cover significantly correlated with total prey biomass, mammal biomass and frequency, and reptile frequency. Red-shouldered hawks were able to find adequate prey to breed successfully over a range of urbanized habitats within Santa Clara Valley and are highly tolerant of human activity in this locality