The Diet of Western Burrowing Owls in an Urban Landscape

Abstract

While we know much about the diet of Western Burrowing Owls (Athene cunicularia hypugaea) in many of their more natural habitats, little is known about their diets in urban environments. We analyzed pellets and prey remains collected at burrows used by Burrowing Owls living in urban grasslands in Santa Clara County, California. We hypothesized that the composition of prey species in the diet of these urban owls would differ from that of owls living in agricultural and more-natural western habitats and, in particular, that rodents would be a smaller component of the diet, We found the invertebrate-to-vertebrate ratio to be approximately 94:6 by number. Orthoptera, Dermaptera, and Coleoptera were the most abundant invertebrate orders, while rodents accounted for 70% of the estimated biomass per burrow of all orders. This overall composition and these taxa are typical for Burrowing Owls in western habitats. However, Botta's pocket gopher (Thomomys bottae) was an important prey species by biomass, a species not often recorded as a dominant prey item of owls living in western habitats. The California vole (Microtus californicus) and house mouse (Mus musculus) were also dominant prey items by biomass. We recommend managing Western Burrowing Owl habitat for species, especially rodents such as pocket gophers and voles, that do well in urban habitats.