eWestern Birds

Diet and Home-Range Size of California Spotted Owls in a Burned Forest

Monica L. Bond, Derek E. Lee, Rodney B. Siegel, and Morgan W. Tingley

ABSTRACT: Fire is pervasive in forests used by California Spotted Owls (Strix occidentalis occidentalis) and their prey species. We assessed the diets and sizes of the breeding-season home ranges of seven Spotted Owls occupying burned forests in the southern Sierra Nevada 4 years after a fire and compared the results with data from previous studies in unburned forests within the range of the subspecies. Prey captured by owls in the burned area comprised 40.3% (by biomass) pocket gophers (Thomomys spp.) and 25.9% northern flying squirrels (Glaucomys sabrinus). In contrast, in unburned areas of the Sierra Nevada Spotted Owls fed primarily on flying squirrels, or on both flying squirrels and woodrats (Neotoma spp); in unburned southern California forests they fed overwhelmingly on woodrats. The owls’ mean home range in the burned forest covered 402 ha, an area similar to that recorded in unburned forests of the Sierra Nevada. Our results are consistent with hypotheses that the burned habitat in our study area was rich in gophers and that Spotted Owls foraging on gophers in burned forests do not require home ranges substantially larger than do owls in unburned forests. With currently available data we could not conclusively attribute variation in diet or home-range size to the influence of fire, so further testing is warranted. Use of rodenticides and herbicides in managing burned Spotted Owl habitat may reduce the owl’s key prey.

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