INFESTATION OF NORTHERN SPOTTED OWLS BY HIPPOBOSCID (DIPTERA) FLIES IN NORTHWESTERN CALIFORNIA

Hippoboscid flies were found on 62 (17%) of 382 northern spotted owls (Strix occidentalis caurina) captured between April and September, 198 6 through 1990. Two species of hippoboscids were identified: Icosta am ericana and Ornithomya anchineuria. Male and female adult spotted owls had similar prevalences and relative densities of hippoboscid flies. juvenile owls had lower prevalence and relative densities than adults. There were no significant differences in mean intensity of hippobosci ds on adult male adult female and juvenile spotted owls. Relative dens ities of flies infesting adult owls were significantly greater during years of increased fall temperatures, decreased winter precipitation, and decreased summer temperatures.