Seasonal variation in the diet of the Barn Owl in northwestern Nevada

The Barn Owl (Tyto alba) is a widespread predator of small mammals that is declining in many parts of its range. We analyzed the Barn Owl's diet at Stillwater National Wildlife Refuge, Churchill County, Nevada, by identifying remains in pellets collected during the summer (May-September 2007) and winter (October 2007-February 2008). In 306 pellets (143 from summer, 163 from winter), we identified 796 vertebrate prey items including 9 genera of mammals and several species of birds. At both seasons, mammals, primarily of the genera Microtus (voles), Peromyscus (whitefooted mice), Reithrodontomys (harvest mice), and Dipodomys (kangaroo rats) were found in >93% of pellets. Bird remains were found in 15.5% and 11.1% of pellets in summer and winter, respectively. Remains of giant water bugs (family Belostomatidae) were present in 7.7% of summer pellets but absent in winter. Although the diet was dominated by the same five categories of prey (four mammal genera and birds) at both seasons, the proportions of Microtus and Peromyscus declined during the winter, while those of Reithrodontomys and Dipodomys increased.