WINTER FORAGING OF SILVER-HAIRED AND CALIFORNIA MYOTIS BATS IN WESTERN WASHINGTON

Abstract

The wintering strategies of many species of bats in the Pacific Northwest are poorly understood (Barbour and Davis 1969; Kunz 1982). Although Silver-haired Bats (Lasionycteris noctivagans) and California Myotis (Myotis californicus) have been observed wintering in Washington State and British Columbia (Nagorsen and others 1993), the specifics of their wintering behaviors and distributions in the region are unclear. Silver-haired Bats are presumed to migrate south to warmer regions during winter (Izor 1979), although limited evidence suggests this species may not be as migratory in the Pacific Northwest as elsewhere (Schowalter and others 1978; Kunz 1982; Cryan 2003). The few observations of winter roosts used by Silverhaired Bats in the Pacific Northwest mostly involved solitary bats found in trees (Cowan 1933; Nagorsen and others 1993). California Myotis are presumed to hibernate through the winter and generally remain dormant in caves, mines, buildings or tree cavities within several hundred kilometers of their summer habitat