INFLUENCE OF ENVIRONMENTAL-CONDITIONS ON FLIGHT ACTIVITY OF PLECOTUS-TOWNSENDII-VIRGINIANUS (CHIROPTERA, VESPERTILIONIDAE)

Flight activity of the Virginia big-eared bat (Plecotus townsendii vir ginianus) was measured in relation to eight environmental variables du ring 1990 and 1991 in Lee County, Kentucky. Activity, measured as the mean nightly detection frequency of bats fitted with transmitters, was positively related to percent relative humidity and negatively relate d to moon phase and wind speed. Multiple regression analysis showed re lative humidity to have the strongest association with night activity of all the environmental variables tested. An explanation for this pat tern was that bats reduced their foraging activity on nights of low re lative humidity to avoid excess water loss because of extremes in vapo r pressure deficits during flight. Other explanations for the observed activity patterns may exist, but they were not investigated in our st udy.