BEHAVIORAL AND THERMOREGULATORY RESPONSES OF FEMALE HOARY BATS, LASIURUS-CINEREUS (CHIROPTERA, VESPERTILIONIDAE), TO VARIATIONS IN PREY AVAILABILITY

Responses of lactating hoary bats, Lasiurus cinereus (Palisot de Beauv ois), to variation in prey availability were studied in 1989 and 1990. We used temperature-sensitive radiotransmitters to monitor the bats' thermoregulatory patterns and a combination of radio-tracking and dire ct observations of bats with unique combinations of colour bands to do cument foraging behaviour. Typically, bats foraged in concentrations o f moths attracted to street lights and tagged bats returned to the sam e site each night. Nightly prey availability varied and bats responded to the changes in food availability by changing their use of space an d entering torpor. Bats spent significantly mole time out of range of our radio-tracking station (and away from their usual foraging sites) when prey availability was low, presumably searching for alternate for aging sites. Bats also used heterothermy, entering torpor when tempera ture and prey availability were low. Lasiurus cinereus always used tor por for part of the night when minimum ambient temperatures were < 13 degrees C. When minimum ambient temperatures were between 13 and 21 de grees C there was individual variation in the thermoregulatory strateg y adopted by different bats on the same night. The same individual som etimes adopted a different thermoregulatory strategy on different nigh ts with the same minimum ambient temperature.