Behavioural and thermoregulatory responses of female hoary bats,Lasiurus cinereus(Chiroptera: Vespertilionidae), to variations in prey availability

Abstract

Responses of lactating hoary bats, Lasiurus cinereus (Palisot de Beauvois), 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 direct observations of bats with unique combinations of colour bands to document foraging behaviour. Typically, bats foraged in concentrations of moths attracted to street lights and tagged bats returned to the same site each night. Nightly prey availability varied and bats responded to the changes in food availability by changing their use of space and entering torpor. Bats spent significantly more 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 foraging sites. Bats also used heterothermy, entering torpor when temperature and prey availability were low. Lasiurus cinereus always used torpor for part of the night when minimum ambient temperatures were < 13°C. When minimum ambient temperatures were between 13 and 21°C there was individual variation in the thermoregulatory strategy adopted by different bats on the same night. The same individual sometimes adopted a different thermoregulatory strategy on different nights with the same minimum ambient temperature.