Meeting Abstract
The torpor-assisted migration hypothesis posits that migratory bats use torpor during daytime roosting to minimize refueling requirements and preserve fuel stores for nocturnal flights. Previous field studies indicate that bats regulate body temperature and time in torpor facultatively so that daily energy expenditure is independent of ambient roosting temperature. However, direct measurements of total roosting energy expenditure in relation to ambient and body temperature are lacking. Our objective was to measure full-day body composition change and energy expenditure of bats roosting at different temperatures to test the prediction of the torpor-assisted migration hypothesis that fat and energy use by bats is independent of ambient roosting temperature. We further tested whether torpor use is affected by migration season, sex and age. We predicted that bats would be more conservative with their fat stores during the spring than the fall, on account of the colder spring weather, especially in females that are gestating and facing imminent lactation. We predicted that juvenile bats would use more torpor than adults in the fall to ensure sufficient fat stores for migration. We captured silver-haired bats (Lasionycteris noctivagans) at Long Point Bird Observatory, Long Point, Ontario, Canada, a prominent stopover site for migrating birds and bats. We used quantitative magnetic resonance analysis to measure change in fat and lean mass and to calculate total energy expenditure during roosting at 10, 17, 25 degrees C for 12 hours (the length of a daytime stopover). Body temperature was continuously monitored with radio-transmitters. This study will test key predictions of the torpor-assisted migration hypothesis and further our understanding of energy management at stopovers for migratory bats species.
