Meeting Abstract
Several North American bat species undertake long-distance latitudinal migrations, which are thought to consist of alternating periods of flight and refueling at stopover sites. Recent work in our lab found that silver-haired bats (Lasionycteris noctivagans) use a torpor-assisted migration strategy, which dramatically reduces daytime thermoregulatory costs, and increases net refueling rate. Daytime torpor facilitates very brief (1-2 day) stopovers in the fall. However, spring and fall migration pose different challenges. The concurrence of migration and pregnancy in the spring creates a conflict for female bats. Daily torpor use will spare energy stores for migratory flight, but delay fetal development. Thus, sex may substantially affect the energy budgets of spring migrating bats in ways that would not occur during the fall. This hypothesis supported by our earlier finding that female bats have significantly longer stopovers, and had larger fat stores than males in the spring, as would be expected if females incurred higher maintenance costs. Here we investigate sex differences in thermoregulation at stopover in the spring. We predicted that female bats would use shorter torpor bouts, enter torpor at lower ambient temperatures than males. Lasionycteris noctivagans were captured in April and May 2014 at Long Point, Ontario, Canada. We measured fat and lean body mass using quantitative magnetic resonance, and fitted each bat with a temperature-sensitive radio transmitter. We tracked bats to their day roost, and measured skin temperature and roost temperature continuously throughout the day. Our data will be used to test our hypotheses about the effects of sex and body composition on torpor use and migratory stopover.
