Migration and thermoregulation strategies of hoary bats (Lasiurus cinereus) in North America

Despite evidence of migration in North American tree bats (genera Lasiurus and Lasionycteris), details regarding seasonal movements in these widely distributed species are few. The first chapter of this thesis describes research that involved mapping occurrence records to infer seasonal distribution patterns of tree bats. Analysis of these records revealed that hoary bats (Lasiurus cinereus) winter mostly in California and Mexico before moving to northern summering grounds. Eastern red bats (Lasiurus borealis) winter in southeastern areas then move to northern regions during warmer months. Silver-haired bats ( Lasionycteris noctivagans) also show movement at the continental scale, although these movements may differ between western and eastern groups. Museum records provide little evidence of major movement by any species between North and South America.;The second chapter describes research into how the stable hydrogen isotope ratios of bat hair (deltaDh) relate to hydrogen isotope ratios of precipitation (deltaDp). Results indicate that stable isotope techniques provide a viable means of determining migratory movements of bats. In particular, we show that a single annual molt occurs in L. cinereus prior to migration and that there is a strong relationship between deltaD h and deltaDp during the molt period. The results of this study reveal that individual hoary bats are capable of traveling distances in excess of 2000 km, that hair is grown at a wide range of latitudes and elevations, and that female bats migrate farther than males.;The third chapter describes a study in which we quantify sex differences in the thermoregulation and water loss of L. cinereus during its spring migration. We measured body temperature, resting metabolic rate, and evaporative water loss of bats over a range of air temperatures. Pregnant females maintained normothermic body temperatures independent of air temperature. In contrast, males became torpid during the majority of exposures to low temperatures. The thermal neutral zone ranged between approximately 30 and 34°C in both sexes and females generally had lower mass-specific metabolic rates than males. Mass-specific rates of evaporative water loss in males were consistently higher than in females at most air temperatures. These results suggest that male and pregnant female L. cinereus employ different thermoregulatory strategies during their spring migration.