In southern, or lower elevation populations, peak in births is May-June, and at higher elevations, peak may be in July. Generally 1 young born each yr. There are a few records of twins. The young are weaned and begin to fly at 3 wk. Early foraging attempts involve fly-catching of passing insects from a perch.
First winter is period of highest mortality.
Average life span is 1-2 yr. Occurs at feeding and roosting sites with many other bat species. Populations in many areas have suffered drastic declines. Fat-soluble pesticides dangerous in combination with migratory stress and depletion of fat reserves in hibernation and migration. Disturbance in winter destructive because of energy expense of arousal.