Biology and Migration of the Bat, Myotis lucifugus, in New England

Abstract

Female bats typically end hibernation in Aeolus Cave in southwestern Vermont from early April to mid-May and males between 7 May and 7 June. They scatter to summer colonies as far distant as 172 miles, predominantly to the southeast. The cave is frequented by bats from mid-July through August. After a night's visit individual bats leave, but return in September and October to hibernate. In Vermont, maternity colonies of a dozen to 1,200 bats start forming in attics as early as 22 April. Adult males compose up to 6% of a colony in June, and up to 34% in September. Parturition occurs between 7 June and 10 July. Old bats give birth earlier than yearlings. Most young can fly by mid-July. Yearlings can sometimes be recognized through June by the shape of the finger joints. Colony breakup is gradual, from late July to mid-September. Juvenile bats and some adults seem to lack homing ability. Old bats become fat in August and enter hibernation before juveniles, many of which appear emaciated. Two abandoned mines appear to serve more localized populations than does the cave most intensively studied. In summer, bats appear to be most abundant in an area of overlap known to be served by these three retreats. The summer population density of an area of approximately 8,600 square miles served by the cave is estimated to be 26 bats per square mile. The population wintering in the cave is estimated to be 300,000 ± 30,000.