ABSTRACT
The little brown bat (Myotis lucifugus), one of the most abundant and widely distributed bats in North America, occurs from Alaska across the Northwest Territories to the coast of Laborador. In spring and summer, females commonly form maternity colonies in a variety of man-made structures, including houses, barns, schools, and churches. This bat regularly engages in a spring and autumn migration and, especially females, exhibit a high degree of fidelity to their natal roost. Spring migration usually takes place directly from a hibernaculum to a maternity site, whereas autumn migration more often involves an interim "swarming" period which is coincident with the mating season, before bats enter hibernation. Ultrasonic detectors can be used to determine the relative abundance of bats (number of bat passes per unit time or area) along flyways or in feeding areas. Mist nets and traps can be used to estimate relative numbers present in one or more habitats.
