Migration and molt patterns of red bats, Lasiurus borealis (Chiroptera: Vespertilionidae), in Illinois

Abstract

Red bats, Lasiurus borealis (Chiroptera: Vespertilionidae), are widespread in North America, but many aspects of their biology are poorly known. In an attempt to elucidate patterns of migration and molt in red bats, data were collected over an eight year period on bats that struck the large glass windows of a major convention center in Chicago, Illinois. Fifty red bats were obtained between autumn 1979 and spring 1987; more females (32) hit the building than males (11). Forty-eight of the fifty red bats struck the building during the autumn. During the autumn months, approximately the same number of adults (19) as young-of-the-year (21) were found. It is postulated that the bats that hit the building were migrating through the area, that the bats are concentrated along the southwestern shore of Lake Michigan due to a funneling effect, and that red bats use visual cues during migration. The color pattern of subadult male red bats is described for the first time as being identical to that of adult females, suggesting that subadult males may have been selected to look like females, a form of mimicry.