Myotis nigricans is a small vespertilionid bat limited in distribution to the neotropical zone. These bats are locally abundant in the Panama Canal Zone, and commonly roost in buildings such as the laboratory on Barro Colorado Island where this study was carried out. Homing experiments showed this species to be capable of returning to the roost from distances up to 50 km, but not from 104 km. Night roosting was not observed.
Little is known of the food habits of M. nigricans, except that they are insectivorous and probably take some Lepidoptera. The young are left behind in the roost when the females leave to forage at night. Females nurse only their own young and are able to pick them out of a group of 50-100 youngsters upon returning in the mornings. During the day the bats undergo behavioural thermoregulation in the roost. These movements result in a mixing of the sexes which are otherwise segregated inside the roost, and copulation occurs at this time.