Myotis lucifugus occupies three types of roosts: day, night, and hibernation roosts. Locations of roosts are chosen based upon the presence of stable ambient temperatures. Myotis lucifugus inhabits forested lands near water, but some subspecies can be found in dry climates where water is not readily available. The fur of M. lucifugus is glossy, and varies in color from dark brown, golden brown, reddish, to olive brown. The length varies between 60 and 102 mm, and the wingspan between 222 and 269 mm. Little brown bats fly at speeds as high as 35 km/hour and average 20 km/hour. Females are larger than males, especially during the winter.Mating occurs in two phases: active and passive. During the active phase, both partners are awake and alert. In the passive phase, active males mate with torpid individuals of both sexes; passive phase mating is approximately 35% homosexual. Mating is random and promiscuous. Females in active phase usually mate with more than one male. In both active and passive phase matings, males mate with multiple females. Mothers nurse their own young and distinguish from other pups by odor and calls. Little brown bats are primarily nocturnal and emerge from their roosts at dusk. Primary activity occurs about two or three hours after dusk and secondary activity may occur before dawn; most individuals return to the roost by four or five o’clock in the morning. Myotis lucifugus invests a large amount of time each day grooming. Individuals use their claws to groom the fur, and tongue and teeth to clean their wing membranes. Myotis lucifugus produces frequency modulated (FM) calls at 45kHz, their fundamental frequency. These calls last 1 to 5 milliseconds and sweep from 80 to 40 kHz. Cruising bats typically produce 20 calls per second to detect prey and objects. Myotis lucifugus alert other bats with non-echolocation calls if they are flying on a collision course during feeding. They emit this call by reducing the frequency of the terminal portion of a sweep call to 25 kHz. Additionally, they may use echolocation calls, visual cues, such as landmarks, and possibly chemical cues to locate roosts; they can find their roosts from 180 miles away. Mother and young communicate through a few, complex vocalizations. There is no information about alarm or distress calls. Myotis lucifugus is an efficient insect predator, especially when insects are in patches and at close range (approximately less than one meter). Little brown bats, along with many other insectivorous bats, are opportunistic feeders and catch prey by aerial hawking and gleaning tactics. Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%.
Source: Myotis lucifugus Little Brown Bat, Animal Diversity Web, University of Michigan Museum of Zoology