Little Brown Bat
Four of the nine species of Adirondack bats belong to the genus Myotis, the mouse-eared bats. The little brown bat is the most abundant of the four, and is the common bat of the region. During the summer, few buildings with cracks or crevices near the eaves of roofs are without a colony of little brown bats. This species has glossy golden to olive brown fur, and is 80-102 mm (31.4-4.0 in) from the tip of its nose to the end of its tail. Its wingspread is 20-25 cm (8-10 in). Adults weigh 7-10 g (0.3-0.4 oz); females are slightly heavier than males.
From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York,College of Environmental Science and Forestry. 216pp
Because of their small size and nocturnal habits, bats are nearly impossible to identify in flight. However, when roosting, or in hand (only experts should handle bats because these small animals are fragile, and a very small percent may be rabid) most Adirondack species vary enough in color and size to permit easy recognition. The little brown bat is an exception because it resembles both Keen's myotis (M. septentrionalis) and the Indiana bat (M. sodalis). The little brown bat has long hairs on each hind foot which extend to, or just beyond the claws on the toes. These hairs are shorter on the grayish brown Indiana bat. Relatively short ears that, when pressed forward, extend less than 2 mm (0.08 in) beyond the nose, distinguish the little brown bat from the longer eared Keen's myotis.
Range and Habitat
The little brown bat's range is a large portion of North America from Alaska to Labrador, south into central Mexico. Its distribution in the southern U.S. is spotty, and it is absent from much of Florida and Texas. This specie is widespread in the Adirondack Park where it inhabits buildings and hollow trees in the summer, and hibernates in mines and caves during the winter. It exists at elevations to at least 657 m (2155 ft), e.g., at Heart Lake, during the warm months of the year.
All species of Adirondack bats forage at twilight or at night, capturing insects which they detect by echolocation. They capture prey with their teeth, and by netting them with the tail membrane, or by deflecting an insect with a wing tip into the tail membrane. While still flying, bats transfer prey caught in the tail membrane to the mouth, quickly chewing and swallowing small insects, alighting on nearby perches to consume larger forms.
The adult stages of midges and other aquatic insects such as stone flies and mayflies make up a large portion of the diet of the little brown bat which often forages near or just over the surface of water. This bat tends to home in on insects 3-10 mm (0.1-0.4 in ) in length at a distance of about 1 m (3.3 ft), frequently attacking swarms of insects. The darting, fast flights of the little brown bat, rapid chewing (the jaws open and close at a rate of 7 cycles per second), and rapid digestion (food may pass through the alimentary canal in 35-54 minutes) enable this species to consume up to 600 insects in one hour. Feeding periods last 1-5 hours, and an individual may roost between foraging bouts. A colony of 100 little brown bats may eat 19.2 kg (42 lb.) of insects in four months, which indicates the important influence this species (and other bats as well ) has on insect populations
Activity and Movement
The little brown bat flies at speeds of approximately 6-34 km (4-21 mph), the wings moving at a rate of 15 strokes per second at intermediate speeds. Most flight occurs at night, and the usual flight pattern is erratic. When knocked to the ground, little brown bats crawl clumsily, and if they land in water, flap across the water for several hundred feet before tiring. Bats hang by their hind feet, head down, while roosting, a position gained by flying near a perch, braking with the wings, and reaching up with the hind feet to grasp the perch with the long, clawed toes. Like most bats, this species flies near the surface of water and drinks while in flight.
Little brown bats hibernate in September and October, emerging in April - June (females emerge first). Fat reserves provide the energy necessary for the long period of torpor. Hibernating individuals roost in dense clusters, often far back in the recesses of caves and abandoned mines where temperatures are cold but above freezing, and where the humidity is high. Although normally inactive, disturbances, such as intrusion by people, may trigger arousal, seriously depleting energy reserves, and in some cases causing mortality
Adults mate in mid to late autumn while swarming near the entrances of hibernation sites. Males arousing during hibernation may also mate with torpid females. Females store sperm from autumn and winter matings. Fertilization occurs in the spring as females leave hibernation to form nursery colonies. The gestation period is variable, usually 50-60 days, and depends on a female's ambient temperature. Females bear their single young in late June or July. During parturition, the female hangs head up, expelling the newborn into the cupped tail membrane. At birth, each young weighs 1.5-2 g (0.07 oz), its flesh colored skin covered with fine silky hair, the eyes opening within 24 hours. For the first few days, young little brown bats cling to their mother's fur, even during nocturnal foraging flights, but at a later age, remain at the roost. Females disperse from nursery colonies when the young are weaned and capable of flight, at approximately 21-28 days. Yearling females may bear young, but males do not breed until the end of their second summer. Potential longevity of the little brown bat is 34 years, although few individuals live this long.
Hawks, owls, and other birds such as common grackles kill and eat little brown bats. The list of mammal predators is long and includes the mink, weasel, raccoon, and rodents. Snakes, fish, and even bullfrogs occasionally capture this species. The little brown bat is an infrequent item in the diets of all these animals
- Social System - The little brown bat is promiscuous and colonial. During the summer, females gather in maternal or nursery colonies of a dozen to more than a thousand, while males roost alone or in small isolated colonies. In autumn, both sexes swarm near the entrances to hibernating sites, then disperse, returning later to hibernate in dense aggregations sometimes numbering in the thousands. Several hundred miles may separate summer roosts from winter hibernation sites. The colonial habits of this species are responses to roosting sites safe from predators, the patchy distribution of its food, and the conservation of body heat by roosting in close proximity. An estimate of the population density of the little brown bat in the northeastern U.S. is 1 bat per 10 ha (1 per 25 acres).
- Communication - Chemical signals, e.g., produced by nasal glands which enlarge during the breeding season, play a primary role in the communication of the little brown bat. Tactile signals synchronize mating. Vocalizations are few but include "honking" which in one context may aid in preventing mid-air collisions among foraging adults. Echolocation calls may enable individuals to locate active roosts and hibernation sites. The young produce isolation calls which aid in mother-young recognition.
Davis, W.H., and H.B. Hitchcock. 1965. Biology and migration of the bat, Myotis lucifigus, in New England. Journal of Mammalogy, 46:296-313.
Fenton, M.B., and R.M.R. Barclay. Myotis lucifigus. Mammalian Species, 142:1-8.
Gould, E. 1955. The feeding efficiency of insectivorous bats. Journal of Mammalogy, 36:399-407.
An excellent source of information on bats is Bat Conservation International