Little Brown Bat: Myotis lucifugus
Taxonomy
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Mammalia Order: Chiroptera Family: Vespertilionidae Subfamily: Vespertilioninae Genus: Myotis Species: Myotis lucifugus (Barbour and Davis 1969)
Myotis lucifugus, whose common name is the little brown bat, is one of the most common species of bat found in the forested areas of the United States. The species can be found as far north as Alaska, as far south as Mexico, and from the Pacific to Atlantic coasts (Nowak 1994).The little brown bat is easily associated with humans, since many colonies form in man made structures like buildings and attics (Barbour and Davis 1969).
Physical Description
The common name of Myotis lucifugus speaks for itself in the description of the bat. The typical weight of the little brown bat is between 5 and 14 grams (Lekagul and McKneely 1977). The total length of the little brown bat is about 84 mm, the forearm is 34-41 mm, the tail around 34 mm, the hind foot about 11 mm, and the ears around 14 mm. The little brown bat has large feet and small ears (Schmidly 1991). The wingspan of Myotis lucifugus ranges from 222 to 269 mm (Griffin 1958). The bats have glossy fur that is evenly colored, and their fur is paler underneath. The brown fur can range from a pale tan, a reddish brown to a dark brown. They have long hair on their toes and the hair extends beyond its claws (Kurta 1995).
The little brown bat has a long range and speed for such a small animal. It can attain flight speeds up to 85 km per hour and averages about 20 km per hour (Nowak 1994). Little brown bats can be released over 200 km away from their roost sight and still find their way back. They will also fly 275 km between summer and winter roosts (Godin 1977).
Reproductive Cycle
For Myotis lucifugus, breeding occurs in the fall and the sperm is stored and remains viable in the uterus of the female throughout the winter. In the spring they leave the hibernacula, the hibernation roost, and fertilization begins (Kurta 1995). After the females leave hibernation and before or shortly after they arrive at nurseries, ovulation begins (Humphrey and Cope 1976). Gestation for Myotis lucifugus lasts 50 to 60 days. To bear young, the female little brown bats form maternity colonies, and there are few or no males present until after the young are born (Nowak 1994). Nursery colonies can range from 15 to 1,200 (Godin 1977). There is usually one baby per litter, only in rare cases have there been two (Humphrey and Cope 1976). During birth the female reverses position, hanging with her head upward and catches the fetus with a cup made from her uropatagium. The newborn bat is blind and opens its eyes on the second day; they attain adult weight in four weeks (Barbour and Davis 1969). The newborn batís jaws and milk teeth are already well developed at birth. Babies are born with 22 milk teeth. Those teeth are replaced by permanent dentition starting the 13th day after birth (Yalden and Morris 1975). The babies attach themselves to their motherís nipple and remain there for about two weeks, or until half grown (Barbour and Davis 1969). Newborn Myotis lucifugus need at least three weeks before they can fly (Humphrey and Cope 1976). Sexual maturity is reached at different time lengths for the males and the females. The male little brown bat reaches sexual maturity in one year and the female reaches it in 6 to 9 months (Nowak 1994). Myotis lucifugus have been recorded to living up to 33 years in the wild, making them some of the oldest bats recorded.
Natural History
Little brown bats like to roost in man-made structures, such as buildings, attics, or bridges. They prefer hot places, and extreme has been recorded with temperatures as high as 131○ F (55○C). Colonies can usually be found close to bodies of water because of the type of insects available there (Barbour and Davis 1969). Groups of males can be found in caves, though solitary males are common as well. Colonies, ranging in size from a few up to a thousand, tend to consist of females that are raising the young. Very few males are part of a colony, and they join the females again during late summer (Barbour and Davis 1969). After the young are weaned the members of the colony separate and travel to certain caves. They live in these caves for a short time then fly to their summer range. For the bats that live in the north, they return to these caves to hibernate late in the fall. During the day, the bats enter torpor to conserve fat for hibernation (Barbour and Davis 1969).
Little brown bats hibernate in the winter and they have the greatest range of body temperature in any vertebrae. Myotis lucifugus have been found cooled to 6.5○C without harm and at 54○C (Barbour and Davis 1969). They hibernate in large colonies; one cave in Vermont had 300,000 hibernating bats (Barbour and Davis 1969).
Myotis lucifugus are insectivores; they eat gnats, beetles, crane flies, wasps and moths. Little brown bats prey on insects with aquatic larval stages, and so they hunt near the water (Kurta 1995). During the summer they are very alert on warm days and as night approaches they become more active, before emerging to feed at dusk. When foraging, individual bats tend to repeatedly pursue the same flight pattern (Barbour and Davis 1969). They return from hunting at dawn to their roost and before entering they defecate (Kurta 1995). They find their prey by echolocation and produce frequency modulated (FM) echolocation pulses. Frequency modulated simply means that the pulse frequency is not constant and FM pulses can be described as a short, steep sweep down the frequencies. The sweep goes from 60 to 30 kHz over 5 ms (Simmons 1971).
The little brown bat can be found all over North America. It is the most abundant bat present in the United States. The highest densities can be found in the northern United States, southern Canada, and southern Alaska; some can even be found in northern Mexico (Kurta 1995).
Conservation Status
There is no conservation status on the little brown bat because of its abundance (Kurta 1995). There are, however, many predators that eat little brown bats, including hawks, owls, raccoons, minks, and leopard frogs (Griffin 1958).
The presence of Myotis lucifugus can have some drawbacks. For other mammals little brown bats pose a problem because they can carry fleas, mites, and chiggers (Barbour and Davis 1969). For humans, the presence of bats can sometimes require costly cleaning. As for the predominant fear of bats transmitting rabies, humans only get infected when they pick up a sick bat. A rabies-infected bat becomes paralyzed and falls to the ground (Kurta 1995). On the positive side, little brown bats eat annoying pests that transmit diseases and eat agricultural products (Barbour and Davis 1969). Myotis lucifugus populations are likely to grow due to the increase in desirable manmade roosting areas .
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Alissa Wigdor
February 23, 2004
HONR278C