The little brown bat (Myotis lucifugus) is one of the six species of mammals endemic to Kodiak Island. The species ranges from Alaska to Labrador and south into central Mexico. It is more prevalent in the northern part of its range and is absent from much of Florida and Texas. It is the most common and widespread bat species in Alaska and lives in a variety of habitats, from the temperate rainforests of southeastern Alaska to the spruce/birch forests of the interior to treeless areas dominated by shrubs in western Alaska. While four other bat species are found in Southeast Alaska, the little brown bat is the only species of bat that lives in the Interior and South Central Alaska, and it is the only species that exists on Kodiak Island.
As their name implies, little brown bats are small mammals. They weigh between .18 and .32 ounces (5-9 grams) and are 3-4.5 inches (7.62-11.43 cm) in length. Their wingspan is 8 to 9 inches (20.32-22.86 cm) wide. They have cinnamon to dark brown fur on their backs, while their undersides are buff to pale gray. The hairs on their backs have long, glossy tips. The tragus, a fleshy projection that covers the ear canal, aids bats in echolocation. The shape and length of the tragus are sometimes used to identify bat species. In little brown bats, the tragus is half as long as the ear and has a blunt tip.
Little brown bats are efficient in the air and can fly at speeds ranging from 4 to 21 mph (6-34km/h). At an intermediate rate of speed, their wings make 15 strokes per second. They are most active at night, and their flight patterns are erratic. If knocked to the ground, they are clumsy crawlers, but if they land on the water, they can flap across the water for several hundred feet before getting tired. When roosting, bats hang upside down, and they achieve this position by flying up to a perch and grasping it with the long, clawed toes on their hind feet.
Little brown bats in Alaska mate between August and October, but fertilization is delayed until spring. After a gestation of 50 to 60 days, a female gives birth to a single pup. It is unusual for a small mammal to have only one baby at a time. Voles and mice give birth to large litters, and sometimes produce many litters per year. Voles and mice only live for one or two years, though, while bats may live 10 to 20 years. Pregnant or nursing females congregate together in maternity roosts. This clustering helps raise the temperature in the roost, speeding growth and development of the young. While bats normally hang with their heads down, a female gives birth with her head up, allowing her to catch the newly born pup with her tail membrane. A baby is born with deciduous incisors that along with its thumb and hind feet, allow it to cling to its mother. Pups are naked and blind at birth. They are weaned and able to fly on their own when they are three weeks old.
Little brown bats eat insects and feed at night, and this can be a problem in Alaska where the short amount of darkness at high latitudes in the summer reduces the amount of time bats can spend feeding. Bats use echolocation to find and capture prey, and they often hunt over lakes, ponds, and slow-moving streams and rivers. Bats drink while flying near the surface of the water. In Alaska, little brown bats eat moths, mosquitos, beetles, a variety of flies, and even spiders. They capture prey with their teeth, by netting them with their tail membrane, or by batting an insect with the tip of a wing and deflecting it into the tail membrane. They can then transfer prey from their tail membrane to their mouth while still in flight. During the day when not feeding, bats rest in roosts, and they conserve energy while roosting by going into torpor. A torpid bat reduces its metabolic rate and temperature, thereby decreasing its energy demands.
Little brown bats communicate with chemical signals produced by the nasal gland. These glands enlarge during the breeding season. Bats also use tactile signals when mating, and while they produce few vocalizations, they do make a honking sound, which may help to prevent mid-air collisions when foraging. Echolocation calls probably help bats locate roosts and hibernation sites.
It is not known how many little brown bats live in Alaska, and not much is known about where they hibernate, or if bats in the interior and far north migrate to warmer coastal areas before hibernating. Biologists hope to learn more about the migration and hibernation of bats in Alaska through ongoing research and bat-monitoring programs.
Bats face many threats, including wind farms. For some reason, bats are more susceptible than birds to being hit by windmill blades. Pesticides are bad for bats for two reasons. They can directly poison bats, and they reduce the number of insects that bats depend on for food. Habitat loss and disturbance can also affect bats, but at present, the greatest threat to bats, especially little brown bats, is a disease called white-nose syndrome. This disease is caused by a fungus that appears white around the nose and on the wing membranes. Biologists believe this fungus, or something associated with the fungus, causes bats to wake and move around when they should be hibernating, forcing the bats to use up all their stored energy and causing them to starve to death. White-nose syndrome has killed more than six million bats in northeastern North America since 2006, and the disease is slowly moving westward.
I have now written posts about the six mammal species endemic to Kodiak Island, and next week, I will begin a series of posts about some of the mammals that have been introduced to Kodiak.
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