Description: The relatively small myotis or "mouse-eared" bats are one of the more primitive groups of American bats. The little brown bat can be distinguished from other Kansas bats by: 1) glossy dorsal fur, due to the lighter appearance of the hair tips (contrasting to the remainder of the dorsal hair), 2) a belly lighter than the back, 3) dark brown tail membrane, 4) rounded naked ears which ar 13-15 mm long with a simple tapering tragus and which, when laid forward, barely reach beyond the nostrils, and 5) lack of a keel on the calcar. Sexes are similar in color and size.
Size: Adults may attain the following dimensions: total length 85-100 mm; tail 33-40 mm; hind foot 10-12 mm; ear 13-15 mm; weight 5.5-8.5 grams.
Range and Habitat: The little brown myotis probably occurs throughout the eastern two-thirds of the state. This common small bat occupies two principal habitats: during winter hibernation, draftless caves where temperatures are low, but above freezing, and humidity is high; and during the rest of the year, in buildings, under loose bark of trees, in hollow trees and in shallow crevices in cliffs. Caves are seldom used except for hibernation; both males and females winter together in groups of up to several hundred bats. In the summer, females from nursery colonies of various sizes, and males are usually solitary. At twilight they forage over fields and water and among trees, wherever insect food is available. Activity is greatest two to three hours after sunset, but then falls off abruptly, and many bats return to their roosts.
Reproduction: Breeding takes place in late autumn, winter (in hibernacula) and early spring. The sperm remain dormant in the uterus until the single egg is released from the ovary. The egg is then fertilized in the right uterus. In approximately two months the young is born, sometime during May, June, or July. The naked newborn is one-fourth the weight of the mother. The eyes open on the second or third day. The young hold onto the mother's hair or nipples with claws and special hook-shaped temporary teeth. While females are foraging, they remain in the nursery colony; they can fly at two to three weeks of age, and by the fourth week they are weaned. At two months they are capable of breeding. Males are not sexually mature until the next year. Juveniles can be distinguished from adults by the elongated cartilaginous joints of the fingers.
Habits: Little brown myotis, like other bats, have developed a system of echolocation for evaluating the distance, size and movement of flying prey, and for evading obstacles. The ultrasonic calls are broadcast from the larynx through the mouth and echoes are reflected from objects back to the bat's ears. The ability to acoustically "see" objects is best demonstrated in total darkness of caves where little brown bat are able to fly about in close quarters with colliding. Echolocation functions with such a high degree of accuracy that the chance of a bat accidentally contacting a human in nature is negligible; the idea of bats attacking humans and becoming entangled in their hair is unfounded. Specializations in bats' ears permit reception of echoes with the least amount of interference from the high frequency calls being emitted. Partial separation of the bony capsule housing the middle and inner ear from the rest of the skull bones also reduces interference.
As cool autumn temperatures arrive the little brown myotis moves to caves and similar protected places such as mines. In hibernation there is a reduction of activity which may be maintained throughout the winter uninterrupted. There is a lower rate of respiration, reduced body temperature and a dramatic slowing of the heart rate. If temperatures of a hibernacula are too cool or too warm, hibernation is interrupted and some individuals temporarily may become active, and move about until optimum conditions are found. Disturbance of bats in caves by humans, especially in winter, is a major factor in bat mortality.
Food: Little brown myotis fill an important ecological niche, taking over the insect foraging activity of birds at night. Their food consists entirely of insects, mostly small beetles, moths and gnats, as well as mosquitoes. Quantities sufficient to maintain flight metabolism require these bats to eat up to half their weight in a night's foraging. Insect larger than those which can be consumed in flight are carried to perches where they are eaten at leisure. The most undigestible parts are dropped to the ground and are telltale signs of feeding perches. In late autumn fat is accumulated for the six to seven months of hibernation.
Remarks: Average longevity of the little brown myotis is from two to three years, but the greatest known age is a remarkable thirty years. The long life is possible because of lack of heavy predation, and inactivity during long periods of hibernation. Natural predators are few, but include the great horned owl at night and blue jays by day. Other predators include snakes which come upon them while these bats are roosting. Ectoparasites are common, especially in roosting sites or in caves. Little brown myotis are presently free of rabies in Kansas and should not cause concern to humans, but although harmless, they can bite. All bats in Kansas are beneficial and should be strictly protected, as should their hibernacula.
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