Little Brown Bat (Myotis lucifugus)

Description
little brown bat

Size

  • On average, adult little brown bats weigh approximately 8.5 grams (0.3 ounces).
  • Wingspan can measure up to 20 centimetres (8 inches).
  • Females are usually larger then males.

Appearance

  • Not surprisingly, the little brown bat (sometimes called the 'little brown myotis') has brown fur, darker on the back than the undersides.
  • The wings generally lack fur.
Distribution
  • The little brown bat is the most common bat in Alberta. The provincial population is estimated at 1 to 1.5 million individuals.
  • The adult females are relatively conspicuous as they roost together in colonies in occupied or unoccupied buildings throughout the province.
Natural History

Habitat

  • Colonies of this species are common in central Alberta and may be found in:
    • Barns
    • Churches
    • Garages
    • Houses
    • Office towers
    • Schools
    • Shopping malls
  • In more remote areas of the province, colonies are found in large hollow trees.
  • Summer cottages close to bodies of water (for example Wabamun Lake, Pigeon Lake, Gull Lake, Beauvais Lake) often are colonized by little brown bats.
  • The largest colonies may be in buildings in good repair.
  • During the summer, colonies consist almost exclusively of pregnant or lactating females and their young (thus the term "nursery" or maternal colonies).
  • Colonies can consist of three to 1100 bats but typically have from 50 to 300 individuals.
  • Little is known about where or how male little brown bats spend their time. A few have been found roosting individually in concealed roosts throughout the summer and are, consequently, difficult to locate.
  • Similarly, juvenile females in Alberta are seldom found during their second summer but apparently join the other adult females after this time.
  • Throughout August and September, many individual bats are seen flying at night or resting on walls and in alcoves during the day. At this time it is easy to find bats on buildings along the main street of many communities such as Edmonton, Innisfail, Lac la Biche or Slave Lake. Red brick buildings seem to be preferred.
  • The use of exposed roosts by bats may be more common in the northern part of their range and may be an adaptation to cooler temperatures. Direct sunlight may be important in providing heat energy during cool days.

When Active

  • Adult females appear at summer roosts in early May.
  • In the summer roosts, bats are often torpid or inactive during the day, especially during cool weather.
  • Activity begins shortly before nightfall as the bats prepare to emerge for the evening feeding period. Not all individuals leave the roost each time.
  • The bats return to the roost during the late evening, but leave again for another feeding period near dawn.
  • They all return to the roost before sunrise and remain inside during the day.
  • Where most little brown bats hibernate in Alberta is not known. Hibernacula usually are cool, dark, humid places in which the air does not move and, thus, the environment is very stable.
  • In the eastern United States, little brown bats hibernate in caves and abandoned mines. In Alberta, a few bats have been found in caves at Cadomin, Jasper, and Nordegg.
  • No doubt other caves in the mountains or foothills also serve as hibernacula, but many bats may migrate to the northern United States or southern British Columbia. A few little brown bats have been found hibernating in caves in Wood Buffalo National Park.
  • Males predominate in the winter roosts and the location of most females during the winter is unknown.
Reproduction and Growth

Breeding Behaviour

  • In the fall, bats of all ages and both sexes rendezvous at caves in the mountains. This is the only period when large numbers of males have been found.
  • This swarming activity is probably important in bringing large numbers of bats together for breeding. During this period, there is a rapid turnover of individuals at each cave which maximizes the exchange of diverse genetic material within the population.
  • The females exhibit high site fidelity and return to the same nursery roost year after year. Females relocated to other roosts during the summer rapidly returned to the original roost.
  • Nursery colonies are characterized by hot, dark conditions. They are poorly ventilated but often have more than one entrance. The high temperature promotes the rapid growth of young bats.
  • Sperm are stored by the hibernating females and fertilization occurs in spring.
  • Up to 98 percent of the females are pregnant each year; after a gestation period of 50 to 60 days, each female gives birth to a single young in late June or early July.

Growth Process

  • The young are born blind, hairless, and unable to fly. They are completely reliant upon the female for care and maintenance during the first three weeks of life.
  • The females are capable of identifying their own young and this is no doubt aided by the continuous squeaking of the juveniles whenever the female is absent.
  • By three weeks of age the young bats generally are able to fly and begin to feed themselves.
Conservation and Management

Status

The little brown bat is classified as Secure in the current General Status of Alberta Wild Species report. See:

Similar Species
  • Long-legged Bat
    The long-legged bat is morphologically similar to the little brown bat and often misidentified.
  • Northern Bat
    Northern bats look very much like little brown bats, but have longer ears.

Record life span

The oldest little brown bat observed in Alberta was banded as an adult in Cadomin Cave in October 1975, and was re-sighted as recently as February 2009, making it at least 35 years of age at that time!

 

Page Information

Updated: Jan 8, 2014