page_title: Little brown bat
section_title: Reproduction and life cycle
hierarchical_section_title: Little brown bat / Biology and ecology / Reproduction and life cycle
caption_attribution_description: English: Recently born little brown myotis (Myotis lucifugus) in maternity colony within Yellowstone National Park
context_page_description: The little brown bat or little brown myotis is a species of mouse-eared microbat found in North America. It has a small body size and glossy brown fur. It is similar in appearance to several other mouse-eared bats, including the Indiana bat, northern long-eared bat, and Arizona myotis, to which it is closely related. Despite its name, the little brown bat is not closely related to the big brown bat, which belongs to a different genus.
  Its mating system is polygynandrous, or promiscuous, and females give birth to one offspring annually. The offspring, called pups, are quickly weaned and reach adult size in some dimensions by three weeks old. The little brown bat has a mean lifespan of 6.5 years, though one individual in the wild reached 34 years old. It is nocturnal, foraging for its insect prey at night and roosting in hollow trees or buildings during the day, among less common roost types. It navigates and locates prey with echolocation.
  It has few natural predators, but may be killed by raptors such as owls, as well as terrestrial predators such as raccoons. Other sources of mortality include diseases such as rabies and white-nose syndrome.
context_section_description: The little brown bat has a promiscuous mating structure, meaning that individual bats of both sexes mate with multiple partners. It is a seasonal breeder, with mating taking place in the fall before the annual hibernation. As a seasonal breeder, males do not produce sperm year-round; instead, spermatogenesis occurs May through August each year. Throughout the spring and summer, males and females roost separately. In the fall, however, individuals of both sexes will congregate in the same roost in a behavior known as "swarming." Like several other bat species, males of this species exhibit homosexual behaviors, with male bats mating indiscriminately with torpid, roosting bats, regardless of sex.
  Although copulation occurs in the fall, fertilization does not occur until the spring due to sperm storage. Gestation proceeds for 50–60 days following fertilization. The litter size is one individual. At birth, pups weigh approximately 2.2 g (0.078 oz) and have a forearm length less than 17.2 mm (0.68 in). While they have a small absolute mass, they are enormous relative to their mothers, weighing up to 30% of her postpartum body weight at birth. Pups' eyes and ears are closed at first, but open within a few hours of birth. They exhibit rapid growth; at around three weeks old, the young start flying, begin the weaning process, and are of a similar size to adults in forearm length but not weight. The young are totally weaned by 26 days old. Females may become sexually mature in the first year of life. Males become sexually mature in their second year.
  It is a very long-lived species relative to its body size. In the wild, individuals have been documented living up to 34 years.
  The average lifespan, however, is around 6.5 years. Males and females have high annual survival rates (probability of surviving another year), though survival rates vary by sex and region. One colony documented in Ontario had a male survival rate of 81.6% and a female survival rate of 70.8%; a colony in southern Indiana had survival rates of 77.1% and 85.7% for males and females, respectively.
caption: Recently born little brown myotis in maternity colony within Yellowstone National Park
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