Natural History:
This is the bat most commonly found in houses in Kansas. They gain entry by way of chimneys, open windows, doors, ventilation ducts, or small cracks between ceilings and walls. In winter, as homes are heated, the bats become active and must search for a cooler location to continue hibernating. Under natural conditions these bats select dry places in caves, and it is for this reason that they are able to hibernate in dry buildings. Flying within a room presents no problem, and, although the bat can bite if captured, it is otherwise harmless and will not intentionally make contact with humans. Big brown bats commonly forage around city lights and over pools of water (including swimming pools and fish ponds). In flight, they follow a slow, straight course in open places but are capable of abrupt turns when encountering an insect. They may emit an audible chattering sound in flight. When big brown bats enter hibernation in late September or October, males usually precede the females. At the beginning of winter the bats already have accumulated a store of energy in the form of fat, and this stored energy maintains their metabolism throughout the winter. Body temperature becomes approximately the temperature of the hibernaculum, which must be cool enough to induce a low level of metabolism. If temperatures abruptly drop too low the bats can freeze, and if temperatures increase the bats will awaken and become active, thus depleting their fat stores. Except for females in maternity colonies, big brown bats are essentially solitary. Even in hibernation they prefer to be alone or in small, loosely aggregated groups. This nonmigratory species may awaken from hibernation in mid-winter and go out in search of a drink of water before resuming hibernation. It again awakens from hibernation in April, and it generally spends the summer near its winter hibernation site.
Adults may attain the following dimensions: total length 110-130 mm; length of tail 39-54 mm; length of hind foot 9-13 mm; length of ear 14-20 mm; weight 16.5-33 g. As in many other species of bats, females average larger than males. Weight is greater in autumn than in spring because of the layer of fat accumulated during summer for use as metabolic energy during winter.
Big brown bats are generalized feeders, although insects of the orders Coleoptera amd Hemiptera predominate. Most insects are captured and eaten on the wing or, if the insects are too large to manage in flight, the bat will consume them at a nearby night feeding roost.
The most common causes of mortality in this species are failure to store sufficient fat for hibernation, accidents, inclement weather, and predation. Documented predators include common grackles, American kestrels, various owls, long-tailed weasels, cats, rats, and bullfrogs. This bat stores agricultural chemicals in its tissues, and this may be a mortality factor. Finally, a low incidence of rabies occurs in this bat, and this species may be a vector of St. Louis encephalitis virus.
This is the bat most commonly found in houses in Kansas. They gain entry by way of chimneys, open windows, doors, ventilation ducts, or small cracks between ceilings and walls. In winter, as homes are heated, the bats become active and must search for a cooler location to continue hibernating. Under natural conditions these bats select dry places in caves, and it is for this reason that they are able to hibernate in dry buildings. Flying within a room presents no problem, and, although the bat can bite if captured, it is otherwise harmless and will not intentionally make contact with humans. Big brown bats commonly forage around city lights and over pools of water (including swimming pools and fish ponds). In flight, they follow a slow, straight course in open places but are capable of abrupt turns when encountering an insect. They may emit an audible chattering sound in flight. When big brown bats enter hibernation in late September or October, males usually precede the females. At the beginning of winter the bats already have accumulated a store of energy in the form of fat, and this stored energy maintains their metabolism throughout the winter. Body temperature becomes approximately the temperature of the hibernaculum, which must be cool enough to induce a low level of metabolism. If temperatures abruptly drop too low the bats can freeze, and if temperatures increase the bats will awaken and become active, thus depleting their fat stores. Except for females in maternity colonies, big brown bats are essentially solitary. Even in hibernation they prefer to be alone or in small, loosely aggregated groups. This nonmigratory species may awaken from hibernation in mid-winter and go out in search of a drink of water before resuming hibernation. It again awakens from hibernation in April, and it generally spends the summer near its winter hibernation site.
Adults may attain the following dimensions: total length 110-130 mm; length of tail 39-54 mm; length of hind foot 9-13 mm; length of ear 14-20 mm; weight 16.5-33 g. As in many other species of bats, females average larger than males. Weight is greater in autumn than in spring because of the layer of fat accumulated during summer for use as metabolic energy during winter.
Big brown bats are generalized feeders, although insects of the orders Coleoptera amd Hemiptera predominate. Most insects are captured and eaten on the wing or, if the insects are too large to manage in flight, the bat will consume them at a nearby night feeding roost.
The most common causes of mortality in this species are failure to store sufficient fat for hibernation, accidents, inclement weather, and predation. Documented predators include common grackles, American kestrels, various owls, long-tailed weasels, cats, rats, and bullfrogs. This bat stores agricultural chemicals in its tissues, and this may be a mortality factor. Finally, a low incidence of rabies occurs in this bat, and this species may be a vector of St. Louis encephalitis virus.
Copulation occurs before entry into hibernation in autumn and also during periods of arousal in winter and spring. Fertilization and implantation occur after ovulation, typically in the first week of April. In early April, females leave hibernation sites and form nursery colonies. Young are born between the end of May and mid-June. Interestingly, big brown bats in Colorado and farther west have just 1 pup per year, whereas bats in the East have 2 pups per year. The only published study in Kansas, based on work done in Russell, revealed that our big brown bats produce 2 pups per year. Young are capable of flight 3 or 4 weeks after birth and are fully grown at about 70 days of age.