Sunday, May 7, 2017

Townsend's Big-eared Bats

Bat flying against black sky. ©BLM
Photo from the National Park Service
One of the many species of animals we are hoping to protect here in Cal Pines is the Townsend's Big-eared Bat.  This bat is known for the unique habit of forming maternity roosts during breeding season. The maternity roosts are established in areas with ideal temperature and humidity, and are easily disturbed; this has made the species somewhat rare. There are only a handful of Big-eared Bat colonies known in the state of California.  One of the residents here was lucky enough to find a few roosting in the walk-in area under their deck.  No maternity roosts have been found in Cal Pines to date however.

This little fellow was roosting under a deck in Cal Pines
Here are some fun facts on this wonderful flying mammal provided by the National Park Service.

  • A Townsend's big-eared bat's average lifespan is 16 years; bats may live up to 30 years.
  • Highly maneuverable flyer; capable of flying at slow hovering speeds.
  • Large ears funnel sound into ear canal, and may also provide lift during flight and assist with temperature regulation.
  • Townsend's big-eared bats are very sedentary, with movement by females during the nursing season rarely exceeding 15 km., and movement at other times usually being less than 50 km.
  • When it's roosting or hibernating, Townsend's big-eared bat curls up its long ears so they look like ram's horns (see adjacent photo of one of our local bats).
  • When flying they can rapidly extend or contract their ears. When flying with their ears extended the ears point forward and are nearly parallel to their body.
  • They do not tuck themselves into cracks and crevices like many bat species do, but prefer open roosting areas in large rooms with their fur erect to provide maximum insulation and with their ears coiled back.

  • Appearance
    Townsend's big-eared bats, previously called lump-nosed bats, are a medium-sized bat with very long ears. Their fur is pale gray or brown above and buff colored on the underside. This bat's ears are enormous, reaching a length of 38 mm. When the ears are laid back they extend to the middle of its body. The face is marked by two large glandular lumps on either side of its nose.

    The Townsend's big-eared bat occurs throughout the west and is distributed from the southern portion of British Columbia south along the Pacific coast to central Mexico and east into the Great Plains, with isolated populations occurring in the central and eastern United States.

    Big-eared bats have been reported in a wide variety of habitat types ranging from sea level to 3,300 meters (10,826 feet). Habitat associations include: coniferous forests, mixed meso-phytic forests, deserts, native prairies, riparian communities, active agricultural areas, and coastal habitat types. Distribution is strongly correlated with the availability of caves and cave-like roosting habitat, with population centers occurring in areas dominated by exposed, cavity forming rock and/or historic mining districts. They prefer open roosting areas in large rooms and do not tuck themselves into cracks and crevices like many bat species do.

    Radio-tracking has shown that the bats forage up to 5 kilometers (about 3 miles) away to feed on moths and other insects, returning to the roost each morning. In contrast to other southwest bats, due to its relatively poor urine concentrating ability, it drinks water.

    Winter hibernation colonies are comprised of males and females and range in size from a few individuals to several hundred bats. If undisturbed, colonies will occupy the same site indefinitely.
    In the summer, the females form a nesting roost. Males are solitary during the maternity periods. The maternity colonies consist of one or more small clusters, which rarely exceed 100 bats. Females are alert and active in the maternity roosts and prefer dark places for their roosts. These colonies form between March and June (depending on climate), with pups born between May and July. Maternity colonies choose sites that have warm, stable temperatures for pup rearing. Female bats usually only have one young a year. The newborns range in weight from 2.1-2.7 grams. There is a strong maternal bond and the young bats squawk when the mother is away. The young bats, however, grow quickly, being able to fly within three weeks. After two months, many of the young bats have left the nursery roosts, with male bats leaving before female. In their first year, male bats are almost certainly incapable of breeding while female bats are able to reproduce at the age of four months.

    Conservation Status
    Historically, this species has declined due to direct killing by people and because of destruction or disturbance of roost sites. These animals are sensitive to light and movement so if they are disturbed during the day, they awake and their ears begin to move as they try to identify the intruder. If the disturbance occurs for more than a few seconds, the entire group takes flight and the roost may be abandoned.

    A study sponsored by the California Department of Fish and Game in the late 1980's documented a population decline of 40-60% in the past 30 years. Only about half of the maternity colonies known to exist in California prior to 1980 were active by 1991, resulting in an estimated 54% decline of adult females. Only three maternity colonies increased in size during the period, and all three are located in National Park areas (Point Reyes National Park, Lava Beds National Monument, and Pinnacles National Monument).

    Of the 23 roosts that are no longer available to bats, 9 (mostly buildings) have been demolished, 4 (all buildings) have burned, 4 (all buildings) have been renovated in such a way that bats were excluded, and 6 (including buildings, caves, mines, and a water diversion tunnel) have had the entrance closed.  Consequently, for this species to exist, minimization of human disturbance is essential. In additional, it is essential that habitat be preserved.

    Human intervention may have helped conserve the population on the west coast of North America, because man-made structures provide a shelter for big-eared bats. However, the Townsend's Big-eared Bat is state-listed as an Endangered species in Washington, a Sensitive species in Oregon, and as a Species of Special Concern in Texas, Montana and California, and they are on the Blue List in British Columbia.

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