Bat Information Continued
An inventory completed in 2004 identified bat habitat and documented the presence of these eight bat species in Yellowstone National Park:
Researchers also found inconclusive evidence of three other species. Most of these bats are considered species of concern by Montana and/or Wyoming because of habitat loss and sensitivity to human disturbance. Two of the species probably migrate south for the winter, but most seek relatively warm places to hibernate a short distance from their summer roosts.
While the bulk of bat-related research investigated the taxonomy and distribution of bats in Yellowstone, recent efforts address population dynamics, summer roost site selection, and places for bats to hibernate in the winter (hibernacula). Researchers also sample for diseases that are affecting bat populations in other parts of North America.
Roosts provide bats with protection from weather and predators, and the type of roosting structure available affects foraging and mating strategies, seasonal movements, morphology, physiology, and population distribution. Bats in Greater Yellowstone use both natural habitats and man-made structures including bridges and abandoned mines.
Through investigations into the roost site characteristics of little brown bat maternal colonies (females with young during pregnancy and lactation) located in park structures, researchers learned the bats were selecting "warm places with tight spaces." The selection of these places makes sense from an evolutionary standpoint. Young bats can maximize their growth rate, wean, and begin to fly and forage earlier because they are not using much energy to stay warm.
Bats are long-lived creatures (10–30 years) and show a strong preference to return to maternal roost sites where they have successfully raised young. For this reason, park managers try to exclude bats from occupying park buildings where they may try to return in the future. In 1904, the "type specimen" describing the subspecies of little brown bat found in Yellowstone was collected from the Lake Hotel. Consequently, most management efforts directed towards bats involve excluding bats from occupying human facilities.
The presence of other bats in Yellowstone is probably restricted by the limited location of suitable roosts and/or the distribution of moths and beetles on which more specialized bats forage. It is likely that most western bat species migrate short distances from their summer roosts to their winter hibernating locations. However, some species migrate long distances to areas where temperature and insect populations remain high enough for continued activity. These species usually do not hibernate. In greater Yellowstone, the hoary bat and silver-haired bat likely migrate south for the winter.
Bats with long, narrow wings (e.g., the hoary bat) are fast but less maneuverable fliers that typically forage in open areas. Bats with short, broad wings (e.g., Townsend's big-eared bat) are slower but more agile and typically forage in forested areas or along the edge of vegetation. A few Yellowstone bats, such as long-eared myotis, pallid bat, and Townsend's bigeared bat can glean insects off the surface of vegetation, and have wing shapes that enable them to hover and carry larger prey.
Audio equipment can be used to listen to vocalizations by bats used for echolocation and to determine the level of bat activity at a site and identify some bat species. High frequency calls are less likely to alert predators and are best for locating prey, although some moths have developed "ears" on their abdomens capable of detecting such calls. Most bats also use lower frequency calls (often audible to humans) to communicate with each other. Also, contrary to the expression "blind as a bat," bats typically have excellent vision that can be used for hunting.
Bats make efficient use of the energy obtained through foraging by regulating their body temperature (thermoregulation). To conserve energy, bats can lower their metabolic rate and body temperature (torpor), but they are then unable to carry out normal activities. Most bat species in Greater Yellowstone undergo torpor that may continue for months and is typically a seasonal response to a prolonged fall in temperature or reduction in food supply.
At rest, bats roost head down, which makes them less vulnerable to predators and facilitates flight. A bat can remain upside down for months because of cavities in its cranium that pool blood and other fluids away from the brain and an arrangement of ligaments and leg muscles that enables them to hang passively from their perch while sleeping.