Bat monitoring efforts using acoustic surveys and mist-net captures have identified the following thirteen bat species in Yellowstone National Park:
Little brown bat (Myotis lucifugus)
Big brown bat (Eptesicus fuscus)
Long-eared myotis (Myotis evotis)
Long-legged myotis (Myotis volans)
Townsend’s big-eared bat (Corynorhinus townsendii)
Fringe-tailed bat (Myotis thysanodes)
Hoary bat (Lasiurus cinereus)
Silver-haired bat (Lasionycteris noctivagans)
Spotted Bat (Euderma maculatum)
Pallid Bat (Antrozous pallidus)
California Myotis (Myotis californicus)
Western-Small-footed Myotis (Myotis ciliolabrum)
Yuma myotis (Myotis yumanensis)
Bat monitoring in Yellowstone seeks to establish baseline data on the distribution, activity, and habitat use by bat species—before we begin to see evidence of the arrival of the disease white-nose syndrome (WNS).
The fungal pathogen, Pseudogymnoascus destructans, that causes WNS has been responsible for declines as high as 99% in wintering bat populations, leading to regional extinctions of several species in northeastern North America. Bats cannot recover quickly (if at all) from these substantial population declines because most species that are vulnerable to WNS rear only a single pup per female each year.
It is important to identify the location of maternity roosts and hibernacula, locations that are used for reproduction and over-winter survival, respectively. Female bats captured with mist-nets and fitted with radio- transmitters have helped to identify buildings that serve as maternity roosts (where females raise young) for little brown bats. This species has experienced substantial declines in the eastern US and Canada as a result of WNS. Research suggests that access to building attics within Yellowstone National Park is critical for reproductive success and the long-term conservation of the little brown bat.
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.
Research suggests that that the thermal conditions within maternity roosts are important for the reproductive success of little brown bats. 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 (10–30 years) and show fidelity to maternal roost sites where they have successfully raised young. For this reason, park managers try to exclude bats from the attics of park buildings. In 1904, the “type specimen” that describes 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, bat activity has been documented during every month of the year, which suggests that multiple species may remain within Yellowstone over winter. 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 likely migrates 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 big-eared bat can glean insects off the surface of vegetation, and have wing shapes that enable them to hover and carry larger prey.
Bats use an echolocation system to navigate and find food in the dark. Many species produce pulses of high frequency ultrasonic sound and listen for the returning echoes. The echoes provide bats with a sonic picture of the environment which includes the movement of prey. High frequency calls are less likely to alert predators and are effective for locating prey, although some moths have developed organs 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.
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Keinath, D.A. 2007. Yellowstone's world of bats: Taking inventory of Yellowstone's night life. Yellowstone Science 15(3):3–13. (1.3 MB PDF)