Bat Information Continued

Population

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 U.S. and Canada as a result of WNS.

 
A bat held by a gloved hand

The Little Brown Myotis, Yellowstone’s most common species, weighs only 6 to 10 grams and has been documented to live over 30 years.

NPS

Habitat

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 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, 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.

Physical Adaptations

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.

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 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.

 

More Information

References

The list below includes academic publications, government publications, management documents that inform the decision-making process at parks and protected areas, as well as links to websites that provide additional relevant information. The Yellowstone Resources and Issues Handbook, updated annually, is the book our rangers use to answer many basic park questions.

Adams, R. A. 2003. Bats of the Rocky Mountain West: natural history, ecology, and conservation. Boulder, CO: University Press of Colorado.

Altringham, J.D. 1996. Bats: biology and behavior. Oxford: Oxford University Press.

Bogan, M.A., and K. Geluso. 1999. Bat roosts and historic structures on National Park Service lands in the Rocky Mountain Region. Final report submitted to the National Park Service, Denver, CO. USGS Midcontinent Ecological Science Center, University of New Mexico, Albuquerque, NM.

Fenton, M.B., and R.M.R. Barclay. 1980. Myotis lucifigus. Mammalian Species Publication No. 142. American Society of Mammalogists. 142:1–8.

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)

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