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Southwestern Bats


Concern for bats in the Southwest (Figure) is a relatively recent phenomenon, although two southwestern bats are listed as endangered by the U.S. Fish and Wildlife Service. Before November 1994, seven species or subspecies of bats in the Southwest were listed as candidates for eventual listing under provisions of the U.S. Endangered Species Act of 1973. The last list (U.S. Fish and Wildlife Service 1994) contained 15 bats, including 10 full species. The total bat fauna of the Southwest is about 30 species, depending on locality, so one-third to one-half of the region's bat species are now considered sensitive. No other group of mammals is a target for such recent concern. In general, we have no long-term population data on status and trends of these bats, mostly because bats, long-lived and with a low reproductive potential, are difficult to study, and their numbers are even more difficult to quantify. No nationwide survey of bat populations exists, and no attempt has been made to quantify existing data so that trends in bat populations can be discerned, although the U.S. Geological Survey has initiated such a study (T. J. O'Shea, U.S. Geological Survey, Fort Collins, Colorado, personal communication). Many of the species added as candidates--now considered species of concern--in November 1994 are widespread in the West and are thought to be relatively secure.

Figure. Endangered lesser long-nosed bat (top), western red bat (center), and Townsend's big-eared bat (bottom).
© J. S. Altenbach, University of New Mexico

Although many bat biologists and state and national groups (for example, Bat Conservation International and Colorado Bat Society) have expressed concern about threats to bats for many years, most land managers have become aware of the potential for declining bat populations only in the last few years. In the West in general, a preeminent concern for bat welfare comes from the widespread closure of abandoned mine entrances. These mines, a historical and common feature of the American West, represent an extreme safety hazard to humans. With funding from the federal government, many western states have set up programs to close such mines, and thousands have been closed. Closures usually occur with no thought or concern that bats might be using these mines as roosting sites, even though many mines have become havens for western bats since the mines were abandoned (K. Navo, Colorado Division of Wildlife, Denver, and J. S. Altenbach, University of New Mexico, Albuquerque, personal communications). Bats have moved into abandoned mines after being driven or excluded from other roosting sites, such as vandalized caverns.


Because topographic diversity, specifically the amount and nature of available roost sites, determines the species diversity of bats (Humphrey 1975), protection of roosts is essential. Thus, many individuals and groups are focusing their efforts on surveying the most likely mines that bats may be inhabiting before these mines are closed. In turn, many states are incorporating results of such surveys into their planning and, when necessary, erecting bat-friendly gates at the mine entrance instead of absolute closures (K. Navo, Colorado Division of Wildlife, Denver, personal communication). The National Biological Service (now the U.S. Geological Survey Biological Resources Division) recently helped fund a cooperative program (Bat Conservation International, Bureau of Mines Management and U.S. Geological Survey) aimed at assessing the magnitude of the threat that mine closures represent to bats. More data, especially long-term data, are needed to assess the status and trends of bats in the Southwest.

  Author
Michael A. Bogan
U.S. Geological Survey
Biological Resources Division
Midcontinent Ecological Science Center
Department of Biology
University of New Mexico
Albuquerque, New Mexico 87131

References


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