Arizona has an estimated 100,000 open abandoned hard rock mines, approximately 22,000 of which occur on lands managed by the Bureau of Land Management (BLM). Nearly 70 percent of the abandoned mines in the western United States show signs of use by a variety of bat species. Although these mines provide important artificial habitats for bats, open mines remain a serious hazard to the general public. Since 2009, AZGFD has been working with their partners at BLM to survey abandoned mines and, when necessary, install gates and other infrastructure at the mine. These efforts simultaneously balance the needs of bat species but also greatly reduce the risk to the public.
The importance of abandoned mines for bats lies in their potential to provide a variety of habitat uses, including maternity and hibernacula. Mines also act as day, night, and interim roosts throughout the year. Maternity roosts provide a secure location for females to give birth and rear their young during the summer season. Hibernacula provide a winter refuge for non-migratory bats. Day roosts are used by non-reproductive individuals of both sexes while night roosts are utilized by all bats, regardless of reproductive status, as a place to rest and to digest their prey between foraging bouts. Night roosts are generally in different locations than day roosts and are used primarily at dawn and dusk. Interim roosts are used in the spring before the young are born and again in the fall before retreating to the hibernation or winter roost. Abandoned mines may serve all of the above functions, thus accurate surveys of bat activity use are essential in identifying and preserving these roosts.
To eliminate the potential hazards to the public these open mines are being closed at an accelerating rate. The National Environmental Policy Act (NEPA) requires that any agency receiving federal funds must evaluate the effects of its proposed actions on a variety of environmental levels, including impacts to wildlife. Given that nearly 70 percent of the abandoned mines in the western United States show signs of bat use, biological surveys for bats are critical to mitigate the loss of historical bat roosts. These surveys play a key role in management decisions that seek to preserve and manage the habitat of bat species, which may be negatively-affected by mine closure activities.
There are still thousands of inactive mines on private, state and federal lands throughout Arizona and the majority of these mines have not been evaluated for bat use. With increasing concerns about the status of bat populations in Arizona and the limited information regarding the utilization of mines, research with a focus on these species is imperative. Meanwhile, land management agencies are increasingly feeling the pressure and need to close abandoned mines for public safety, due in part to recent fatalities that resulted from recreationalists falling into abandoned mine shafts.
By the Numbers:
AZGFD biologists have conducted more than 6,000 abandoned mine surveys across the state
Installed 185 fences and 125 wildlife-friendly gates to conserve and protect high value bat habitat throughout Arizona