Bat Cave Restoration Project Proposed


   In order to provide optimal conditions for restoring the Mexican free-tailed bat (Tadarida brasiliensis) population, protect the visiting public, and regain wilderness values, the Park Service is proposing closing the “Bat Cave” at River Mile 266 to visitation. Removal of the three derelict tram towers, constructed to mine bat guano is also proposed. The project location is the north shore within Grand Canyon National Park.

   The Mexican free-tailed bat, a relatively small bat with brown fur and an extended tail, is a voracious insect consumer capable of speeds in excess of 65 miles per hour. These swift creatures are believed to forage in areas up to 50 miles from their roosts. They also form great colonies of hundreds of thousands, even millions of individuals. In fact, the largest colony in Arizona is thought to have contained as many as 20 million bats at one time. Spectacular black clouds of bats visible many miles away result as a healthy colony exits the roost.

   Grand Canyon’s most famous colony, “the Bat Cave,” Mile 266, contained what must have been a massive colony of Mexican free-tailed bats, judging from a scanty historical record and the discovery in the 1930s of the cavern’s one thousand tons of bat guano. Unfortunately for the animals, prospectors soon realized the economic value of bat guano for use a fertilizer and estimated the cave’s worth between ten million and ninety million dollars. The bats are very susceptible to human disturbance, especially during the maternity season. Their low reproductive rate complicates recovery from catastrophic disturbances such as the protracted and extensive mining operation that occurred at the Bat Cave. These activities unquestionably decimated this colony of Mexican free-tailed bats.

   The mining operations ceased by 1962, and the 1975 Grand Canyon Enlargement Act incorporated the cave and surrounding area into the Park. Although the bat population is believed to be slowly improving, greatly reduced but significant impacts affect the natural values of the area, including the bat colony. The miners left an incapacitated aerial tram system consisting of three conspicuous towers within the Park, the longest being 75 feet in height. The towers constitute a significant visual intrusion on the natural environment and lie within the recommended wilderness of Grand Canyon National Park. The towers attract an unknown number of visitors to the cave itself. The extent of visitor impact on the bat population is unknown, but extensive multiple trailing on the steep slopes leading to the site indicates at least occasional visitation. Repeated disturbance of the colony is considered detrimental to the colony’s long term well being. The trailing itself is creating visual as well as natural resource impacts.

   The towers also comprise an attractive nuisance that creates a hazardous setting for visitors. Wood planking is in poor condition and offers treacherous footing. Steel railing and ladders are in various states of disrepair and constitute a hazard. Caves containing bat colonies are generally unhealthy, potentially hazardous environments because of rabies and histoplasmosis.

   A draft environmental assessment is being prepared for the restoration project tentatively scheduled for late this winter. Anyone interested in obtaining a copy of the draft environmental assessment please contact me.

Kim Crumbo