PHOENIX — Only pitch-black shafts with drops of up to 600 feet are left where roughly 100,000 copper, gold and silver mines once operated throughout Arizona.
To humans, these abandoned mines represent an injury waiting to happen because of their collapsing tunnel walls and leftover toxic gases. But to the 28 bat species living in Arizona, they're home.
The Bureau of Land Management and the Arizona Department of Game and Fish are working to eliminate the threat by building bat gates that will still allow bats in while keeping humans out.
"For bats, (the mines) are a way to escape the heat," said Elroy Masters, a wildlife biologist for BLM in Lake Havasu City. "And the mines protect them over the winter if we get freezing days so they can hibernate."
The gates are made of steel and iron and have small spaces that are just large enough to let bats through.
Masters is working to construct fencing and bat gates at Lake Havasu's Cienega Mining District, where there are about 90 open shafts.
"We're trying to protect bats to keep them from becoming listed on the Endangered Species Act," Masters said.
Bats have a low reproductive rate of about one baby per year, said Tim Snow, a non-game specialist for Arizona Game and Fish.
Despite their relatively well-hidden existence, biologists say bats serve several important functions, such as pollinating saguaro and agave plants and controlling insects.
"They're prolific insect catchers," said Yar Petryszun, a bat researcher with the Department of Ecology and Evolutionary Biology at the University of Arizona. One bat can consume about 200 insects an hour — up to half its weight in one night, he said.
Petryszun works with the U.S. Forest Service monitoring bat populations and studying how they adapt to using bat gates at an abandoned copper mine at the Coronado National Memorial on the Arizona-Mexico border.
"They're real interested in being able to keep people out of these abandoned mines for safety reasons and to keep disturbance of the bats down," said Petryszun.
In western Maricopa County, about 40,000 bats live in the Tonopah Bellmont Mine — one of the most dangerous mines for humans, said Alene Jones, supervisor of the abandoned mines program at the state mine inspector's office. The bats often fly 30 to 40 miles south to Tonopah and eat insects off crops there, she said.
The mine inspector's office is working with several bat experts at the Tonopah Bellmont Mine and plans to put up bat gates at two of the openings, Jones said.
Mine openings that are deemed not to be significant bat or wildlife habitat get filled. But with some 100,000 abandoned mines in Arizona and limited funding, surveying the mines is a huge project. Only a few of these mines, most of which were built in the 1930s or 1940s, get filled or gated each year.
Arizona Game and Fish had to put on hold its Bat Management Project, which began in 1992, because there's not enough funding, Snow said. However, he continues to monitor abandoned mine projects.
"We are in the process of creating more bat friendly habitats knowing the importance of abandoned mines to that," he said.