Driving Miners Batty
If I were a gold miner, I'd probably be investigating the cost of nets. No, not because fishing looks more profitable than mining, but because miners soon might need a way to fend off bats.
Wait, now. This is not the introduction to a horror movie in which hardy prospectors are pursued by flitting hordes that have mistaken our heroes for giant mosquitoes. It's another example of new technology confusing evolved behavior.
Modern, large-scale gold mines like the ones now operating near Fairbanks use a technique known as heap leaching to coax fractions of an ounce of flour-fine gold from tons of rock. Cyanide is the indispensable ingredient in the leaching fluid, and cyanide-tainted water is the inescapable by-product. Cyanide is poisonous, so the solution is kept in lined ponds. It can't flow away to other water bodies or soak into the water table.
Wandering wildlife or would-be swimmers can be kept at bay with fences. But the ponds are open to the air, and it's from the air that thirsty bats descend. They like to skim over calm water, scooping up a drink as they go.
Catching a sip on the wing has worked well for thousands of years; bats haven't had to worry about water quality. In some places, the cyanide-laced ponds have changed that. No one is sure exactly how big a problem the ponds have been. It's hard to tally dead bats. The animals are likely to be little and dark, hard to see at the best of times and nearly impossible to discern if they fall into a pond. It is known that a population of big-eared bats in California was extirpated after cyanide gold mining came to their area, and at least one expert thinks the mining effluent caused their demise.
Most of the known cyanide-caused bat deaths have occurred in the southwestern states, where the dangerous ponds probably look like oases in the desert to bats. No bat death has been reported in Alaska, and it's likely that few---if any---have occurred. That's partly because Alaska offers more water sources, but mainly because the only bat species common near the active mines prefers to live in floodplain terrain, while the mines are on higher ground.
That, at least, is the view of two people who know something about Alaska's bats. Joe Cook of the University of Alaska Museum and Brian Lawhead of Alaska Biological Research. Inc. (Both deny that they are experts on Alaska bats---they believe no one is.) Though six different species of bats live in the state, the only one usually seen in the Interior is the little brown bat. Little brown bats head for high ground only at summer's end, when---perhaps---they are beginning to swarm up before migrating, if they migrate, or---maybe---the young animals are forming the bat equivalent of teen-age gangs to venture away from the family flyways. As Lawhead and Cook made very clear, so little is known about the little brown bats of Alaska that all one can do is speculate.
It is known that local bats, like their kindred elsewhere, can eat prodigious numbers of flying insects. Dealing with short summer evenings means they must eat faster than southern bats do, and laboratory tests of their southern cousins have shown they can snap up 600 mosquitoes in an hour. A researcher in Arkansas once calculated that a colony of gray bats, which are in the same genus as little brown bats, ate the equivalent of 70 half-ton pickup loads of insects in a summer.
So bats are definitely worth protecting, and the U.S. Fish and Wildlife Service is beginning to grow concerned about protecting them from cyanide ponds. But, if regulations extend to Alaska, it shouldn't mean more than a small nuisance for local miners. Studies in Arizona showed that draping netting over a pond was all it took to keep the bats away.
