Humans hard on bats at Boulder Cave

In the cave chambers once used for winter hibernation by more than 2,000 bats, there are now mere dozens.

And with a deadly fungus wiping out entire bat populations in the eastern United States, the idea of the Pacific Northwest's bats dying off and leaving a gaping void in the ecosystem has become a very real possibility.

Without bats that feed voraciously on moths, the spruce budworm infestation that has already withered huge swaths of this region's forests would worsen. And because many bats can consume more than their weight in mosquitoes overnight, West Nile virus and other mosquito-borne illnesses would almost certainly spread.

But the dwindling bat numbers in Boulder Cave are not evidence of the "White Nose Syndrome" that has killed more than a million bats in New England in less than three years. Experts hope that plague, which has exacted a 90 percent bat mortality rate in affected caves throughout nine Eastern states, may be halted at the Great Plains or the Rockies.

No, the death of bats in Boulder Cave is testament instead to bats' intolerance to human disturbance and, to a far greater extent, humans' intolerance to bats.

The Naches Ranger District was already considering whether to limit Boulder Cave to ranger-led interpretive tours when wildlife biologist Joan St. Hilaire and new district ranger Irene Davidson hiked in to the popular day-use site off State Route 410 on Wednesday to survey the cave's hibernating bats.

Before they were within a half-mile of the cave entrance, Davidson was already seeing the need for more changes — like, for example, unmistakable CAVE CLOSED signs.

"You hardly even notice the sign at the gate" adjacent to Camp Roganunda, where the road to Boulder Cave is closed in winter, Davidson said to St. Hilaire. "Having the interpretive stuff about the bats is fine, but what we really need is for people to know at a glance the cave is closed."

Although the gate and trailhead signs both say the cave is closed in winter, the type is small and the most visible thing on each is an artist's rendering of a bat — an unintended invitation to the curious.

And clearly, there are still people curious enough to ignore the signs and risk endangering the bats.

In the popular summer months, Boulder Cave is closed from dusk to dawn to minimize disturbance to bats, and in winter it's closed for that reason and also because of treacherously slick conditions on some portions of the path. But as St. Hilaire and Davidson trekked up the snow-covered path to the cave, there were already others' tracks on the trail.

Once inside the cave, the two surveyors found a tunnel someone had dug beneath a gate erected specifically to protect the bats in the low-hanging chamber beyond it.

Even after they filled in the excavated area, almost everywhere St. Hilaire and Davidson looked were other signs of illegal human visitation — crumbled aluminum cans and plastic bottles, plastic cups, pieces of charred wood from a small campfire.

And it used to be a lot worse.

Before the Civilian Conservation Corps built a trail to Boulder Cave in 1935, federal biologists had counted about 2,000 bats within its chambers. By 1937, after people began touring the cave in huge throngs — and killing bats in huge numbers — the population was down to fewer than 75.

"People thought of bats as these rabid things," St. Hilaire said, "and people were using tennis rackets and hitting them off the walls to exterminate them."

Human fear of bats is largely unfounded: Of the approximately 30,000 people who die annually from rabies around the world, an average of just one — one — is the result of a bat bite. Nor can bats transmit West Nile virus. Those vampire bats from the movies? Almost all are in Central and South America, and they are essentially benign. There aren't any here.

But the damage had been done. Between the wanton killing of bats and the casual disturbance of their nesting sites, Boulder Cave's bat population was down to 32 by the time the Naches Ranger District began doing biennial surveys in 1989.

Since the two gates were installed in 1997 to minimize disturbance to the bats, the numbers have gone up but only slightly, ranging from 50 to 85. On Wednesday, St. Hilaire and Davidson counted 75.

"We want to educate people," St. Hilaire said. "The more they go in there, the worse it is for the bats."

Davidson said she hopes to be able to find funding to have an interpretive ranger at the site on a daily basis to give guided tours of the cave. Ultimately, that may be the only way people can enter.

"And not," St. Hilaire added, "have people go willy-nilly everywhere in the cave and do what they want."

Here's something worth knowing: The bats in Boulder Cave simply aren't that interesting to look at.

Both the Townsend's big-eared bat and the "Little Brown" myotis, the two species of bats that populate Boulder Cave, look in repose on the cave ceiling like a small dirt clod roughly the size of a preschooler's palm. The Townsend's weighs as much as a pair of nickels, the myotis barely more than one.

A bat nestled into a tiny nook within the cave looks pretty much like any one of the dark spots that are everywhere in the rock of the cave. When St. Hilaire spotted the first bat of the day with her headlamp and tried to point it out to Davidson and the two journalists along on the survey, this is how the conversation went:

"Can you see it?"

"No."

"OK." The light of a second headlamp was focused on the bat. "Can you see it now?"

"No."

"OK, look through the binoculars. Can you see it now?"

"I think so ... no. I'm not sure. I can't tell if it's a bat or just a spot."

Either way, there isn't a single bat in Boulder Cave fascinating enough to warrant the curiosity that bedevils its very existence.

Information from: Yakima Herald-Republic