Intruders devastate a once-thriving bat colony

  • By Scott Sandsberry Yakima Herald-Republic
  • Saturday, February 6, 2010 11:12pm
  • Local NewsNorthwest

CLIFFDELL — At Boulder Cave, curiosity has all but killed the bat.

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

Without the bats, which 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.

The decline of bats in Boulder Cave is a testament 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 to the popular day-use site off Highway 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 — such as 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.

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 because of treacherous 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 tracks on the trail.

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. Almost everywhere St. Hilaire and Davidson looked, there were 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 throngs — and killing bats in huge numbers — the population was 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.”

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 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 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 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.”

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