Pennsylvania's bat population dwindles while eagles rebound
These are two species headed in opposite directions.
One — the kind biologists refer to as “charismatic megafauna” for their broad public appeal — is majestic and bold looking, a symbol of freedom. Its numbers have been climbing for decades.
The other has an equally vital ecological role, controlling insects in back yards as well as in the wild. But sight of it gives lots of people the heebie-jeebies.
They are bald eagles and bats.
The bald eagle story is one of recovery. There were just three eagle nests in the state as recently as 1980.
This year, 237 have been confirmed so far, and that number is expected to approach or even surpass 250, said Douglas Gross, ornithologist for the Pennsylvania Game Commission.
“We have more bald eagle habitat than people ever realized,” Gross said. “We've even got three nests in Pittsburgh. Why are they there? Because we've got clean rivers. We've got lots of green space around that water.”
The birds are not completely free of peril just yet. They're still listed as “threatened” on a state level.
But this year's nesting season produced a minimum of 214 fledglings, Gross said. The public is fascinated by them, too.
Some of the densest concentrations of eagle nests are located in northwestern Pennsylvania. But the commission gets most of its eagle calls from the public and media in Pittsburgh and Philadelphia, Gross said.
“The public really, really cares about these birds. Eagles are our ambassadors to the urban landscape,” he said.
The story is not nearly so positive when it comes to cave bats and to little brown, tri-colored and long-eared bats in particular. The presence of white-nose syndrome — a fungal infection that causes bats in winter hibernacula, or hibernation sites, to wake up repeatedly, burn stored energy until they become emaciated and ultimately perish — has caused populations to decline by up to 99 percent statewide.
A hibernacula in an old mine in Canoe Creek State Park in Blair County, for example, had 35,000 bats in it prior to the discovery of white-nose syndrome in April 2010, said commission biologist Greg Turner. When surveyed this past winter, it had 155.
“As you can see, declines are severe, and they occur pretty quickly,” Turner said.
No one knows what causes the disease, which first showed up in 2006 in New York and has spread to 22 states and five Canadian provinces across the Northeast and even into the Midwest. Nor is there any known treatment.
That presents “an unprecedented wildlife management challenge,” said Dan Brauning, chief of the commission's bureau of wildlife diversity.
“We're in uncharted territory with a mammal going from being one of the most common in the state to almost extirpated,” he said.
The agency hopes to tackle that challenge and save bats by focusing on “survivor management,” or protecting those that remain, said commission mammalogist Cal Butchkoski.
“Today's challenge is to find white nose survivors to work with. I'll keep repeating that,” he said.
The commission may employ several strategies, including restricting caving activity in winter, when bats are most vulnerable to disturbance, instituting conservation measures on state-owned land, such as gating the entrances to caves and mines and protecting small — previously thought to be unimportant — hibernacula that might serve as refuges from disease. The commission also may try to develop summer roost sites, he said.
The U.S. Fish and Wildlife Service also may get involved. It's considering whether to list certain species of bats as federally threatened or endangered.
Success in helping populations recover — if it can be achieved — won't come quickly.
Commission president Bob Schlemmer of Export asked how long it would take, if white-nose syndrome disappeared today, for bat populations to return to previous levels.
Bats can live a long time; up to 34 years, in one case, Butchkoski said. But they only have one pup per year, and not all of them survive.
“With that reproductive rate, it's not going to happen in our lifetime. It's probably going to take 100 years,” he said.
Still, bats need help, said Game Commissioner Ralph Martone of New Castle. The commission needs to do what it can to provide it, he said.
“When you have a handful of survivors, the value of those is enormous. If two passenger pigeons came back today, they'd be worth their weight in gold because they'd be it,” he said. “We are getting very close to that stage with some of these bat survivors.”
Perhaps eagles provide hope for bats, executive director Carl Roe said. There was a time 30 years ago when they were virtually gone from Pennsylvania. Many probably thought they'd never return.
But they have, and so, too, may bats.
“Hopefully in 30 years people will be talking about the success stories we started today,” Roe said.