Science & Tech

Bat die-off in Northeast still mysterious

5 min read

With white nose syndrome mortality at 90-95 percent, species is threatened

There’ll be fewer bats in backyards across the Northeast this summer after a mysterious ailment drove starving bats from their caves in the dead of winter in a futile, desperate search for insects in the region’s frozen, bug-free landscape.

Normally crowded together in large, hibernating colonies, all but a few of the rousted bats died — totaling hundreds of thousands since the ailment was first noticed during the winter of 2006-07.

This past winter Massachusetts biologists confirmed that the ailment, called white nose syndrome, is present in the few large colonies of bats that winter-over in Massachusetts caves and old mines.

Tom French, assistant director of natural heritage and endangered species for the Massachusetts Department of Fisheries and Wildlife, described the disease and its impact on bats across the Northeast during a talk sponsored by the Harvard Museum of Natural History (HMNH) at the Geological Lecture Hall on May 21.

French, who spoke for about an hour, was introduced by HMNH Executive Director Elisabeth Werby, who called the talk’s subject “an important and frightening topic.”

White nose syndrome was first noticed by a New York state biologist and has since been confirmed in 26 wintering colonies in New York, Massachusetts, Vermont, and Connecticut, according to the U.S. Fish and Wildlife Service.

Although several laboratories are currently searching for clues about the condition, French said that it remains a mystery. Tests have been run on both sick and healthy bats, but no bacteria, virus, fungi, pollutant, or environmental condition has been identified that would explain what’s going on.

What is known is that significant numbers of bats in the hibernating colonies are marked by a white fungal growth on their noses and sometimes other body parts. Though the ailment was named after the fungus, which makes the bats look as if their noses were dipped in sugar, researchers don’t believe it is the cause of the condition. Rather, they believe the fungus is one normally found in the bats’ environment that, as the creatures decline, blooms abnormally on the bats’ bodies.

The other characteristic, French said, is that the bats appear to be starving. Instead of carrying enough body fat when they enter the caves in the fall to last through the winter’s hibernation, the bats are waking up midwinter starving and setting out in daylight in search of food.

With freezing temperatures and no insects to be found, the bats are turning up dead around the mouths of caves and at nearby homes where they seek the warmth of south-facing rooftops. Though hundreds of dead bats have been found, French said, there are many, many more deaths. Predatory birds have been seen hanging around outside the mouths of caves, raccoon tracks and scat containing bat remains have been found near and within caves.

Among the bats that remain inside the caves, French said they are far more deeply asleep than normal. Although people moving around usually cause some bats to rouse, the afflicted bats remain asleep for much longer periods before waking, French said.

“The only thing we know is these guys are starving to death when they shouldn’t be,” French said. “They’re coming out in January absolutely desperate, flying around when there’s no chance of finding a flying insect.”

Massachusetts has nine species of bats, though the federally endangered Indiana bat hasn’t been seen in years. Although bats are the second-most abundant species of mammal, after rodents, and make their living in a variety of ways, from eating fruit to lapping blood, Massachusetts bats are all fairly small and all eat insects. During the summer months, bats are so widespread in the state that just about every yard with trees has at least one, French said.

Most commonly seen are the little brown bat and the big brown bat, which can roost in the attics of people’s homes during summer months. Within the bounds of Route 128 alone, French estimated there were 50,000 big brown bats living in attics.

The three species of migratory bats that only spend the summer here don’t seem to be affected by white nose syndrome, French said. Of the remaining bats that do winter over, the big brown bat, which is at home in attics, seems to be doing fine. The other species, including the attic-breeding little brown bat — which abandons houses for winter roosts in caves — the Indiana bat, northern long-eared bat, small-footed bat, and eastern pipistrelle, are all vulnerable.

French said scientists estimate that there are 12,000 cave bats wintering in Massachusetts that might be vulnerable to white nose syndrome. Unfortunately, the ailment doesn’t have far to go, as 8,000 of them roost in the same abandoned mine in Chester, Mass.

Bats are voracious insect-eaters, with just one bat eating 1,000 or more insects in a night’s foraging. They also are adept fliers and spread out hundreds of miles from their wintering caves during warmer weather, which means there is a potential that they will spread the syndrome to other populations. French said the condition has not yet been found in New Hampshire or Maine.

Estimates are that the condition has claimed at least 250,000 bats and perhaps as many as 500,000.

Surviving populations will be slow to recover, French said, because the affected bats are long-lived and have just a single young each breeding season.

“Their strategy is to live a long time. They don’t need to have a lot of babies,” French said.