Bat Plague Found in West: What s It Mean For California?

Examining a bats wing for the characteristic lesions of White Nose Syndrome | Photo: USFWS/Ann Froschauer, some rights reserved

Last weeks confirmation that White Nose Syndrome was found in a sick bat in the Seattle area has startled and worried wildlife biologists, who fear a faster-than-anticipated spread of the disease that has killed more than six million bats in eastern North America. But what does the discovery mean for Californias 27 bat species?

The disease, caused by the fungus Pseudogymnoascus destructans, was first detected in New York State in 2006, Since then it has spread throughout 28 states and five Canadian provinces, killing as many as 6.7 million bats by 2012. (The fingus doesnt seem to harm anything other than bats.) Wildlife biologists had feared that the fungus spread to the West Coast was inevitable, but hoped that the disease would find its way across the continent more slowly, perhaps giving researchers a chance to find a treatment for the almost uniformly fatal disease.

But the March 31 announcement that a sick bat found in North Bend, Washington was suffering from White Nose Syndrome changed all that. The discovery of one infected bat likely means that many more in Washington are infected, and that the fungus has been present for some time. And thats not good news for bats in California, or indeed for bats living from Alaska to Western Mexico.

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No one knows how White Nose Syndrome arrived in North America, though its widespread in Europe, where bats seem not to suffer from the disease even when exposed to the fungus. In North America, bats that hibernate in groups contract the fungus from other bats that have already been infected, often when a spore lands on the bare skin of the bats wing. From there, the fungus spread throughout the bats body, causing a characteristic white powdery growth on the bats body that gave White Nose Syndrome its name.

Bats with White Nose Syndrome suffer from a number of ill effects, but the most devastating seems to be something like starvation: hibernating bats with White Nose wake up more often, using up their stored body fat. Thats a problem for hibernating bats in cold-winter climates, where their insect prey are almost always extremely scarce in winter. Unable to find food to fatten themselves back up, the bats succumb -- and their bodies continue to give off spores of Pseudogymnoascus destructans.

In some parts of the Northeastern United States, bat populations have plummeted by 90 percent or more. Even if a solution to the disease is found and bat populations can begin to recover, it may take them a very long time to do so: bats of many species typically produce just one or two young per mating pair in a good year.

Thats the real-life scenario that biologists fear may soon be playing out for western bat populations. Or make that may already be playing out. As small-mammal specialist Purnima Govindarajulu of the British Columbia Ministry of Environment told the Toronto Globe and Mail this week, When we talk to disease experts their response is if you are detecting it in a wild animal, the disease has been here at least for a year, maybe more.

Given the rate of spread of White Nose Syndrome on the East Coast and in the Midwest, we can likely expect documented cases of the disease in California within the next five years or so, if nothing else changes. But not all bats are equally susceptible to White Nose Syndrome, and that fact may offer some slender hope for some of Californias bats.

There are a few ways in which White Nose Syndrome affects different kinds of bats in different ways. The biggest and broadest such difference is related to the fact that White Nose Syndrome seems to spread primarily among hibernating bats. That makes sense when you think of the common image of bat hibernacula (the spaces where they hibernate): dozens, perhaps hundreds or thousands of small mammals hanging literally cheek-by-jowl in a cave or mine, with little air circulation to flush out drifting fungal spores.

But not all bat species hibernate. Throughout the southern half of North America, including all of California, winter temperatures are mild enough that many species of bats can stay active year-round. Others migrate to warmer climes. Without visiting crowded bat hibernacula that serve as incubators for White Nose Syndrome, such bats may be less likely to contract the disease.

The Mexican free-tailed bat, for example, found throughout California in the warm season, heads south for the winter rather than hibernating. In places farther east where White Nose Syndrome overlaps Mexican free-tailed bat habitat, the bats havent been found to succumb to the disease. But its not all great news for the Mexican free-tailed bat: their occasional habit of spending the day in large groups in caves shared by hibernating bat species may mean they help spread the disease, even if they dont necessarily fall prey to it themselves.

Another California bat that may not be as at great a risk from White Nose Syndrome is the California leaf-nosed bat, a desert dweller that neither hibernates nor migrates. During the day the California leaf-nosed bat roosts in mines and caves when theyre available, but in relatively small groups of not more than 100 bats, with none of the bats touching each other, a preference that would seem to eliminate much of the opportunity for fungus transmission.

If the California leaf-nosed bat does prove to be less susceptible to White Nose Syndrome that would be a long-overdue bit of good news for the species, which is seriously threatened by destruction of its desert habitat.

That said, cave hibernation seems not to be an absolute requirement for the spread of White Nose Syndrome. The bat found in Washington in March as a little brown bat, Myotis lucifugus, which often roosts and hibernates in crevices in th

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