Last week's 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 California's 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 doesn't 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 that's not good news for bats in California, or indeed for bats living from Alaska to Western Mexico.
No one knows how White Nose Syndrome arrived in North America, though it's 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 bat's wing. From there, the fungus spread throughout the bat's body, causing a characteristic white powdery growth on the bat's 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. That's 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.
That's 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 California's 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 haven't been found to succumb to the disease. But it's 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 don't 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 they're 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 the wild, and in human-made structures as well. And yet the little brown bat is one of the species most devastated by White Nose Syndrome. As the group Bat Conservation International puts it: "Today, this species has been heavily impacted by the devastating disease, white-nose syndrome. Once abundant throughout eastern North America, the species is now uncommon throughout much of its eastern range."
The factor that has likely consigned the little brown bat to being a poster child for White Nose Syndrome mortality is the species' extremely gregarious habit, forming hibernating and childrearing colonies that can number in the tens of thousands. Even in an abandoned building, that may well provide enough critical mass for White Nose to spread effectively.
To make things a bit more complicated, there isn't a bright and clear line dividing hibernating bat species from non-hibernating species. Some California bats, such as the western red bat (Lasiurus blossevillii), will hibernate in some places and some years, while choosing to migrate in other years.
The red bat is an interesting case. The closely related species Lasiurus borealis, the eastern red bat, lives in the heart of White Nose Syndrome land back East. There are no known eastern red bat fatalities from the disease, but a study published last year found two eastern red bats that had Pseudogymnoascus on their skin, suggesting a possible degree of resistance to, or even immunity from, the disease.
Another bat species that's been found exposed to White Nose Syndrome without developing the disease, the critically endangered Virginia big-eared bat (Corynorhinus townsendii virginianus), is very closely related to a California bat species that might be among the first to be exposed to White Nose as it heads south, The Townsend's big-eared bat (Corynorhinus townsendii), which hibernates in caves and mines throughout the west, is a Species of Special Concern in California and a chronic candidate for protection under the Endangered Species Act.
One of the places where Townsend's big-eared bats congregate is in the far northeastern corner of the state, in the extensive volcanic cave systems at Lava Beds National Monument and the nearby plateaus of the southern Cascades, where they may well be among the first bats exposed to any "front" of fungal spread from the Pacific Northwest. If the species does indeed enjoy some immunity to the disease, that — as in the case of the California leaf-nosed bat — would be a lucky break, as the Townsend's big-eared bat is declining due to its sensitivity to disturbance by humans invading its habitat.
California bats in general may get a bit of a break due to the state's climate. Pseudogymnoascus destructans spreads more effectively in cold, humid environments. Some places in California, such as along the North Coast, may be cold and humid enough during the winter for the disease to wreak havoc among local bat populations. Other places? Maybe not so much. It may be that White Nose Syndrome manifests as a regional issue when it hits California, more of a problem in the northwestern part of the state than in the arid, warmer, more deserty regions.
Or it might be that as the fungus spreads into California, it evolves to suit the climate and starts to affect bats in places like the California desert.
Even in hard-hit areas with highly susceptible bat species, wildlife biologists are starting to find evidence that bats — including the devstated little brown bat and its relatives — may be evolving resistance to the disease. In New York and Vermont, researchers have found as many as 50 percent of the population of little brown bats in infected caves surviving from winter to winter, a predictable outcome given that bats in that part of the world have had several years for more-susceptible bats to be removed from the population.
That's not particularly cause for cheer, as populations remain shockingly low compared to pre-White Nose levels even where bats are surviving. But it does offer hope for bat species in the long-term, assuming we can refrain from destroying their habitat for long enough — centuries, perhaps — for the bats to recover.
In the meantime, Californians concerned about White Nose Syndrome can learn how they can help, or at least not make things worse, by checking out the information at the interagency White Nose Syndrome website at whitenosesyndrome.org. There's information there that's especially useful for cavers, who may be a minor vector for spreading the fungus from cave to cave. Some scientists are speculating the Washington bat's fungus may have come from unsterilized caving gear also used in caves back east; cavers, by and large an environmentally sensitive group, are likely to redouble their efforts to protect bats. Here's hoping something works, anyway.