Bats heat up with white nose syndrome
Twenty-seven miles due east of the Baseball Hall of Fame in Cooperstown is the second most popular natural attraction, after Niagara Falls, in New York State. Howe Caverns is a complex of limestone caves 160-200 feet below ground that today attracts upwards of 200,000 visitors each year.
Feb. 7, 2006, hydrologist Paul Rubin was exploring a non-commercial section of the cavern system when he encountered a group of sick-looking bats with a white powder on their faces. Snapping a couple of photos, he proceeded with his work, soon forgetting about the bats.
In January of the following year, wildlife biologists started receiving reports of unusual wintertime activity and mortality of normally hibernating bats at the mouth of nearby Schoharie Cavern. By March, three other area caves were experiencing the same curious phenomenon. Bare skin on the muzzles, ears and wings of many bats exhibited a mysterious white dusting which researchers and the media began to call white-nose syndrome, or WNS.
In the winter of 2007-08, WNS was widely reported in New York, Massachusetts, Vermont and Connecticut. Biologists had by then identified the white fuzz as a previously unknown type of fungus, which they initially named Geomyces destructans but subsequently revised to Pseudogymnoascus destructans, Pd for short.
The fungus only thrives in dark, moist and cool (less than 68 degrees) conditions such as those found in caves where many of our hibernating bat species take winter refuge. As endothermic (warm-blooded) mammals, bats’ high body temperature during spring-autumn prevents Pd from gaining a foothold. But hibernating species can see a 40- to 80-degree drop in body temperature during the winter, which is why symptoms of the disease are confined to winter hibernators.
Under suitable conditions, Pd releases a mixture of digestive enzymes that break down exposed areas of skin, causing a sharp increase in an infected animal’s metabolism. This unanticipated demand on a torpid bat’s energy resources drains much of the precious fat reserves needed to survive the winter, causing it to awaken prematurely and emerge from its hibernaculum.
Unsurprisingly, the chief cause of death is then starvation due to the absence of flying insects to feed on in mid-winter.
Monitoring bat population size is a difficult business, but in 2011, a group of experts estimated that 5.7-6.7 million bats had succumbed to WNS in the five years since Rubin’s photos first demonstrated its existence in North America.
Until 2016, the disease had only been reported east of the Mississippi River, but in that year, infected bats were recorded in western Washington. As of 2018, confirmed cases of WNS have been documented in 33 states and seven Canadian provinces. (The presence of Pd, without certified evidence of disease syndrome, has been detected in an additional three states).
So, what’s the prognosis? More than half of North America’s 47 bat species are hibernators and therefore at special risk. At present, 11 species (including two endangered and one threatened species) have shown WNS, with mortality rates ranging as high as 90-100 percent at some sites. Pd has been found on an additional six species without confirmed evidence of WNS.
Once researchers knew what to look for, they found Pd on 21 species of European and Asian bats. Although 14 of these have shown some signs of the syndrome, the symptoms are much less life-threatening than seen here, suggesting Eurasian bats have adapted fairly well to the fungus after having lived with it for many generations.
Hard to say if we might see something similar happen on this side of the Atlantic during our lifetime. One of the hardest-hit North American species is the little brown bat. Until the onset of WNS, it was one of the most abundant and widespread of all our bats, but is now uncommon throughout much of the east. Nonetheless, recent surveys in New England have suggested their populations seem to be stabilizing at some sites, albeit at far lower densities than before WNS.
But bats typically have just 1-2 offspring per year; if the little brown, Indiana, northern long-eared and tricolored bats — four of our most severely impacted species — are to return to their former numbers through adaptation to Pd, it will likely take a very long time.
Meanwhile, numerous research efforts are underway to identify workable methods to buy the bats time. The 2018 annual meeting of WNS researchers in Tacoma last month was brimming with papers discussing biological, chemical, genetic and environmental procedures to mitigate the impact of the fungus.
Though promising, a modeling study presented at the conference suggests even the most effective of such procedures would only have a decent shot at protecting a given population if a large proportion of its members can be treated.
Unfortunately, there’s no quick fix in sight for this disheartening situation.
Ken Baker is a scientist and a retired biology professor. If you have a natural history topic you’d like the author to consider for an upcoming column, email your idea to firstname.lastname@example.org.