Caves left empty

Pictured is a Little Brown bat.

By Zack Metcalfe

It’s said that between the ages of 18-25 we lose our ability to hear the ultrasonic whine of the bat.

This depends, of course, on the person, the species of bat and the type of call they’re emitting, but generally yes, as they soar overhead, snatching everything from mosquitoes to dragonflies, we adults wander obliviously below. Maybe that’s why their collapse so thoroughly escaped our notice.

Nova Scotia supports three species of bat year round – the Little Brown, Northern Long-Eared and Tri-Coloured bats – all of whom were at one time widespread, except in winter when they retreated by the tens of thousands to the limestone caves of the Annapolis Valley. This strange and beautiful spectacle was available to those researchers who knew where to look, keeping tabs of all three species by way of these seasonal congregations. This changed abruptly in the winter of 2012-2013, when a plague found its way to Nova Scotia and emptied these caves with alarming efficiency.

White Nose Syndrome, we call it, a fungal infection of the skin which thrives in spaces cold and damp. This fungus is native to Europe and was probably delivered accidentally to New York State by tourism in 2006. From there, it spread outward at a pace of 150-200 kilometres a year, infecting North America’s bats which, unlike their European counterparts, possessed no immunity.

Our resident bats engage in torpor throughout winter (a process not unlike hibernation) in order to conserve fat and water, but this fungal infection causes them to wake up and mount a costly immune response, depleting their body’s reserves and forcing them into the cold in search of food, where they invariably die of exposure. It’s been estimated a staggering 95 per cent of our resident bats died when the syndrome struck, their bodies covered in white snow, their noses in white fungus.

Those who survived probably did so because they were larger, storing more fat with which to combat the fungus, or else because they occupied drier parts of the cave where this fungus struggled to spread. Bats seek out warmth and dryness during summer, both conditions inhospitable to this fungus. In this fashion the survivors may have cured themselves after that first winter.

Researchers continue to find these bats in the warm season, but their caves have remained empty through the cold; tombs where the fungus lies in wait. This gives rise to mystery. Surveys through summer suggest that our three species of bat have been growing modestly in number since the hecatomb of 2012-2013, but where then are they spending their winters? Are there uninfected caves we haven’t yet found, or do they have a means of surviving the winter we’ve yet to discover? Are there so few bats that White Nose Syndrome is struggling to transmit from cave to cave or individual to individual, becoming a victim of its own success? The adaptability of life is a wonderful thing and might account for the continuity of these bats, recovering inexplicably in the face of our indiscretions.

But then, it could be that once bat populations sufficiently recover, this fungus will spread anew. It might also be that our surviving bats possess a natural resistance to this syndrome we have yet to appreciate. Simply put, there’s a lot we don’t understand about the plight of these beleaguered insectivores, maybe destined for a gradual recovery, or maybe another collapse. In the meantime, conservation organizations, like the Mersey Tobeatic Research Institute, have been locating the maternal colonies where the females of each species congregate to have and raise their pups through the warm season. Once identified, these colonies can be protected and used to gauge the health of each population.

Our resident bats face an uncertain future and the fungus which devastated them continues to spread, presently tearing through Newfoundland and the states of the midwest. Things are going to get a lot worse before they get better, if they get better. We can only watch, wait and hope.

Zack Metcalfe is a freelance journalist, columnist and author active across the Maritimes. He can be reached at: zack.metcalfe@gmail.com.