Years ago, Manitoba Conservation officer Bill Stilwell revealed to a newspaper I was the working for at the time that a series of limestone caves existed in the Interlake. This was well before the caves and their mammal inhabitants — bats— became celebrities of a sort. He kept the exact location of the caves a secret, merely providing the tidbit of information that they were in the Grand Rapids area of the Interlake. Stilwell, now retired from the conservation department and an author of three books about Manitoba’s national wonders, had explored and photographed some of the caves. When relating the presence of the caves, he enthused that they were marvels of Manitoba that very few people knew about.
It was Stilwell’s desire to have the caves scientifically explored and prevent amateurs from damaging their splendor and disturbing their tiny winged inhabitants at critical times of the year. For decades, the world has known that Manitoba’s Interlake possesses limestone sinkholes that house tens of thousands of slithering garter snakes during the winter, but only a handful of people knew about the furry creatures who also took to below-ground limestone formations to survive the rigours of Manitoba’s cold season.
But as with any secret, regardless of how well guarded, the existence of the caves became common knowledge after a flurry of newspaper articles about their contents were written.
Bats are one of nature’s wonders that both fascinate and instill fear in some people, making them a perfect subject for the media.They are commonly associated with vampire legends and the old wive’s tale that a bat will get tangled in hair. Even someone who seems to be a bit loopy in the head is said to have bats in his or her belfry.
The nocturnal nature of the animals is probably what has made them the stuff of nightmares, but such musings detract from the benefits they provide. It is estimated that one little brown bat (Myotis lucifugus), a species inhabiting the Interlake caves, can consume from 500 to 1,000 insects every hour of every evening. It’s a miraculous accomplishment given that the adult bats weigh just 20 grams, or a third of an ounce, each, as a result every bat provides an invaluable service to their human neighbours by consuming large quantities of mosquitoes.
The Interlake caves — caves are referred to as hibernacula when bats overwinter — house tens of thousands of hibernating little brown bats. Banding by the Manitoba Speleological Society has revealed that the little brown bats return winter after winter to the same caves to roost. Since the bats can live up to 30 years, they can each make a serious dent in insect populations harmful to agricultural production. The one thing that boosts their significance to Manitoba farmers is that the bats disperse across province in April, and only return to the caves in early August. The summer months in between are a period of prime insect proliferation and potential harm to crops.
One cave in the Hodgson area is about 100 metres in depth and from 20 metres in width and height and houses about 10,000 overwintering bats. Of the 250 or so caves that have been explored in the Interlake, only about two per cent house bats.
The advantage of the habitable caves for the bats is that they provide a structure that maintains a temperature of 5°C, which is absolutely necessary for the bats to survive a Manitoba winter where the outside temperature can fall to -40°C or more. The caves also offer a high humidity environment, which is very important to the bats’ survival.
A problem has arisen in recent years that threatens one of North American agriculture’s important pest consumers, and insect pests are responsible for the destruction of billions of dollars worth of crops annually. Millions of bats hibernating in caves are dying each year as a result of a baffling disease referred to as white-nose syndrome. The fungus (Geomyces destructans), which looks like a white, powdery substance and was previously unknown to science, grows on the wings, faces and patches of exposed bat skin, which appears to wake the bats when they should be hibernating.
By having their hibernation disturbed, a bat’s metabolism rises from what should be a mid-winter torpor to full-fledged activity. Bats displaying the white fungus are seen flying about caves in a disoriented manner. Since it’s winter, the tiny creatures quickly use up their fat reserves — meant to only maintain them during the inactivity of hibernation — in an attempt to keep warm. And with no insects available, the bats then starve to death.
The death rate in bats showing the effects of white-nose syndrome is estimated to be from 90 to 100 per cent. Recent population counts in Canada’s infested areas show declines in little brown bat populations of 94 to 99 per cent within two years of exposure. The disease has been linked to the deaths of about 5.7-million bats in North America.
Since it was first observed in 2006 by biologists in Howe Caverns near Albany, New York, white-nose syndrome has spread north and west and is now found next door to Manitoba in Ontario, as well as in Québec, New Brunswick and Nova Scotia. The fear is that the disease will find its way to the Interlake and the caves used by bats to hibernate. The rate of spread has been calculated to be between 200 and 400 kilometres a year, so it’s not a question of if white-nose syndrome will arrive in Manitoba, but when.
The disease has become so devastating that the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in an emergency assessment declared the little brown bat, the tri-coloured bat and northern brown bat as endangered. Both the little brown and northern brown bats overwinter in Manitoba caves.
The committee said white-nose syndrome “poses a serious and imminent threat to the survival of the three species.”
Currently there is no treatment or means of preventing the spread of the disease, which is believed to be bat-to-bat, and possible tranmission by human clothing to bat caves.
“Efforts are underway to reduce or remove the possibility of transfer of the fungus by humans through reducing visits to caves and through biosecurity protocols for researchers,” according to a COSEWIC press release.
It would be quite a blow to Manitoba’s essential bio-diversity if the caves found in the Interlake, which only become widely known as bat hibernation sites in the 1980s, were just three short decades later no longer home to one of the province’s natural wonders.