by Patrica Robertson
The only bat you’re likely to see around the Yukon this time of year is a costumed human.
Yukon’s two known bat species - the little brown bat (Myotis lucifugus) and the northern long-eared bat (Myotis septentrionalis) - both disappear by early October, long before Halloween.
But where they spend the winters, like much of bat behaviour, is a mystery. That’s a concern to biologist Thomas Jung of Environment Yukon because of the presence of a new and deadly disease called white nose syndrome.
White nose syndrome is caused by a fungus (Geomyces destructans) that grows on bats while they hibernate in caves (known as hibernaculums) during the winter. First spotted in a bat cave in eastern New York state in 2006, it is most visible on the nose, but also attacks bats’ wings and other areas of exposed skin, such as the ears and tail membrane.
Not all species of bats are susceptible. “The endangered Virginia big-eared bat hasn’t been affected, but little brown bats roosting in the same cave in Virginia have been quite affected,” says Jung.
In fact the disease is estimated to have killed between 5.5 to 6.5 million little brown bats in the US since it was first noticed.
“If you’d asked biologists six or seven years ago if they’d be concerned about the conservation of little brown bats, they would definitely have said no, not at all,” Jung says. “But a once-common species of bat is now in great danger.”
Since both of the known Yukon species have been hit hard by white nose syndrome elsewhere, its arrival in the territory would be cause for alarm.
The disease has spread as far west as Oklahoma and as far north as northern Ontario, Quebec, and the Maritimes. It may also be present in Manitoba, though that isn’t yet confirmed.
“White nose syndrome moves at a rate of 400 kilometres a year,” explains Jung. “It’s believed that it will be in B.C. and coastal Alaska in the next few years, unless the Rockies turn out to be a barrier to bats moving west.”
Coastal Alaska is where some of the Yukon’s little brown bats are thought to overwinter. “It’s a shorter winter there, but more importantly it’s a more humid environment,” Jung says. “The Yukon is a very dry environment, and it may be too long a winter for the bats to go without dehydrating.”
Bats in the southeastern Yukon are probably migrating into a more humid zone as well - the limestone areas of the Rocky Mountains.
Why has white nose syndrome suddenly begun infecting North American bat species? No one knows for sure, but the leading theory is that the fungal spores were transported here from Europe on the boots or clothing of people who had visited caves.
In North America, unlike Europe, little brown bats form very large wintering colonies of thousands of individuals, so they’re able to quickly transmit the disease far and wide.
In the Yukon, the little brown bat is found throughout southern and central areas as far north as Dawson City, while the northern long-eared bat has only been found in the Watson Lake area and nearby watersheds. Recordings of bats’ ultrasonic calls suggest there are other species in the Yukon, possibly five or six.
“We don’t really know what would happen if the disease arrived here,” says Jung. “There may be subtle environmental or genetic differences between Yukon’s bats and those species elsewhere, or some difference in where the bats hibernate or the way they hibernate. We may not see the same consequences of white nose syndrome as in northeastern North America, but we simply don’t know.”
Bats normally hibernate throughout the winter, relying on stored fat and water to sustain them despite their small size. (They weigh less than 10 grams.) “They’re very small for a hibernating species - so small that they can’t carry a lot of water,” Jung explains.
It’s partly that vulnerability to dehydration that makes white nose syndrome so deadly. “The main theory is that it’s not the fungus itself that directly kills the bat, but it’s an irritant and it wakes them up from hibernation.”
Once bats wake up, they fly outside looking for food and water, which is of limited availability in northeastern North America where the disease first took hold. That means they’re using up precious fuel reserves, and although they try to re-enter hibernation, they don’t survive the winter.
“One of the first indications of white nose syndrome is that people see bats flying around in February or March when they shouldn’t be. Another indication is the massive number of dead bats at the bottom of the caves.”
Researchers around North America are working hard to understand how the disease functions. Artificially heating a cave is one possibly strategy to prevent or slow transmission, but so far the only way to manage the spread is with cave closures. In the U.S., all caves on federal lands are closed to recreational activity, while Parks Canada is considering closing all caves to the public.
In the Yukon, Jung and his colleague, Brian Slough, are monitoring a small number of bat colonies. “One in the Teslin region is about 850 bats, and another one in the Little Atlin Lake area is a couple of thousand bats,” says Jung. “We hope that by monitoring a few important colonies we’d be able to notice any large decline and infer that there was something going on there. White nose syndrome would be front and centre as a possible reason for declines in the colonies here.”
The other strategy would be to find out where Yukon bats are spending their winters. “We’ve banded several thousand bats over the last 13 or 14 years, and we’re hoping someone will report a banded bat and we can start identifying where they’re overwintering.
“Then we could monitor them more closely for the disease and see whether it’s affecting those hibernaculums or wintering places.”
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.