On Halloween night, you might see plenty of ghosts and goblins roaming the Yukon, but you probably will not see any bats. Not real ones anyway. That is because Yukon bats seem to disappear into thin air in winter, and no one knows for sure where they go.

The little brown myotis bats most commonly seen in the Yukon hibernate in winter, and are probably already hanging upside down from the roof of a cave or old mineshaft, their favoured winter roosts. But if they want to wake up again in spring, the bats have to make sure that they pick shelters where temperatures do not drop below freezing.

Bats are mammals, not birds, and they do not pack on a lot of weight like some animals that hibernate. One might think that a tropical vacation would be just the ticket for animals without much stored fat, but little brown myotis bats are not known to be long-distance flyers.

Studies from eastern North America show that these bats typically do not migrate more than 300 kilometres. Since little brown myotis bats live as far north as Dawson City in the summer, tropical beaches are definitely out of range.

So what are the winter options for Yukon bats? Alaskan bats winter in southeast Alaska, and it has always been assumed that Yukon bats head for the same area. Dead bats have been found in the Kluane icefields, showing that bats do migrate towards the coast.

One person is interested in finding out whether maybe, just maybe, some bats winter right here in the Yukon, and we have just not found their colonies yet. Bruce Bennett, a wildlife- viewing biologist with the Yukon Department of Renewable Resources, says that people usually do not spot bats very often after the middle of September. But this year they were sighted as late as October 20, and that got him to thinking.

"Bats arrive soon after the ice breaks up in the spring and the first insects are around. If they have to migrate for several hundred kilometres from the coast, I wonder whether they could get here so quickly," says Bennett.

Bennett has been asking around to see whether anyone has ever seen any signs of winter bat colonies in the territory, and has not had any luck yet. He speculates that somewhere in the territory there could be a cave or mineshaft heated with geothermal energy that keeps temperatures warm enough for bats to survive in winter.

He says that some people have reported bats attempting to hibernate in buildings in the Yukon, but does not think that these incidents really count. The bats could have been preparing to migrate and just stayed too late.

Dave Nagorsen, the mammal curator at the Royal British Columbia Museum in Victoria and the author of "Bats in British Columbia," has never heard of a bat migrating farther than 500 kilometres. He thinks that even that distance is exceptionally long. "A more typical distance would be 50 to a few 100 kilometres," he says.

Nagorsen says that BC bats have not been reported hibernating further north than Prince George, but that could be because not much work has been done on bats in the North. He does not rule out the possibility that bats could winter in the North if they find an appropriate site, and says that identifying such sites is very important for bat conservation.

Bats are very vulnerable to disturbance while hibernating. If they are aroused, they can use up their critical fat reserves and die. These winter roosts are called hibernacula, and in some places gates have been installed on the entrances to these sites to prevent people from disturbing the bats.

But here in the North, we have to find these sites first. Bennett asks anyone who has seen any evidence of hibernating bats to give him a call at 667-5331, or contact him by e-mail at bruce.bennett@gov.yk.ca.