Bats are out everywhere out at Hallowe'en -- plastic bats, paper bats, cloth bats. But the Yukon's real bats are long gone, wintering somewhere along the warm coast of Alaska or in British Columbia, Brian Slough suspects.

Where Yukon bats go in winter is one of the things the Whitehorse biologist hopes to discover through a research project begun in the summer of 1997. With the aid of a grant from the Northern Research Institute, Slough set out to learn more about one of the territory's least-known and most-misunderstood wildlife species.

He was starting almost from scratch. The existing literature on Yukon bats consists of a 1975 study based mainly on museum specimens and a one-page Yukon government brochure on the little brown bat.

"We have virtually no baseline data on Yukon bats that can be used to evaluate abundance, species richness, population trends, habitat use, or the impacts of human activities," Slough says.

In fact, we're not even sure what species of bats come to the Yukon in the summer or where they spend the rest of their time. So far, only the little brown bat has been sighted in the territory, as far north as Dawson and Mayo.

However, Slough suspects other species are out there. World-wide, there are about 950 species of bats, almost a quarter of all mammal species. Sixteen species of bats have been reported in British Columbia.

"I'd bet my bottom dollar there are a few more here," says Slough.

If there are, it's good news. Small as they are, bats can be mighty hunters of insects. The little brown bat, weighing only a few grams, can eat 1200 mosquito-sized insects in an hour. A nursing female might eat 4500 insects a night.

Bats arrive in the Yukon in early May and stay as late as mid-September, Slough says. Many roost in human-made structures; others find shelter in cavities under the bark of dead trees. Although bats are famous for inhabiting caves and rock crevices, no bat caves have been documented in the Yukon.

Males and females live separately because of their differing energy needs in summer. Males nest in small groups, hunt at night, and conserve energy by going into torpor, a hibernation-like state, during the day.

"The females are nursing young during the day, so they can't do that," says Slough. "They need prime habitat and they roost together in large numbers in order to raise the ambient temperature for the young ones."

Slough used a bat-detector to find places were bats were living and hunting. The bat detector is a tunable narrow-band audio detector that can pick up the high-pitched sounds used by bats to find their way around in the dark.

Bats are experts at echolocation -- navigating by the use of reflected sound. Slough says the sounds recorded on the bat-detector indicate when a bat is homing in on an insect. The regular pattern of chirps the bat uses to scan its surroundings changes to a "feeding buzz" or high pulse repetition of calls as it tracks its prey.

All of the bats Slough located and studied were males living in small groups near water. In the Yukon, bats seem to rely heavily on aquatic insects, he says, so they tend to roost near wetlands or lakes.

One goal of the study was to capture and tag bats to find out where they go in winter. Slough used a mist net, a net with very fine strands, which is widely used for capturing small birds. However, the bats' skill in echolocation made catching them difficult.

"They're fairly hard to capture," he says. "They can avoid mist nets, so you have to set up the nets where they're commuting between their roosts and foraging sites. Then they fly by memory and don't constantly use echolocation."

Altogether, Slough managed to band 14 bats. He also weighed, measured, sexed, and aged them, and took small tissue samples to send to an Alaskan researcher who is trying to trace migration patterns through genetics.

Slough is hoping to continue the bat study next year, possibly with better equipment and more help.

"Bats are part of the Yukon's biodiversity, part of the complexity of organisms that makes up the ecosystem," he says. "They're fascinating."

People can attract bats to their yards and help bat conservation efforts by putting up bat houses in favourable habitat. Plans and placement instructions are available from the Wildlife Viewing Program (867-667-8291) at Yukon Government Renewable Resources.

For more information about Yukon bats, or to report bat sightings, call Brian Slough at (867) 668-3295 or e-mail him at bslough@yknet.yk.ca. Or, contact Bat Conservation International, P.O. Box 162603, Austin, TX 78716, U.S.A.