When it comes to Yukon wildlife, the focus is usually on the big species like moose and bears and caribou. But this summer, some Yukon biologists will be trying to learn more about the smallest mammals of all, the different species of shrews that live around the territory.

There is even some chance that they might find a new species never before confirmed in the Yukon, the Alaska Tiny Shrew, the world's smallest mammal.

"It was first reported in 1997 in Alaska, and if it does live here, it would be a brand new species for the Yukon," says Tom Jung, the biodiversity biologist with the Yukon Government. "It is kind of odd that even in North America we can still find new mammal species."

This shrew weighs in at only one and a half to two grams, about the size of a penny. Over the years a few specimens had been brought to the University of Alaska Museum in Fairbanks, but no one had recognized them as a never-before-seen species. It took a visiting shrew specialist from Russia to notice that there was something a bit different about these shrews, and identify them as a new species.

"It is very hard to tell shrews apart," notes Jung.

Shrews are so tiny and quick that it can be hard to spot them, much less get a close look at them. But wherever you live in the territory, there is a good chance that one of the Yukon's five identified species of shrews lives somewhere in the area.

Shrews are well adapted to life in the North, which is quite a feat since they do not hibernate and have a high metabolic rate similar to that of a hummingbird. The key to shrew survival is living fast and furiously, about eighteen months on average, and eating around the clock.

A normal schedule for a shrew is feeding for about half an hour, and then resting for an hour before heading out to look for the next meal. For most shrews, this means eating insects in all stages of life, including dormant adults and eggs in winter.

And then there is the water shrew, which ups the survival ante by diving into ice-cold streams in search of aquatic insects. The largest of the Yukon shrews, measuring about 15 centimetres from nose to tail, this shrew has several unique adaptations that allow it to survive such hardships.

When the shrew dives, a layer of air surrounds its fur, giving it a silvery appearance and reducing by half the amount of heat that the animal loses while wet. This layer of air makes them so buoyant that they must paddle furiously to dive beneath the surface.

This effect only lasts for about a minute, so shrews must find food underwater quickly. Some water shrews have been seen actually running across the surface of the water, and it has been suggested that air bubbles trapped in the stiff hairs of their feet make this possible. Back on land, they groom themselves vigorously with their hind feet to get rid of any dampness.

When you must eat as often as a shrew, you cannot be too picky about the source of calories. Shrews are classified as insectivores, but Brian Slough, a Yukon biologist who has studied small mammals extensively, has seen shrews come into cabins and eat hamburger meat thawing on the windowsill.

He occasionally spots shrews that have been killed in winter while trying to cross roads, pointing out that these shrews are usually killed by exposure, not cars. They die when they cannot find their way back into the subnivean layer, the layer of snow closest to the ground, where the earth's heat keeps temperatures close to 0° Celsius.

Aided by a grant from the National Research Institute as well as by the Yukon Government, Slough plans to set traps for both shrews and lemmings this summer. For the shrews he will use special pitfall traps, cone-shaped devices that are set into the ground.

In addition to looking for the Tiny Alaska Shrew, Slough wants to gather better information on where different species of shrews occur in the territory. Yukon Government biologists will also set traps for shrews as they are working on other projects around the territory.

For Tom Jung, finding the world's smallest shrew would nicely round out the Yukon's biodiversity, in terms of size anyway, since the continent's largest mammal, the wood bison, already lives here.

For more information on shrews, contact Tom Jung at thomas.jung@gov.yk.ca or 667-5766 or Brian Slough at bslough@yknet.yk.ca or 668-3295.