Pam Sinclair, wildlife biologist with Environment Canada's Canadian Wildlife Service, first saw the La Biche River valley in southeast Yukon on a hot June afternoon in 1995. It was the time of day when birds usually retire into the shade and fall silent, but the La Biche was different.

"There was just a wall of song," Sinclair says. There were so many songbirds nesting and feeding in the surrounding forest that even the midday heat couldn't silence them.

Since then, Sinclair and her colleagues have gone back to the La Biche and surveyed several other lakes and river valleys east of Watson Lake. The results have astonished them.

"There are about 15 songbird species found in southeast Yukon forests that are not found elsewhere in the territory," says Sinclair.

As a result of the Canadian Wildlife Service surveys, nine songbird species have been added to the checklist of Yukon birds, including such exotic sounding birds as the Magnolia Warbler and the Philadelphia Vireo.

"These are species that were never before reported or even thought of in the Yukon," Sinclair says. Many of them are at the extreme northwestern edge of their range.

The Canadian Wildlife Service chose to investigate the relatively-inaccessible valleys of the southeast Yukon, in part, because the area has come under heavy logging pressure in the past few years. "We really didn't even know what was there," says Sinclair. "We were concerned that it might be gone before we knew what we'd lost."

The songbirds require special kinds of habitat provided by the old forests of the area, she says. "These are species that do not use the pine forest and do not use clearcuts."

Many of them need a forest 150 to 200 years old, old enough that some trees have died and fallen over, opening up pockets of sunlight that are filled in by fast-growing deciduous trees and an understory of dense shrubs. The shrubs, live trees and dead trees provide nest sites, and the older trees attract insects that the songbirds feed on.

"The forests of the La Biche River valley are very different from the rest of the Yukon," says Sinclair.

The old-growth forest of the La Biche valley is a mix of white spruce, trembling aspen, white birch, and balsam poplar. There are huge fallen trees, thick undergrowth, and ostrich ferns that grow head-high.

These old forests are valuable to the timber industry, but they're also valuable as preserves of biodiversity, the mix of plants and animals that provides a broad range of genetic material and keeps the ecosystem resilient.

It's possible to balance the needs of the timber industry with those of the ecosystem, Sinclair says, but it will take ecologically sensitive management. "You can't just manage for timber and expect to have a healthy forest over the decades and the centuries."

"Biodiversity is very complex and forests are very complex, and we have to realize that in managing forests. Nobody pretends to understand all the interrelationships between all the plants and animals in the forest, but what we do know is that no one element can be successfully managed in isolation. By altering one part of an ecosystem, we affect a suite of other parts as well."

Forest songbirds are part of a healthy forest ecosystem, the biologist says. Warblers, for example, eat spruce bud worms, and woodpeckers love spruce bark beetles. The birds, in turn, provide food for other animals. If loss of nesting sites and other habitat drives the birds away, the effects will be felt through the entire ecosystem.

The major threat to the birds of the southeast Yukon, Sinclair says, is the current lack of a plan for sustainable forest management in the area. "If we lose too much habitat in southeast Yukon, we could lose quite a few species because they simply don't occur elsewhere in the Yukon," she says.

For more information about the Yukon's forest birds, contact the Canadian Wildlife Service, Environment Canada, Whitehorse, at (867) 393-6700.