Every year about half a million waterfowl descend upon the Old Crow Flats in the northern Yukon to nest, breed and moult. Made up of more than 2,000 shallow lakes and ponds, this internationally significant wetland has always been considered a very predictable and safe haven for waterbirds, largely because the water there is locked into place by permafrost.

The birds are also more concentrated there than at other locations in the North. In years when drought dries up nesting sites on the Canadian prairies, even more birds fly north to the Flats. More than 100 different bird species have been recorded in the Flats, including 21 species of waterfowl.

But the Vuntut Gwitchin, whose name means "People of the Crow Flats," are worried that the Flats are changing. They are concerned that the warmer temperatures and earlier springs of recent years are drying up these critical wetlands, causing water levels to drop in the lakes and threatening the land that is at the very heart of their culture.

Researchers working in the Flats have also noticed changes and wonder whether they are seeing a trend. Jim Hawkings, a biologist with the Canadian Wildlife Service, has been working in the area for many years. "It's a natural phenomenon for permafrost lakes to drain," he says. "But when you see several of them draining at the same time, you have to wonder whether the balance has tipped in the last 15 years."

Hawkings is trying to evaluate whether the Flats are really drying up. By comparing a series of satellite images taken of the area between 1973 and 1998, he hopes to determine whether there has bee a net change in the amount of water in the Flats.

But measuring change in this dynamic landscape is no easy task as the lakes are constantly changing, sometimes dramatically. One lake will drain into a lower one, allowing vegetation to invade the drained lake. In other places the Old Crow River will eat away at its banks until it breaks through the side of a bordering lake, causing it to drain.

The permafrost is about 60 metres thick in the Flats, but there is no frozen soil underneath the lakes. After a lake has drained, the permafrost will start to develop again, trapping surface water and causing the lake to refill. With these cycles of draining and refilling, it can be difficult to tell whether the water lost from drained lakes is being captured somewhere else in this vast system.

During the last major glacial period, the Old Crow Flats were part of glacial refugium called Beringia that was not covered by ice. A single large lake covered the Flats until the Old Crow River cut through a bedrock barrier about 12,000 years ago and drained the lake. The river continued cutting down through the layers of clay, leaving the maze of lakes perched above the level of the river on the ancient lake bottom.

Located 110 kilometres south of the Beaufort Sea, the Flats are ringed by mountains and low hills that shelter the area from cold arctic winds. In summer, the Flats get 24 hours of daylight and temperatures can soar to 30°C.

The shallow lakes support thick growths of pondweed and a host of invertebrates. Moose travel all the way from Alaska to summer in the Flats, and the Porcupine Caribou Herd migrates through the surrounding hills. The area also supports muskrats, bears and peregrine falcons.

This complex unique ecosystem looks somewhat like a tie-dyed shirt on a satellite image. Lush growths of willows show up as bands of red, while vegetation such as sedges and horsetails produce a range of greens. It is even possible to distinguish between lakes with clay bottoms, which appear blue, and those with peat bottoms, which are black on the images.

While Hawkings hopes to develop a computer program that can assess these different habitats and determine whether change is really taking place, he knows that it will be a difficult task. For one, the technology used to take the satellite images has changed over the last 25 years, so the images do not all provide the same information. "It can be like comparing three apples and four oranges," he says.

And if the analysis shows that the Flats are drying up, what are the consequences? Hawkings points out three examples of major lakes in which half of the water has disappeared, replaced by lush growths of vegetation. "For some critters these changes are probably good. If you get more willows, that's just great for the moose and an increase in emergent vegetation is good for some types of ducks," he says.

But the change would most likely not be good for the vast majority of the waterbirds that use the area. Annual surveys conducted by the U.S. Fish and Wildlife Service have not shown any dramatic fluctuations in the numbers of waterfowl breeding in the Flats. But these surveys are more useful for monitoring the species found in an area than the population dynamics.

Hawkings says it is still too early to speculate on what any changes could mean. "We're just trying to determine if there is a trend, and then we can look for an explanation," he says. "Is it happening at all? That is the first question."

For more information on Old Crow Flats, contact the Canadian Wildlife Service at 667-3400 or view the section on Taiga Net on the Old Crow Flats.