Even after hundreds or thousands of years trapped in snow and ice, caribou droppings are powerful stuff.

Don Russell of Environment Canada in Whitehorse knows. He's seen, and smelled, several large deposits of ancient caribou droppings that are slowly being revealed as warm temperatures eat away at the Yukon's high-altitude snow pack.

"It smells like a barnyard," says Russell.

The droppings have not only kept their smell over the years. They've also preserved a wealth of information about Yukon prehistory that scientists are just beginning to analyze.

The first deposit of caribou droppings was discovered in the summer of 1997. Gerald Kuzyk of the Yukon Department of Renewable Resources noticed a large concentration of caribou fecal pellets and a caribou antler on a permanent snow patch about 600 metres above Kusawa Lake. Kuzyk is now spearheading the multidisciplinary team that is studying the site, says Russell.

When he took Russell, a caribou researcher, to look at the site, Russell spotted the remains of a feathered dart or arrow at the edge of the snow patch. The dart was later dated at more than 4,000 years before present.

"There was immediate interest in the site because caribou do not currently occupy this area," says Russell. "The last reported herds were seen in the winter of 1932."

The snow patch where the droppings were found is 1830 metres above sea level, in a north-facing alpine basin. Russell speculates that the caribou left their mark during summer when the animals gathered on high snow patches for relief from heat and insects.

At the time of the discovery, the snow patch was about 750 metres long, 100 metres wide, and 5 to 10 metres thick. However fecal pellets found on top of large boulders at the edge of the ice indicate that it has been shrinking. The scientists estimate that as much as 60 centimetres' depth of ice have melted in recent years.

To assess the depth and age of the fecal deposit, an ice core drill was used to sample below the surface of the ice pack. Caribou fecal pellets were found intermittently throughout the 1.6-metre core sample. Radiocarbon dating of pellets from 1.6 metres below the surface set the age at about 2500 years before present.

"With ice thickness estimated at 5 to 10 metres, it's possible the snow patch contains layers of caribou fecal pellets extending back more than 4,000 years," says Russell.

The Kusawa Lake site was discovered late in the 1997 season, too late to go looking for more sites. In the summer of 1998 scientists checked more high-altitude snow patches in the southern Yukon and were amazed at what they found.

"I think there are over 30 new sites stretching from Haines Junction to Whitehorse and south to the B.C. border (in some places)," says Russell. "In terms of caribou, the significance of this summer is the regional nature of this phenomenon."

A region where only a few small fragmented herds of caribou remain was apparently once home to a vast herd -- or possibly several large herds -- of caribou. Analyzing what the animals left behind, however smelly, could provide important information about how they lived and why they disappeared.

"Some of the important questions will be to reconstruct cooling and warming trends from oxygen levels in the ice samples and from sediment cores of nearby lakes and to observe changes in diet associated with those trends," says Russell.

"Also we are interested to see if there was occupation by these large herds after the eruption of the volcano that left ash throughout southern Yukon about 1200 years ago."

Analysis of the fecal pellets will provide information about the animals' diet, DNA analysis might reveal links between the ancient herds and modern caribou, and evidence of human activity at the sites will tell us more about how ancient Yukoners lived.

That amount of information makes the smell seem unimportant.

For more information, contact Don Russell at Environment Canada in Whitehorse, 393-6700, or Gerry Kuzyk at Yukon Renewable Resources, 667-5649.