Scan the skies in the southern Yukon in late September and you just might see a juvenile golden eagle passing overhead, headed south to its wintering grounds. These large birds of prey spend their summers in the mountains of Alaska and the Yukon, but until recently, very little was known about their whereabouts during the rest of the year.

Some of the juvenile eagles heading south are carrying a bit of extra baggage -- little backpacks containing satellite transmitters that are providing a wealth of information about these birds. Part of an on-going study on Golden Eagles in Denali National Park, this research has helped biologists learn where these birds head in winter, and a lot more as well.

"The whole reason we started our study in Denali in 1987 was because in Alaska we really did not know much about Golden Eagles other than that they like to live in mountains and eat small mammals," says Carol McIntyre, a biologist working with the National Park Service. "They are big birds, but not a lot of work has been done on them."

In western North America, most of the previous research has focussed on nesting Golden Eagles. McIntyre and her colleagues wanted to learn more about what happened to the young eagles after they left the nest.

"Our first questions were based on survival rate of these young birds," she explains.

Since 1997, they have put satellite transmitters on 48 juvenile eagles, but only 20 to 40 percent of the birds survive their first year out of the nest.

"It is very low rate of survivorship, and that has a lot to do with both starvation and electrocution," she says.

In general, the young eagles seem to fare well on the first part of their migration. Most of them head southwest after leaving the park in late September, passing through the southern Yukon, northeastern British Columbia and then on into Alberta.

The eagles seem to start running into problems when they reach north-central Alberta, and McIntyre speculates that the timing of their migration could explain why so many of them starve to death there.

When they leave their nests in early August, the young birds are flying for the first time and have always been fed by their parents. The birds only have six to eight weeks to hone both their flying and hunting skills.

"When migration day comes, they are totally independent; they are on their own and have to make their own way. They probably have enough body reserves when they start out, but they do not carry a lot of fat like other birds," she says.

McIntyre speculates that there is also another reason why timing creates problems for the young eagles. They reach Alberta during hunting season, when gut piles might offer a ready source of food and encourage the eagles to stop migrating.

"The gut piles probably short-stop them. Then, after hunting season, they have to move on or find other prey," she says.

Further south, many eagles are electrocuted when they perch on top of utility poles. This problem is quite severe in some western states such as Montana, and McIntyren is thankful that many power companies are retrofitting their poles so that they will not conduct current.

When birds do die, McIntyre must rely on a network of volunteers along the migration routes to help her locate the dead birds and then send the carcasses on to a lab where they can be autopsied.

The satellite signal gives the general location of the dead birds. The volunteers find the bodies by tracking radio signals, emitted by a second small transmitter that automatically turns on when a bird stops moving.

But finding the dead bird on the ground can still be a challenge. Todd Powell with the Yukon's Wildlife Viewing Program helped her track two dead eagles in the Whitehorse area. Both birds died when there was already snow on the ground, and he eventually had to use a helicopter to reach the spots where the birds had died.

By November the juvenile eagles have arrived at their wintering grounds, which cover an area from central British Columbia and parts of southern Alberta and Saskatchewan south to the southwestern United States and central Mexico.

In late April they begin to head north again towards their summer range, which is scattered across the northern Yukon as well as northern and central Alaska.

McIntyre says she finds the extent of the summer range one of the most interesting parts of the whole study. "Who would have thought that eagles from Denali park would summer in the Ogilvie Mountains," she says.

She describes these birds as being like "teenagers on the loose. In some cases they may be following caribou herds, or they may be going where there are Dall sheep and picking up young lambs. In many cases, they may be trying to avoid areas where there are dense populations of breeding eagles just so that they stay out of fights."

But the teenagers who make it back to the North have a very good chance of surviving to a ripe old age. Survival rates increase to about 95 percent during their second and third years, and adult eagles can survive into their 20s.

For more information on this project Carol McIntyre can be contacted at carol_mcintyre@nps.gov or at (907) 456-0423.