The days are getting shorter, the air is getting cooler, and the leaves are beginning to change. It must be time for the birds to start heading south for the winter.

Actually, many of them are long gone, says Pam Sinclair, a biologist with Environment Canada in Whitehorse.

"It's such a short summer here," she explains. "The last spring migrants arrive in the first week of June, and the first fall migrants leave about the last week in June."

The first to leave are usually shorebirds that have failed to nest. They hang around for a while and then start the long journey back south to wintering grounds as far away as Central and South America. Last spring, Environment Canada biologists caught a sandpiper that had been banded while wintering in Ecuador.

Other birds stay longer. Then, species by species, they disappear.

"Suddenly, in August, there's not a swallow in sight," says Sinclair. And the Mew Gulls that have been plentiful in downtown Whitehorse have all vanished, although other kinds of gulls stay longer.

For many birds, summer in the Yukon proceeds on a very tight schedule. Nighthawks arrive at the end of May and leave at the end of July. The young birds spend three weeks in the egg, three weeks in the nest, and two weeks learning how to fly and feed themselves. Then they're off with their parents to South America.

Other parent birds leave even before their young are ready for the journey. In fact, most of the songbirds still in the Yukon in August are this year's young, still preparing for adult life.

"Not only do they have to learn how to feed and how to get enough food without their parents," says Sinclair, "but most grow one set of feathers in the nest and another set before beginning their migration. That's another huge demand on their energy resources."

More than 270 species of bird have been recorded in the Yukon, but only about 40 regularly spend the winter here. The rest are currently building up their strength and resources for travel.

Most of the songbirds eat insects, Sinclair says, but this year the insects haven't been particularly plentiful so they might have trouble finding enough food.

Some eat seeds, and they are easy to attract to a bird feeder at this season. Sunflower seeds will draw birds like Red Cross-bills and Siskins.

"There's a big build-up of Pine Siskins at this time of year," says Sinclair. "They're great feeder birds."

If you spread millet and mixed seed on the ground, she says, you can attract a variety of sparrows, including White-crowned Sparrows, Tree Sparrows, Golden-crowned Sparrows, and Lincoln's Sparrows. Seeds spread on the ground in a very open yard in October might tempt a flock of Lapland Longspurs.

"Some of the birds at this time of year are starting to cache food," she says. If you see a Chickadee or Gray Jay returning to the bird feeder again and again, it is probably hiding the food for later use rather than eating it right away.

Sometimes the food isn't very effectively hidden. Sinclair says one Chickadee at her feeder spent a good deal of time and effort storing seeds in the tire treads of a truck that was driven almost daily.

Water birds are also returning south at this time of year, but they follow a different route from their spring migration path. In the spring, Marsh Lake, the Yukon River valley, and Lake Laberge are alive with ducks, geese, swans, and shorebirds. However, in the fall the water levels in those areas are too high for feeding, so thousands waterbirds stop over in the shallows of the Nisutlin Delta, near Teslin.

And wherever birds are congregating to head south, you're likely to see hawks, falcons, owls, and eagles.

"Migration is a good time of year to see birds of prey," says Sinclair. "Wherever you see a flock of birds, you're likely to see a hawk or a falcon."

For more information about fall migration or for a checklist of Yukon birds, contact Pam Sinclair at Environment Canada in Whitehorse, 667-3931.