The series of nets erected around this small lake south of Whitehorse look like oversized badminton nets at first glance, except that the fine netting is barely noticeable when seen at certain angles. Designed to trap small songbirds, the mist nets are made up of four wide bands of netting strung up one above the other.

When birds fly into the nets, they drop unharmed into a pocket at the bottom of each band of netting, and are entangled by the fine mesh. They don't stay there for long, as the biologists running the program make their rounds every 20 to 30 minutes.

When they find a bird, they gently untangle it, calm it by placing it in a cloth bag, band the bird and take a series of measurements before releasing it again.

The Canadian Wildlife Service (CWS) has run a mist-netting program at this site every summer since 1993, often with help from volunteers. Called Monitoring Avian Productivity and Survivorship -- MAPS for short -- the program provides information on the number of adults returning to nest each year, and the number of young that successfully leave the nest.

"MAPS gives us baseline data that will show any drastic short-term shifts in the population or gradual long-term shifts," says Wendy Nixon, a CWS biologist. "You need a long-term data base as populations of some species are more likely to fluctuate than others because of short-term changes in factors such as weather, food availability or changes to habitat."

Information from MAPS helps biologists determine whether a population might be declining because fewer birds are hatching or because more birds are dying. This information gives direction to further research on biological or physical factors.

"MAPS results are seldom if ever used in isolation," explains Nixon. "They are always used along with other data, like the Breeding Bird Survey."

MAPS and the Breeding Bird Survey (BBS) are the two main tools used for measuring songbird populations. For the BBS, conducted in June, volunteers drive a route with 50 stops along the way. They spend three minutes at each point recording any bird activity that they can see or hear.

The BBS, conducted across North America, gives a basic snapshot of bird populations, but it does not help explain why the numbers of a particular species might be declining. Data from MAPS sites can help tease out whether the birds are having trouble breeding or whether the problem is related to overwinter survival.

But not much data is being gathered this particular morning. Two biologists and one assistant have been monitoring the nets since 5:30 AM, but no birds have been caught. On an average morning ten to twenty birds might be caught in the mist nets, and all three banders will be busy checking nets, banding and taking measurements. But this morning there is time to check field guides and update records.

The MAPS site is monitored every ten days during the summer breeding season, for a total of six sessions.This morning has been the least productive session of the season, but Nixon says that it has been a slow year in general for the MAPS site, possibly because some species do not breed when migration is delayed due to a late spring.

The species that they have caught at the site include Yellow-rumped Warblers, Swainson's Thrush, Ruby-crowned Kinglets and Chipping Sparrows. Lincoln's Sparrows distinguish themselves by showing up as repeat customers, more so than any other species.

"The Lincoln's Sparrows seem to be less likely to learn where the nets are placed, so they will fly into the nets again and again," says Nixon.

This is the only MAPS site in the Yukon, and data from it is pooled with data from sites in Alaska. Similar sites located across North America are run by a combination of public agencies, private organizations and individual birders.

As the emphasis is on long-term records, a station must be run in a standardized manner for at least five years to provide reliable data. The nets are placed to cover different habitats around the site. They are usually located near shrubs where birds will fly through at lower levels instead of in the tall trees where the birds tend to stay up high.

When a bird is caught, they are handled with what's known as the "banders grip." This hold keeps the wings folded against the body and allows the biologists to check the general condition of the bird, including its age and sex. The condition of the female indicates whether or not it is incubating eggs.

Nixon says that handling these tiny songbirds can be unnerving at first, but one learns that they are sturdier than they first appear. Of the birds that regularly end up in the nets, the concensus is that chickadees can be the toughest to handle. While most birds will just stay quiet while they are handled, chickadees will peck and bite at the banders' fingers.

But this morning there are no displays for a drop-in visitor. Later in the morning, at the very end of the six-hour session, one bird is caught in the nets. This is definitely an unusual year, but low numbers are still valid data.

For more information on the mist-netting program, contact the Canadian Wildlife Service at 667-3929.