THIS PROJECT IS FOR THE BIRDS.

Byline: Scott Maben The Register-Guard

McKENZIE BRIDGE - The small bird offers no resistance, shows no signs of panic.

Its round, black eyes stare blankly as Alejandra Martinez holds its fragile head between two fingers and gently blows on its chest to reveal molting - one of several characteristics that completes a portrait of the common yellowthroat.

Working quickly, Martinez records observations such as the warbler's sex, age and wing dimensions. She places it head-first in a plastic tube set on scales - it weighs 10 grams - then pulls it out and lets it go.

With a whoosh of feathers, the young bird disappears into the woods near Clear Lake flashing a new piece of jewelry - a metal band fixed loosely around its right leg. The band includes a nine-digit number that identifies when and where the bird was caught and measured.

With that, the record on Neotropical birds that migrate between Central America and North America grows by one morsel of data.

Martinez, 25, and Michelle Murdock, 24, are spending most of the summer catching and documenting warblers and other kinds of migratory birds at six sites representing a variety of habitats in the Willamette National Forest.

They and hundreds of other teams across the United States and Canada are helping gather information on Neotropical bird reproduction and survival for the Institute for Bird Populations in Port Reyes, Calif., north of San Francisco.

The effort to provide demographic details on North American landbirds is one of several projects the nonprofit organization leads to research changes in bird populations, including what may cause rising or falling numbers of certain species.

Martinez is here from Masaya, Nicaragua, under an internship with the Willamette National Forest. Murdock recently finished undergraduate work at Columbia University in New York and is bound for Yale to do graduate work in environmental management.

For 2 1/2 months, the duo will rotate between the six sites every 10 days. Arriving before sunrise, they string up 10 mist-nets, which resemble volleyball nets made of fine, nearly invisible nylon mesh. When a bird flies into it, it falls into a pocket and is trapped.

The site near Clear Lake is a lush, marshy clearing - a haven for birds but a bit of an obstacle course for humans, with deep, muddy holes lining the path between nets.

In the morning, when the birds are busy foraging at first light, a single net can snare five to 10 birds at a time.

"The first thing they do is wake up and eat, eat, eat," Martinez said.

As the temperature rises, fewer birds are caught. Often the nets are empty as the noon hour approaches.

The women walk the circuit of nets every 40 minutes and empty the traps, placing the birds in white cloth bags for the short walk back to the recording station.

"We like the warblers," Murdock said. "They're so sweet. When we come up to the net, they're like, `OK, take me out.' '

The team readily identifies many species. Others pose more of a challenge.

"They look so alike," Murdock said. "They're so hard to tell apart."

In time, they see dozens of species, from sparrows to sapsuckers, thrushes to flycatchers. Woodpeckers and hummingbirds, too large and small for the bands, are immediately released. And if a bird shows signs of stress, it's released early as well.

The team, based in Blue River, also listens for the songs of birds in the trees overhead, taking note of the species present.

"We use all observations over the season to figure out what species are breeding here and which are migrants or transients - are just passing through," said Sara Martin, a staff biologist with the institute who supervises three banding teams working on the Willamette, Siuslaw and Fremont national forests.

"We also look for territorial behavior, like if we see birds mating or carrying nest material or food to their young," Martin said.

Many of the birds caught now are juveniles, giving the team good data on reproduction success. Some of the adults are "recaptures" - birds banded in a previous year. They fill in the picture on survival rates, especially with the accumulation of data over several years.

To augment the extensive monitoring in summer breeding grounds, ornithologists and birders in Central America are starting to set up similar studies of migratory birds in winter habitats.

Knowing what's happening on the southern end of the range will help explain what biologists are seeing in northern areas, Martin said.

Martinez, a graduate of Central American University in Managua, participated in a pilot project in Nicaragua last winter to catch and band the same types of birds that she's tracking now. She said she hopes to return home armed with more knowledge and skills to share with others.

"It's such a great opportunity," she said.

Her country doesn't even have a field guide on its birds yet, but it's in the works, Martinez said. "It's sad we don't have any information on our resident birds," she said.

Beyond merely monitoring population changes, researchers hope to learn enough to influence the management of habitat for the birds.

"The whole idea is not just to do the monitoring, but to look at landscapes as a whole and conservation on both ends for Neotropical migrants," Martin said.

BIRD TALK

Three women gathering data on Neotropical migratory birds in the Willamette National Forest this summer will give a presentation on their work.

When: 8 p.m. July 26

Where: Delta Campground amphitheater on Forest Road 19 near the junction with Highway 126, east of Blue River

Information: www.birdpop.org

CAPTION(S):

Alejandra Martinez from Masaya, Nicaragua, examines a juvenile common yellowthroat after freeing it from a net.