By Yereth Rosen

ANCHORAGE, Alaska (Reuters) - From the recently thawed tidal flats that edge Anchorage to the tundra of western Alaska, the hunt for deadly avian influenza virus is on.

Biologists and rural hunters have begun testing wild birds to search for signs of the H5N1 virus that has infected birds in Asia, Africa and Europe and caused more than 120 deaths on those continents.

But if the virus is invading North America through Alaska, there was no outward sign of it among the shorebirds pecking for food in the mud flats of Anchorage on a sunny, picture-postcard morning this week.

With snow-capped Mount Susitna looming behind them, hungry birds dug into the water and mud for food before continuing their migration to Arctic breeding grounds, just as they do each spring.

The few that have flown into the wide nets pitched in the mud appear hale, hearty and free from any infection, said the government biologists who have been watching them for the past week.

"Everything we´ve caught has been very healthy and flying and looking like good shorebirds should," said Bob Gill, a U.S. Geological Survey biologist who is part of a team monitoring migrating birds in Anchorage.

Alaska is considered North America´s most likely entry point for the virus, and federal and state agencies have launched an aggressive testing program here.

Samples from about 15,000 birds, both live migrants and hunted fowl, will be taken over the summer and fall and evaluated in laboratories for signs of the virus. Twenty-eight migrating species are targeted for testing because of their travels between bird-flu hotspots in Asia and Alaska.  

Government agencies have set up a hotline for citizens to report any unusual die-offs. State and federal agencies are maintaining Web pages with detailed information about migratory birds, influenza and possible relationships between the two.

And there are numerous public advisories, in English and in Alaska Native languages, giving virus-avoiding precautions to hunters and anyone else who might encounter infected birds.

"Our challenge is trying to get information out that´s useful and pertinent and would mean something," said Lynda Giguere, a spokeswoman for the Alaska Department of Environmental Conservation.

COLD SPRING BRINGS SLOW START

The field sampling of birds has started slowly because of a cold spring and a later-than-expected bird migration.

By the end of the week, the first Alaska samples -- about 1,300 in all -- are expected to arrive at a federal laboratory in Wisconsin, said Catherine Puckett, a USGS spokeswoman.

Most of the samples are being taken by subsistence hunters in 10 native villages in western Alaska´s Yukon-Kuskokwim Delta, she said.

Only a few samples will be sent from the Cook Inlet tidal flats, where biologists were struggling to net two species of tiny shorebirds -- pectoral sandpipers and long-billed dowitchers. They are not hunted for food and the only practical way to test them is to have them fly into nets.

It is a difficult way to capture birds that are using the area only as a feeding stop, said Lee Tibbetts, a USGS biologist.

"They have no reason to be here, so if you scare them off once, they´ll leave," she said. "These spring migrants are in a hurry."

She and other biologists tried to "twinkle" the birds by gently shooing them into the nets but the birds responded by flying over or around the netting. On that day, not a single bird went into the nets.

"They´re too smart for us today," said Dan Ruthrauff, a USGS biologist who spent the morning on the shoreline waiting in vain for a bird to swab.

When birds do fly into the nets, they are banded, weighed and measured in addition to having a swab of their anal cavity to detect the H5N1 virus.

Biologists are sampling blood to better understand genetics, clipping feather samples for analysis that will help pinpoint wintering grounds and banding the birds´ legs to help track their movements, Tibbetts said.

Later in the summer, when various shorebirds are in their flightless, feather-shedding molt period, it will be easier to herd them into nets for testing.

But for now, opportunities for sampling live birds -- like the birds´ presence on the mud flats -- are fleeting.

"Most birds in the spring, they´re in a hurry to get to where they´re going and do what they´re going to do," Gill said.