ABOVE THE RAPPAHANNOCK RIVER - Because it takes one to know one, Jim Wortham flies low and fast toward the river.
His quarry, bobbing on the surface and resting in marsh grass, begin to rise in pairs and flocks, their shadows and the shadow of the pontoon plane skimming together along the brown water.
As the formation sorts itself out, Wortham starts his head count, a sophisticated game of duck, duck, goose, with some swans thrown in for good measure.
"As a biologist, there's no better perspective," says Wortham, a Baltimore resident who has been with the U.S. Fish and Wildlife Service for eight years. "In Maryland, we do every piece of water - it's a big job. It takes a couple of weeks and two planes."
For nearly 50 years, pilot/biologists for the federal agency have conducted an aerial winter waterfowl survey, a snapshot of the population used to help detect a species or habitat in danger.
The numbers they gather added to those collected during the spring breeding survey in the Arctic help determine the length of waterfowl hunting seasons and numbers of birds that hunters can kill.
The agency also queries thousands of hunters by mail to get a tally of birds killed each year.
"We have the largest and most reliable set of surveys in the world and that doesn't come overnight," says Paul Schmidt, the agency's assistant director for migratory birds. "When we have to make tough decisions, like closing a season, we have the science to back it up."
Information from the surveys was used to close the migratory Canada goose season for six years starting in 1995.
In the Atlantic flyway, the number of breeding pairs had dropped to only 29,000 in 1990 from 118,000 in 1988. During the closure, the population rose to 93,000 breeding pairs by 2000.
"We did the right thing," says Schmidt, "and we have a wonderful success story as a result."
Closing or altering seasons is politically touchy. Waterfowl hunting is a $1.4 billion industry nationwide. During its heyday, it put $50 million into the economy of the Eastern Shore.
"I remember that very vividly, when the Eastern Shore guides testified before the season was closed," says Schmidt.
"I took that seriously; it gets my attention. But it's not my opinion vs. the hunters' opinion. I wouldn't want to make decisions without the surveys. They are a powerful tool."
The Rappahannock, which defines the lower edge of Virginia's Northern Neck peninsula, is one of the many Mid-Atlantic rivers where migrating birds take refuge in the winter and fatten up for their return flight north.
The landscape is dotted with large waterfront homes, subdivisions and large landfills. In the distance, 42 miles away, is the silhouette of Washington.
Wortham's plane - a modified single-engine Cessna crammed with fuel tanks and recording gear - has covered the migratory route from the Arctic to Nicaragua. Together, the 12 pilots in the continental United States (there are four more in Alaska) fly 80,000 miles annually.
When he's not counting birds, Wortham is borrowed by other agencies. In December, for example, he flew NOAA scientists 70 miles off the Maine coast for a whale survey.
Although he loves his work, Wortham acknowledges it's not an easy job, flying a small plane at tree-top level and doing a census of moving creatures.
"You're navigating, talking to the control tower and all the while you're counting ducks and assessing the habitat," says Wortham, 38. "You have to know where to look for them. Some guys have the knack and some don't."
Even though he takes precautions, sometimes the birds find him. A mallard bounced off the wing once and a vulture crashed through the windshield.
"Usually if they're going to strike, it'll come from above you," he says.
The rule of thumb is to quickly count the birds you recognize so that you can focus on the ones you don't. Sometimes, it takes more than one pass to count a large or partially obscured flock.
"We count by groups of 10 in a swath one-eighth mile on either side of the plane. Sometimes, with snow geese, we're counting in groups of 1,000," he says. "Once you get a main count, you drop down and get species specific."
Counters spend about three years, paired with a mentor, riding in the plane's right-hand seat. As proficiency improves, the trainee begins to spend more time in the pilot's seat.
Checks by ground crews with binoculars put the aerial accuracy at plus or minus 5 percent.
Despite its value, the winter survey was almost grounded in late December, about the time Wortham made his flight over the Rappahannock.
A $4 million cost overrun in migratory bird programs forced the agency to weigh its worth against the more-important breeding ground survey.
But after sending a letter to state wildlife officials warning of the cutback, agency managers developed a scaled-down survey to cover black ducks, tundra swans and brants in Maryland, Delaware and New Jersey.
Paul Peditto, director of the Wildlife and Heritage Service for the Maryland Department of Natural Resources, says the state found money to continue the flights without the usual federal stipend "on a limited basis without interruption."
While Peditto says he can understand the dilemma caused by budget cutbacks, he is concerned about what drove the last-minute decision.
"I wish we could have had this discussion in August," he says. "It's appropriate to give these programs a hard look from a scientific standpoint, but at the end of the day I hope the cuts are made because it's the right thing to do not because they ran out of money."
Schmidt says the shortfall caused the agency to conduct "a self-evaluation and cleansing" that had been long overdue.
"It takes a crisis to take that look," he acknowledges. "Now, we're retooling and taking a look at all our surveys. It may be that we cut one survey but add others."