Chandler S. Robbins steered his government-issue sedan to a pull-off near a one-lane bridge that crosses the muddy Patuxent River near Bowie.

"Let's see what we can find," he said, grabbing a clipboard. As he closed the car door, he began dissecting a woodland chorus of trills and whistles after an early morning rain.

"Indigo bunting, right here. Yellow-throated vireo, over here," he said, pointing with a pen toward the dripping trees. He fiddled with the hearing aids nestled in his ears. "They're proclaiming their territory." A noisy cardinal tried to dominate the conversation as Robbins marked his list.

He made his way along a footpath deeper into woods, deftly navigating mudpuddles, gnarled tree roots, overhanging branches. A low chirruping started, but he dismissed it. "I didn't come to hear frogs. I came to hear birds."

America's foremost birder is still tramping the woods at age 85. And across the country, a multitude of people is following in his steady footsteps, identifying birds from a guide he edited, counting birds for studies he designed and pursuing conservation projects drawn from his research.

"I don't think there's anyone living today who has done as much as Chan has for bird conservation," said Columbia resident David H. Pardoe, who serves on the board of directors of the National Audubon Society and who nominated Robbins for two national conservation awards.

During his long career, Robbins has helped stoke a national passion for birding, now the second most popular recreational activity among Americans, drawing 46 million people in 2001, according to a U.S. Fish and Wildlife Service study.

His early bird surveys helped document the far-reaching effects of DDT and contributed to the U.S. ban on the pesticide in 1972, said Steve R. Runnels, president and chief executive of the American Birding Association. Those surveys also ushered in "citizen science," using volunteers to systematically collect large amounts of data to plan and carry out conservation programs.

"He's like the godfather," said Doug Ryan, a federal biologist for the wildlife service.

This founding father of modern ornithology reports to work as he has for 59 years at the Patuxent Wildlife Research Center in Laurel, where he's the center's longest-serving employee. When the center celebrated its 65th birthday last week, Robbins, dressed in a colorful print shirt of flying ducks, cut the cake next to center director Judd Howell, whose first bird guide was a book Robbins edited.

Robbins rejects the idea of retirement.

"I don't think I want to lead a life of leisure," he said. "There is so much that needs to be done."

Robbins is traveling across Maryland to tally birds for the Maryland-D.C. breeding bird atlas, a survey he introduced to the United States in the 1970s that is now conducted in most states. More than 500 volunteers have joined Robbins in the five-year study, coordinated through the Maryland Ornithological Society, to map where birds are breeding in every corner of the state and the District.

The undertaking, in its third year, has drawn first-timer Denise Ryan, who spends evenings and weekends peering through binoculars on the grounds of university campuses, McMillan Reservoir and Rock Creek Park.

"There are many undone chores at home," said Ryan, who lives in the District. "It has become a bit of an obsession."

Even for veterans such as Jo Solem, who worked on the prototype atlas in the 1970s in Howard and Montgomery counties, the project is "an excellent way of learning about birds. You watch, you observe, you try to determine what it is you're seeing."

The current effort documents the decline of forest-dwelling warblers trying to nest in woodlands stripped by voracious deer. Development and intensive farming have claimed many open fields and hedgerows, causing bobwhites, ring-necked pheasant, field sparrows and meadowlarks to disappear in Maryland. The population boom of nonnative species, such as Canada geese and house finch, also is noted.

Robbins's passion began while growing up in the Boston suburbs as the oldest of three boys. His college professor father and mother took their boys on bird walks on Sunday afternoons, and "we just grew up knowing the birds," Robbins said.

At Harvard, he wanted to study biology, but the course work was daunting so he switched his major to physics. He graduated in 1940, and because he was a conscientious objector during World War II, he came to the Patuxent research center as a member of a civilian public service corps. At the war's close, he got a job at the center, banding birds.

He and his wife, Eleanor, settled along the Patuxent River near Laurel, where they raised four children. Robbins attended George Washington University at night to receive his master's degree in biology in 1950. Surprisingly, ornithology was not included in his course work. "I've taught it, but I never studied it," he said.

Robbins's first landmark initiative was prompted in the early 1960s by a letter from a midwestern woman who worried that too many robins were dying from DDT spraying. Robbins couldn't tell her how the species was faring, but he decided to find out by devising a reliable, annual one-day survey of breeding birds.

Because there weren't enough federal or state wildlife employees to do the fieldwork, Robbins turned to knowledgeable amateurs who belonged to local birding societies. The survey had its trial run in Maryland and Delaware in 1965, and eventually spread to thousands of routes covered each spring and summer across the United States and Canada. Mexico is planning its first breeding bird survey for 2006.

Robbins also served as principal author of a popular one-volume field guide, "Birds of North America," first published as a Golden Guide in 1966 and revised under his editorship in 1983. He is also the author or co-author of more than 500 scientific papers.

In the 1980s, Robbins and Patuxent Wildlife Center researcher Barbara A. Dowell began documenting how the fragmenting of the mid-Atlantic forests reduced breeding by certain birds. They took that message to countries in Central and South America and for 16 years worked with researchers to show them how to band birds, protect forests and conduct bird censuses.

Another result, conservationists said, was Partners in Flight, a 14-year-old coalition of government and environmental groups in North and South America to monitor and protect migratory birds.

Robbins still handles a very crowded schedule. Some days start at 3:30 a.m., when he drives to the Eastern Shore to listen for night birds as part of his atlas work.

Oddly enough, though, this meticulous scholar has neglected to update his "life list," a record of every species observed that often is the hallmark of a serious birder. His incomplete records are stuffed in a bird book at home.

"Someday I'll do all these things," he said, "but I've got other things that keep me busy."

Wildlife researcher Chandler S. Robbins, 85, climbing up the Duvall Bridge in Laurel to inspect a nest, has helped stoke a national passion for bird conservation.A baby tree swallow rests after being checked on.The father of modern ornithology, Chandler Robbins is considered to be the nation's preeminent birder.