When David W. Johnston stands by the Potomac on a summer morning, he prefers to imagine the river as it would have been on a winter day more than 200 years ago.

In the early 1800s, the river would have been packed with canvasback ducks, so many that a hunter easily could bring back a barrelful destined for dinner tables in well-off households.

Duck, though, was only one of many birds that Virginians consumed.

"They ate everything," said Johnston, a Fairfax County resident who examined hundreds of archaeological records and historical accounts for his recent book, "The History of Ornithology in Virginia." "Robins, bluebirds and blue jays -- many songbirds that we would not think of eating today."

Bird study in Virginia, it turns out, has links not only to the Colonial-era diet, but also to the leisure habits of U.S. presidents, mistaken Colonial-era beliefs about geography, and the design of women's jewelry boxes, among many other topics. Johnston makes the case that Virginia may be the birthplace of ornithology in the United States, because it is where many common birds and their habits were first chronicled.

In Colonial days, outsize images were common in writings about Virginia birds. There were flocks of passenger pigeons that darkened the sky for hours, partridges so thick that a single shot could bring down a half-dozen, and wild turkeys that ran as fast as greyhounds.

Passenger pigeons, once widespread in the East, Midwest and South, are a theme in Johnston's book. Before Europeans arrived, Virginia's Indians used torches at night to blind them in their roosts and killed them for food. They were the most commonly found bird in archaeological excavations, a sign of how important they were in diets. But their tendency to gather in big flocks made them easy pickings for hunters with guns or nets.

By the early 1900s, they were seldom seen. In 1907, Theodore Roosevelt reported spotting a half-dozen in a field in Albemarle County, where he had a retreat.

"I have not seen any for 25 years and never dreamed I should see any again," the president wrote in a letter to a scientist. Some experts doubted him because the bird was rare by then, but others, including Johnston, believe him. Roosevelt, well known for hunting and nature study, probably took notes about what he saw, Johnston said, but they have never been found.

In 1914, the nation's last passenger pigeon died in captivity.

Another ornithologist president was Thomas Jefferson, a Virginian who kept a mockingbird in a cage at the White House and had a broad interest in the natural world. Writes Johnston, hopefully: "Jefferson is likewise unique among our presidents in having known more about birds than any other presidential candidate at the time, and he might well inspire other busy men of the government to seek nature as an occasional refuge from public life."

Well-known naturalists have studied the state's birds since Colonial days, among them Roger Tory Peterson, whose field guides popularized the hobby of birding. Peterson entered the Army at Fort Belvoir in 1943, where Johnston says he persuaded his superiors to reroute a drill march to avoid a lark's nest.

Johnston, 77, got the idea for his book during nearly two decades teaching ornithology at the University of Virginia's Mountain Lake Biological Station, in the southwestern part of the state. There, he came upon century-old records of bird sightings, and said he was troubled by how many species no longer could be seen because timber-harvesting had eliminated their living space.

Nowadays, he is critical of the cutting of trees he witnesses throughout the Washington suburbs as development paves over former forests. Colonial-era explorers wrote of bear and buffalo in the forests of Fairfax County. His own back yard, Johnston said, used to fill with scarlet tanagers and the call of the wood thrush. No more.

"Birders in particular are very concerned about the degree to which habitats are being destroyed," he said. "The developers have got all the laws in their favor."

David W. Johnston found century-old records of bird sightings while teaching in the southwestern part of the state.