The populations of nearly two dozen common American birds — the fence-sitting meadowlark, the frenetic Rufous hummingbird and the whippoorwill with its haunting call — are half what they were 40 years ago, a new analysis by the National Audubon Society has found.
The northern bobwhite and its familiar wake-up whistle once seemed to be everywhere in the East. Last Christmas, volunteer bird counters could find just three of them and just 18 Eastern meadowlarks in Massachusetts.
Twenty common bird species — those with populations of more than half a million and covering a wide range — have seen populations fall at least in half since 1967, according to the Audubon study. The bird group compared databases for 550 species from two bird surveys: its own Christmas bird count and the U.S. Geological Survey's breeding bird survey in June.
Some of the birds, such as the evening grosbeak, used to be so plentiful that people would complain about how they crowded bird feeders and finished off 50-pound sacks of sunflower seeds in just a couple of days. However, the colorful and gregarious grosbeak's numbers have plummeted 78 percent in the past 40 years.
"It was an amazing phenomena all through the '70s that's just disappeared. It's just a really dramatic thing because it was in people's back yards and [now] it's not in people's back yards," said study author Greg Butcher, Audubon's bird conservation director.
Many of the species in decline depend on open grassy habitats that are disappearing because of suburban sprawl. Climate change and invasive species are to blame, too, he said.
"Most of these we don't expect will go extinct," Mr. Butcher said. "We think they reflect other things that are happening in the environment that we should be worried about."
Audubon Board Chairman Carol Browner, former U.S. Environmental Protection Agency administrator, called the declines "a warning signal."
"We are concerned. Is it an emergency? No, but concerns can quickly become an emergency," Mrs. Browner said.
Compared with 1967, there are 432 million fewer of these bird species, including the northern pintail, greater scaup, boreal chickadee, common tern, loggerhead shrike, field sparrow, grasshopper sparrow, snow bunting, black-throated sparrow, lark sparrow, common grackle, American bittern, horned lark, little blue heron and ruffed grouse.
"Things we all think of as familiar backyard birds ... they appear in books and children's stories and suddenly some of them are way less familiar than they should be," said John Fitzpatrick, director of the Cornell ornithology lab, who was not part of the study.
The northern bobwhite had the biggest drop among common birds. In 1967, there were 31 million of the plump ground-loving bird. Now they number closer to 5.5 million.
"If you look in the Northeast, it's almost gone from New England and pretty much New York as well," Mr. Butcher said.
In some cases, there are still plenty of birds left, despite large surprising drop-offs. The common grackle used to be as plentiful as people in 1967, with both human and grackle populations hovering around 200 million. Now the grackle is down to 73 million and humans are up to 300 million.
But while these common birds are in decline, others are taking their place or even elbowing them aside. The wild turkey, once in deep trouble, is growing at a rate of 14 percent a year. The double-crested cormorant, pushed nearly to extinction by DDT, is growing at a rate of 8 percent a year and populations of the pesky Canada goose increase by 7 percent yearly.
Many of the birds that are disappearing are specialists, while the thriving ones are generalists that do well in urban sprawl and all kinds of environments, Mr. Butcher said. In a way, it's the Wal-Mart-ization of America's skies, he said.
"The robins, the Carolina wrens, the blue jays, the crows, those kinds of birds, are doing just fine, thank you," he said. "They really get along in suburban habitats. Most of them even like city parks, so they are not as susceptible to the human changes in environment."
But nothing matches the takeover ability of one invading bird.
"Right now the Eurasian collared-dove is conquering America," Mr. Butcher said. A dovelike bird that first entered Florida in the 1980s, it now is the most prevalent bird in the Sunshine State and is in more than 30 states.
"Soon you'll be seeing Eurasian collared-doves in any city in the world," he said.