WASHINGTON -- The loss of millions of acres of grasslands and shrubs nationwide to suburban sprawl and agriculture -- along with a warming planet -- has dramatically reduced the numbers of common birds seen across the United States over the past 40 years, according to a National Audubon Society study released yesterday.
In Massachusetts, several birds seen regularly three or four decades ago, including the Northern bobwhite and the Eastern meadowlark, have all but disappeared, according to the study.
Human encroachment on their habitats has so vastly diminished their populations that specialists now consider it rare to see those birds, as well as several others, according to annual counts.
"It shows how suburban development really affects bird habitats," said Greg Butcher , national director of bird conservation for Audubon. "In many cases the development destroys the habitat outright or causes fragmented spaces for them."
The nationwide analysis looked at data collected by volunteer bird-watchers in the Audubon's annual Christmas Bird Count , which started 107 years ago and is held over a 20-day period before and after Christmas, and the annual North American Breeding Bird Survey organized by the US Geological Survey every June. Combining the data from both surveys produced a snapshot of 550 bird species from roughly 5,000 sites in 48 states, Butcher said. Alaska and Hawaii have had fewer sites and were not included.
The researchers determined that the percentage declines by comparing bird counts from the mid-1960s with those of the past few years.
"These are not rare or exotic birds we're talking about ; these are the birds that visit our feeders and congregate at nearby lakes and seashores, and yet they are disappearing day by day," said Carol Browner , Audubon board chairwoman and former Environmental Protection Agency administrator in the Clinton administration. "Their decline tells us we have serious work to do, from protecting local habitats to addressing the huge threats from global warming."
Butcher said global warming was hurting birds in numerous ways as well, including the weather-related reduction of habitat in the far north, the destruction of trees in pristine northern forests because of northward-moving pests, and migratory patterns that have shifted north, too, as the climate warms.
"Birds are wintering farther north. In the fall, they are migrating south only as far as need be to survive," Butcher said.
Audubon officials said national policy decisions have the greatest effect on the birds' survival, including current legislation on global warming, energy, and agricultural policy.
One key fight for conservationists is in Congress, where lawmakers are set to consider a farm bill that includes the Conservation Reserve Program , which has preserved 36 million acres nationwide in grasslands. But the drive to produce more ethanol -- a corn-based alternative fuel that many contend can help solve America's energy woes -- has spurred proposals that could transform those grasslands into cornfields.
In the nation's Midwest, the Audubon researchers attribute the steep decline of bird populations to vast commercial agriculture operations, which consumed bird habitats in the prairies to create huge produce farms and sprawling livestock feed lots over the past several decades.
In Massachusetts, Butcher said, volunteers recorded a 62 percent decline in the snow bunting, a bird of the high Arctic, and a 52 percent decline of the greater scaup, a small duck that breeds in Alaska and northern Canada, over the past 40 years, according to the Audubon Christmas counts. Both species' migratory patterns include stops in Massachusetts.
Scott Weidensaul , a nationally renowned naturalist and author, said bird-watchers have known for years that some species' populations were falling in areas where they had once been abundant. "For the first time we are able to put numbers to a phenomenon so gradual for so long that it's been easy to overlook -- until this point," Weidensaul said.
When he was growing up in eastern Pennsylvania, Weidensaul said, the sounds of the bobwhite quail awakened him in the morning and he drifted asleep to the whip-poor-will's calls at night. Now, he added, "you can't find a bobwhite in Pennsylvania and the whip-poor-whirl is increasingly rare."
A similar scenario has emerged in Massachusetts over the past four decades, according to the data: The bobwhite population has declined by 99 percent, and the whip-poor-will count has plunged by 88 percent. Other birds in dramatic decline in the state include the evening grosbeak, common grackle, horned lark, field sparrow, ruffed grouse, and American bittern; all of the species' populations are down by 70 percent or more.
Nationally, the bobwhite population dropped by 82 percent, the steepest species decline in 40 years. But other species whose populations fell by at least 70 percent in four decades include the evening grosbeak, the Northern pintail, the greater scaup, meadowlarks, and the common terns.
According to the Audubon analysis of the annual June counts, the numbers of grackles have declined 68 percent over the past 40 years, a development some local bird-watchers found baffling.
"The grackle is the most common bird in my yard," said Brian Condron , who maintains a bird feeder on a half-acre of land behind his Hingham house. "They eat me out of house and home."
Butcher, the Audubon official, said the grackle is in decline, but it remains among the more common birds in Massachusetts, and he acknowledged that several bird species still have robust populations. Nevertheless, the comparison of 40 years ' worth of data confirms that environmental changes have hurt many types of birds.
Condron agreed that he would be hard pressed to find a bobwhite or a meadowlark near his home. Still, he said, he sees a wide variety of birds in his backyard each day: orioles, goldfinches, downy woodpeckers, and red-tailed hawks.
"Anybody with a bird feeder in the Greater Boston area who maintains it and watches it on a regular basis will be surprised," he said.
Individuals can help stem the decline of common birds in several ways, including dedicating parts of backyards to native plants and shrubs that "produce berries, rich and fat ones, which are tremendous help for migratory birds in the spring and fall," Weidensaul said. He also doesn't cut back his perennial flower beds in wintertime, which attracts birds "scuffing around for seeds."
John Donnelly can be reached at email@example.com.