Study: Erosion Program Increases Bird Populations

May 29, 1997

WEST LAFAYETTE, Ind. -- A study of the federal Conservation Reserve Program, an agricultural program aimed at reducing erosion, finds that the program also provides suitable bird habitat for many declining species of grassland birds.

"The Conservation Reserve Program has been critical to help stem the decline in grassland bird populations in the north central region," says Harmon Weeks, professor of wildlife at Purdue University.

The Conservation Reserve Program, or CRP, was established by Congress in the 1985 Food Security Act, commonly known as the '85 Farm Bill. It was designed to control soil erosion and to limit agricultural production to provide price stability. Through the program, farmers receive payments for setting aside tracts of land for a mandatory 10-year period. So far 31 million acres have been taken out of agricultural production, although the 1996 Farm Bill authorized up to 36.4 million acres to be retired at any one time out of an eligible 240 million acres.

Researchers from six universities in the north central region of the United States compared the CRP lands that had been set aside to land that was being farmed over a five-year period to determine whether the program was providing usable habitat and for which species.

"Just the presence of birds isn't enough. It's really only good habitat if they are successfully breeding," Weeks says. "These small grassland birds have a high annual turnover in their populations -- over 50 percent for many species. If you don't replace this turnover, you have a real problem."

Mark Ryan, a wildlife biologist at the University of Missouri, says the study found that CRP lands are beneficial. "The work clearly demonstrates the enormous use of CRP land by birds for reproduction," he says. "CRP is providing substantial breeding habitat."

The study examined bird populations in both CRP land and in nearby land being used to grow row crops such as corn and soybeans. Only farmland that was being planted using no-till methods was examined, however.

Census counts were conducted in winter as well as summer. "Different birds use CRP lands in the winter, and they use the CRP habitat for different things," Ryan explains. "Some birds use CRP lands in the summer for their nests. In the winter, other birds use CRP lands as habitat because they provide cover from the weather and from predators."

The study found that the most common species wintering in CRP lands were ring-necked pheasant, American tree sparrow, northern bobwhite, dark-eyed junco and American goldfinch. The most common species in farm fields included horned lark, American tree sparrow, European starling, mourning dove, lapland longspur, meadowlark and Canada goose. Not surprisingly, bird species that typically frequent agricultural row-crop fields are experiencing long- term population increases that mirror the increases in the number of acres planted in these crops.

Although the study didn't do a long-term comparative analysis, the researchers say that the program appears to be helping to stop the decline in the populations of many bird species.

During the preceding two decades, bird populations had decreased as much as 90 percent in some areas, wildlife scientists say.

"It was a staggering decline," Weeks says. "In Illinois, some species saw a 90 percent decline over a couple of decades. It was almost catastrophic for these species."

A variety of changes in American rural society over the past 50 years have brought about the rapid decline in bird populations:

-- Fewer family farms resulted in a less diversified landscape, which reduced habitat.
-- Improved farm production methods left fewer rough or odd areas of fields unplanted.
-- Industrialized livestock production reduced the need for farmers to leave land in pasture.
-- Many farmers switched from growing small grain crops to growing crops such as corn or soybeans.
-- Increasing suburbanization of many areas further fragmented and isolated available habitat.

Although the Conservation Reserve Program seems to have stemmed the decline in many species of grassland birds, the researchers caution that bird populations are still at risk.

"These increases may be ephemeral" Weeks says. "If next year all of these areas are planted in row crops, those birds are all dead. They have to place else to go. They can't just crowd into some other, smaller area. It simply doesn't work that way.

"If Congress hadn't kept the Conservation Reserve Program in the '96 Farm Bill, it would have been devastating to the populations of quail, pheasant and songbirds."

One success story of the CRP set-aside is in the numbers of ringneck pheasant. Minnesota saw a threefold increase in pheasant population from 1984 to 1991, and in Dixon County, Neb., the pheasant population increased at least fivefold from 1985 to 1994. The areas that had the most success with pheasant population were those that had about 20 percent of the farmland in set-aside. The researchers speculate that the dense cover of CRP lands sustains the populations by providing thermal cover during harsh winter weather.

The story isn't so positive for another popular game bird, the bobwhite. The study found no evidence of an increase in bobwhite populations brought about by the CRP set-aside.

Although most farmers enjoy having gamebirds on their property, some other species are not welcome.

"All farmers delight in having some wildlife on their farms if it doesn't hurt crop production," Weeks says. "Unfortunately, some of the species that have the highest populations, such as the red-winged blackbird, are birds that are occasionally harmful to agriculture."

In the case of some of these birds, however, raw population numbers might not be telling the entire story. According to Ryan, follow-up research in Missouri has found that although the population numbers for the blackbirds may be high, that doesn't mean that their numbers are increasing. In fact, there is some evidence that CRP land is causing a slight decrease in blackbird populations.

"This surprised the heck out of us," Ryan says. "Everybody just assumed that because of CRP habitat, the number of blackbirds was increasing.

Ryan says there may be a simple explanation. "Blackbirds nest either in wetlands or in grasslands. In the CRP lands (grasslands) the nests are an easy victim to predators. In the grasslands, the blackbirds also have their nests taken over by parasitic brown-headed cowbirds," he says.

"In essence, CRP lands aren't good habitat for red-winged blackbirds, even though you find a lot of them in the set-aside land."

Sources: Harmon Weeks, (765) 494-3567 Mark Ryan, (573) 882-9425; e-mail,

Writer: Steve Tally, (765) 494-9809; e-mail,

NOTE TO JOURNALISTS: The researchers involved in the study mentioned in this news release were Louis B. Best, Department of Animal Ecology, Iowa State University; Henry Campa III and Scott R. Winterstein, Department Fisheries and Wildlife, Michigan State University; Kenneth E. Kemp and Robert J. Robel, Division of Biology, Kansas State University; Mark R. Ryan, The School of Natural Resources, University of Missouri; Julie A. Savidge, Department of Forestry, Fisheries and Wildlife, University of Nebraska; and, Harmon P. Weeks Jr., Department of Forestry and Natural Resources, Purdue University.

Purdue University

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