By SCOTT McMILLION, June 15, 2007.

Some common Montana bird species have declined by more than 80 percent over the past 40 years, according to a new study from the National Audubon Society, and more than two dozen have seen their numbers drop by at least half.

Similar trends are happening across the nation, Audubon officials said Thursday in a teleconference with reporters.

Audubon volunteers stage organized bird counts every winter and summer and have compiled a large database going back to 1967.

In Montana, the study says, killdeer numbers are down by 80 percent during spring breeding counts.

Great blue heron numbers dropped by 81 percent, and blue-winged teal were off by 72 percent.

Springtime Western meadowlark populations have fallen by 25 percent, and the pine grosbeak population has sunk by 89 percent.

The study listed 26 species in Montana that have declined by more than 50 percent.

“We're looking at a 40-year trend,” said Steve Hoffman, executive director of Montana Audubon.

Some of the species rely on wetlands, while others need forest, shrub or grassland habitats, Hoffman said.

The causes of the declines are as diverse as the species of birds, the report says.

Intensive, large-scale agriculture removes habitat, as do invasive weeds. Pesticides have a secondary impact on birds because they kill the plants or bugs they eat. And rural and suburban development, especially along streams, displaces a wide variety of birds.

However, since birds are declining in all types of habitats, that indicates widespread problems, Hoffman said.

He drew particular attention to problems concerning wetlands and waterways, which are used at some point by 88 percent of Montana's 421 bird species.

“As Montana grows and develops, we see more and more pressure on our rare wetland and streamside habitat,” Hoffman said. “Once we lose these places, it's difficult, if not impossible, to bring them back.”

He cited the stately and magnificent great blue heron is an example. It appears to be suffering from drought and stream modifications, like flood control and straightening measures. That kind of work reduces the number of large cottonwood trees the birds need for nesting sites, Hoffman said.

The health of bird populations indicates the health of the environment, Audubon officials said.

One state official agreed.

Birds “reflect the diversity of native habitats unique to Montana, which are important to our way of life and our outdoor heritage,” Rick Northrup, statewide bird coordinator for the Montana Department of Fish, Wildlife and Parks, said in a press release.

The birds cited in the report are not threatened or endangered, but the time to protect them is before they decline to that level, Audubon officials in New York City said in the teleconference.

“Their decline tells us we have serious work to do, from protecting local habitats to addressing the huge threats from global warming,” said Carol Browner, Audubon chairperson and administrator of the Environmental Protection Agency during the Clinton administration.

While some species are declining, others are booming.

Canada Geese are one example. In many places around the country, they congregate on playing fields and parks, fouling the ground with their waste and becoming a nuisance for athletes and picnickers.

Greg Butcher, Audubon's bird conservation director, said that's because Canada geese select the same kinds of habitat that humans enjoy: closely cropped grasslands near water.

Crows, robins and some wrens also are increasing, Butcher said, but birds that need some type of specialized habitat appear to be suffering the worst.