BOZEMAN--Although Yellowstone National Park is associated with bears and elk, it may be the birds who best signal whether humans are changing the surrounding ecosystem, a study at Montana State University-Bozeman has found.

Songbirds generally are less common in higher elevations within the protective borders of park than they are at lower elevations on or near the private lands outside the park, according to the study led by Montana State University ecologists Andy Hansen and Jay Rotella.

"The big message is that both the density of birds and the intensity of human land use vary with elevation and habitat type," said Rotella, an avian ecologist and head of the MSU Ecology Department.

Few songbirds were found up high where soils are poor and winters are long. Instead, "hot spots" of biodiversity exist down along river beds and riparian zones surrounded by willow, aspen and cottonwood forests.

While that sounds good for the birds, these low-lying hot spots tend to occur on or near private lands. Rural residential development and other land uses can reduce nesting success in these hot spots. Bird reproduction in these areas can be too low to outweigh the number of deaths, especially for species like the yellow warbler that are vulnerable to nest raiders.

"Birds still seem to want to come into these cottonwood forests in large numbers, despite the fact that most don't have good breeding success," Rotella said. "That's sort of a shock in a way and maybe not as big of a surprise in another way."

Birds likely choose breeding sites based on vegetation characteristics. This likely worked well over evolutionary time. But nesting success now seems also to relate to the density of homes in the area, with impacts reaching as far as three to five miles of home sites, Rotella said. That's because predators, such as magpies, cow birds, skunks and raccoons, increase with agricultural and residential land uses.

The five-year songbird study, now complete, was just one part of a broad look at how human populations around Yellowstone affect the entire 60-000 square mile mosaic of National Park Service, Forest Service and private lands known as the Greater Yellowstone Ecosystem. The study also asked, in turn, how the ecosystem affects human behavior, such as the desire to live near beautiful scenery.

"We found that many new residents are attracted by the nature and beauty of Yellowstone," Hansen said. "However, we may be harming wildlife by where we place our homes. The challenge around Yellowstone is to manage future growth to maintain the qualities of the ecosystem that we value so highly."

Funded by NASA and a variety of other federal and state agencies, the songbird project called upon satellite images, geographic information systems and the auditory skills of a dozen or so bleary-eyed college students. The students rose well before dawn each summer day to tally birds and document vegetation at field sites in Bozeman, West Yellowstone and Island Park, Idaho.

"After six weeks or so of surveying birds, our crews tend to be a little grumpy, a little sleep-deprived," Hansen said.

Nevertheless, said crew leader Matt Kraska, each day offered something new.

"Every day I saw something I'd never seen before, even though I'd been there maybe 80 times," Kraska said. "That was the most wonderful thing about it."

Hansen said the next step should be to see if the results for songbirds apply to other species such as bears, ungulates and native trout that may be at-risk from rural residential development.

"By simply letting folks know the importance of that aspen grove on their land or those riparian cottonwoods, a lot of landowners may be very interested in maintaining those habitats," Hansen said.

The team also plans a two-year study of biodiversity hot spots in an area stretching from the eastern side of the Northern Rockies to the Oregon and Washington coasts. That project would be funded by the National Council on Air and Stream Improvement, a consortium of timber companies.