Song and sprawl. (Clippings).

Yellowstone National Park is one of the most famous of America's protected areas, providing crucial habitat to many wildlife species. But recent research suggests the lands surrounding the park may be even more important.

In a study published in the August issue of the journal Conservation Biology, Montana State University researchers Andrew Hansen and Jay Rotella found that due to climate and soil differences, birds are more likely to live on lower-elevation private lands than in higher-elevation nature reserves like Yellowstone.

Furthermore, increased rural development on those private lands may be leading to certain bird species' demise by making them more susceptible to parasites and predators.

Studying bird populations over a 3,600-acre study area, Hansen and Rotella hypothesized that low-elevation areas, with their milder climates and longer breeding seasons, function as population growth areas for bird species. For the American robin, a bird not susceptible to parasites and predators, the researchers found this to indeed be the case. But the situation is worse for the yellow warbler, which the researchers found to be increasingly attacked by predators and cowbirds. Cowbirds lay their eggs in other birds' nests and the cowbird hatchlings often outcompete their nestmates for food.

Hansen said the strength of predators and parasites can be directly tied to development, which provides food and habitat for these enemies of the yellow warbler. He said it now appears that the only reason the warbler population in the area has not disappeared is the arrival of new birds from elsewhere.

Officials can no longer safely ignore the areas surrounding nature reserves, Hansen says, because these areas are often essential to the survival of protected species.

"These findings are important because they suggest this kind of development could in fact have important consequences for nature reserves," Hansen says. "We need to learn more about this in more settings around the world."