Since dogs were first trained to hunt birds, relations haven't been especially rosy between the two. Dog walkers and bird watchers have a prickly relationship too, often clashing over the use of recreation areas. And now a new study threatens to inflame tempers even more, suggesting that bird sanctuaries be off limits to even those pooches on short leashes.

Currently, dogs roam triumphant in many places, although the Audubon Society lists bird habitats (in Alaska, California, Oregon, Florida, South Carolina and New Jersey) where it considers dog walking to be a threat. Other areas established to safeguard critically endangered birds, such as the Mississippi Sandhill Crane National Wildlife Refuge along the Gulf Coast, currently allow pups in select pockets as long as they are leashed.

But new research indicates it's a bad idea to let even leashed dogs near their feathered foes. Wildlife ecologists Peter B. Banks and Jessica V. Bryant of the University of New South Wales in Australia report in the journal Biology Letters that dog walking led to a 41 percent decline in the number of birds as well as a 35 percent dip in species diversity in conservation areas and parkland north of Sydney. These drops in abundance and diversity reflect the immediate consequences of dogs passing through the park on trails, however, not long-term effects.

During the week-long study, the researchers found similar results in areas that ban dogs and those that allow them, indicating that even birds accustomed to being around dogs tend to flutter away when they approach.  Perhaps more striking, the scientists say that a leashed dog scared off twice as many birds as a couple of humans strolling though the same park.

"This is useful information,'' Banks says, "because now [officials] have some hard evidence to be able to say, 'You can't have your dogs here and this is the reason why,' whereas in the past they didn't have that."

Banks, who doesn't own a dog but insists he's "not a dog hater," says he launched this research to introduce science into the raging debate over what he calls "walking a predator through the bush." He recalled a recent incident in which a dogged (so to speak) lobbyist brought a city council member to tears while arguing for greater access for man's best friend.

Banks says that Australian, British and Canadian conservationists and government officials have been bombarding him with requests for copies of the study and that individuals in the U.S., Switzerland and Ireland have also expressed interest in it. He was careful to stress that the results do not justify a "blanket banning of dogs" in parks. Banks is currently conducting two follow-up studies: one to compare the impact of dogs on and off leash, and another to gauge the long-term consequences of dog-walking in conservation areas.

There are similar concerns in the U.S. at such places as the Mississippi Sandhill Crane National Wildlife Refuge, where one of North America's rarest birds nest amid the preserve's wet pine savanna. Access here is extremely restricted, because only about a hundred of the red-browed Mississippi sandhill cranes remain. (The Mississippi crane once ranged from western Texas to the Florida panhandle, but its habitat and abundance were already dwindling at the time of the first survey of their population in the 1920s. Today they are typically found only in tiny pockets of Mississippi's Jackson County.)

People and pups visiting the 20,000-acre sanctuary are only allowed on two short trails. Park ranger Emily Neidigh says there are no plans to provide wider access, because its main purpose is to protect the tiny population of cranes living there. But that doesn't stop people from trying, she says, noting that there is still "quite a bit of pressure" to open up more of the preserve.  In this case, though, it's hunters eager to kill deer and ducks who are pushing for greater access.

It's a different story in urban areas, where dogs abound but spaces for them to romp are a relatively rare commodity. Bird watchers and dog walkers, for example, both covet Manhattan's sprawling Central Park and Brooklyn's Prospect Park, which the Audubon Society lists as important green "islands" for migrating birds. While no known endangered birds pass through the parks, conservationists are concerned about a handful of species, including the wood thrush, the seaside sparrow and several types of warblers.

So will the new findings galvanize birders to call for more restrictions on Fido and friends in major U.S. metropolitan areas like New York City? Nicole Delacrétaz of New York City Audubon says it's unlikely they would be so bold as to try to close off such a dog-friendly place as Central Park, considering the high volume of people who circulate there and the constant chaos of concerts and other noise. She says, however, that birds might benefit from restrictions in such places as Prospect Park, where dogs can currently run off leash.

Delacrétaz, who isn't a pet owner, also recommended prohibiting pets at beaches such as Fire Island National Seashore, a long strip of sand and pines off the coast of Long Island, N.Y., where the endangered piping plover can be found. Some stretches of beach there are already closed to pets during piping plover nesting season, and identified nests are protected with fencing. Occasionally, though, piping plovers settle on open beaches where pets can roam until birders sound the alarm.

"The piping plover nests right on the beach, and here I can definitely imagine very big problems with dog walking," Delacrétaz says. "It's probably not only a direct effect of the dog going to the nest and possibly harming or killing the chicks, but also the fact that the presence of dogs will prevent them from nesting in the first place."

Sydney birders and dog owners may have their knives drawn, but some New York City dog owners feel fortunate to have so much freedom to roam. "We consider it to be an amazing privilege," says Susan Buckley, founder and president of Central Park Paws, a dog owners' advisory group to the Central Park Conservancy. "If [dog walking] did harm the birds then I would certainly be in favor of not having dogs in those areas."

This article is provided by Scienceline a project of New York University's Science, Health and Environmental Reporting Program.