People in Middleburg have wondered jokingly if starlings could read the signs, "Bird Sanctuary," which until recently marked the boundaries of the Loudoun County town.

No one has been able to come up with a better reason why hundreds of thousands of the pesky birds have filled the sky every summer for at least a dozen years.

They arrive around suppertime like an unwanted guest, settling in residents' trees and filling back yards with malodorous droppings.

"If you're looking up, all of a sudden the sky becomes black with them, and then they pass," Town Manager William Leach said.

On the advice of state animal control officials, police officers have cruised the infested neighborhoods blaring tapes of birds in distress. They have fired guns using exploding blanks. They have set off propane cannons.

The birds won't leave.

Resident Phillip Thomas, owner of a real estate company, became so frustrated this year that he gave the town $700 to help get rid of the feathered pests. The town itself has spent thousands, Leach said.

The birds don't care.

"I think," said former mayor Loyal McMillin, "that the birds have outwitted us all."

Starlings, a type of blackbird imported from England and first released in New York City's Central Park a century ago, are now one of this country's most prolific birds. The estimated several hundred million birds -- more than 600 million around the world -- invade many communities every year, fouling rooftops and yards, eating vegetables and grains and generally making life miserable for their unlucky hosts.

Larry Thomas, a wildlife biologist with the U.S. Department of Agriculture's animal damage control division, said it is common for the birds to return to a favored place. But he said season-long stays usually occur in warmer climates during winter. The Middleburg situation, in which the birds stay from late spring to early fall, suggests an unusually strong attraction to the area.

Thomas said killing them, which is extremely difficult, may be the only way to get rid of them.

That would suit Phillip Thomas just fine.

"If I had my way I'd issue shotguns," he said. "They can't come back if they can't fly, can they?"

Besides creating a stench that makes some residents gag, starling droppings can make people sick, according to Larry Thomas and Richard Falkenstein, a Middleburg family physician. The droppings breed a spore that can cause histoplasmosis, which attacks the lungs.

Falkenstein said he hasn't encountered a case yet. But Larry Thomas said it is possible to have the disease and not know it. People may think they have pneumonia or the flu, he said.

Mayor Anne Lackman said the town plans to bring in an exterminator next year because "the bang methods" employed by the town's police force are not working. She also suggests that residents thin their trees, which may discourage the birds from roosting.

This year, though, Police Chief David Simpson allowed himself some hope. In late spring, he and his three officers waited for the first flocks to arrive. Then, they attacked.

Out came the propane cannons, which the officers fired for seven nights. At the end of the week, it appeared as if the birds had dispersed.

"In the latter part of July, they came back in droves," Simpson said. "After a while . . . they really are not that startled by the explosives. They get used to it."

Babies and pets, on the other hand, do not. Lackman has responded to complaints from both sides: Those residents who are plagued by birds want to know what the town is doing about it; those who are not want to know why they must be subjected to the racket.

Phillip Thomas, who said he can't use his back yard or pool because of the stench, said he has seen some of his neighbors, mostly senior citizens, attempt to take matters into their own hands. "They're out there beating pans with wooden spoons," trying to scare the birds away, he said. "It's kind of sad."