Flock of trouble roosts on Causeway St.

Skip Perry has to collect himself every time he looks outside his Causeway Street photo shop, where it's been two months since the elevated Green Line cloaked the street in shadow. Perry says he can now see the spire of Old North Church, and, on a clear day, the mast of the USS Constitution. But lately there's been something new clouding the skies, and it has wings.

Each day at dusk since mid-November, thousands of starlings swarm toward the cornices, ledges, and fire escapes of the area's historic buildings, where they roost. When they fly away at dawn, the birds leave behind a mess: Awnings, signs, and sidewalks are covered with bird droppings.

''These windows were washed two days ago," Perry lamented yesterday, pointing out several heavily streaked panes of his shop. ''It's unbelievable."

No one is yet certain about the reasons for the sudden onslaught, but the consensus among shop owners is that demolition of the rusty train tracks that marred the view for so long also displaced the starlings, which roosted on the platform. The birds appeared shortly after the last remnants of the Green Line came down last month, business owners say.

''They probably inadvertently revealed a perfect nesting area," said Bob O'Brien, head of the local civic association. ''We're sort of infested now."

Desperate to do something about the problem, O'Brien this week led officials from City Hall and the Big Dig on a tour of the street in a bid for help. City officials then contacted the Massachusetts Bay Transportation Authority. Both the Big Dig and the T had instituted dust- and noise-control programs in an effort to mitigate the effects of demolition on neighbors, but it's unclear whether bird displacement falls under their remediation responsibilities. Representatives of both agencies pledged yesterday to look into the neighborhood's plight.

''We are certainly willing to look into the matter to see if we can assist the neighborhood in any way," Big Dig spokesman Doug Hanchett said.

The officials said they will meet again next month to try to come up with a solution, but in the meantime, shop owners are dealing with the daily droppings as best they can, some with daily scrubbing, others with sweeping. One building owner plans to put sticky tape on ledges, while another tried installing spikes to discourage birds from perching. The starlings, though, don't appear to be getting the message.

''You see how well it's working?" quipped Perry, gesturing toward a pigeon nestled amid spikes above Burger King.

After reading about a pair of red-tailed hawks evicted this month from a Fifth Avenue apartment building across from Central Park in New York, Perry and other business owners discussed bringing the birds, affectionately known as Pale Male and Lola, to the Bulfinch Triangle, in hopes they would scare away the avian hordes. Hawks and falcons sometimes feed on starlings.

The idea was rejected because the local civic association said the woodsy look of the hawks' 9-foot nest wouldn't fit with the image it is trying to promote of a hip, rejuvenated warehouse district.

''We are not the sort of district where a pair of hawks will work that well," O'Brien said.

Starlings and Massachusetts have had a long and somewhat contentious relationship. Officials at Logan Airport began an extensive bird-control program after a flock of starlings was sucked into a jet's engines in 1960, causing the plane to crash, killing 62 people on board. After starlings repeatedly fouled two statues of James Michael Curley in a Congress Street park, the city replaced the park's zelkova trees -- which draw starlings with their blossoms and tiny berries -- with trees that don't bear starling food. The tactic worked. In Springfield in 1996, city workers trying to ward off starlings in the downtown center strung up 3-foot-high balloons adorned with pictures of large eyes. The theory was that starlings don't like to be stared at.

The birds have been likened to flying rats, and their calls compared to the screech of nails on a schoolroom blackboard. Sixty of the medium-size, black-feathered scavengers were introduced to the United States in the 1890s by a man who wanted to populate Central Park with every bird species mentioned in William Shakespeare's plays. Within 20 years, flocks of 100,000 starlings soared through North American skies.

Specialists say that on cold nights, the birds gather in large flocks to roost in cozy nooks, especially near windows where heat radiates from inside and they may find relief from biting winds, snow, and rain. Ledges and fire escapes on the five- and six-story brick buildings on Causeway Street probably are providing ideal wintertime perches, said Richard C. Banks, an ornithologist with the Pawtuxent Wildlife Research Center at the National Museum of Natural History in Washington, D.C. During the day, starlings leave their roosts and often travel far afield to feed, but they usually return to familiar perches at nightfall.

''When the weather gets warmer, they'll disperse out into the less-populated, more rural areas," Banks said. ''But next [winter], they'll be back."

When the starlings roosted on the Green Line and elevated artery structures, shop owners say, their droppings apparently stayed on the transportation viaducts or fell into the street, away from the buildings and sidewalks.

''We never had this problem in years past," said Dave Devine, who owns Mulligans, a sandwich shop with a sign out front that's more than a little bespeckled. ''There's always been birds, but it's never been this bad."

The fouling has created something of an obstacle course for pedestrians. The unlucky ones often stop in at Halftime Pizza, asking for a napkin or towel. Mark Eden got nailed yesterday morning. He often walks across Causeway Street to get to his Portland Street office.

''Right there," he said, pointing to a big, white splotch on his right shoe. ''We have nothing against birds. It's just they've got to find a new place to roost."

Many people are trying to keep a sense of humor about the deliveries from above. O'Brien himself acknowledges that the rebirth of the triangle may have something to do with the onslaught of starlings.

''We wanted to make the Bulfinch Triangle an attractive place," he said. ''But I guess you should be careful what you wish for."

Donovan Slack can be reached at dslack@globe.com