HADLEY — Every spring, they faithfully return.
Scores of the small birds with the long, forked tail and dark rump flutter through openings in a dimly lit, dilapidated stable, where they use mud and grass to build a labyrinth of nests.
They make up the state’s largest-known colony of barn swallows, a species in decline in New England and listed as endangered in parts of Canada. And they should be safe here, if anywhere; the abandoned stable, after all, is in a wildlife refuge.
But the birds now face eviction by those charged with protecting them — federal wildlife officials.
The manager of the Silvio O. Conte National Fish and Wildlife Refuge said the 22,500-square-foot building must go, because of the risk it could collapse and damage the refuge’s main power transformer.
“It’s not that I hate barn swallows,” said Andrew French, who has been leading the effort to raze the stable. “But keeping this building standing could impair our ability to protect the land.”
To local advocates, those priorities are upside-down. They should be: protect the birds. And so in an effort to save the building as a nesting site for the flock, members of a group called Save Our Swallows have filed a notice of intent to sue the US Fish and Wildlife Service, arguing that the agency would be violating federal rules and its mission, which includes protecting endangered and other threatened species. Evicting the swallows, they say, could threaten the colony’s survival.
“Why destroy a prime nesting spot of a declining species, when it is so easy to help it?” said Mara Silver, a local ornithologist who has been studying the colony for years and founded Save Our Swallows, which she likes to abbreviate to SOS.
The advocates have even offered to provide the agency with private donations to repair the barn, which French has declined, mainly because he doesn’t think it should be rebuilt.
This isn’t the first time the agency has sought to keep the birds out of the building, known as Bri-Mar Stable. Five years ago, in an effort to prod the swallows to nest in a nearby building, agency officials boarded up the barn, Silver said.
The officials only relented and allowed the birds back after they became “visibly distressed,” she said.
The swallows are among a species of bird known as aerial insectivores, which feed on insects while flying. Their numbers have dwindled in recent decades, which ornithologists attribute to a loss of farmland where they forage, increased use of pesticides, and a changing climate that has caused more mismatches in the timing of insects hatching and the insectivores’ nesting periods, when their food needs peak.
In New England, barn swallows have declined by more than 50 percent since the 1980s, ornithologists say. But the population at the refuge in Hadley has been growing. Colonies of more than 15 pairs are rare, but last year, SOS volunteers counted 37 pairs nesting in the barn.
“In these uncertain climate-changing times, it would be prudent to take steps to safeguard these birds before they become threatened or endangered — or, at the very least, to avoid taking steps that actually imperil their well-being,” Silver said.
If the colony is forced to find new nesting grounds, especially one without the protections afforded by the refuge, it could disband, she said.
But refuge officials insist the barn is too decrepit to keep. On a recent tour of the property, French used a flashlight to point out its structural failings. Parts of the roof are buckling. Beams are rotting. There are holes in the brittle walls.
He declined the donation offers, he said, mainly because he doesn’t think it prudent to preserve the building, which an assessment commissioned by the refuge deemed a threat to other nearby structures, to visitors, and staff. Moreover, he said, the offers were significantly less than the costs of work required, which he said could run to hundreds of thousands of dollars.
“It’s in such poor condition,” he said. “We have other priorities.”
He also noted that fear for the barn swallows may be somewhat overwrought. The birds, while in decline in northern latitudes, remain widely distributed throughout the world, and in the southern United States, their numbers have been increasing.
The refuge has proposed taking down the stable in phases, closing off portions of the building at a time to allow the swallows two seasons to find new nesting areas.
Refuge officials also have been trying to entice the birds to occupy another nearby building. In an experiment, they’ve installed scores of different kinds of perches in the rafters, to see what they prefer. They’re even playing a recording of nesting swallows near an opening.
“We’re not trying to move them,” French insisted. “We’re trying to recruit first-time nesters.”
Baker administration officials declined to allow the state ornithologist to comment, following a pattern of refusing to allow many state scientists to speak to the Globe. State officials acknowledged, however, that the swallows are experiencing “a long-term decline.”
If the stable is removed, they added, they would work with federal officials “to help promote the swallows on the property.”
Other environmental groups have also urged the agency to let the building stand.
In a letter to the agency, Ted Cheskey, naturalist director of Nature Canada, wrote that the “destruction of the stable will cause the colony to decline and eventually disappear, if there is not a similar-sized and quality replacement habitat created nearby.”
He noted that barn swallows are listed as a threatened species in Ontario, where his advocacy group is based. “Alternate structures will only hypothetically provide habitat for a fraction of the existing population,” Cheskey said.
If the agency proceeds with its plans, officials from Mass Audubon, which promotes conservation to protect wildlife, have urged them to proceed cautiously.
“With a carefully considered monitoring effort, I would hope that we could learn important lessons that might be applied to similar situations that regularly occur,” said Jonathan Atwood, director of bird conservation at Mass Audubon.
As he led a visitor on a tour of the maintenance building where he’s trying to lure swallows, French beamed as two of the small birds swooped in through an open window. One landed on a wire attached to a platform hanging from the ceiling. Another alighted on a perch on a metal box screwed into a wooden beam.
The birds chirped, looked around for a bit, and then flew out.
“If there’s one thing I’ve learned,” he said, “it’s that a lot of people care about barn swallows.”