PORTLAND – The pigeon repellent that Casco Bay Lines applied to pipes and ledges at its ferry terminal worked like a charm all summer. The sticky substance turned away the pesky birds and eased the problem of pigeon droppings.

But the repellent, marketed as Bird-Proof, is being removed because it is trapping and killing warblers, sparrows and other migrating songbirds, as well.

“They’re just sticking there and dying, and it isn’t pretty,” Cyrus Hagge, president of the Bay Lines’ board of directors, said Tuesday.

General Manager Patrick Christian said he knows of about 15 small birds that were removed from the gluelike substance and released by workers. Concerned passengers have tried to rescue others and took six birds – yellow-rumped warblers, sparrows, a brown creeper and an Eastern phoebe – to be cleaned and rehabilitated at the Center for Wildlife in Cape Neddick.

Three of the six died by Tuesday afternoon, said Chris Marsh, director of rehabilitation at the center.

Bird-Proof, manufactured by a company called Bird-X, makes perches sticky and uncomfortable to pigeons, which are large enough to simply fly off the tacky material.

Less costly solutions, including tape recordings of vocalizations of such predators as owls and red-tailed hawks, failed to keep the smaller birds away from the booby-trapped terminal. The ferry line then hired a contractor to begin removing the repellent.

“Removal of Bird-X will be costly and time-consuming and will leave us with the pigeon issue unresolved,” Christian wrote in an open letter to ferry riders. “Nonetheless, we believe that protecting small birds is important and removal of the Bird-X is the only option.”