The fact that there are endangered terns on Marion’s Bird Island may not be well known, said resident Tinker Saltonstall. But, their protection has always been a labor of love for local wildlife enthusiasts.

On April 14, Saltonstall, her husband Bill, biologists Carolyn Mostello and Dorie Stolley, Marion Harbormaster Michael Cormier, and a slew of volunteers embarked on a mission to create a more welcoming habitat for nesting roseate and common terns.

Found on both the federal and state-endangered species list, roseate terns annually make Bird Island their summer home, where they nest alongside common terns.

“The clean up has been going on many years,” Tinker Saltonstall said. “It’s always fun to be out there and enjoy the wildlife.”

For Stolley, the chance to prepare the vegetation and shelters for the terns was exciting given that 99 percent of roseate terns in Massachusetts make their nests in Marion, Buzzards Bay, Ram and Penikese Islands.

This is also nearly 50 percent of the world’s population for roseate terns.

“Literally thousands of roseate terns come in during the summer,” Stolley said.

Armed with rakes and mowers, the crew cleared the debris on the island where they were able to set up hundreds of boxed shelters for the terns.

While common terns prefer to nest in open areas to see if a predator is coming, Stolley said the roseate terns prefer a covered home.

“The idea for the shelters was really two-fold,” Stolley said. “We put them up to protect the terns from avian predators, such as falcons, and to protect them from their neighbors.”

Their protective nature, she said, is the main reason visitors are warned to stay away from the terns’ fenced-in area on Bird Island during the summer. The terns may become aggressive if they feel someone is a threat to their young.

Volunteers will continue working at Bird Island over the next few months, preparing for the imminent arrival of the terns.

Overall, Stolley said the group was successful.

“We accomplished 110 percent of what we set out to do,” Stolley said. “It’s fascinating to see a town pull together to coordinate this effort. The terns have such a rich cultural and historical heritage.”