Biologists working to protect the Island’s fragile piping plover population have turned their attention to a primary predator: cats, both feral and domestic.

Wildlife biologist Luanne Johnson has been setting traps in two locations this spring as a response to piping plover mortality during last year's nesting season. In at least three of the shorebird deaths, cats were found to be responsible.

At Cedar Tree Neck, a cat killed an adult male in 2013, leaving his mate to care for their four chicks. The chicks died soon after.

“The female couldn’t care for them all alone,” said Adam Moore, executive director of Sheriff’s Meadow Foundation, which owns Cedar Tree Neck and contracts with Ms. Johnson’s nonprofit, Biodiversity Works, to monitor their plover population. Ms. Johnson has also set traps on private property in Aquinnah.

The death of adult piping plovers poses a significant threat to the bird population, Ms. Johnson said.

“As a population, the most valuable part is the breeding adult birds,” she said. These birds have reached many difficult milestones, from egg to chick, chick to fledgling, and have migrated back safely from their winter spot, she said.

The piping plover is listed as a threatened species. In 1993, the U.S. Fish and Wildlife Service set a goal to reach 2,000 breeding pairs along the Atlantic Coast.

In order to reach that goal, predation threatening the shore birds must be minimized, Ms. Johnson said.

Each year, about 50 plover pairs make their nests on Martha’s Vineyard.

Besides cats, the other predator that takes adult predators are raptors, including the migratory falcon, the merlin and the northern harrier.

But those predation events are very infrequent, Ms. Johnson said.

More often, it is the cat, a nonnative mammal, that hunts the plovers.

Ms. Johnson uses Havahart traps, which she says are humane and provide food, bedding and cover for animals trapped inside.

So far she has trapped three cats this season, she said. In each case, she involved the town animal control officer and made efforts to locate any possible owner.

In one case, the cat was taken to Boston for spaying, but was returned to the Island.

Ms. Johnson said the cats appeared to be feral, but residents should know to keep their domestic cats away from shorebird habitat.

“If your cat is documented killing piping plovers, they are responsible under the Endangered Species Act,” she said. She said it is advisable to attach a safe breakaway collar to all cats.

 The issue ignited a flurry of posts and heated debate on Facebook, including on the Facebook group “MV Helping Animals.”

Kym Cyr, a cat lover who runs Martha’s Vineyard Helping Homeless Animals, said she doesn’t object to the idea of protecting the birds but can’t support taking cats away from their homes, especially to a far-off shelter like Boston, where they could be euthanized.

“My only concern is that these animals belong to somebody, whether they are feral or they are not,” she said. She said for some cats, a cat colony is their home. “Whether we approve of that being their home or not, that is their home,” she said. “To take them away, it really seems unfair.”

Of the three cats trapped by Ms. Johnson, one has been returned to its owner. Ms. Cyr has the other two at her house in Oak Bluffs, where she boards more than 20 cats.

She said she knew of a gentleman who runs a cat colony near Cedar Tree Neck, but didn’t know his name. If she did, she said she would go in and make sure the cats were spayed and neutered.

“It’s just unfair to think it’s a competition between the birds and the cats,” she said. “I hope we can reach a happy medium between the cats and the birds. I can’t say the cats are more important than the birds and I can’t say the birds are more important than the cats.”

Ms. Cyr said she held one of the Cedar Tree Neck cats on her lap as she spoke. She described herself as a voice for the cats and the dogs.

“I feel strongly that the cats have had an injustice here,” she said.

She said she had not relayed her concerns directly to Ms. Johnson.

“The way I live my life is if I know I can change something, I will go forward with it,” she explained. “If I don’t think it is going to be changed, I don’t waste my time with it.”