Peter Blanchard is attuned to the rhythms of Great Duck Island and its most populous inhabitants, the rare Leach’s storm petrel.

“They make a riotous laughter when they return from the sea, combined with a purring noise,” Blanchard said. “It’s like being in a room with thousands of children, all giggling at once. It’s a magical experience.”

Blanchard got a case of “island fever” while serving as a teacher for the Maine Island Ecological Program. He has been a volunteer steward at Great Duck Island for three years, and has gotten to know the petrels quite well.

Around 15,000 of the small brown-gray birds, about the size of robins, nest annually each spring and summer on the island, located in the Atlantic Ocean about eight miles south of Mount Desert Island. Great Duck Island, one of 55 islands in Maine administered by the Nature Conservancy, boasts the largest colony of Leach’s storm petrels in the United States.

The nocturnal birds never set foot on land, except at nesting time, preferring to range all over the Atlantic Ocean. The birds flutter over the waves, sometimes pattering on the surface, snatching small fish, crustaceans and tiny squid.

While nesting on Great Duck, the male petrel digs a 3-foot-deep burrow at the roots of spruce trees or under rocks. The female lays one egg, which is incubated for 41 days. The chick is born blind and helpless, and is cared for another 71 days by the adults.

Blanchard explained that one adult sits in the burrow, while the other flies out to sea, seeking food.

“They return, half-walking and half-flying to find their burrow,” he said. “It’s a mystery how that works.”

The petrels have to beware of natural predators like herring gulls, which will attack petrels in flight, and ravens and crows, which will dig into the burrows and steal eggs.

Joanna Thomas of the Nature Conservancy explained that habitats for Leach’s storm petrels are rare because the birds require the right conditions and soil types.

That’s why, she said, the Nature Conservancy tries to keep people off the island during nesting season, except for occasional guided tours. Stewards like Blanchard check the island three or four times each summer, making sure the land isn’t being misused.

Surrounded by crystal-clear blue water, the 356-acre island’s shore of steep granite ledges and boulder beaches makes it fairly inaccessible. Only small boats, like a rubber dinghy on one recent day, can make it ashore.

The island’s history is evident in the buildings that remain. Remnants of stone walls and foundations and rusting implements reveal its farming past. The lighthouse of the island’s southern tip, automated in 1986, was built by the Coast Guard in 1890, to keep ships off its rocky shores. In the early 1980s, Great Duck was used as a retreat by a Gestalt psychiatrist who also had run a clinic on the island for almost a decade in the 1960s.

The Conservancy bought the island for $350,000 in 1985. As a fund-raising campaign, the group sold petrel burrows (the space, not the birds) to people. The Department of Inland Fisheries and Wildlife purchased a 10-percent interest in the island, and now shares responsibility for the island and its nesting birds. There is one private lot on the island’s northern shore.

The petrels share the island, considered one of the most important seabird sanctuaries in the Northeast, with black guillemots (the largest colony in the East), common eiders, herring gulls and a bald eagle. A colony of Wilson’s storm petrels, one of the most common birds in the world, summers there after nesting in the Falkland Islands, near Argentina.

Also, there are plant species considered rare or endangered. These include the white-fringed orchid, which grows along an abandoned airplane runway. Another plant, its seed carried by airplane wheels, grows only there and in Newfoundland.

“There’s tremendous potential for different types of research in many branches of natural resources,” said Blanchard, although there is currently no research being done on Great Duck.

So Great Duck Island has more to offer than just one large colony of petrels.

“What makes the island special is the combination of history and nature,” said Thomas.