Manchester - Scientists are struggling to explain the rare death of 17 loons in New Hampshire, saying warm weather may have confused the threatened species of bird which typically heads to the ocean for winter.

Twenty-two male and female Great Northern Divers, known as Common Loons, were found on Saturday and Sunday on Lake Winnipesaukee, many them covered in snow from wind gusts with their heads tucked into their wings to keep warm.

Biologists are unclear why the loons congregated on the ice deep in New Hampshire when they normally migrate to open water such as the ocean in winter. The five that survived were transported to the ocean and released.

"This is the first time I ever have seen this," said senior biologist and executive director of the Loon Preservation Committee, Harry Vogel. "It's unprecedented."

The mild early winter - including the warmest December on record in New Hampshire and an unseasonably warm January - may have contributed to the confusion of the loons, biologists said.

Lake Winnipesaukee, which usually freezes by the first week of January, did not fully ice over until January 25, said Don Miller, a large lake fisheries biologist with New Hampshire Fish and Game.

Initial evidence suggests that the loons were in the process of molting new flying feathers, an annual event that usually happens after the birds have migrated for the winter.

If that was the case, Vogel said, there must have been some open water on the lake for them to live.

Last winter, large expanses of the lake did not fully freeze, and some of the loons did not migrate to the ocean. Vogel suggests that the stranded loons may have stayed at the lake last year as well.

Loons, which number about 500 000 in the United States, are heavy birds that need open water to fly. They take off like planes, requiring a runway of 90m of water to gather enough speed to lift off.

Their feet are placed in the back of their bodies, which makes them great swimmers and divers, but terrible walkers on land or ice.

Emily Brunkhurst, a conservation biologist with New Hampshire Fish and Game, said the deaths are worrisome for the loon, which has been on New Hampshire's threatened species list since 1980. The 17 represented about 3 percent of New Hampshire's loon population.

"The loss of so many adult birds has a stronger impact on the populations of loons than other species because they don't breed as often as other species," Brunkhurst said.

Loons, which live from 25 to 30 years, don't breed until they are about 7 years old, and on average, produce a chick every other year.

Vogel, who has the birds' carcasses, will send them to Tufts University in neighbouring Massachusetts for a necropsy, where they will be tested for lead, mercury and other viral diseases.

But, if his early suspicions are right, the loons thought they could get away this winter without migrating.

"They gambled and lost," he said.

Original Source: IOL News