Scientists studying the death of 17 loons on a frozen lake said Tuesday that unseasonable weather might have confused the threatened species of bird, which typically heads to the open ocean for winter.
Twenty-two male and female Great Northern Divers, known as Common Loons, were found over the weekend on Lake Winnipesaukee, many of them covered in snow with their heads tucked into their wings.
Biologists were unclear why the loons congregated on the ice deep in New Hampshire when they normally migrate to open ocean in winter. The five that survived were transported to the sea and released.
"This is the first time I ever have seen this," said Harry Vogel, senior biologist and executive director of the Loon Preservation Committee.
The mild winter -- including the warmest December on record in New Hampshire and an unseasonably warm January -- might have been a factor, biologists said.
Lake Winnipesaukee, which usually freezes by the first week of January, did not fully ice over until Jan. 25, said Don Miller, a state biologist.
Biologists said that the loons were in the process of molting new flying feathers, which usually happens after the birds have migrated for the winter.
Last year, large expanses of the lake did not freeze and some of the loons did not migrate. Vogel said the stranded loons might have stayed at the lake last year as well.
Loons are heavy birds that need open water to fly. They take off like planes, requiring a runway of 100 yards of water to gather enough speed to lift off.
Their feet are at the back of their bodies, which makes them great swimmers and divers, but terrible walkers on land or ice.