Tuesday, March 25, 2008
How do these birds do it? How do they stay in Alaska all winter when the temperatures can drop below –40 degrees F.? These birds have a variety of adaptations to cold, and in fact can’t survive in warmer climates. The high temperatures (close to 90 degrees F.) during the summer in the interior of Alaska cause them stress more than the low temperatures of winter. During the winter they mainly eat seeds from birch and alder trees, and in the summer insects. They do have pouches in the esophagus where they can temporarily store seeds and digest them through the night to help them stay warm. Birch seeds are high in calories and by digesting them through the night, their metabolism helps keep them warm.
They also eat about 30-40 % of their body mass a day! The pouches can hold about 15% of their body mass in food. For a 100 pound person that would be like holding 15 pounds of food in your esophagus to digest during the night.
Alaskan redpolls also have heavier plumage in the winter than they do in the summer. The weight of the plumage can increase over 30% which provides them an important source of insulation against the cold. They also dive into the snow and create roosting burrows where they are protected against the bitterly cold wind. Notice how the bird in the picture above tucks it's bare legs into the insulating blanket of its feathers. I took dozens of photos of redpolls while I was in Alaska, and in all of them the birds have their legs covered by the feathers like this to retain body heat.