During a recent ecosystems program I gave to an elementary school class one student was concerned that animals would die because temperatures have been so cold. I assured her that wouldn’t happen, because animals have evolved some amazing adaptations to deal with harsh winter weather.
If you have looked out your window lately and have seen a “fat” bird, you’re not imagining that. It has fluffed its feathers to create air pockets among the many dense, down feathers that hold heat next to its body. It’s like wearing an extra layer of long underwear. The bird’s outer contour feathers seal the trapped air. Also, birds that inhabit colder environments like ours have higher feather mass and more dense downy feathers than those from warmer habitats.
Birds can lose body heat through their beaks and feet, so they often tuck their heads down over their shoulder or under a wing. They keep their feathers dry and waterproof by spreading oil from glands at the base of the tail on their feathers, in a process called preening.
Black-capped Chickadees (Poecile atricapillus) have some remarkable strategies to stay alive and healthy in winter. When they travel together they help each other find food. Birds burn calories when they fly. By eating overwintering insects and seeds, which are often high in fat, birds maintain their warmth and fuel metabolism. Chickadees and most other winter birds can also generate heat and stay warm by shivering.
A chickadee’s normal daytime body temperature is about 108 °F (42 °C ). Researchers have found that a chickadee at night can lower this by 12 to 15 °F (6 to 8 °C) and enter a state of torpor. By reducing its metabolism in this way, it can conserve 25% to 30% of its fat stores from the previous day.
Last fall, chickadees started caching seeds. They are remarkable for their memory and remember hundreds of cracks and crevices in bark where they have stored food. Studies have shown that a chickadee’s hippocampus, the part of the brain responsible for memory, expands by 30% in the fall. In the spring when food is more plentiful it shrinks back to its normal size.
Thick brush, as well as dense conifers like spruces (Picea sp.), junipers (Juniperus sp.), and pines (Pinus sp.), can keep animals warm by reducing their exposure to the wind. If a thick, insulating layer of snow covers the branches, all the better.
Golden-crowned Kinglets (Regulus satrapa), one of the smallest birds of the Northeast, have been observed feeding at –30 °F (–34 °C). Like chickadees, they often travel in groups and can be in a mixed flock with chickadees, nuthatches, and other birds. How do these tiny birds—which lose more heat than larger birds—keep warm at night?
Biologist Bernd Heinrich observed four Golden-crowned Kinglets huddled together at night on a conifer branch in thick cover. By huddling or roosting in cavities animals can heat the air around them. Some species of woodpeckers chisel out roosting cavities in tree trunks and usually spend the night in them individually. Eastern Bluebirds (Sialia sialis) and flying squirrels (Glaucomys sp.) sometimes use woodpecker holes at night. More than a dozen Eastern Bluebirds have been found huddled together for the night in a bluebird nest box.
You can help birds and other wildlife get through the winter by planting native, berry-producing shrubs and trees. Coniferous trees and shrubs provide winter cover and seed from cones, and shelter wildlife from wind and weather. A wildlife brush pile can help too. Set up a feeding station with high quality seed for birds, particularly during late winter and ice storms when the seed and fruit crop is lower. That way, you can admire winter wildlife up close and help them keep warm.