How Do Birds Keep Warm In Winter?
During the cold weeks of the early New Year, gardens can be a real haven for birds looking for warmth and shelter. Many natural food and water sources will be in short supply so the food and water found in gardens can be a literal life saver.
Birds are warm-blooded and have a higher metabolism and body temperature than humans. The average bird’s body temperature is 40° Centigrade although this will fluctuate during the day depending on climate and activity. It can therefore be a challenge for birds to maintain this high temperature when temperatures fall sharply. Small birds are most at risk as they have a proportionally larger surface area on their bodies.
The main insulation against the cold are feathers. Many species of birds grow extra feathers during the late autumn to give them more protection during the winter. The oil that coats their feathers provides another layer of insulation as well as help keep them protected from water. During cold weather you may see birds that appear to be fatter than usual – they are in fact fluffing their feathers to trap warm air beneath them.
Birds’ legs and feet are covered in scales that minimise heat loss. They are also able to constrict blood flow to their extremities which reduces heat loss further. You may see birds standing on one leg in the cold or crouched over to cover both legs with feathers. They are also able to tuck their bills into the feathers at their shoulders.
Most birds will build up fat reserves before the winter which provides extra insulation and energy for generating body heat. During the autumn food is abundant and you will often see birds gorging on berries, insects and from bird feeders.
On sunny days during the winter birds will turn their backs to the sun and raise their feathers to absorb the maximum solar heat. They may also droop their wings and spread their tails. On very cold days they will shiver to raise their metabolic rate and generate more body heat. Shivering is an effective but short term way to stay warm.
In the winter you may see large flocks of birds gathered together in small spaces to share body heat. They will roost in shrubs and trees, empty bird houses and other spots that have residual heat from the day’s sunlight.
During the night birds will enter torpor to conserve energy. Torpor is a state of reduced metabolism that occurs when birds lower their body temperature which requires less energy to maintain the correct heat. Most birds can lower their body temperature by a few degrees but it has been known for some birds to lower their temperature by as much as 50 degrees. Torpor can be dangerous as reactions become slower and birds are more vulnerable from predators.