How DO crows (and other birds) stay warm in the winter?
Crows have a higher body temperature than humans due to their significantly higher metabolism. While the average human’s body temperature is 98.6ºF (37ºC), the average bird’s body temperature is appriximately 105ºF (40ºC). To maintain this higher temperature birds have a few physical helpers as well as some behavioral helpers.
Birds have unique scales that cover their feet and legs which minimize heat loss.
Birds have an extraordinary circulatory system in their legs to help them cope with cold temperatures. Warm arterial blood from the birds interior that is on its way to the bird’s feet passes through a network of small passages that runs along side the cold returning venous blood from the feet. The network of vessels acts like a radiator and exchanges the heat from the out-going arterial blood to the cold venous blood. This system insures that no heat is lost and the bird’s feet receive a constant supply of life sustaining blood. That’s also why ducks can swim in freezing water and not get cold.
Birds have feathers coated in oil which is important for waterpoofing / snowproofing. Birds often grow more feathers during late fall to give them extra protection for winter. They can also fluff up their feathers during particularly colder days and nights which can reduce the amount of heat loss by up to 30%!!!
Birds have a different kind of fat than humans. Birds have white fat which is a high-energy fuel used to power the birds warming process, shivering. Shivering produces heat five times their normal basal rate and can maintain a normal body temperature for six to eigh hours at temperatures minus 70ºF. Since this fat is so important to our feathered friends, birds will often try to store extra fat for winter.
Crows often go into a state called torpor where they lie on the ground with their bills half-open when sunning themselves, looking to all the world as if they are about to succumb to some terrible malady. Torpor is a state of unconsciousness where the bird is inactive and their core temperature drops approximately 10-12 degrees, respiration and heart rate drop and the bird’s body then needs less energy, thus saving approximately 20% of the energy which is then used to maintain body temperature.
Birds use some particular behavior to conserve heat as well:
Tucking: When birds stand on one leg or crouch down covering their legs with its feathers. Birds can also tuck their bills into their shoulders as well.
Fluffing: Birds will fluff out their feathers to create air pockets for additional insulation in cold temperatures.
Shivering: As I mentioned above, shivering is an important behavior for birds. Birds will shiver to raise their metabolic rate and generate more body heat as a short term solution to extreme cold. While shivering does require more calories, it is an effective way to stay warm.
Sunning: On sunny winter days, many birds will take advantage of solar heat by turning their backs to the sun (therefore exposing the largest surface of their bodies to the heat) and raising their feathers slightly. This allows the sun to heat the skin and feathers more efficiently. Wings may also be drooped or spread while sunning, and the tail may be spread as well.
Roosting: Crows roost, as many birds do, gathering in large flocks at night and crowd together in a small, tight space so they can share body heat. You can often see thousands of crows roosting together, and boy what a site that is for crow lovers!
Want to help keep crows warm in the winter?
- Put out winter bird foods such as suet, the bird peanut butter, seeds and other bird foods high in fat. Keep your feeders full, check daily.
- Put out fresh water daily. This will save them the energy of trying to find water.
- Build or buy crow birdhouses and roost boxes.
- Plant trees common for crows to roost in. Crows usually choose evergreen and deciduous trees. (To find a crow roost, watch for birds at sundown and follow them.)