It happens every year, but we never seem quite prepared for it. We begin to bundle up with our sweaters, big winter coats, mittens and hats to keep warm… but what about the birds?
How do the birds stay warm?
Birds have many physical and behavioral adaptations to keep warm, no matter how chilly it is outside! But birds are only able to regulate their body temperature through metabolic heat production which means balancing the intake of energy with what has been consumed.
There are three physical adaptations which keep your backyard birds warm during the cold winter months; their legs and feet, feathers, and fat reserves.
Legs & Feet: Birds’ legs and feet help minimize heat loss through their unique circulatory system of arteries and veins. In many birds, arteries and veins in their legs lie in contact with each other in order to exchange heat and maintain temperature. Arterial blood it is normally at body temperature and it is sent to the feet through a series of conducts that run along with the cold returning venous blood. This keeps the heat toward the core of their body, by constricting blood flow to their extremities. But, they are also able to minimize heat loss through the specialized scales on their legs and feet.
This varies amongst birds as ground foraging birds such as sparrows and juncos typically drop down covering their legs and feet as a way to transfer body heat.
Feathers: Birds’ feathers provide remarkable insulation against the cold, and many bird species grow extra feathers as part of a late fall molt to give them thicker protection in the winter. Birds also produce a special type of oil which coats their feathers to
provide insulation as well as waterproofing.
Fat Reserves: Birds build up fat reserves to serve as insulation and extra energy for generating body heat. Many birds will gorge during the fall when food sources are abundant, giving them an extra fatty layer before winter arrives.
In addition to physical adaptations, birds use their behavioral adaptations such as fluffing, tucking, sunning, and shivering. In severe situations, they may go into torpor in efforts to survive a cold winter night.
Fluffing: Birds will fluff out their feathers to create air pockets for additional insulation in cold temperatures.
Tucking: It is not unusual to see a bird standing on one leg or crouched to cover both legs with its feathers to shield them from the cold. Birds can also tuck their bills into their shoulder feathers for protection.
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: Many small birds, including bluebirds, chickadees and titmice, will gather in large flocks at night and crowd together in a small, tight space to share body heat. They can roost in shrubbery or trees, and empty birdhouses are also popular locations to conserve heat. Even individual birds choose roost spots that may have residual heat from the day’s sunlight, such as close to the trunk of a tree or near any dark surface.
Shivering: Birds produce heat during the winter nights and cold storms by shivering, a process called thermogenesis. During this process the birds will shiver to raise their metabolic rate and generate body heat by consuming their fat perseveres. Shivering allows birds to maintain their body temperature up to 8-10 hours depending on the species and their intake of energy from food during the day.
TORPOR: As a last resort to stay warm, songbirds such as Chickadees (and Hummingbirds) will enter a state of unconsciousness or torpor to stay warm during severely cold winter nights. During the torpor state body temperature may drop between 10 to15 degrees, but could be as much as 50 degrees! This can be very dangerous as it leads to reduced reactions and greater vulnerability to predators. In the morning, they will then decrease their periods of inactivity and will start shivering again, increasing body heat and becoming active. There is; however, a high metabolic cost incurred by awakening from torpor that demands immediate payback in energy from food intake.
But that’s also why it is extremely important for winter songbirds to find food early in the morning regardless of weather conditions. If the bird does not find enough food to produce the necessary energy to make it through the night or a severe storm, the bird will die.
DID YOU KNOW?
During the winter, thermogenic capabilities of some birds such as Goldfinches, House Finches and Redpolls are impressive, in many cases better than the ability of mammals. The same species will become hypothermic during a cold front in the springtime, due to the lower feather cover and the low fat preserves.
Helping Keep Birds Warm
Even with all these adaptations to conserve heat and stay warm, many birds still succumb to frigid temperatures and bird mortality can be very high during severe winters. Birders who know how to keep wild birds warm in winter can help their backyard birds have an edge over the cruelest weather.
Feeding birds, especially during the winter months, can be a very rewarding and enjoyable hobby for all. If you provide food in the winter, keeping the feeder full will help the birds as many birds will rely on it as a regular place to eat. Keep the following tips in mind for a successful winter bird feeding season!
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- Clean off feeders, platforms and perches after each snowfall so seed is easily accessible.
- Leave fruit and berries on trees, hedges and bushes to provide a natural source of food throughout the winter.
- Add a heated birdbath to your backyard or place a safe heating element in a regular birdbath to provide birds with liquid water
- Stamp or shovel snow around feeders to provide easier access to spilled seed for ground feeding birds.
- Leave nesting boxes and birdhouses up all year round to provide winter roosting sites. To maximize the number of species that visit your feeders, you'll want to offer a variety of food in several feeders.