Birds and Winter Survival
by Stan Tekiela
December 12, 2003
Photo by Stan Tekiela©
Peering into the steel blue stillness of a mid-winter
evening, I am struck by the profound coldness. When the temperatures plummet to
near zero my mind turns to the amazing ways that animals and birds cope with such
Winter poses several challenges to birds and animals. Scarce food supplies and
limited water are just a few obvious challenges to winter survival. Extremely cold
temperatures, strong winds, driving snow and nights that seem to go on forever can
be deadly for birds. Each winter we loose many of our feathered friends to the
rigors of winter. Itís how nature works-- the survival of the fittest.
Birds have many adaptations to survive winter weather. Wintering birds such as
the American Goldfinch and Black-capped Chickadee add additional feathers in preparation
for winter. The typical goldfinch or chickadee is coved with about 1,000 feathers during
summer and over 2,000 in winter. During very cold days, and nights, birds fluff up their
feathers, reducing the amount of heat loss by up to 30 percent. However, extra feathers
alone are not enough to make it through a winter night.
Birds have a unique 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 birdís 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 birdís feet
receive a constant supply of life sustaining blood. Thatís also why ducks can swim in freezing
water and not get cold.
Fat is another important winter weather survival adaptation. Fat acts as an insulator in
addition to an energy reserve. During the day, birds eat to build up fat reserves. On average
a bird can put on up to 15 to 20 percent of its body weight in extra fat before it has troubles
Birds donít have brown fat, the kind you and I have. Instead they have white fat. White fat
is a high-energy fuel used to power the birds warming process, which is called thermogenisous.
Thermogenosis is just a fancy name for the act of shivering. All birds from crows to chickadees
continually shiver during cold weather to maintain their core body temperature at about 106 to
109 degrees F, depending upon the species. That is an amazing high temperature when compared
to the surrounding air temperature. Only a thin layer of feathers separates what could be a
temperature difference of over a hundred degrees from the inside of a bird to the air temperature.
Shivering produces heat five times their normal basal rate and can maintain a normal body
temperature for six to eight hours at temperatures minus 70 degrees Fahrenheit. Without shivering
the birds body temperature would quickly drop and the bird would become hypothermic.
At night, birds such as chickadees take shivering or I should say the lack of shivering one step
further. To conserve heat, chickadees can lower their body temperature by interrupting their
shivering. These periods of inactivity allow the birdís body temperature to slowly cool, until
it drops about 10 to 12 degrees. At this point the bird enters a state of unconsciousness called
torpor. Respiration and heart rate will also drop during the period of torpor.
Nearing morning the periods of inactivity decrease until the bird is constantly shivering
again and the body temperature is back in the normal range and the bird regains consciousness.
The result of this controlled hypothermia is an energy savings of up to 20 percent during a
typical winter night. Energy conservation is very important when you consider how little fat
a bird can store.
Based on a daily increase of body fat of (15%) a typical chickadee has about 16 to 24 hours
of energy reserves to carry it through a winter night. That is why it is imperative that a bird
gets out early in the morning and finds food regardless of the weather. If it doesnít replenish
its fat reserves during the day, the bird will not have enough energy to make it through the
You could help our bird friends survive another cold winter simply by filling your feeder
with some black oil sunflowers and filling up your suet feeders.
Until next time...
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