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How do birds cope with winter?

How do birds cope with winter?

-Susan Sharma

The winter season is still going strong in the North of India.  Winter poses several challenges for birds as well, especially when the temperatures dip, and dip some more in the night.

Here are some important ways that "Nature" helps birds to stay warm during the cold winter.  

Many birds must at least triple their normal intake to survive.  Birds have many adaptations to survive the extremes of winter.

Fat treepie

Some birds migrate.

Some adjust their diet habits.

Fat magpie robin
By the time winter arrives, many have doubled their feather count.   

Birds have a unique circulatory system in there legs to help them cope with cold temperatures.  Warm arterial blood from the birds interior, which is on its way to the bird's legs and feet, passes through a network of small passages that runs alongside the cold returning blood veins from the feet.  The network of vessels acts like a radiator and exchanges the heat from the out-going warm arterial blood to the cold venous blood.

Fat parakeet and not so fat mynah
By warming up the old blood, no heat is lost and the feet receive a constant supply of life sustaining blood. Because the blood doesn't warm up a bird's feet and because of the scales (no skin, no sweat or evaporation), birds don't freeze to metal poles or birdbaths.

Fat, is another important winter weather survival adaption.  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% of body weight in fat before it becomes to heavy to fly. 

The smaller he bird, the higher the metabolism (more energy burned).  Birds don't have brown fat, the kind we have. Instead they have white fat. White fat is a high-energy fuel used to power the bird's warming process.

Thermogenesis is a fancy name for shivering.  You can't really see it, but all birds shiver in the cold of winter.  From the largest of birds like eagles and water fowl to the smallest of birds, like hummingbirds.  They all shiver to maintain their core body temperature at about 40 degree centigrade.  That is an amazing high temperature compared to the surrounding air temperatures. Without shivering the bird's body temperature would quickly drop and the bird would become hypothermic.

I have observed kingfishers go into a state of unconsciousness called "torpor" during winter season. Respiration and heart rate will also drop during this period. The bird remains in one position without moving for a long long period. 

(All photographs of birds clicked in the moth of January)
(The details are courtesy Ronald Patterson of http://www.gardening-for-wildlife.com/ )

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