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Q: Why do birds have down?

January 3, 2019

Birds are very well insulated. They have fluffy down feathers to trap body heat in when it is cold. One has just got to think about the warmth of a real down jacket or sleeping bag. But what happens to birds when it is hot? Last Christmas Day was very hot and the birds around the birdbath (pictured) were behaving in some peculiar ways.

Animals like humans have sweat glands in the skin. These glands produce moisture on the skin surface which evaporates, producing an evaporative cooling effect. Birds however do not have sweat glands and resort to a number of other methods to stay cool.

When it is hot birds, like dogs (which only have sweat glands in select parts of the body e.g. nose & feet), cool themselves by panting. An open mouth combined with an increase in the breathing frequency allows evaporative cooling to take place on the moist surfaces of the lungs and air sacs. The more rapid the breathing rate the greater the heat transfer. Through this process heat is lost from the body but so is moisture. Birds need to drink need to replace this moisture. Pictured above left is a Common Blackbird (Turdus merula) in a typical panting stance.

Birds can also shed heat by spreading their wings and promoting airflow in less feathered parts of their bodies such as this Willie Wagtail (Rhipidura leucophrys) pictured right . Anybody who has owned chickens will be familiar with this pose in hot weather.

And internally birds can control heat by redirecting blood flow away from areas such as the gut which produces metabolic heat (stopping eating has the same effect) to areas where heat transfer to the surrounding air is easier e.g legs or combs in the case of chickens.

So the answer to the question posed in the title…

A: So they don’t fly too high…obviously.

One Comment leave one →
  1. Chris Cobern permalink
    January 3, 2019 7:47 am

    How do you get down from an elephant?
    You don’t, you get down from a duck.

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