Birds Fluffing Feathers in Cold
Why do birds fluff their feathers when they are cold?
The most obvious reason might be to allow their feathers to keep them warmer than otherwise by
trapping more air as an insulator...but...this is a guess on my part and nature has a way of
sometimes hiding secrets behind the obvious.
Fluffing their feathers makes the layer of still air trapped between their feathers thicker.
That makes it a better insulator, more able to keep their body heat inside.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
The protein material of which feathers are made allow heat to be transferred by conduction and,
as such, it is not quite as good as an insulator as is air. When the bird fluffs it feathers, it
loosens them so as to trap air between the fibrils. The combination of trapped air and feathers
is a much better insulator that feathers alone.
As you may already know, wet feathers stick together very tenaciously. That is why down-filled
garments and blankets must be thoroughly dried and tumbled after washing in order to loosen the
feathers and restore the "loft" of the insulating material.
Bird feathers work as insulation by trapping small pockets of air that are separated from the
outside and warmed by the bird's body heat from within. The more they are fluffed out the more
air they trap. That is why a down sleeping bag is rated by "loft" the amount of air that is
trapped within the down feathers in the bag, the higher the loft, the more air, and greater
Birds fluffing create tiny air pockets between their feathers. Air is a really great
insulator. So they are simply insulating themselves against the cold. Ever sleep under a
down comforter? Very light, very fluffy, very warm. Same theory.
Click here to return to the General Topics Archives
Update: June 2012