When the cold fronts start moving through the South, the birdwatching web sites light up with posts from many new birders along the lines of: “Bless their hearts, are my poor little babies going to freeze to death?”
The answers back are along the lines of: One way birds stay warm is by using their feathers to trap pockets of air around their bodies. A highly water resistant and efficient insulation.
A key to the efficiency is maintaining these layers of air by having clean, dry and flexible feathers. The cleaning process – preening – depends on the species of bird. There are a wide variety of methods. Most songbirds, use their bills and feet to preen each feather on their body. They methodically nibble or stroke each feather from base to tip to get it properly aligned. Many spread a preening ‘oil’ from their uropygial gland. Bird photographers are familiar with the contortions birds will use in order to reach every feather. These unusual and odd positions make for fun (and sometimes funny) shots of routine daily behaviors.
But regardless of the weatherproofing method, the result is a water resistant top layer and a toasty warm inner layer.
I do not know for a fact, but I do suspect, that the popular puffer jacket is a case of biomicry of this highly successful natural design.
A few examples from our yard in Decatur GA, deep inside metro-Atlanta, this January.