How feathers insulate

[Donna]

A single Canada Goose has between 20 and 25 thousand feathers.    Some are designed to help the bird fly or shed water. Many are the short, fluffy kind, the down that insulates the bird from the cold. Birds survive in sub-zero weather by fluffing their feathers, creating layers of air and feathers. Just a fraction of an inch of this insulation can keep a bird's body temperature at 104 degrees, even in freezing weather.    too hot for me!

[MAK]

Me too! 

[BIGFRANK]

Peregrines have 20000 feathers too. The bands put on them only weighs what one feather does,so 20001 doesnt inhibit them.
Birds also pump blood faster and different to the legs and feet,so its warmer.