For those who have wondered about birds in the cold, overheard on NPR: Their feather layers are adjustable. They can be raised or lowered to create more or less of a heat-layer around them. They can also be turned to different angles to release heat like louvers.
This tender feature of Divine design cares for all creatures. One day it will be like this for human beings as well who will be able to work with their individual energy fields in order, like birds, to adapt them to particular situations.