Birds have a number of ways to beat the cold, but none so important as their feathers. You may have noticed how on a very cold day the birds at your feeder seem rounder and more puffed-up than usual. This is a way of keeping warm by raising the feathers to create pockets of warm air and enhance insulation. In addition, many species change their plumage, molting into a fresh thick set of feathers prior to the colder months.
Especially helpful are the very fluffy and soft body feathers known as down. These feathers provide super insulation, much like the goose down we use in coats and comforters.
At night, birds can dramatically slow down their body's metabolic rate (the rate at which the body consumes energy) and lower their body temperature to conserve energy. During very cold nights, small birds such as chickadees and nuthatches may find a tree cavity or birdhouse where they can spend the night, huddled together with several other birds of the same species. Such communal roosting permits the birds to share body heat. There have been reports of as many as 20 pygmy nuthatches sharing a single tree cavity. Ducks can swim in water that is almost frozen because their feathers have natural oils and are waterproof. Waterproof feathers retain all of their insulating ability. Ducks have a netlike system of blood vessels in their legs that brings warm blood from the heart alongside cold blood returning from the feet, keeping the feet warm in icy water.
What do birds do when it's windy?
When it comes to wind, birds have many coping behaviors. They face the wind so moving air does not ruffle their feathers, thereby robbing them of the insulating heat layer between feathers and skin. They stay low to the ground, where the wind speed is lower, and in the lee of any objects that can deflect the wind: tree trunks, power poles, fenceposts, shrubs, grass clumps, buildings. Birds also move as little as possible, thus conserving energy. Because they keep to dense cover, birding in high winds may be a bird-free proposition.
Anything I can do to help?
We all know by now that birds can survive without our help in the winter. Some ornithologists have even suggested that bird feeding is more beneficial to us (humans) than it is to the birds. Be that as it may, studies have shown that birds with access to bird feeders in winter survive at a higher rate than birds without access to feeders. The difference between the haves and the have-nots is not huge, but it's there. Feeding birds in winter, if done right, is a good thing for the birds (and for us, too).