So how DO birds survive the brutal cold of winter? Here's some info from the Audubon Society:

audubon.org/magazine/ho….

And more from Google:

Birds don't freeze in cold weather primarily because of their feather insulation, which traps a layer of air around their bodies, keeping them warm even in frigid temperatures; they also often fluff up their feathers to create a thicker insulating layer, and some species may even build up fat reserves for additional energy during cold periods.

Key points about how birds stay warm in cold weather:

Feathers:

The primary mechanism for heat retention, acting like a downy blanket by trapping air pockets between feathers.

Fluffing up:

Birds can expand their feathers to create a thicker layer of insulation when it's cold.

Down feathers:

A layer of soft down feathers close to the bird's body provides excellent insulation.

Fat reserves:

Some birds store extra fat during warmer months to use as energy during cold weather.

Shelter seeking:

Birds often roost in sheltered areas like tree cavities or under eaves to minimize heat loss.

Counter-current heat exchange:

In some birds like waterfowl, blood vessels in their legs are arranged in a way that helps maintain core body temperature even when their feet are exposed to cold water.