White-tailed deer in its winter coat (photo by Carolyn Lehrke via Flickr Creative Commons license)

20 November 2025

Now that it’s cold we’re all wearing winter coats.

We humans make decisions every day about what layers to put on, but birds and animals changed into their winter coats a couple of months ago.

White-tailed deer have two different coats of hair during the year. The gray winter coat is comprised of longer guard hairs and a soft wooly underfur that provide insulation from the cold. This thicker winter coat is shed prior to the hot summer months. The shorter summer coat is reddish-brown and lacks the thick insulating underfur. The summer coat hairs are short and wiry.

Non-migratory birds molt into fresh new feathers with added insulation in late summer. House sparrows (Passer domesticus) increase their plumage weight by 70% between August and September.  Their typical summer plumage weight is 0.9 grams, winter weight is 1.5 grams, but they won’t look heavier until it’s really cold.

House sparrow in January (photo from Wikimedia Commons)

To stay warm in really cold weather birds fluff out their down to hold warm air near their skin. They look fat but it’s all air.

Female and male cardinal in winter (photo from Wikimedia Commons)

Maybe it’s easier to be a bird.