This bluebird in our front yard today was so puffily fluffed it looked like a downy chick.
Maybe a downy penguin chick.
How Birds Survive the Cold: Feathers + Food = Warmth (five step survival guide from All About Birds)
3. When you can’t eat more, get puffy and rest
Your fluffy down feathers help complete the food + feathers = warmth equation. With food in your belly, you can use your metabolism to generate heat. Feathers, in addition to keeping cold air away from your skin, do a great job of trapping body heat instead of letting it dissipate.
After dining all morning on my homemade suet dough, five of these little fatlings were roosting in our front yard trees around noon in sunshine.