As winter weather sets in all throughout eastern Ontario, backyard birdwatchers may peer outside and see little “fluffballs” resting on branches. You’re bearing witness to one of their cold-weather survival strategies. Underneath a bird’s contour adornment lay plumulaceous down feathers. These down feathers are excellent at trapping warm air mass. Birds “puff” their contour and down feathers up, creating a self-contained heat island; the feathers are used to trap the bird’s body heat. Amazingly, it has been shown that a mere half-inch of feathers (on a Black-capped Chickadee for this example) can result in a difference of 50 degrees Celsius between the bird’s bare skin and the outer surface of its feathers!