For the most part, it’s the insect-eating birds that migrate
south. Those that stay behind are either seed eaters or insect
eaters that have perfected techniques, which allow them to
extract morsels hidden behind and between the bark of trees, as
do woodpeckers and nuthatches. It’s not difficult to observe
birds preening themselves with their bills and feet to carefully
clean, rearrange and oil their feathers. They do so, in part, to
maintain flight capabilities, but in winter, the process is
essential for heat regulation. Birds have a “preen gland”
located on their rumps just below the upper tail feathers. Oil
squeezed from this gland is rubbed over the body as a
waterproofing agent. Birds have over 25% more feathers in winter
than during the summer months. Growing beneath the large, outer
flight feathers are tiny, tuft-like, down feathers that provide
one of the world’s most effective heat traps. It’s the same
stuff humans have adapted for use in hats, coats and other cold-
weather apparel. When fluffed and