Penguins are feathered birds , but they are, differently feathered. Because they spend so much of their lives in the water, they keep their feathers slicked down and waterproofed. Penguins have a special oil gland, called a preen gland, that produces a steady supply of waterproofing oil. A penguin uses its beak to apply the substance to its feathers regularly. Their oiled feathers help keep them warm in the frigid waters, and also reduce drag when they're swimming. Like other birds, penguins molt old feathers and regrow replacements. But instead of losing some feathers at different times throughout the year, penguins do their molting all at once. This is known as a catastrophic molt . Once each year, the penguin bulks up on fish to prepare for its annual changing of the feathers. Then, over a period of a few weeks, it molts all of its feathers and grows new ones. Because its feathers are so vital to its ability to survive in cold waters, it makes ...