Not only is this duckling adorable, but the photograph wonderfully illustrates the waterproof abilities of ducks. Did you know a special gland called the uropygial gland (or the preen gland) is one key physical trait that helps to keep ducks on top of the water? This gland, located at the base of their tail, produces an oil that the ducks spread over their bodies to make their feathers water-repellent. Since duck feathers resist getting saturated with water, the birds weigh less than they would if their feathers absorbed that water. [Source]