Penguins are flightless seabirds that get around by swimming and diving, waddling around on land, and, sometimes, slipping and sliding on their bellies. Scientists have identified more than a dozen penguin species, and each one has an outer layer of waterproof feathers, webbed feet, and flippers for swimming. Penguins frequently preen (groom) and spread an oil-like substance on their feathers, which helps keep their bodies dry and insulated against water and wind.