Duck is the common name for a number of species in the Anatidae family of birds. The ducks are divided between several subfamilies listed in full in the Anatidae article. Ducks are mostly aquatic birds, mostly smaller than their relatives the swans and geese, and may be found in both fresh water and sea water. Most ducks have a wide flat beak adapted for dredging. They exploit a variety of food sources such as grasses, grains and aquatic plants, fish, and insects. Some (the diving ducks) forage deep underwater; the others (the dabbling ducks feed from the surface of water or on land. Dabbling ducks have special plates called lamellae that are similar to a whale's baleen. These tiny rows of plates along the inside of the bill allow them to filter water out of the side of their bills and keep the food inside. To be able to submerge easier, the diving ducks are heavier for size than dabbling ducks, and therefore have more difficulty taking off to fly. A few specialized species (the goosander and the mergansers) are adapted to catch large fish.