Divers are freshwater waterfowl and they receive their name from their ability to dive underwater. The primary reasons for these waterfowl to dive underwater are food searches and protection from predators. Divers have dense, compact bodies, which assist them in entering the water; other types of waterfowl are too light to submerge themselves. These types of birds also have fusiform body types. Fusiform bodies are wide in the middle, but their size tapers towards the tail. Divers have compact wings, which makes it easier for the birds to dive. However, the wings' structure requires these birds to get a running start when they want to fly.
A dabbler is a waterfowl species that doesn't dive underwater for food. Instead, these birds nibble at food near the water's surface by “dabbling” their heads and bills into the water. Since they don't dive, dabblers don't have the same body structure as divers. The dabblers' body densities aren't as heavy as a diver's body. However, a dabbler's body is broad since the bird's legs are closer to its front than a diver's legs. Dabblers also have broader wings than divers. As a result, dabblers don't need a running start to fly.
The largest aquatic bird in the world is the swan; these birds grow up to 60 inches long. Some swan specimens have longer necks than they do bodies. Swans are dabbler ducks. The trumpeter swan, mute swan and tundra swan are some of the swan's species. Other broad-bodied dabblers are geese, muscovy ducks and pelicans. Pelicans also live in marine environments. Among the broad-bodied diving ducks are canvasbacks, pochards, scaups, ring-necked ducks and marbled ducks. The largest freshwater diving duck in the United States is the canvasback, which has a length of 21 inches and a wingspan of approximately 35 inches.
One sea duck species, the common eider, is larger than other marine-dwelling birds. Sea ducks is the term applied to waterfowl living in saltwater environments, such as oceans, estuaries, bays and seas. The common eider and its relatives--king eider, spectacled eider and Steller's eider, grow to approximately two feet long. These birds are similar to diving birds as they dive underwater for food. As a result, eiders require heavy body densities to submerge their bodies. Other broad-bodied sea ducks are scoters, mergansers and goldeneyes.