Anatidae belong to the order Anseriformes.
Ducks have long, broad bodies.
Their legs are set far back on their bodies. This arrangement causes them to waddle when they walk on land.
The necks of ducks are long relative to many other birds, but shorter than the necks of geese or swans.
A duck's wings are usually short and pointed. The wings are very powerful.
Many species of duck lose the ability to fly when they are molting (losing old feathers and replacing them with new ones - an event that takes place periodically).
Ducks often molt just before they migrate. Some species of duck undergo long migrations.
During breeding season, male ducks are often more brightly colored than females of the same species.
Sexual dimorphism is the condition in which males and females of the same species share physical differences other than differences in their sexual organs.
Outside of breeding season, the plumage of male ducks becomes duller and more closely resembles the plumage of females.
When male birds develop duller coloring outside of breeding season, so that they look like females, the males are said to be wearing eclipse plumage.
A duck's diet can include grass, water plants, insects, worms, fish, frogs and small mollusks.
Ducks have broad, flat beaks, or bills.
They can use their bills to tear up grasses and to dredge worms and small mollusks out of mud.
Ducks have comb-like structure on the sides of their bills, which they use to strain water while food remains trapped inside and to preen (groom) themselves.
A duck's bill, like the bills of other anseriformes, contains plates known as lamellae. Ducks use these lamellae to filter food particles from the water.
Ducks are usually monogamous.
Humans often hunt wild ducks for food or for sport.
Many duck species have been domesticated for their meat, their eggs and their feathers.
The down of ducks is particularly valuable.
Down is a layer of fine feathers that lies under the outer feathers of birds. It can provides excellent insulation.
When birds are very young, they are covered in down. They grow feathers as they get older.
Ducks were first domesticated thousands of years ago.
Some people keep ducks as pets.
A female duck is called a hen. A male duck is a drake. Young ducks are known as ducklings.
Some species of duck obtain food on land, or on or just below the water's surface. These species are known as dabbling ducks.
Dabbling ducks may feed in the water either by surface dipping or by upending.
With surface dipping, a duck immerses only its head and neck under water. When it upends, the duck immerses the entire front half of its body in the water, sticking its hind parts in the air.
Dabbling ducks may also graze for food on land. They walk and run on land very easily.
Usually dabbling ducks can be found in shallow marshes and rivers.
The mallard is an example of a dabbling duck.
Other species, known as diving ducks, dive underwater to get food.
Some ducks can dive more than 50 feet below the surface of the water.
Diving ducks will swim underwater for long distances in order to escape danger.
They walk more awkwardly on land than dabbling ducks.
Diving ducks can be found in relatively deep, large rivers and lakes, and in inlets and bays along coasts.
Those that live along marine coasts are known as sea ducks.
Eiders are diving ducks.
A small number of diving duck species eat large fish, which they catch under water. These species are known as fish-eating ducks, or mergansers.
Some mergansers have serrated bills. Therefore, they are sometimes called sawbills.
Shelducks, which belong to the genus Tadorna, are considered ducks, but they share characteristics of both ducks and geese.
They are large for ducks, about 1 ½ to 2 feet long, with long legs.
Shelducks live in the eastern hemisphere.
They eat plants, including grasses, and small invertebrates that live along shores and banks.
Shelducks are similar to sheldgeese. They are smaller than sheldgeese.
There are six known living species of shelduck:
A seventh species, the crested shelduck (Tadorna cristata), sometimes called the Korean crested shelduck, may be extinct. There hasn’t been a confirmed sighting of a crested shelduck since 1964.