Ducks are medium sized aquatic birds. They are related to other aquatic birds such as geese and swans, although ducks differ from geese and swans in their tendency to dive.
Ducks can be roughly broken down into two basic categories; there are the surface feeders, which rarely dive for food, and diving ducks, which go under the surface of the water for their food. Due to the duck's diverse ability to feed on both land and in the water, it is one of the most widespread birds in the entire world. Ducks are found on every continent with the exception of Antarctica.