A Duck is an animal that can be purchased at Marnie's Ranch for 4,000g, after owning a Big Coop.
A Duck will produce a Duck Egg every two days, which can be placed in an Incubator to hatch another duck, or sold for 95g. Once sufficient friendship (Minimum 200, or 1 heart) is reached, they have a chance to produce a Duck Feather, which sells for 125g.
A Duck Egg can be placed in a Mayonnaise Machine to produce Duck Mayonnaise, which sells for 375g.
It is possible to sell the Duck. The amount of gold obtained for doing so is dependent on how many hearts the animal has. The more hearts; the higher amount of gold fetched for selling it. The amount of gold obtained for selling a maximum-heart Duck is 5,200g and for a recently hatched Baby Duck without any heart 1,260g.
In the game, the female, egg-laying ducks have green heads. In actuality, male mallard Mallard ducks have the characteristic green heads. Females are brown. However, domesticated Cayuga ducks have green feathers in both sexes.