Swans are unique animals and in FarmVille. Swans cannot be bought at the market, cannot be received as a gift and cannot be adopted. Instead, swans must be obtained by an Ugly duckling transforming. A swan will take 2 days to grow and will give a farmer swan feathers, worth 80 coins. The total time for it to grow would be 5 days (growing the Ugly Duckling takes 3 days). It is based off the real world swan.
The Swan can be seen as a prize on the Milk Bottle Game.