From Toadwater Guide
A bird that lives in a birdhouse on a Black tupelo tree. Once in your inventory (see Birds) you are immediately transported to South Winter Island. To be transported back immediately to its home birdhouse, select the duck then do anything with it (like selecting a square next to yourself) -- the exception to this is a wood duck will not fly you back home when you are in the mines as it is too scared to fly when it cannot see where it is going.
If the duck is not used within an hour, it will automatically transport you back to its home birdhouse (and it will fly back to its home birdhouse if it has at least one more use). Mousing over a duck in inventory will show the time remaining before this happens.
Whenever a duck transports you back to its home birdhouse, it will also fly out of your inventory (and back to its home birdhouse if it has at least one more use).