ANSWER: Well, here are a bunch of answers:
1. All birds have feathers and everything with feathers is a bird. ALL fowl are birds but not all birds are fowl. Very rarely, birds are called fowl in general, but not often.
2. Fowl are those birds that belong to two bird groups, waterfowl like ducks and geese and swans and those in the chicken family - chickens, turkeys, quail, peacock, etc.
3. Fowl are those birds that are raised for food - chickens, turkeys, ducks, geese.
Fowls are the birds that belong to two specified groups - waterfowls and swans, whereas a bird is a warm-blooded egg-laying vertebrate animal distinguished by the possession of feathers, wings, a beak, and typically by being able to fly.