We have a fairly large pond in the backyard. There is a female duck that is ALWAYS alone. She practically lives in this surrounding area. She swims and quack. Sometimes makes a few splashes. She goes bottom up sometimes, and I imagine she's eating things that live in the water. Its really sad though, because she's never with other ducks. Last year, there was a pair of ducks (couple) in the pond, but this year its only a female. What could be wrong?