Mallards have been feeding and sunning themselves all day on the pond, even though we had a few snow squalls.  They must be getting ready to head south for the winter.  At dusk, the muskrat came out to gather a meal.  Seeing the ducks, he swam towards them again and again, trying to chase them away.  Defending his territory, or maybe since it is autumn he does not want to share the dwindling green plant material left to eat in the pond?