Predator Identification

We have a free range flock of buffs and khakis on a 1 acre pond. Recently we had a predator attack. In one night we had two ducks mortally injured and one duck killed and defeathered. The mortally injured ducks were able to get away from the attackers but died from their wounds. Here is the real kicker. The duck that was caught and killed was sitting on a nest on a small island. It is pretty dense and she certainly got cornered. Can anyone think of anything besides a dog that would chase down three ducks and cross 10 feet of open water?

 

While I couldn't absolutely rule out a fox or raccoon, neither of them like to swim. Raccoons are regular visitors and have never caused a problem.

We cannot fence the pond. We have had ducks for a long time and you have a loss occasionally. This was different.

My first thought is coyote. This pond is not up against the woods. What ever it was had to cross an open grass field and would have been very exposed at the cleared and mowed pond edges.