Just an update ....
I never learned why I found a dead goose in the pond. No marks on it, and I haven't observed any predators even with game cameras. Or why a different goose wound up with a missing leg.
All geese are now gone-- I presume they flew to Canada for the summer. Except one lone goose, which stayed behind. It's wandering around and honking as if to say: "where is everyone?"
Finally, a few days ago I noticed a turtle in the pond. First ever. No idea where it came from. Shell from head to tail is about 7" long. (We don't have snapping turtles here.)