We recently added a pair of geese to our flock of Muscovy ducks.
For over a month no problems at all.
However, a couple of nights ago we heard an extremely loud goose honk. The next morning we noticed one of the gander's eyes was closed and swollen. When checking it out and disinfecting it we noticed he lost his eye, but no sign of other injuries.
Since then we monitored the Drake and we indeed noticed that every so often he attacks the geese and the gander pushes him away by lowering his neck and hissing.
My guess is that he lost his eye in a similar situation.
Is this behaviour common? Should we separate the geese from the ducks?
For over a month no problems at all.
However, a couple of nights ago we heard an extremely loud goose honk. The next morning we noticed one of the gander's eyes was closed and swollen. When checking it out and disinfecting it we noticed he lost his eye, but no sign of other injuries.
Since then we monitored the Drake and we indeed noticed that every so often he attacks the geese and the gander pushes him away by lowering his neck and hissing.
My guess is that he lost his eye in a similar situation.
Is this behaviour common? Should we separate the geese from the ducks?
A long time ago I had a RIR rooster and a Muscovy drake that would have periodic fights. One day the drake killed the rooster and one hen and was attacking other hens - I dispatched the drake. I would be tempted to separate them as the gander with only one eye is at a disadvantage. Muscovy drakes when they get something in that little pea brain can be very single minded and tenacious.
I am sorry your gander lost his eye I would def keep them separated as 
