Your two swans are hiding from the swans that they were fighting. The dominating swans basically have told your swans that they own the pond. So, for the time being, your swans are hiding and will probably stay there for a couple more days until the coast is clear and they are certain that the other swans are not in the area. If the male swan (yours) lost the fight, he and his mate are hiding to allow him time to heal from the possible beating and as things die down, your swans should return to using their part of the pond.

Additionally, if there is a predator in the area, domestic (dogs, cats) or wild (raccoons, foxes, etc.), then the swans will hide in the taller grass for protection. In any case, this situation should rectify itself shortly and things return to normal. The Regal Swan