I'm having the same concern with my two geese. One I know is a dewlap brown African, (Bosley), the other looks exactly the same but is much smaller and no dewlap. The smaller one (Faline) is a female for certain as she laid her first egg today.
When they are together (I seperated them as I was scared for her) the larger one tries to mount her, grabbing her neck & being really rough. I'm afraid he's/she's going to break Faline's neck. They're in really close quarters right now as I am trying to get a larger area fenced for them. She has very little room to get away from him and when she does she seems almost frantic to do so. This has been going on for about the last week and a half. (They are both 10 months old - I hatched the larger one and bought the other as a two-day old gosling.)
Is this just typical breeding behavior, or do I possibly have two females & one (Bosley) wants to kill the other?