I work near a small lake that has had two swans living on it for at least seven years. The other day a third swan appeared(intruder). It immediatley started bullying and harassing one of the resident swans. (which I presumed was the male). The harrassment continued well into the night and at times the resident male went up onto the bank to get away. Eventually, the next day, the resident male was on the bank permanently and made no further attempt to get into the water. The resident female would swim up to the swan on the bank but never made any attempt to join it. From time to time the intruder would leave the water to threaten and drive the resident swan away. The resident swan was obviously exhausted and vulnerable. The RSPCA were contacted and they came out and took the exhausted, possibly injured, swan away. My questions are: Is my assumptions the most likely interpretation of what happened? I thought swans paired off for life. Why didn't the resident pair turn on the intruder, as a team, and drive him off? What will happen to the usurped swan, will it be re-located somewhere else?