I have a four year old pair of trumpeter swans. Last year the male began to show aggression towards the female in the spring. This year this began to happen again but now the female refuses to go near the water. Because she will not go near the food and her attempts to get through the fencing is hard to bear, I have removed her from the pond. Is there such a thing as a pair of swans that will not bond? What can be done at this point?