The inclement weather has had a significant impact on winter migratory paths for many species of birds, blowing them in areas that they normally would not visit. In the case of the swans, they may know that this is their spring nesting area, but because of the cold weather, ice and snow, the food resources may be very limited due to frozen waterways. The only way they can find food is to circle and find an open waterway. If they are trying to return to a familiar area which is frozen, they will also fly to another area to spend the night so they are protected from predators which can access the birds on ice. The swans will then frequently fly back and forth looking for open waterways to reside. This is probably the behavior you are witnessing. Once the waterways thaw, the swans will return to their normal habitat. The Regal Swan