Introduce the hay right now as the swans are using so they get used to this normal material introduction. If you wait until spring, you may actually scare them and they may not get back on the island for nesting. Keep a minimum amount of hay on the nest. Once you start observing mating (springtime) then add more hay for nesting. It will be fairly obvious when the swans begin serious mating as they will mate several times during the week and look for nesting material. Other birds may use the island, but if the swans claim the island as their own immediately, they should own the island in the spring fo nesting. Good luck. The Regal Swan