This is absolutely normal behavior for a swan. During mating/nesting season, regardless of the presence of a mate, the sex hormones increase. Male swans will build nests and obviously, no eggs are laid. However, the male swans will sit on the nest until the testosterone levels return to normal.

Female swans will build nests and lay eggs, obviously infertile if there is no mate. She will sit on the eggs until she realizes that the eggs are not viable and her hormone levels return to normal.

If you disturb the eggs before the female swan's hormones return to normal, she will just keep laying eggs. This is called double clutching and is detrimental to the female as she loses approximately 30% of her energy reserves. To keep laying, places undue stress on her system and can even result in egg impaction which can be fatal. It is best to let nature take its course and let the female swan either roll the eggs into the water or abandon the nest.

Should the female swan abandon the nest, take the eggs and throw them into the water. This will prevent predators from finding the nest and being attracted to the swan. It will also prevent any messy, smelly explosions of the eggs which will be extremely unpleasant to the nose for several days. By placing in the pond, the eggs will be eaten by predators and smelly messes will be avoided. The Regal Swan