A swan will not sit on the eggs forever. Once the parents know that the eggs are not viable, they will abandon the nest and will continue about their business. If they are young swans, they may not readily understand this concept and may stay on the eggs a little longer than normal.

Do you know when the last egg was laid? If so, count 40 days. If the swan has been sitting for about 35-45 days, then there is a possibility that the eggs are still viable. Even if you do know the time of the last egg, give the bird approximately 2-3 more weeks to see if anything hatches. If these are new birds and you know for sure that you are in the 50-60 day mark, then you can actually remove the eggs to see if the swan leaves the nest. But, it is better to let the swans do their own thing as they know when the eggs are viable. The Regal Swan