Yes, is the answer to sensitivity of the eggs as well as abandoning eggs. Swans know when their eggs are fertile and if they are going to hatch. If the eggs are infertile or do not have signs of life, the swans will abandon them. They will also abandon the eggs if cygnets begin to hatch and will take care of the hatched cygnets and not worry about the unhatched eggs. Swans keep their eggs safe by chasing predators or intruders from the nest and sit on the eggs to keep them warm and protected. The Regal Swan