If the park staff or a predator removed the eggs, this would cause the swans to know that something is amiss and then they will either abandon the nest entirely or try to replenish the nest by laying more eggs. This is called double clutching which is extremely detrimental to the health of the female swan.

If the eggs are still in the nest, the birds will continue sitting until they ensure that none of the eggs are viable. Once they realize this, they will stop sitting.

If the parents are going out onto the pond for brief periods to bathe, mate and eat, then they will cover the eggs so that predators cannot find the eggs. Usually, this behavior becomes less and less frequent by the female as the eggs approach hatching. Then, the female leaves the nest for less visits to the pond and for shorter periods of time. The Regal Swan