Yes, swans will abandon their eggs, especially if a predator (domestic or wild) disturbed the nest. More than likely, a predator chased the parents from the nest or raided the nest while the swans were out foraging for food. Until the last egg is laid, incubation does not take place, so the swans will leave the eggs unattended, covered by vegetation to protect from the elements and hopefully, predators, but this does not always work.

The bad news is that the predator could have been a human, primarily children who disturb the nest by playing or displacing the eggs.

If there is something wrong with the eggs, infertile or rotting, the swans will roll them into the water to prevent a predator from smelling the rotten egg and following the scent back to the nest. Also, bad swan eggs will result in a nasty explosion that will contaminate the nest. If a cygnet should die in the nest or die while hatching, the swans will carry the carcass out into the water and dispose of the carcass in the same manner as a bad egg. Hopefully, the adults were just displaced and are trying to find another area to safely nest because nesting near a fence and heavy human traffic is not a suitable nesting habitat. The Regal Swan