Yes, swans will abandon their nests.There could be various reasons for swans to abandon their nests. However, there are several most logical: eggs were not fertile or were not viable; flooding of the nest due to heavy rains or swans building in an area susceptible to flooding or the presence of human/predator disturbance. Although you may not see the presence of cygnets, there is always the possibility that they did hatch and are on mom's back or very close to bank which is why they may not be readily seen. If you still do not see any cygnets or other activity in the next few days, then the swans have probably left the nest for good. The Regal Swan