You will need to have an experienced avian (bird or waterfowl) veterinarian sex the swan by using a procedure known as probing. If the cygnet is not old enough to have the genitalia developed, this procedure may not be reliable. The most reliable method is to submit a feather or blood sample to a licensed veterinary laboratory which can determine the gender through DNA Sequencing which is the most reliable method of sexing.

Finally, if the older swans are not allowing the cygnet to enter or exit the water, you need to find a good home for the cygnet as this stress can kill the bird by causing starvation, illness, temperature stress (heat or cold), and other problems from being constantly chased and not allowed to eat, bathe, preen, etc. This is not a situation in which you want to introduce another swan as this may cause the new and old swans to be severely injured or killed during ensuing fights. The Regal Swan