Since the cygnets do not have mature sexual organs, probing is not a reliable means to determine gender. The most reliable test is to submit a feather to a reputable veterinary DNA Sequencing laboratory. The cygnet must be identified in some way prior to the testing so that you know which cygnet has been tested. Mini-microchipping or a temporary band may be possible. You will need to check with your local avian/waterfowl veterinarian to see which identification system they would recommend. The Regal Swan