Usually, the male will have a larger knob on its bill and will usually be larger in size. Obviously, during mating season, the gender will become readily apparent, but until the swan is at least 1 year old, gender is an educated guess at best. The only way to be a hundred percent sure is through DNA Sequencing, which can be conducted through blood or feather testing. The second (least reliable unless the bird is mature) is to vent check the bird and probe which can be conducted by an experienced veterinarian. We hope this information will be beneficial. The Regal Swan