There is no concrete way to tell the difference in genders just by looking, although many individuals state that the male is larger and has a larger knob on his bill. However, these points can be rendered useless based upon a swan's age.

Basically, there are 3 methods to ascertain the gender:

1. Cloacal -This is a good way as long as the swans are older than 1 year of age because the genitals may not be developed.

2. Wait until nesting season and ascertain which swan lays the eggs. However, this is not the best system as female swans can pair and each produce non-fertile eggs.

3. DNA Sequencing- The most reliable of all methods. Feathers or blood samples can be taken and sent to an avian laboratory.

Incubation begins when the last egg is laid. Depending upon species of swan, incubation can last from 30-40 days.