This is a complex question because it depends on species, age, habitat resources and individual attributes. Typically, all swans excluding Australian Black Swans can produce 1-8 cygnets, however, 1-4 cygnets actually produced is typical. Most cygnets do not survive due to predation (domestic, wild and human), disease and injury.

Australian Black Swans can produce two broods a year with 1-8 cygnets, with 1-4 being the typical number.

Swans will also practice birth control and some years not produce young. This is dependent upon habitat resources. Additionally, each swan (bird) is programmed with the number of eggs that she is to lay during each mating season which equals the number of eggs that she is to produce in a lifetime. So, as you can see, this is a complex question, but in simplistic terms- 1-8 cygnets can be produced at a time. The Regal Swan