During nesting season, female swans, due to sex hormone levels, can lay eggs although obviously infertile. So, the female swan may have laid eggs and then when nothing was viable, left the nest. Female birds are programmed with the number of eggs they will lay during the course of their lives and how many they will lay per nesting season. Therefore, female swans will nest and can lay eggs regardless of the presence of a male swan.

Conversely, male swans due to sex hormones, will build nests and sit on the nests for several weeks until the hormone levels return to normal levels regardless of the presence of a female swan. The Regal Swan
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