How long do Swans sit on eggs?

Hi,

 

I have been watching the progress of the pair of Swans on Black Park lake. They built and stared sitting on he nest over 5 weeks ago now. Last week female was off the nest but seemed to be putting week back into it and today she was back on it. What is the usual hatching time for swans eggs? How long do signets stay in the nest beofore they venuture out.

This pair has never produced a brood before and I am worried that they may have failed again this year too. 

Sarah

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