A colony of the birds has lived at Abbotsbury sanctuary since medieval times and keeping track of their numbers has become an annual tradition.
Between 600 and 1,000 flying swans breed, nest and hatch there every year.
They provide feathers for the helmets of the Gentlemen at Arms, the Queen's bodyguard. in addition, Lloyds of London use quills from Abbotsbury swan feathers to register insurance losses in their 'Doom' book.
