SHEPPERTON, England — Royal officials clad in scarlet outfits took to the River Thames in traditional boats on Monday for the annual "Swan Upping" ceremony, an 800-year-old tradition of counting the swans owned by Britain’s Queen Elizabeth.

Teams in old fashioned skiffs will row up a stretch of the river over the next five days to carry out the annual census of the birds, shouting "all up" when they come across a mute swan and its family.

The swans and their young cygnets are then counted, weighed and checked for injury. "I am pleased to see that the breeding season has begun very well this year with a high level of nesting activity on the river," said David Barber, the queen's Swan Marker.

The ancient ceremony dates back to the 12th century when the English crown first claimed ownership of all mute swans, which have long curved necks, orange beaks and white feathers and were then considered a delicacy that would be served at banquets.

Nowadays, Britons no longer eat swans which are protected by law and the upping ceremony of has become more about wildlife conservation and educating children.

Barber said there were a high number of swans dying or their nests being destroyed as a result of dog attacks, which had led to appeals to dog walkers to keep their pets under control.

The queen shares ownership of mute swans on the Thames with the old trade associations of the Vintners and Dyers who also join in the upping.

However, the monarch retains the right of ownership of all unmarked mute swans swimming in open waters, although this is mainly exercised on certain stretches of the Thames.

The Swan Uppers began their census-taking in Sunbury, west London, and will end at Abingdon Bridge in Oxfordshire to the west of the British capital on Friday. — Reuters