Queen's swans 'killed by floods, disease and yobs' The number of vandal attacks has continued to increase over the past year. Shootings with air rifles and catapults cause horrific injuries, unnecessary suffering and slow deaths. Mr Barber also noted that the swan population on the Thames suffered from a severe attack of the disease duck virus enteritis in early 2011. This resulted in an "extremely disappointing" reduction of 20% in the number of cygnets counted during last year's Swan Upping. This year's Swan Upping ceremony will start at Sunbury, Surrey, on July 16 and end at Abingdon, Oxfordshire, on July 20. The annual ritual used to be a way of providing food for the Royal dinner table, with some cygnets taken away to be fattened, but today the event is about conservation rather than consumption. A team of boatmen called Swan Uppers have the job of corralling, catching and marking the swans on the water. When a brood of cygnets is sighted, a cry of "All up" is given to signal that the boats should get into position. The swans, usually two parent birds and three cygnets, are then weighed, ringed and checked for signs of disease or injury. The ceremony dates back to the 12th century, when the ownership of all unmarked mute swans in open water in Britain was claimed by the Crown in order to ensure a ready supply for feasts. Today the Queen exercises this right only on certain stretches of the River Thames and surrounding tributaries. The ownership is shared with the Worshipful Company of Vintners and the Worshipful Company of Dyers, who were granted rights of ownership by the Crown in the 15th century. Mr Barber said his team would get more schoolchildren involved in Swan Upping this year as part of the celebrations of the Queen's Diamond Jubilee.