By prerogative right, the British Crown enjoys ownership of all unmarked mute swans in open water. Rights over swans may, however, be granted to a subject by the Crown (accordingly they may also be claimed by prescription.) The ownership of swans in a given body of water was commonly granted to landowners up to the 16th century. The only bodies still to exercise such rights are two livery companies of the City of London. Thus the ownership of swans in the Thames is shared equally among the Crown, the Vintners' Company and the Dyers' Company.
Swan upping is the traditional means by which the swans on the Thames are apportioned among the three proprietors. Its main practical purposes today are to conduct a census of swans and check their health. It occurs annually during the third week of July. Over five days, the Queen's, Vintners' and the Dyers' respective swan uppers row up the river in skiffs. Swans caught by the Queen's swan uppers under the direction of the Swan Marker are left unmarked, except for a ring linked to the database of the British Trust for Ornithology (BTO). Those caught by the Dyers and Vintners are identified as theirs by means of a further ring on the other leg. Originally, rather than being ringed, the swans would be marked on the bill, a practice reflected in the pub name The Swan with Two Necks, a corruption of "The Swan with Two Nicks".
On 20 July 2009, Queen Elizabeth II, as "Seigneur of the Swans," attended the Swan Upping ceremony for the first time in her reign. This was the first time that the monarch had personally watched the ceremony in centuries.
A Queen's swan upper with a mute swan during 2010 swan upping at Henley-on-Thames
Swan Upping at Cookham, by Stanley Spencer, oil on canvas, 1915-19
- Norman Frederic Ticehurst, The Mute Swan in England: Its History, and the Ancient Custom of Swan Keeping (1957).
Media related to Swan Upping at Wikimedia Commons