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 British subject by the Crown (accordingly they may also be claimed by prescription). Until the 16th century, the ownership of swans in a given body of water was commonly granted to landowners. The only bodies who still exercise such rights are two livery companies of the City of London, the Worshipful Company of Vintners and the Worshipful Company of Dyers, who thus share equally with the Crown in the number of swans in the Thames that they own. The tradition of swan upping on the Thames began in the 12th century.
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 in the third week of July. Over five days, the Crown's, the Vintners' and the Dyers' respective 'swan uppers' row up the river in skiffs (in recent centuries from Sunbury to Abingdon).
The Crown's swans are recorded by the Marker of the Swans, who is rowed in a skiff by oarsmen from the Company of Watermen and Lightermen. The Crown's swan uppers, who wear distinctive red uniforms, catch the swans, weigh and measure the cygnets, and check them for injuries.
Cygnets are determined to belong to the Crown, the Dyers or the Vintners based on their parentage. Swans belonging to the Crown are left unmarked, except for a lightweight ring linked to the database of the British Trust for Ornithology. Those belonging to the Dyers and Vintners receive a similar ring on the other leg. The rings have replaced nicks on the swans' bills, which used to be made with a metal implement, one nick for the Dyers and one on each side for the Vintners. The former practice is reflected in the The Swan with Two Necks, the name of a former pub in the City connected with the Vintners, which was a corruption of "The Swan with Two Nicks".
"Swan Upping on the Thames", from Henry Robert Robertson's Life on the Upper Thames, (1875)
A Queen's swan upper with a mute swan during 2010 swan upping at Henley-on-Thames
Swan marker of the Worshipful Company of Vintners, in his blue uniform, during 2011 swan upping, Abingdon.
Swan Upping at Cookham, by Stanley Spencer, oil on canvas, 1915–19
- The Case of Swans (1592) 7 Co. Rep. 15b
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- Wheals, Brian Brenchley (1984). Theirs Were But Human Hearts: A Local History of Three Thameside Parishes. H.S. Publishing. p. 65. ISBN 0-9509053-0-5.
- The Queen's Swan Marker (2018), Royal Swan Upping, Trinityweb Ltd
- "A Day with the Uppers". Hear the Boat Sing. 22 July 2011.
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- Singh, Anita (16 May 2020). "Royal tradition of swan upping cancelled this year due to coronavirus". The Telegraph.
- Norman Frederic Ticehurst, The Mute Swan in England: Its History, and the Ancient Custom of Swan Keeping (1957).