According to Wikipedia, "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). 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 in the third week of July ... Swans caught by the Queen's swan uppers under the direction of the Swan Marker are left unmarked, except for a lightweight ring linked to the database of the British Trust for Ornithology (BTO). Those caught by the Dyers and Vintners receive a similar ring on the other leg. Originally, rather than being ringed, swans' bills would be nicked using a metal implement, a practice reflected in the pub name The Swan with Two Necks in the City connected with the Vintners, a corruption of 'The Swan with Two Nicks'".
© Haydn Thompson 2022