<P> Swan upping is an annual ceremony in England in which mute swans on the River Thames are rounded up, caught, ringed, and then released . </P> <P> 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 . </P> <P> 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 Queen's, Vintners' and the Dyers' respective swan uppers row up the river in skiffs in recent centuries from Sunbury - on - Thames to mid Oxfordshire . 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". </P>

Who do all the swans in england belong to