Swan upping is the traditional means by which the Mute swans on the Thames are apportioned among three proprietors; this is because ownership of swans on the Thames is shared equally between The Crown, the Vintners’ Company and the Dyers’ Company. [All three are seen surrounding the swans in these pictures - Vintners' red flags; Dyers' blue flags & Royal Insignia]
Its main purposes today are to conduct a census of swans on the Thames and specifically to count and allocate the apportioned ownership of that year’s signets while checking 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 small skiffs. In recent centuries this has been from Sunbury-on-Thames to Abingdon-on-Thames.
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. Those caught by the Dyers and Vintners receive a similar ring of their respective ownership on the other leg.
Originally, rather than being ringed, swans' bills would have been nicked using a metal implement, a practice reflected in the pub ‘The Swan with Two Necks’ in the City of London which is actually connected with the Vintners, being a corruption of "The Swan with Two Nicks".
Dr David Bartle