Members of the Vintners' and Dyers' Companies use traditional Thames rowing skiffs in their five-day journey up-river to conduct swan upping, the annual census of the swan population on stretches of the Thames. When a brood of cygnets is sighted, a cry of "All up!" is given to signal that the boats should get into position. Image: © Press Association
It's a charming and practical tradition. The Queen's right to ownership of all unmarked mute swans in open water includes their protection and is shared with the Vintners' and Dyers' Companies. She is the Seigneur of the Swans.
The red-coated members of the Vintners and Dyers count all the swans and cygnets, and weigh and measure the cygnets. The Queen's Swan Warden, the Professor of Ornithology at the University of Oxford, gives them health checks. A yearly report is produced so that conservation measures can be reviewed and expanded if necessary.
More photos and details are here, and include a Swan Upping brochure for children.