The census — it takes five days — is operated by the Swan Marker and the Swan Uppers of two of the ancient trade guilds of London, the Vintners’ and Dyers’ livery companies. The census is said to date from the twelfth century, at a time when the sovereign claimed ownership of all swans (they were valuable birds that were served up at banquets and feasts).Photo credit.
These days, royal ownership is claimed only on the Thames and some tributaries and — you may be pleased to learn — the Queen doesn’t actually eat any of her swans. The birds used to be tagged by nicks on their beaks — which is why the Swan Marker has that name — but these days are ringed on their legs.
Two nicks put on a swan’s bill at the time of swan-upping signified that it was owned by the Vintners, hence the connection with pubs. The link has often puzzled people. Down the centuries several such pubs changed their names to Swan With Two Necks, in the toponymic equivalent of popular etymology.