WINDSOR, England, July 20 (Reuters) - Royal officials took to the River Thames on Tuesday to count the swans that belong to Britain"s Queen Elizabeth at the start of the "Swan Upping" ceremony which dates back to the 12th Century. Teams in traditional skiffs rowed up a stretch of the river to begin the annual census of the birds that was postponed in 2020 because of the coronavirus pandemic. "Swans were a very, very important food, and they were served up at banquets and feasts," David Barber, the queen"s Swan Marker, said. "Of course today swan upping is all about conservation and education." Officials return the swans to the Thanes River during the annual census of the Queen"s swans, known as "Swan Upping", in Maidenhead, near London, Britain, July 20, 2021. REUTERS/Peter Nicholls Queen"s Swan Marker David Barber prepares a swan for its release back to the river during the annual census of the Queen"s swans, known as "Swan Upping", along the River Thames near London, Britain, July 20, 2021. REUTERS/Peter Nicholls A swan is released during the annual census of the Queen"s swans, known as "Swan Upping", along the River Thames near London, Britain, July 20, 2021. REUTERS/Peter Nicholls 1/8 Queen"s Swan Marker David Barber prepares a swan for its release back to the river during the annual census of the Queen"s swans, known as "Swan Upping", along the River Thames near London, Britain, July 20, 2021. REUTERS/Peter Nicholls The ceremony dates back 800 years to when the English crown first claimed ownership of all mute swans, which have long curved necks, orange beaks and white feathers. Barber and his team lift up the swans - which can weigh as much as 15 kg - to check for any injuries, typically caused by fishing tackle. Young cygnets are taken ashore to be weighed and measured. Barber said there had been more shootings of birds, often with air rifles, and more water pollution than in previous years. "The shootings, I think, really is because youngsters can go into a shop and buy an air rifle, they go down to the river, they see a big white target, bang. And it"s appalling," he said.