Great Britain is the land of seemingly endless weird and ancient traditions, like racing #link:http://www.otterytarbarrels.co.uk/:flaming barrels of tar# through the streets or the surprisingly dangerous activity of chasing #link:http://www.cheese-rolling.co.uk/index1.htm:wheels of cheese# down hills. But one old British custom also has a nature conservation element: the annual swan census on London's River Thames.

Known as #link:http://www.royal.gov.uk/LatestNewsandDiary/Pressreleases/2015/SwanUpping.aspx:"Swan Upping"#, the event happens in the third week of July and involves catching, marking and releasing mute swans on the river. The annual ceremony dates back to the 12th century when all swans were declared royal property. Back then the birds were a delicacy at banquets and parties, says Buckingham Palace.

Queen Elizabeth II still has a claim to all of the unmarked swans on the UK's open waters - alongside dolphins, whales and sturgeons - thanks to a 1324 law still on the books. But today, the emphasis is on protecting the swan population and not eating it. And while they are no longer a sought-after dish, swans still need protection.

This year the swan uppers, as the census takers are known, have so far found one third fewer cygnets than in 2014. The animals are increasingly falling victim to air guns, which cause "horrific injuries and often death", says the palace. Fishhooks and natural predators, such as foxes, also pose a danger.

During the ceremony, the Queen's Swan Uppers, accompanied by uppers from the companies of Vintners and Dyers - who have also had a claim to the birds since the 15th century - row up the river in skiffs in search of swans. When the uppers, who don large feathers on their sailor hats, come across any, they signal their find by shouting "all up." Then everything has to happen in a matter of minutes - the birds aren't fans of being captured.

The uppers measure and weigh the swans and search for injuries. The Queen's Swan Warden, a Professor in Ornithology at Oxford University's zoology department gives them a health check and rings them with individual identification numbers. Originally, they were marked on the beak - one nick for a Dyers' bird and two for a Vintners'.

Counting swans is a fun job but there's a danger of being toppled into the water, says David Barber, who has led the swan counters since 1993 as the Queen's Swan Marker. "The adults don't bite but they way up to 15 kilos and are very strong," says Barber.

td (dpa)