Copenhagen - The remains of what is believed to have been the world's oldest mute swan have been found in Denmark, researchers at Copenhagen University said Friday.

The dead ringed bird was discovered on December 25 near the town of Korsor on the island of Zealand by swan expert Pelle Andersen- Harild.

The leg ring was sent to the Copenhagen Bird Ringing Centre at the Zoological Museum at Copenhagen University where records suggested that the swan had been ringed on February 21, 1970, at Heikendorf near Kiel in northern Germany.

At the time of the ringing, the swan was estimated to have been at least a year and a half old, suggesting it was 40 years old at the time of death - a new longevity record for Denmark's national bird.

The previous known record, was 28 years for the species.

Denmark, home to story-teller Hans Christian Andersen who penned the fairy tale The Ugly Duckling, lays claim as the first country where birds were systematically ringed.

Hans Christian C Mortensen, a head teacher in Viborg, thought up the idea in 1899. (dpa)