Staff hope that Dario and Dorcus will arrive soon
Experts who thought the life partner of a swan at a nature reserve in Gloucestershire had died have realised they identified the wrong bird.
Staff at the Wildfowl and Wetlands Trust in Slimbridge thought that a Bewick swan had lost his partner.
Dario's mate Dorcus could not be traced but staff now realise they had mixed up Dario with another male swan - Tournai.
A spokesperson said: "This is great news as there is still hope that the pair will soon arrive together."
Tournai first came to Slimbridge in 2003 and has not yet found a mate.
Staff took a closer look at the swan they thought to be Dario and discovered their mistake.
Julia Newth, a wildlife research officer at Slimbridge, said: "After having a closer look at the swan we suspected as being Dario, I can confirm that it is actually a bird named Tournai.
"Tournai has been feeding right outside of the Peng Observatory, so I have managed to get a really close look.
"Their bill patterns are very similar so I was very surprised to see Tournai swimming about Swan Lake."
The swans arrived at Slimbridge later than usual this year due to warmer weather from the Arctic which delayed their annual migration journey from Russia to the UK.