In 1997 a survey revealed only 11 bitterns across the UK
One of Britain's rarest birds has been given extra protection at the site of disused clay pits in Cambridgeshire.
Ely Pits and Meadows has been given site of special scientific interest (SSSI) status to protect the bittern.
Natural England says the inland site of old clay pits and wetlands is one of only eight in England to be designated as an SSSI because of its bitterns.
Other wetland and reedbed birds found at the site include bearded tits and marsh harriers.
An inland site is particularly important as many other areas where bitterns live and breed are near coasts under threat from erosion and rising sea levels.
The decision to make Ely Pits and Meadows an SSSI also expands the area of "Kimmeridge clay" deposits that will be preserved.
In the past, the deposits have turned up fossils including dinosaurs, turtles and crocodiles.
Shaun Thomas from Natural England said: "The designation of Ely Pits and Meadows SSSI ensures that the nationally important wildlife and geology of the area will be fully recognised and taken into account in the future management and uses of the site."