This marsh heron (Botaurus stellaris) went extinct in the UK by the end of the 19th century and was not breeding there between 1870 and 1911 when the first breeding male was recorded. Bitterns reached a peak population in the 90's with around 80 breeding males before decline set in due to marshland loss. A concerted conservation effort began to prevent the bittern from a second extinction in the UK. RSPB video here.
Conservation has been a success with 150 breeding males heard in England and Wales. Researchers count bitterns by the male's booming, foghorn-like call [audio]. Breeders prefers large areas of marsh that became scarce in Great Britian two decades ago. Efforts to save marsh habitat were funded by the Royal Society for Preservation of Birds and the EU. One of the wetland sites restored is near Lakenheath, Suffolk. It was a carrot field in 1995 before being converted to marsh. Bitterns began booming there in 2006. Six breeding males are now recorded on the new marsh. Somerset county is the top destination for breeding bitterns with over 40 boomers, but East Anglia remains the regional stronghold for the bird with over 80 birds. Bitterns are protected under European Union directives.