Dr Andrew Kelly, manager of Stapeley Grange, said that for species like the bittern, every individual counted.

BBC: Rescued rare bird to be released

The bittern, which lives in reedbed habitat, was once widespread across the UK, but stopped nesting in the UK in the 19th Century after drainage of wetlands.

BBC: Rescued rare bird to be released

Funded by Natural England, the Broads Authority hopes stonewort, pondweed and lilies will return to the area, along with a more diverse selection of fish and birds including the booming bittern.

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They included an 1840 portrait of William Stratton, "head keeper to Sir John Cope of Bramshill Park, Hampshire", by Edmund Havell, and a 1797 Philip Reinagle painting Harrier Killing a Bittern.

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He said it was not clear if the bittern was one of the breeding birds from Leighton Moss or one of the species' foreign visitors, which come to Britain to overwinter and escape colder weather on the continent.

BBC: Rescued rare bird to be released