The numbers of one of Britain's rarest birds, the great bittern, have increased in the East Anglian Fens, the RSPB has revealed.

Newly created habitats are helping the bittern, known for its "booming" call, recover from losing breeding grounds.

Pairs have been recorded nesting in newly created reedbeds, as conservationists attempt to prevent loss of habitat for the birds.

The bird is nesting in more sites in the UK than in any year since 1990.

A privately owned wetland site converted from farmland in Cambridgeshire had evidence of four nests involving three different breeding females, the RSPB said.

Climate change

The great bittern was extinct in Britain between 1886 and 1911 and had to be reintroduced to the country. In the 1990s, research found reedbeds were drying out, threatening their survival once again.

But 10 years after the UK's bittern population hit a new low of just eleven males in 1997, the RSPB and Natural England have recorded at least 51 male birds across 33 sites this year.

The numbers are up from last year's 44 male bitterns and only four behind the recent record of 55 in 2004.

The news that they were nesting in man-made reedbeds was seen as a positive sign as many of their traditional natural habitats were threatened by rising sea levels, the RSPB said.

Dr Mark Avery, conservation director of the RSPB, added: "The spread of bitterns into newly created reedbeds is a testament to all those involved with habitat creation, especially in the East Anglian Fens.

"Encouraging bitterns to nest in newly created sites away from the coast helps to buffer these sensitive birds against the impacts of climate change."