Chris Bishop Some of our rarest species of birds are on the increase, thanks to major efforts to conserve them.But while bitterns are booming and osprey numbers are soaring, some of our once commonest species are in steep decline.

Chris Bishop

Some of our rarest species of birds are on the increase, thanks to major efforts to conserve them.

But while bitterns are booming and osprey numbers are soaring, some of our once commonest species are in steep decline.

A 10th edition of the State of the UK's Birds report, published by conservation groups like the RSPB and Thetford-based British Trust for Ornithology (BTO), reveals that almost 60 pc of the UK's rarest birds have increased over the last ten years. Four out of 10 of our commonest birds have decreased over the same period.

One of the most spectacular increases has been seen in numbers of male bitterns, which have increased from 19 to 82.

East Anglian bird reserves such as Minsmere and Titchwell form the bird's final stronghold, as rising sea levels threaten the low-lying freshwater reed beds it nests in.

Other rare birds whose populations are increasing include the stone-curlew, of which 260 of the UK's 370 breeding pairs nest in the Brecks.

Breeding schemes on reservoirs such as Anglian Water's Rutland Water have helped reverse the osprey's decline. Marsh harriers are another breeding success on the Norfolk Coast, where numbers are steadily increasing, along with the avocet, corncrake and cirl bunting.

Declining common birds include the linnet, nightingale, swift, guillemot, starling, and house sparrow. In Norfolk, conservationists hope to reverse falling numbers of grey partridge by working more closely with farmers and estate managers.

Graham Appleton of the BTO said: “The main threat that's coming out of this 10 year look back is we can spend a lot of time looking after individual species, but we haven't solved the problems for farmland birds.”

Destruction of hedgerows and field margins to make way for intensive food production has eaten up vital habitat. But grey partridges have also been seen on sale in Norwich supermarkets in recent seasons, and while the native game bird is on the red threatened list, it can still be shot over a longer season than the pheasant.

Dr Mark Avery, the RSPB's conservation director, said: “Over the last decade we've enjoyed some cracking conservation successes, including removing some threatened species from the red list and increasing the populations of red kite, bittern, avocet, osprey, stone-curlew and cirl bunting.

“However, these triumphs are countered by continued declines of some widespread species, like the skylark, kestrel, willow warbler and grey partridge.”

Tom Tew, Natural England's chief scientist, said: “By working closely with farmers and other land managers we need to ensure that these benefits are spread into the wider countryside where more common birds continue to suffer from declines.”

The report is published by the RSPB for a coalition of conservation organisations, including: RSPB, British Trust for Ornithology; The Wildfowl & Wetlands Trust; The Countryside Council for Wales; Natural England; Northern Ireland Environment Agency; Scottish Natural Heritage and the Joint Nature Conservation Committee.