Trying to protect one of the UK's rarest and most secretive birds has always presented a major challenge to conservationists and now the unpredictable British weather has placed another major hurdle in their way.

Trying to protect one of the UK's rarest and most secretive birds has always presented a major challenge to conservationists and now the unpredictable British weather has placed another major hurdle in their way.

Torrential rain during the last Bank Holiday weekend washed away nests inhabited by breeding bitterns and almost certainly killed new born chicks, investigations have revealed.

Reserve managers at sites along the north Suffolk coast had been confident of a successful breeding season and last night admitted the setback could have repercussions across the country because the region is a key area for bitterns.

It is feared that of nine nests recorded recently at nature reserves or coastal sites in Suffolk, only two remained intact following the heavy downpours.

Adam Rowlands, site manager for Minsmere and North Warren, said: “This is a serious setback for the bittern. Suffolk has been the engine room for the recent recovery of the species in the UK, with the RSPB's reserves playing a key role.

“Anything that affects breeding success here is likely to have a knock-on effect across the country.”

Latest figures show the UK population of the booming male bitterns had fallen to 44 from a half-century high of 55 in 2004, but RSPB officials believed 2007 would prove a key breeding season.

Mr Rowlands added: “The one glimmer of hope is that the birds did get off to an early start this breeding season and there may still be time for some of them to try again, but it is getting late in the year.”

There is one glimmer of hope at Minsmere where the famous 'V' female is still feeding her young in one of the site's surviving nests. 'V' - so named for a distinctive kink in her neck - has been breeding continuously since 1996 and is mother to a large proportion of the UK's bitterns.

Last November, there were fears for the region's bitterns after fierce storms caused saltwater to infiltrate a freshwater site at Dingle Marshes and also threatened the sea defences at nearby Minsmere.

While the prospects for breeding subsequently improved, Mr Rowlands said it was feared that three nests at Dingle and Westwood marshes had also been destroyed.

Dr Mark Avery, the RSPB's director of conservation, said: “Despite our success in recent years, bittern numbers remain perilously low. That one spell of bad weather can have such potential serious consequences is proof of that.

“Bitterns need large areas of wet reedbed if they are to breed and find enough food. Far too many of the UK's reedbeds have been

lost and this is another reminder that we must continue to create new ones - as the RSPB is doing - if the bittern and many other species are to have a future in our islands.”

Hunting and habitat loss saw the bittern vanish from the UK by 1886. It returned in 1911 and numbers rose to about 80 booming males by the 1950s before crashing to a low of 11 in 1997.

RSPB research carried out at Minsmere led to the reserve's famous reedbeds being completely re-profiled to suit the birds' needs.

Because bitterns are so secretive, their numbers of determined from the males' boom - a foghorn sound to announce their territory and attract females, which can be heard up to three miles away.

Colloquial names for the bittern include bitter bum; bog blutter; bog-bull; bog bumper; bog drum; boom bird; bottle-bump; bull of the bog; bumpy cors; butter bump and heather blutter.