It's been a boom time for the secretive bittern – one of the most iconic of all East Anglia's wildlife species and the loudest bird in Britain, the RSPB announced.

But although the bird that more than 100 years ago was thought to have been lost as a breeding species in the UK hit record British population levels this year, the numbers in Suffolk and Norfolk dipped slightly.

The RSPB announced that the minimum of 164 'booming' males found across the UK this spring was the highest number discovered since records began. Surveyors, listening for the male's far-carrying and foghorn-like 'booming' call that can reach a volume of more than 100 decibels, heard it at a total of 71 sites.

'That compares to 162 at 78 sites in 2016, and is a positive sign that bitterns are back from the brink and thriving,' the society said.

In Suffolk's coastal reedbeds there were 33 'booming' males compared to a record 36 in 2016. In the Fens there were 27 compared with a record 28 the previous year, in the Norfolk Broads there were 16 compared with 17 and in north Norfolk there were five - as there were in 2016.

The slight reduction in East Anglian numbers was 'offset by increases in specially created bittern habitat in other regions,' the RSPB said. And, despite the regional reductions, at the RSPB's Lakenheath Fen nature reserve there was a record eight 'booming' males.

'The decrease in numbers of 'booming' bitterns in East Anglia this year is thought to be the result of a drier-than-average winter causing some reedbeds to by too dry in the spring when bitterns start looking for nesting sites,' said the society.

Some coastal sites, such as Easton Broad near Southwold, were also affected by sea incursion, which was a threat to many coastal reedbeds that were traditionally a bittern stronghold.

Simon Wotton, senior conservation scientist at the RSPB, said the society was 'delighted' at the record year. The decrease at some sites highlighted the vulnerability of some habitats and the importance of creating new reedbeds in areas safe from coastal flooding. 'This has been the approach of conservation efforts for bitterns in the UK since 1996, and the spread of bitterns to these new breeding sites and fantastic increase in numbers nationally is proof of its success,' he added.