A deep hoot in the night - like air blowing over the top of a glass bottle - signals the presence of one of Britain's rarest and most beautiful owls. Secretive and strictly nocturnal, the long-eared owl (asio otus) is at home in woods near rough grassland. Its reclusive nature and excellent camouflage make it devilishly hard to find, which has meant previous studies of this species have been difficult - and results limited.
However, recent research by Robert Williams of the University of East Anglia in Norwich has revealed important new information about this elusive bird of prey. Dr Williams has found more evidence to suggest that Britain has a self-supporting resident population but also fears that the bird is suffering a decline in numbers.
A self-supporting resident population has been suspected by scientists and ornithologists but Dr Williams's evidence is the strongest yet to prove it exists. "There have been records of long-eared owls here for years. All the places in East Anglia ending in Hoo were named after the call of the male long-eared owl," Dr Williams said. "It was not known whether all the winter migrants returned to Scandinavia in the spring or whether some stayed here to breed."
Many long-eared owls still make that perilous journey each spring from Britain to their northern breeding grounds. Their numbers vary from year to year, with peaks every three to five years. But Dr Williams discovered that those owls living in southern England, where prey is more consistent and reliable, seem to be resident year-round.
"If it is a particularly poor year for prey or an especially harsh winter, the resident birds will moderate their breeding and maybe not even breed at all," he said.
During his PhD study, Dr Williams also discovered that long-eared owls have lower juvenile and adult survival rates than tawny owls, which are doing well at the moment, and that the UK population was dwindling, with the major causes of death being predation, starvation and bad weather, as well as increasing numbers being killed on the road.
"They do seem to have declined this century. We don't know what their natural level is because they are so secretive, but the Victorian naturalists talked about them as if they were much more widespread than they are today.
"The naturalist C B Ticehurst said they were more common in parts of the south than the tawny owl," Dr Williams added. "As the tawny has increased in numbers recently, the long-eared owl has appeared to decline. We still don't know if there is a connection between the two. We also know about the decline from local county bird reports. They don't breed at all in Cornwall and there are very few pairs in the south west of England. It is estimated there are between 1,000 and 10,000 pairs in the UK now. My guess would be around 2,000 pairs."
The chief reason behind the decline is the problem affecting many bird species - agricultural and land-use changes which have meant the destruction of the blackthorn scrub and fenland of the long-eared owl's natural habitat. The owl is a vole specialist and relies on this rough grassland for hunting.
Dr Williams is keen to draw attention to the plight of the species and possibly get it registered as a bird of concern. During his three-year study he found 24 nests with eggs (indicating a breeding pair) and went to extraordinary lengths to get those results, spending nine months in the wilds of Kielder Forest in Northumbria, living owl hours, with only one trip home every four weeks, and braving an icy Force Six wind on the Old Hall Marshes in Essex.
"Radio tracking long-eared owls is really difficult because their range is so great," Dr Williams explained. "They are not like tawny owls, which fly from perch to perch to hunt for food, they hunt while flying over open grassland. The only way to follow them is to run after them, so I spent many nights running across wild moorland trying to keep them in range. I fell down pits and holes and into bogs. I was stopped by the police several times when farmers called in to say they'd seen this character running across the moors adjacent to their land in the middle of the night."
He also had some close encounters with his subjects. While he was ringing chicks in a nest, one female long-eared owl made fly-pasts near the nest, clipping the back of his head with her wings, trying to scare him off.
But despite the hardships, he brought home results which will go some way in helping us to understand this most elusive of birds and to ensure its survival.
To find out more about long-eared owls, contact the Hawk and Owl Trust's education centre on 01494 876262 and look out for a book, `The Long-eared Owl' by Derrick Scott (Hawk and Owl Trust, pounds 17.95).