ITS nocturnal hooting call is synonymous with the hours of darkness in the countryside – and its stern, wise face was the inspiration for the character Owl in Winnie the Pooh.
But now Britain’s beloved tawny owls could be under threat – due to the declining population of their main source of food – the vole.
Scientists from Aberdeen University and Aix-Marseilles in France have discovered that numbers of field voles, tawny owls’ main prey, have decreased dramatically in the UK.
A 27-year study of tawny owls and field voles just south of the Border in Northumberland’s Kielder Water and Forest Park discovered a major decline in the population of the grass-eating vole and warned that the change could lead to a reduction in breeding by tawny owls.
Xavier Lambin, professor of ecology at Aberdeen University, said: “Tawny owls only breed when there is sufficient prey. If they breed, how many eggs they lay, and how successful they are when they fledge their chicks –all rely heavily on vole density.”
The professor said researchers believed that climate change was to blame for the consistent reduction in vole numbers, which usually fluctuates naturally from year to year but has recently remained at a low level.
In “off years”, the number of voles in a typical habitat can be as low as 20 per hectare, but during busy seasons can rise to as many as 700. The pattern usually repeats itself every three to four years.
“What we expect at the moment every year is nothing more than 100 per hectare or so,” said Prof Lambin, whose paper is published this week in journal Global Change Biology. “There are no longer these years of plenty which encourage owls to breed. Instead, the owls will just sit it out and be miserable, waiting for the voles to return. But that is no longer happening.”
The researchers predicted that changes to the “boom and bust” vole cycle could have a knock-on effect on other species where voles are the food staple and where they also play a key role in the ecosystem.
Although the owl population has not yet started to decrease, researchers said they have noticed that they are beginning to breed less – which will be more evident as the existing owls, which live for an average of five years, age.
Prof Lambin said: “We have already noticed this in kestrels, which tend to live for less time. They also rely on voles for food and we have already seen a reduction in their population.
He added: “Owls are a much-loved species. People expect to hear their calls and they expect their children to hear their calls. While we are not saying that they are likely to die out entirely, we are likely to see a reduction in population.”
The paper cited concerns that the problems with the vole population could have a knock-on effect for other species which rely on the small creatures for their main source of food, such as buzzards, foxes, badgers and weasels.
Dr Staffan Roos, a research scientist with RSPB Scotland, said: “Whilst voles are widely known to experience cyclical population fluctuations, and it is true that the numbers of tawny owls go up or down in tandem with this, they have an additional wide prey community.
“This study is quite representative of one habitat type – coniferous plantation forests. It is important to remember that the British Isles are comprised of a rich diversity of habitat types, including many areas of natural and ancient woodland, where tawny owls are doing very well.”