Outdoors: Boxes helping owls thrive

On a still, cold misty winter morning, a ghostly barn owl flutters and swoops on moth-like wings over the unkempt tussocks of a rough field.

The owl hovers for a second or two, then plummets into the grass before quickly rising up again with a field vole gripped firmly in its talons.

A hunting barn owl is a memorable sight, whether it be on a frosty white winter morning or in the soft light of a summer evening when adults are out and about well before dark because of the need to hunt for field voles and other small creatures for their hungry chicks.

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In Scotland, the barn owl is on the north-western fringes of a global range that stretches across much of Europe and Asia.

It prefers low-lying ground in central and southern areas, although it does occur in other parts, especially Aberdeenshire, along the Moray Firth coast and Argyll.

But in central Scotland the bird has been given a remarkable helping hand in recent years through a scheme to provide new nesting sites.

The initiative is co-ordinated by Mike Steward, a retired conservation manager with Forestry Commission Scotland (FCS), who is now putting his spare time to good use by monitoring the barn owl population and erecting nest boxes in suitable habitat throughout the Forth Valley region.

The nest box and monitoring project began in 1990, when Mike still worked for FCS, with boxes being erected in Queen Elizabeth Forest Park.

Since then the scheme has spread to many other low-lying parts of central Scotland in an area stretching from the Trossachs through to Falkirk and Clackmannanshire. Two types of wooden nest box are typically used - those in trees are triangular-shaped and enclosed with an access hole near the top, while ones placed inside old buildings have a more open construction.

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The initiative, funded by a variety of bodies, has proved a spectacular success, with numbers soaring from just four recorded pairs in 1990 to 77 in 2010.

"One of the main constraining factors on the barn owl population in recent decades has been the loss of suitable nesting sites due to old farm buildings being modernised or demolished, and hollow trees blowing down in strong winds or being felled for health and safety reasons," explains Mike.

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"We have simply been helping the birds by providing suitable nest sites that were otherwise not available."

Mike admits that the success of the 2010 breeding season was something of a surprise, given the very cold winter. While the number of pairs on forestry ground in the Trossachs did drop due to prolonged snow cover preventing the capture of field voles, breeding pairs in other low-lying agricultural parts of the region doubled in number compared with the previous best year in 2007.

"We were lucky that the field vole population peaked during the breeding season, meaning that food was plentiful for barn owls that had survived the winter," he says.

"It was also fortunate that there was not a long period of snow cover in Clackmannanshire, Falkirk and Stirling compared with other parts of the country. Vole numbers do not peak and crash at the same time nationwide, which is why there tends to be different regional trends in barn owl populations."

Around 260 nest boxes have been erected and Mike believes that with a firm foothold throughout the region the future bodes well for the barn owl population in central Scotland.

"There is a good amount of habitat for the owls throughout central Scotland and there is potential for further expansion in range. It is also possible that climate change is opening up new areas of ground in higher altitude areas that formerly were not suitable for barn owls."

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This article was first published in The Scotsman, 11 December, 2010