Colin Shawyer, a raptor biologist and professional ecologist specialising in barn owls, estimates 2021 could be an early and productive year for barn owls on Lark Rise Farm due to a regional peak in the vole cycle.  

Barn owl with vole



Fluctuations in the short-tailed field vole, Microtus agrestis, populations significantly impact barn owl numbers. This vole species, particularly the males which spend a lot of time above ground looking for females, make up the predominant part of the barn owl diet, and they adjust their breeding output according to the availability of the voles. With a clement winter and early spring, the female barn owls should be able to catch plenty of voles ready to build up their body condition and enable them to produce many eggs; barn owls are incredibly flexible in their breeding performance, missing some years altogether and laying over 10 eggs in a single clutch in other years! The highest egg count we have had at Lark Rise was 7. 

Short-tailed voleField vole population trends typically peak and trough in roughly a 3.4-year cycle – peak numbers can be 10 times higher than the lows. I recently spoke with Colin Shawyer, and he stated that we're at a high point in the vole cycle like he predicted seven years ago when we had the last big barn owl year! The intermediate peak would have coincided with winter 2017/18, followed by a crash which coincided with our worst year for Barn Owl breeding, when none of the four pairs laid an egg. The gradual increase in voles encourages bigger populations of all the predators that feed on them, leading to a situation where very many predators deplete the vole population in the winter months and hardly any survive to produce the prey required for the next owl breeding season. 

Although seldom seen as they spend much of their time among vegetation in runs and burrows, field voles are currently thought to be the most common British mammal. According to The Mammal Society, a recent population estimate put the number of field voles in Britain at 75,000,000. They are also key prey for other species such as kestrels, weasels, stoats and foxes.  

Colin Shawyer ringing
owlets 2019As founder and UK and Northern Ireland coordinator of the Barn Owl Conservation Network (BOCN), the early summer is a busy few months for Colin Shawyer. He oversees over 3,000 barn owl nest sites' annual monitoring, Lark Rise Farm being just one of these locations. 

Together with Colin, we fit leg rings to both the adult and young barn owls during our annual monitoring. Bird ringing involves placing a harmless, individually numbered ring on one leg and includes the sexing and ageing of each bird. In Britain, wild bird rings are provided solely by the British Trust for Ornithology (BTO) to conservationists and researchers who are both trained and licensed to carry out this specialised work.  

This winter, we were lucky enough to get some funding to replace many of the barn owl nest boxes on the farm, and our stalwart volunteer Ray Thorne built six for us which are now up and ready to hopefully give our birds safe dry homes to rear their chicks this year. Some of these have already had signs of a visit from barn owls, with droppings and pellets being seen. I look forward to welcoming Colin back to the farm, where we hope for a bumper barn owl year!  

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Dr Vince Lea
Head of Wildlife Monitoring