2014 proved to be a particularly good year for barn owls, their breeding success in East Anglia well above average. Most of the volunteers monitoring barn owl nest box schemes reported high levels of box occupancy and large broods, reflecting the abundance of small mammal prey available.
Just how much of this success carries through into 2015 will very much depend on the availability of mice and voles over the next few weeks – that difficult late winter period when levels of owl mortality increase as the weather bites. The long growing season last year, with grass continuing to grow well into the autumn, will have benefited the herbivorous field voles and should mean that there are plenty of voles around for owls and the other predators who feed on them. The challenge will come from the weather.
Barn owls are surprisingly light birds, soft plumaged and poorly equipped to deal with difficult winter weather. High winds and heavy rain reduce the owl’s opportunities to hunt. Even if they can get out the noise of wind and rain can limit their ability to locate small mammal prey – barn owls have sensitive hearing and use this as their main means of locating prey moving about in the grassy swards over which they hunt.
Barn owls are able to catch voles through a light covering of snow but deep snow presents a real problem. Unable to detect and capture voles still active under snow a barn owl loses weight quickly and may die from starvation within just a few days. In response to deep snow cover a barn owl may move away from its usual foraging range to seek opportunities elsewhere. It may also switch to hunting other prey, notably small birds which may be taken from their roosts. Small birds are probably more of a challenge for a hunting owl, which lacks the speed and manoeuvrability of those raptors that specialise on such prey, and any shift in hunting range may expose the bird to roads and other hazards.
Daylight hunting may also become more evident at this time of the year, benefiting those of us who like to see the county’s barn owls, and it is worth keeping an eye out for these enigmatic birds.