Land of opportunity
The much-loved Barn Owl is a skilled hunter when it comes to searching for food in the countryside – but its success in securing a meal depends on how land is farmed
How the farming of our countryside can have a huge impact on Barn Owl survival
ONE OF MY earliest memories was of my Dad and I driving home in the winter. We rounded a bend on a lonely fenland road in Dad’s old van and were greeted by an apparition, a white ghost, a Barn Owl hovering above the grass verge. I was eight years old and can still remember it clearly. White feathers with mottled fawn upper edges and those haunting eyes. Of the five species of owl in the UK, the Barn Owl is probably the easiest to see – the best time being on a warm summer evening during still conditions.
In my experience, Barn Owls normally follow the same hunting pattern each night, moving further away from their roost or nest site until they make a successful kill. They tend to take the prey to a favoured perch to devour it whole or, if they have young, back to the nest. In the breeding season, most of the hunting is carried out by the male. He will bring food for the chicks and his mate while she is at the nest. I’m fortunate in that, for several years, I’ve been able to watch two pairs of Barn Owls. One pair live near my home in the Midlands, which I call the Ash Tree Pair, and the second pair live in East Anglia where I grew up – I call them the Fenland Pair. The Ash Tree Pair roost in one of four Ash trees, the remnants of an old hedge line. They select one of these trees to nest in each year. All four trees are suitable for Barn Owl nesting but they have competition from Tawny Owls and Kestrels, who also use the trees. The Fenland Pair nest in the eaves of an old barn that is used to store farm machinery. Outside of the breeding season the male roosts in the barn on his own. I am not sure where the female goes as there are very few trees in the area. She probably roosts in an old agricultural building somewhere close by. The Ash Tree Pair’s hunting territory is smaller than that of the Fenland Pair’s, because food is much more abundant, so they don’t need such a large territory. The Ash trees are surrounded by hay meadow, which the farmer cuts in late August to give the Barn Owls every opportunity to find food for their young. Large areas of scrub, a buffer zone, are left at the edges of the fields to encourage wildlife and provide cover for Brown Hares. In contrast, the Fenland Pair have a much larger territory, covering several square miles. In the fens, hedges have been pulled out to
create large fields to maximise agricultural production. Less cover means fewer Field Voles, their main prey item. As a consequence, the Fenland Pair spend considerably longer hunting, each night. There is, however, a small area of scrub, perhaps an acre in size, next to the barn, and the Fenland Pair always start their hunting trips by quartering this field. I suspect this small area of scrub is why the barn was chosen by these owls. I have only ever seen the Ash Tree Pair hunting in good weather and on clear, still nights. Conversely, I have seen the Fenland Pair hunting in gales and driving rain at midday. Hunger will drive Barn Owls to hunt at any time of day and in any weather. The Ash Tree Pair generally focus their hunting in the summer months in the hay meadows. Normally, it only takes a few minutes to catch a vole. The Fenland Pair, though, can be away from the nest for long periods of time trying to find enough food to raise their family.
Using senses to the full
Barn Owls hunt using sight and sound and are perfectly adapted to make best use of these senses. Their vision is much more acute than ours; they can spot tiny voles in long grass and can probably see urine trails made by the rodents. Barn Owls’ eyes are actually tubular in shape, which provides a greater distance between the front lens and the rear of the eye. This has the same effect as a telephoto lens, making it easier to spot small rodents by magnifying the image from further away. Their eyes are so large they cannot move them in their eye sockets, so they have to move their heads if they want to look somewhere, other than immediately in front of them. Owls compensate for this lack of eye movement by having a greater number of neck bones,
allowing the head to swivel as much as 280°. I have carried out experiments with the Ash Tree Pair by leaving dead mice in the hay meadow for them to feed on, but they completely ignore them. This is because their vision is based on movement – voles are safe if they stay still. Barn Owls, like other owls, bob their heads, to help to gauge distance when looking for prey. This behaviour can also be observed in two other birds that hunt or find food underwater, the Kingfisher and the Dipper. The Barn Owl’s heart-shaped head is a function of how evolution has adapted its hearing. The shape of the face acts like a radar dish capturing sounds and funnelling it to the ears, which are hidden under the facial disk feathers. One of their ears is set further back in the head than the other. It is thought that the purpose of this is to enable the owl to better gauge distance to prey by differentiating how quickly the sound reaches each ear. Unlike most other birds, Barn Owls fly silently. This ensures that their prey is not alerted to their presence. Flying silently also enables Barn Owls to hear movement from below without the sounds being masked by the owl’s own wingbeats. Silent flight is achieved by having wing feathers that are frayed at the edges, which create less friction with the air, and also the downy plumage helps to dampen noise. The feathers are more flexible than those found on other birds, but the disadvantage is that they are not waterproof. Their leisurely, slow flight is ideally suited for scanning the ground below. Once a vole is spotted, the owl spills the air from its wings and drops onto it from above. The talons make sure the prey is immobilised before the owl dispatches it with a bite to the neck. Like other birds of prey, adult Barn Owls swallow their prey whole and later regurgitate a pellet containing the indigestible parts (fur and bones). From examining the pellets of both the Ash Tree Pair and the Fenland Pair, both pairs eat predominantly Field Voles. The pellets are easy to spot under preferred perches. The Ash Tree Pair tend to sit in one of the ash trees to digest their meal. The Fenland Pair prefer to perch on the top of the barn. It can take between six and 12 hours after eating before a pellet is regurgitated. Normally a pellet can contain the remains of more than one prey item.
Barn Owls have up to five chicks in a brood and can have more than one brood in a year if the weather is good. The female lays her eggs over several weeks and they hatch in the order they were laid. The result is that the chicks vary in size. If the adult birds struggle to find enough food, it can become a fight for survival and the chicks may become cannibalistic. The life expectancy for a Barn Owl in the wild is about four years, although the mortality rate is high. Collisions with cars have a significant impact on owl numbers, especially in the breeding season, and the loss of either bird if they have young, can result in the chicks starving. During 2016, the Ash Tree Pair had a successful breeding season rearing their young. However, the Fenland Pair were less fortunate, as the barn they use was unintentionally disturbed during the summer months by farm workers, causing the pair to abandon the nest site. I am not sure if they had actually started nesting beforehand. Maybe the pair will try to nest in the barn this year. The success of breeding is directly related to the abundance of prey and lack of disturbance, and farmers can have a significant influence on both of these.
The Barn Owl’s feathers are modified for silent flying
A classic Barn Owl barn
Barn Owls are not above perching in trees, even among the cover of Ivy