Under the cover of darkened skies, the spectral silhouette of a barn owl glides low over the fields, soundlessly seeking its prey.
Slowly, silently, as the light fades on a spring evening, a ghostly form floats over a grassy field. Stealthily, its curved wings making no sound and head moving constantly to and fro, a barn owl hunts.
Seemingly gliding just above the ground, it is seeking out mice and voles below. At this time of year, this owl will be a male, looking for food not just for himself, but also for his mate. She is back in the nest, sitting on a clutch of eggs.
Barn owls hunt at dawn or dusk, when light is rising or fading, or at night, when it may be almost completely dark. It is rare to see them in full daylight. They are, however, supremely well adapted for their nocturnal life.
Their large, forward-facing eyes provide binocular vision, allowing them to see an object with both eyes. These are in fact elongated tubes, rather than balls, held in place by bony structures called sclerotic rings. Because of this, they cannot move their eyes, which always look straight ahead. Instead, the owls have a long, flexible neck that gives them the ability to turn their head through 270 degrees.
Their hearing is excellent, enabling the hunter to pick up the slightest rustle from a small rodent hidden in the long grass below. The heart-shaped face acts as a parabolic reflector or radar dish, concentrating and focusing the sound towards its ears. These are behind the eyes at the side of the head and are covered by the feathers of the facial disc. The ears are asymmetrical, with the left one slightly higher. This enables the bird to judge the exact distance between itself and its potential prey.
When the owl hears a noise, there is a minute difference in the time in which the sound is heard in each ear. If the sound is to the left, the left ear will hear it before the right. A sound from below the owl will be received in the right ear first.
The owl’s brain is capable of working out from these minute differences exactly where its prey is. Once it has located the vole or mouse, the bird flies towards it, its head in line with the last sound. If the prey moves, the bird makes mid-flight recalculations. Finally, once within striking distance, approximately 2ft (60cm), the owl brings its feet forward. Its sharp, curved talons are spread, ready to grasp their prey.
Designed to hunt
The owl is able to get close enough to catch its prey because of its silent flight. Its rounded wings have extremely soft feathers, which means the air makes almost no sound as it passes through. This has two benefits. The owl is able to detect even tiny, momentary sounds from its intended prey. The victim, on the other hand, is unable to hear the owl approach until it is too late to escape. The owl’s lightweight body is supported by very large wings. This allows them to fly very slowly, without stalling, as they hunt.
Despite their skills, the majority of hunting attempts end in failure. A barn owl needs to catch up to half a dozen small mammals every night just to survive. That represents approximately one third of its body weight. It sometimes takes other prey, such as small birds, seized from night-time roosts, frogs and bats.
There is a downside to those soft, silent feathers. In heavy rain, or even a sudden shower, they can easily get waterlogged, so barn owls rarely hunt when it is raining. This means that during prolonged periods of wet weather they, and in spring or summer their chicks, can starve to death.
Hard winters also cause problems, as small mammals are able to hide beneath the snow. Those owls that survive are able to take advantage of a bonanza of voles the following spring. These tiny animals will have bred beneath the protective layer of snow where their young are safe.
Barn owls hunt in open country, with large, uninterrupted areas of rough grassland the best areas. However, intensive farming means that in many parts of Britain these are in short supply. They also suffer from the use of rodenticides, which kill any owl that
eats a poisoned rodent.
Pushed to the edge
As a result, barn owls are often found on the fringes. They hunt along roadside verges, railway cuttings, wetlands, coastal marshes and any areas of farmland where the grass is allowed to grow long and left unsprayed. They can be found in rural areas across much of lowland England, Wales and southern and eastern Scotland, though often in very low densities. They are scarce in Northern Ireland and absent from the offshore islands of the Western Isles, Orkney and Shetland. Their main stronghold is East Anglia, especially the wilder parts of coastal Norfolk, Suffolk and the Brecks.
The species has been declining since the middle of the 19th century, largely because of changing agricultural practices. Numbers fell substantially between the 1960s and late 1980s, but have since risen slightly in the following decades. There are now approximately 4,000 breeding pairs in the UK. This number fluctuates dramatically with the rises and falls in the population of voles, their favourite food.
Barn owls, as their name suggests, have long lived alongside human beings. They still often nest in barns and other farm buildings, though they will also use natural sites such as a crevice in a cliff or a hole in a tree. They readily take to artificial nest boxes. Schemes up and down the country have been successful at increasing owl populations in specific areas.
Outside the breeding season, barn owls are generally solitary. In winter, their home range can cover 12,300 acres.
From the start of the year they form pairs, usually staying with last year’s mate, if they have both survived the winter.
To cement the pair bond, the male pursues the female in flight. He takes a position just above and behind her as they twist and turn through the air, screeching constantly at one another. Their wide repertoire of sounds includes hisses, wheezes and screeches. These, along with their pale appearance and silent flight, may be responsible for many stories of ghosts in church towers and abandoned castles.
Once a nest site is chosen, the male establishes his home range around it, a smaller area than the winter territory, at just 86 acres. He may ‘call’, making a series of loud screeches, and display, to fend off possible rivals.
A clutch of between four and six white, slightly rounded eggs, is laid from April or May onwards. The female sits tight on the eggs for approximately a month, while the male does all the hunting for both birds.
Survival of fittest
Barn owls incubate as soon as the first egg is laid, which means the young hatch asynchronously, often several days apart. There may be as much as a two-week gap between the oldest and youngest chick.
This has evolved as a method of ensuring the survival of at least one chick. In good vole years, when fine weather allows the owls to hunt frequently and bring back lots of food, all the chicks may survive. In poor years, or during bad weather, only the eldest may do so. Larger chicks have been known to eat their younger siblings when food is scarce.
Once hatched, owlets grow rapidly, though they remain covered in down for several weeks. They stay in the nest for up to 55 days, constantly calling to their parents and begging to be fed when the adult returns. The larger siblings tend to get the lion’s share of the food. This results in the younger ones dying sometimes, even when there is plenty to go round. Prey is eaten whole, the indigestible skin and bones regurgitated in the form of pellets.
By the time the young barn owls leave the nest, they are fully feathered and able to fly. They remain dependent on their parents for food for another three to five weeks. If the conditions stay favourable, the adults may then have a second clutch, and raise a new brood later in the summer.
By then, the youngsters are on their own. This is a period of real danger, when many birds are lost. Some starve, others are struck by vehicles as they fly low over roads. Once these critical weeks are survived, barn owls usually live to three or four years old. The oldest recorded wild bird, however, lived for 17 years.
Few venture far from where they were born, rarely travelling more than 30 miles. Once settled, they, too, will glide effortlessly across the countryside, scaring and delighting anyone lucky enough to spot one of these beautiful white ghosts gleaming in the twilight.
Words: Stephen Moss Photography: Alamy