Reading passage
Of all the birds that hunt after sunset, owls are the most specialised. Around 200 species inhabit every continent except Antarctica, and together they form one of the most successful groups of nocturnal predators on Earth. Their success rests on a set of physical adaptations so refined that an owl can locate, pursue and kill prey in conditions of near total darkness, often without making any sound that its victim could detect.
The most visible of these adaptations is the facial disc, the circular arrangement of stiff feathers that gives an owl its characteristic flat face. The disc works rather like a satellite dish, collecting sound waves and channelling them towards the ears. In many species, such as the barn owl, the two ears are positioned asymmetrically on the skull, one higher than the other. This arrangement allows the bird to compare tiny differences in the timing and loudness of a sound arriving at each ear, and so to pinpoint its source both horizontally and vertically with remarkable precision.
Experiments carried out in the 1970s by the American biologist Roger Payne demonstrated just how accurate this system is. Working with barn owls in a completely dark laboratory, Payne showed that the birds could strike a mouse using hearing alone, typically landing within a few centimetres of the target. Even when the floor was covered with dead leaves, which muffled the sounds made by the prey, the owls rarely missed. Payne concluded that a barn owl's hearing is roughly ten times more sensitive than a human's at the frequencies produced by rustling rodents.
Vision also plays a part. An owl's eyes are enormous relative to its skull, and their tubular shape packs in a dense layer of rod cells, the photoreceptors that work in dim light. Behind the retina lies a reflective layer called the tapetum lucidum, which bounces light back through the photoreceptors for a second chance at detection. Because the eyes are fixed in their sockets, owls must turn the whole head to look sideways, a feat made possible by fourteen neck vertebrae, twice as many as a human possesses. This anatomy lets an owl rotate its head through about 270 degrees without cutting off the blood supply to the brain.
Perhaps the most famous owl adaptation is silent flight. Three feather features combine to suppress noise: a comb-like fringe on the leading edge of the wing, a soft velvety surface that absorbs higher frequencies, and a ragged trailing edge that breaks up the turbulence generated as air leaves the wing. In addition, owl wings are very large relative to body weight, so the bird flies slowly and needs to flap only rarely. Engineers studying these structures have borrowed their principles to reduce noise in wind turbine blades and high-speed trains.
Hunting technique varies with species and habitat. Barn owls hunt on the wing, quartering low over open ground with the head angled down towards the sound of prey. Tawny owls, by contrast, are perch hunters: they sit motionless on a branch, listening, and drop onto victims below. Once prey is caught, it is usually swallowed whole or in large pieces. The indigestible parts, fur, bones and teeth, are compressed in the stomach and later regurgitated as compact pellets, which scientists collect and dissect to reconstruct the bird's diet.
These pellets reveal how valuable owls can be to people. Studies in Europe and Asia suggest that a single barn owl family raising chicks may catch between 2,000 and 3,000 rodents in a year, many of them species that damage stored grain and growing crops. Recognising this, farmers from Malaysia to Israel have installed nest boxes to attract barn owls as a form of biological pest control, reducing their dependence on chemical rodenticides.
Despite their formidable equipment, owls are vulnerable to human pressures. The loss of old trees and barns removes nesting sites, intensive farming reduces populations of small mammals, and poisoned prey can kill the predator that eats it. Traffic is another serious hazard: low-flying barn owls are frequently struck by vehicles on roads that cut through their hunting grounds. Conservation programmes now combine nest box schemes with the protection of rough grassland, aiming to ensure that the night sky keeps its silent hunters.