From soundproof feathers to extraordinary eyesight, owls are marvels of natural engineering. There is something special about knowing that a pair of Spotted Eagle-Owls has nested for several years on a rocky ledge overlooking the sea near Hermanus. While we sleep, these remarkable birds hunt under cover of darkness, utilising an extraordinary collection of adaptations that make them among nature’s most accomplished nocturnal predators.
Their first weapon is silence.
Most birds produce an audible swishing sound as air rushes over their wings. Owls, however, have evolved specialised flight feathers that reduce this noise. The leading edges of their outer flight feathers have tiny, comb-like serrations that modify airflow. Fine fringes along the feather edges and a soft, velvety surface further reduce aerodynamic noise. Their broad wings also allow them to fly relatively slowly. All this helps them to approach prey without announcing their presence.
Prey is less likely to hear an approaching owl, while the owl can listen for the faint sounds of small animals moving through vegetation.
And what extraordinary hearing abilities! An owl’s facial disc — the circle of feathers surrounding its eyes — helps collect and direct sound to its ears. In some species, the ear openings are positioned asymmetrically, allowing the brain to compare tiny differences in the sounds reaching each ear.
This helps the bird accurately determine where a sound originates from, even in darkness. A mouse rustling beneath leaves may be invisible, but its movements can betray its position to an owl’s ears.
The owl’s eyes are equally remarkable. They are large and tube-shaped rather than spherical, with a retina rich in rod cells that are highly sensitive even in low light. Their forward-facing position provides binocular vision; this helps the bird judge distances accurately when striking at prey.
An owl, however, cannot move its eyes around in their sockets. Its eyes are relatively fixed, so to look behind itself it must turn its head.
This brings us to one of the owl’s most astonishing abilities: it can rotate its head up to 270 degrees. That is three-quarters of a full circle. To make this possible, owls have more neck vertebrae than humans, together with specially adapted joints and blood vessels that help maintain circulation during these extreme movements. Without these adaptations, such rotation could seriously restrict the blood supply to the brain.
Then there are the feet. Strong toes, powerful gripping muscles, and sharply curved talons enable an owl to seize and hold prey firmly.
Once caught, small prey can be swallowed whole and again, impressive adaptations come into play in the owl’s digestive system. The undigested fur, feathers, and bones are separated and compressed into compact pellets. These are regurgitated later. These pellets provide fascinating clues to an owl’s diet: examining their contents can reveal the tiny skulls and bones of the animals it has eaten.
With all these abilities, Spotted Eagle-Owls are adaptable hunters. Depending on what is available, their diet may include insects, rodents, birds, frogs and reptiles.
By feeding on rodents, they provide a valuable natural pest eradication service. That is why using common rodenticides such as Rattex can damage the whole environment, even when used carefully.
Poisoned rodents may, in turn, poison owls and small carnivorous mammals such as jackals, Cape foxes, African wildcats, caracals and several mongoose species that eat rodents. We need to consider the wider environmental ecology before using poisons of any kind.
Apart from the ‘Spotties', other owl species that may be seen in our area include the Cape Eagle Owl, Barn Owl and Pearl-Spotted Owlet. The latter has two fake eyes on the back of its head, so would-be predators can’t tell whether it’s coming or going.
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