In a recent article about birds of prey, we told you how you can tell eagles, falcons and hawks apart, but one equally efficient hunter we didn’t mention is the owl. We left these unique-looking birds out as they are just so easily identifiable as owls.
Many species across the world will hunt for their prey using the advantage of daylight, known as diurnal animals. As with all things, there is balance, and this leaves the night-time as a niche to fill. Owls fill that evolutionary gap nicely with most species being highly adapted to successfully hunting at night, making them nocturnal.
This behaviour helped create the spooky reputation owls have earned over the centuries, not least because they look so distinct: they all sit bolt upright and have a round or heart-shaped, mostly flat face, in which sit two large bright orange and black orbs for eyes and a small, downward facing sharp beak.
Nothing else looks like an owl, except perhaps frogmouths, but this common name for those night-hunters comes from that large gaping beak, distinctly lacking in an owl, and their talons are far weaker than our supreme predator. The species name for frogmouths Strigoides literally means owl-like, but they are in fact more related to nightjars, also nocturnal birds.
ALL IN THE HEAD
There are around 250 species of owl in the world today, in the order Strigiformes, which is split into two families: true or typical owls called Strigidae, and the barn-owl family, Tytonidae. The most noticeable difference between these two families are the face shapes, with the former having a round face and the latter having a heart-shaped face. This feature is created by a concave collection of facial feathers, referred to as the facial disc.
Sound waves are directed by this parabolic arrangement to the owl’s ears, which are situated just behind the eyes within the facial disc perimeter. The resulting auditory effect is so incredible that this natural physiology was the inspiration behind the huge concrete acoustic mirrors erected on the southern coasts of England during the Second World War, before radar was developed which eventually replaced them. Given the right atmospheric conditions, it was possible to hear the engines of approaching enemy planes across the waters long before they could be seen, and make ready the anti-aircraft guns.
The large eyes of an owl are not spherical like ours, but flat at the front and extend back into the skull in a cone shape, which is what gives these birds their excellent night vision, allowing more moon and starlight in. This binocular vision means owls are hyperopic – far-sighted – giving them great depth perception, particularly in low light.
Chances are if you do see one, you will do so at or just after dusk, whilst people like me are squinting through spectacles at that time of day, making yet another mental note to go to the opticians.
Their far-sight vision does mean they can’t see anything clearly close up, however. They can spot and seize a vole the size of your forefinger at 200m but once in their grasp and ready to be consumed, it is just a blurry blob. They sense their food instead by the presence of tiny hair-like feathers on their beak called filoplumes, a rare type of feather not found in many birds, and entirely absent in ratites (flightless) birds.
Owl eyes are fixed in their sockets, always facing forward, so they do need to turn their heads to look at something out of their field of vision, but owls possess even greater scope in this too – we have 7 vertebrae in our necks, and we can turn our heads about 180°, but owls have 14, allowing them a rotation range of around 270°.
This degree of rotation, especially with the speed at which they turn their heads, would ordinarily result in a stroke or embolism as a result of damage to the blood supply, but for owls, the mystery of why they weren’t all dropping dead to the floor was solved in 2012.
Researchers in neurological imaging at the John Hopkins University, Maryland USA, discovered that their circulatory system has adapted for this too: the gaps in our vertebrae through which the vertebral arteries pass are just a tiny bit bigger than the diameter of the blood vessels themselves, but in owls, these gaps (known as foramina) are ten times the diameter.
The position and design of the junction of the arteries as they branch off around the head as carotid arteries is also higher and wider. This gives the vessels more flexibility and prevents cutting off the supply altogether, which would otherwise lead to blood clots and eventual death.
Owls can’t see in total darkness, which is where their amazing hearing comes in. Owl ears exhibit yet more unique oddities: neither ear is the same shape as the other and they are set asymmetrically which enables the owl to differentiate between types of sound such as high frequency vocalisations made by small mammals, and lower frequency ones of them moving through foliage. Those sounds waves are then triangulated in the brain giving the exact position of the sound source.
So, they can often see and definitely hear you out there – but how come they don’t scare away the prey as they approach? We know wings make noise through the air, as anyone can tell you who has heard a sudden flurry of sparrows head to a tree top as a cat approaches, or a murmuration of starlings passing overhead, or the ear-drum throbbing womp of swan wings as they run up into flight from the water.
Owl wings are made up of specialised feathers that break up this noise from air turbulence. The feathers on the leading edge of the wings end in tiny hooks, giving a sort of serrated edge that reduces noise especially when at a sharp angle, as in a dive. Owls will hunt either from a perched position in a tree or from a surveillance flight, and as 99% of an owl’s prey is on the ground they need to drop fast and directly, often requiring steep descents. The broken-up airflow rolls along the wing’s edge and then any sound that still remains is then absorbed by velvety down feathers on the legs and rest of the wing.
When owls strike, they almost always do so with their death-dealing feet. They can position the back toes to form a claw of two front toes and two back, or three front and one back, and the long, curved talons make short work of anything alive in a strong muscled grip. Crushing their prey’s head and body whilst landing on the ground usually dispatches it instantly, they will then carry it off to a branch to swallow whole. Owls kill silently and quickly, as they are vulnerable to their own predators when on the ground.
Owls can and do attack humans, if they feel threatened, with enough wallop to cause blunt force trauma that can result in severe injury and even death. They will always dive-bomb and attack the head, and in 2015 a handful of joggers experienced this painful assault from one or possibly more barred owls, whilst exercising in a park in Salem, Oregon.
At one point a number of years ago, the defence counsel for a high-profile alleged murder case was ready to use The Owl Theory, although the trial proceeded without it in the end. But for a time, renowned ornithologists were ready to go on record to testify that the deep trident-shaped lacerations in the head of the victim were not the marks of a bludgeoning from a fireside tool, as was eventually declared the case, but were in fact the result of an attack from an individual barred owl whose species was common to the area.
It was suggested that this was what had caused the victim to lose her balance resulting in her tragic fall and subsequent death at the foot of her tight, winding stairs
.The theory was considered to have weight rather than just being a fanciful excuse as not only had there been no skull fractures from the alleged blows, feathers like the ones found on the feet of barred owls were tangled in her hair and in one of the woman’s hands, along with pine needles. The Owl Theory could also have explained how she received strange defensive marks on the backs of her hands, small pockmarks just like the point of a beak. It would have been an interesting day in court.
Same but different
Owls are found in all ecosystems of the planet save for the icy wastes of the Antarctic, and they tend to exhibit the same characteristics across species, but there’s always one, or in this case, two, that have to be different. These two types of owl who go against “type” are the northern hawk-owl, who hunts in the day using their sight like a hawk; it does this because for some reason its ears have developed symmetrically so it can’t hear as well as other species.
There is also the very comedic burrowing owl which goes against type in a few ways: they are also active during the day, they are gregarious i.e., they live in groups, and their long legs are on show for all to see, unlike other owls who discreetly hide them among many layers of feathers.
As the name suggests, they nest in burrows, but not as the name suggests, from burrows they have made themselves. Like all owls, they are secondary cavity nesters, meaning they occupy holes left by other species, or utilise natural or manmade holes in structures.
Owls are generally quite bad at making their own nests, let alone digging tunnels, so they live in holes made by far superior diggers, prairie dogs. As they live in the open grasslands and deserts of North and South America, where there are no trees, they hunt by sprinting after their prey, hence the long legs.
Many birders will give their right arm to spot an owl, such is their elusive and alluring nature. The association with the night is fascinating, and some have spent huge sums of money on infra-red equipment to see them.
Of course, your money is yours to do with as you please, but we suggest becoming familiar with the sound of owls before you go investing in any night goggles. Owls are very species-orientated, i.e., females will only respond to the call of a male from her own species. Owl vocalizations can be quite loud and often low, which helps the sound travel long distances through the night air.
We tend to associate a hooting noise made by owls, and whilst some do make this noise, like the Great Horned Owl, you may also hear shrieks, hissing, and crying. Research your area and the typOwle of owl you may find there, then spend an hour or two on a clear night out near woods, and listen.
Is there a strange sound almost like a high-pitched horse? That will be an Eastern Screech Owl. The call and respond exchange for Tawny Owls has the male calling the stuttered hoot and the female responding “key-wick!” You may hear a strangled kr-i-i-i-ick sound, which would actually be a Barn Owl.The Long-Eared Owl sounds like it is trying to blow a party horn whose paper end has fallen off, and a Barred Owl asks “who cooks for you?”.
One thing to be aware of, however, is if you hear a kind of barking noise – owls will make this noise when threatened, so if you hear this then we strongly suggest you keep your head down, make haste, and try again another time, as we think we can safely say there is little worse than being harassed by an owl.