Owls: Who Are They?

Taxon StudyBirds
Written By Alexander Julius Jensen
 

A barn owl (Tyto alba).

The Small, The Big, & The Old

Owls. They are perhaps the most enigmatic order of birds. Denizens of the night with glaring eyes and swivelling heads, sharp downward curving beaks and taloned feet. Flying with but the merest whisper of noise. But owls are a diverse bunch; there are 250 currently recognised species around the world, diveded into two families. The Tytonidae are dubbed the “barn owls” of which there are some 20 different species. Members of the Strigidae family, regarded to as “true owls”, make up the rest. Generally speaking, owls are solitary and nocturnal birds of prey, typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers adapted for silent flight. In size, they range from the miniscule elf owl (Micrathene whitneyi) — standing at 13.5 cm (5.3 inches) short — to Blakiston's fish owl (Bubo blakistoni) — a fierce looking owl that stands at 71 cm (28 inches) tall and weighs 4.2 kg (9.3 lbs). One is as a big as a soda can and the other a fire hydrant. The longest-lived owl ever recorded was a great horned owl (Bubo virginianus) — a large owl with feathered tufts on its head that resemble horns — that went by the name of “King Richard” — who was incidentally a female. While the average owl lifespan is about 10 years in the wild and reaches an upper limit of around 30 years in captivity (taking into account the extreme variability in species; usually, the smaller the owl, the shorter the life), King Richard reigned for 50 years before he bit the dust.

A side-by-side comparison of the world’s smallest owl species — the elf owl (Micrathene whitneyi) — and the largest — Blakiston's fish owl (Ketupa blakistoni).

Night Sight & Stereo Hearing

Large eyes are a predominant characteristic of nocturnal creatures and nighttime hunters. An owls’ eyes are so large that it cannot move them. What you’re doing now, shifting your eyes from side to side to read the lines of this book, an owl couldn’t do. That’s what its famously manoeuvrable head is for. The 360 degree turn, often seen in media, isn’t a real possibility — to do so an owl would need to break blood vessels and tear tendons in its neck. But it does get close. Able to swivel its neck 135 degrees in either direction gives it a 270 degree view of its surroundings without needing to move its body. So large are the eyes that supporting bone structures — called sclerotic rings — are needed to hold them in place. If you want to make yourself slightly uncomfortable and see how much skull space the eyes take up in certain owl species, all you’d need to do is take a peek beneath an owls feathers and into its ear to see the base of its massive eye. These massive orbs give owls some of the best night vision of any animal, and by sitting on the front of its flat face, it allows the owl a greater depth of field — as well as prevents it from having that somewhat brainless look that other birds have when viewed from the front.

Aside from eyes, an owls most notable characteristics may be the disk-shaped head and acute sense of hearing. These two traits are linked. Remember that ear you peeked into before? Well if you look for the ear on the other side of the owls head, you’ll find that it happens to be misaligned. The left ear of many owl species is positioned lower than the right and the two holes are out of alignment on the vertical plain as well. This isn’t just some quirk of anatomy, it’s yet another sensory adaptation for nocturnal hunting. The disparity in alignment causes incoming sounds to hit an owls ears at slightly different times, drastically improving its ability to localise the direction, height, and distance of the sounds source. In contrast, our symmetrically placed ear openings only give us a rudimentary sense of the direction a sound is coming from. In some extreme cases, such as the Tengmalm’s Owl, also known as the boreal owl (Aegolius funereus), the asymmetry is quite apparent in the structure of the skull. Although, typically, an owls ear holes are hidden beneath the feathery ruff of its facials disk. Thi circular face shape isn’t just decorative; made from a thickened ruff and filamentous ‘auricular’ feathers — “hearing feathers” — it’s structure guides incoming soundwaves to the owls ears, like a satellite dish picking up signals.

The skull of boreal owl ( Aegolius funereus).

You can see the asymmetrical ear openings — the lower one on the right and the higher one on the left.

Imagine a vole, a hamster-like rodent and common owl prey item, making its way through a grassy meadow, rustling a few blades of grass, maybe nibbling on some bulbs along the way. Hidden in the underbrush and under the cover of night, it feels safe as it goes about its business. However, unbeknownst to the vole, it is broadcasting its signal to a vigilant sentinel, one with asymmetrical ears and a disc-shaped face, that sits waiting in a nearby tree. The owl listens to the rodents movements. It gathers this data to construct a map in its head, pinpointing the voles precise coordinates. It hears the voles every move but the vole doesn’t hear the owl until a cage of talons encloses around its furry body, until its bones are crushes and its body is punctured — the grip of death is the last thing it hears and feels. How does an owl have such a mastery over sound? To hear everything but never be heard.

Silent Hunter

The owl's secret lies in its wing and feather structure. Broad and long, the wings of an owl can carry its body in a precise glide to intercept its prey. With fewer wing beats — less flapping, less noise — the owl can make a quiet kill, like floating death. But the true innovation lies in the unique leading edge of its primary feathers. Positioned at the front of its wing, the leading edge is where air meets the flying bird and causes gusts to blow over the rest of the wing. This turbulence creates noise. In some cases, this noise can be heard from far away; like the whistling of a soaring pigeon or the rhythmic humming of a swan in flight — a sound that they may use to communicate with one another over long distances. An owl, solitary as it is, has no need for this kind of communication. Instead, it opts to silence itself almost completely. Its primary feathers are serrated like a comb. This structure breaks down the turbulence and muffles the noise of air flowing over the wing as well as shifts the angle at which it flows — possibly shifting the noise to a higher frequency, one that its prey cannot hear. The velvety softness of the feathers allows air to pass through them, further eliminating noise. As the incoming air meets the secondary feathers, it hits soft fringes and tattered end feathers that break down sound waves moving over the wings. Finally, the fluffy down on the rest of the wings and legs absorbs any sound that remains.

Studies done to determine exactly how loud — or silent — an owls flight is have run into issues. One study (Wagner et al., 2017) on the features of owl wings and how they effect sound during flight, states:

But it has turned out a very difficult measurement problem to determine how quiet the flight of the owl is in absolute terms. The reason for this is that the flight of owls is so faint that even the most sensitive microphones are at their limit.

So, instead of taking the approach of unstoppable speed and a direct attack like many other birds of prey, such as hawks and falcons, owls take it slow — able to float at 3.2 km/h (2 mph) while listening for prey before gliding down to catch it by surprise. Generally, owl species that hunt for more cautious prey, like skittish rodents rather than oblivious fish, will have adapted broader combs on their leading edges. This widened structure further helps in reducing sound, allowing even gliding giants, like the barn owl (Tyto alba) or great grey owl (Strix nebulosa), to silently surprise jumpy mice and skittish lizards. Once prey is in its grasp, an owl uses tiny feathers — mostly bare barbs with a soft tuft at the end — called filoplumes attached around its beak and to its feet as "feelers", to discern and manoeuvre the prey before devouring it.

The structure of owl feathers and wings are the secret to their silent flight.

But not all species conform to the stereotype of a silent, arboreal, nighttime hunter. For one — or four, as there are four species — there are the fish owls (Ketupa spp.), who catch their aquatic prey on not-so-silent wings, as they lack the quieting comb-like fringes on their outer primary feathers. There is the burrowing owl (Athene cunicularia), a long legged and dower looking bird that spends most of its time on the ground and — as its name suggests — nests in underground burrows. The iconic snowy owl (Bubo scandiacus) bucks the trend of nocturnal hunter, forced to catch prey during the day due to the the extreme shifts in daylight in its Arctic habitat.

Deadly Omen or Wise Bird?

A finger painting of a long-eared owl in Chauvet-Pont-d’Arc Cave, thought to be over 30,000 years old.

Owls have long flown silently through the minds of humans. Their eyes reflecting the luminescent moon, like celestial lanterns, holding us captive in their gaze. The spectral echoes of their hoots; the language of a nocturnal woodland realm that both enchants and haunts us. One of the earliest depictions of owls made by human hands comes from a cave in southern France named the Chauvet-Pont-d’Arc Cave. It is a finger painting more than than 30,000 years old. From there, owls appear in myths and stories around the world; showing up in Ancient Greece in Aesop's Fables and as the goddess Athena’s companion — minted on coins and painted on pottery. They represent a bridge between the surface world and underworld in Norse myths; able to move between the worlds of the living and the dead. In Hindu myths they are the vehicle of Lakshimi, the goddess of wealth. In certain African cultures their body parts are used in witch doctor rituals and medicines. They appear in petroglyphs made by Indian American groups and in English literature through poets by the likes of Robert Blair and William Wordsworth.

A painting of a pair of barn owls by Robert Havell for John James Audubon from 1827.

Over the millennia, we can trace our conflicted relationship with these birds — varying, of course, between cultures — from wise seers and benevolent guides for those who’ve perished, to omens of illness and certain death. The use of their parts by witch doctors may be the result of their long-perceived status as harbingers of ill fortune. In some cultures, the hoot of an owl proclaims a person's death — used by Shakespeare in Macbeth and Julius Caesar and present in Māori myths about the ruru (Ninox novaeseelandiae) — in others — such as in the Middle East — the sight of an owl may be associated with great violence and much death in an upcoming battle, while the call of an owl forecasts an unfavourable day. In the Christian religion, the owl, particularly the barn owl, foretells one's doom and its shriek is evil and demonic.

Why do owls captivate us so? Maybe it’s because they represent such an inverse of our own lifestyles or because of our associations with the night; a place of mystery, where darkness obscures and hides the world from our eyes. Creatures that dominate this domain, whose senses have the power to pierce its darkness, would understandably fascinate us light-loving animals. Owls keep watch of the night. They see things that most animals don’t. Their nocturnal behaviour, combined with their cryptic plumage, large eyes, and keen hunting talents, create the image of an intelligent bird. But, do actual owls exhibit the wisdom & intelligence of their mythological counterparts?

While we can be pretty certain that owls aren’t portents of death, and hearing one hoot won’t make you drop ill with a fatal disease, it is harder to test the owls sharp-minded and/or wise reputation. This is mostly due to the slippery problem of defining intelligence itself. As a social species, we humans have placed certain social behaviours and abilities on a pedestal. We are biassed towards the species that can form tight bonds and cooperate together in groups, for example. Owls are solitary species, not evolving complex social abilities because these simply didn’t help them survive, given the way in which they live.

What about puzzles and tests of problem solving?

When compared to other avian groups — especially those of a particularly social sort, like corvids and parrots, those that we consider to be the “smartest” — the owls do not fare well. It’s sometimes said that owls are stupid or perform very poorly in animal cognition tests, but this doesn’t tell the whole story. Studies have found that about 75% of owl’s brain is devoted to the senses of sight and hearing. That leaves owls with 25% the brain to process that data and make decisions. Owls can judge the distance, speed, and weight of prey in near-pitch black. Their night vision is often superior to a crow, who has to rely on resourcefulness rather than hunting to survive. Similarly, owls are the masters of stealth movement. In one experiment, an owl took flight from one location to another without creating any sensation. Even the sensitivity of microphones didn’t pick up any sounds.

An owl may not be able to fill a beaker with stones until it can reach the water or use a stick to excavate burrowing insects but it can, for example, identify the scuffling of a mouse under a pile of snow, precisely pinpoint its location using its hearing alone, and noiselessly swoop to snatch the surprised rodent up in its talons, all in the dead of night. This is partially why calling an owl “dimwitted” feels erroneous.

The hunting talents of owls extend beyond catching prey at night. For example, the little owl (Athene noctua) stashes meat to cultivate maggots and larvae as a food source, and burrowing owls use dung as bait to attract dung beetles. Owls are certainly capable of intelligent behaviours. They just don’t rely on them in order to survive most of the time. They’re purpose built for the hunt; their senses honed to perfection, they are some of the stealthiest animals alive. Perhaps that makes their symbolism as a death omen more accurate than that of the wise owl — they certainly spell death for any small animal bold enough to be noisy at night. At the end of the day they may not fit our definition of intelligence, but they should perhaps be regarded as extremely specialised, experts in what they’ve evolved to do, and be thought of as no less for it.

 
Alexander Julius Jensen