The Owl Who Liked Sitting on Caesar

by Windrow, Martin

Tawnies have an acutely hooked beak, to keep it out of the way of their field of vision, and the thick face feathers make it look much shorter than it really is. It is made of bone, but with an outer layer of keratin; Mumble’s beak was dull yellow, fading to pale grey at the sensitive base or cere, where the nostrils were just visible under a fringe of whiskers. Most of the textbooks say that owls have almost no sense of smell, but some experienced handlers dispute this. The fact that tawnies won’t touch carrion in the wild, but accept fresh dead chicks in captivity, would suggest that they can certainly tell how old meat is. The whole subject of the sense of smell in birds is only sparsely researched, and much of the work that has been done focuses on a few species for whom it clearly is important, such as the dim-sighted, ground-hunting New Zealand kiwi, and some types of far-roving seabirds. However, a study of the Short-Eared Owl established that the part of its brain that processes smell – the olfactory bulb – is of comparable size to that in pigeons and chickens, and bigger than that found in starlings. This is significant, because pigeons, chickens and starlings are all known to make quite subtle use of their sense of smell. (Dr Graham Martin, from whose book Birds at Night I gratefully harvest this fact, follows it with a dry comment to the effect that it therefore seems ‘inappropriate to conclude that a sense of smell is irrelevant to owls’. And Dr Martin had a long-lived pet tawny, too.)

  Mumble’s ‘whiskers’ were a moustache-shaped array of bristly little rictal feathers that spread out sideways from immediately above her beak – the ‘bridge of her nose’ – and extended down and outwards under her eyes. Owls’ vision is surprisingly poor at very close range, and they close their eyes to protect them while they are using their beak. There is a rich supply of nerves at the base of these rictal whiskers, so they must trigger sensory receptors that pass information to the brain about anything they touch.

  Usually only the central hook of Mumble’s beak was visible, above a brown ‘goatee’ mark among the pale feathers covering her throat. However, when she yawned she revealed a wide gape, and the corners of her mouth were actually aligned with the centres of her eyes. The hooked upper mandible overlapped the lower one all round, and both were edged with sharp blades that closed across one another like a pair of scissors. The beak was not only part of Mumble’s killing equipment but also her knife and fork, as well as sharing to some extent the role of ‘fingers’ with her toes. Since a bird’s upper limbs are devoted almost entirely to flight, it has to use its beak to check things out and make small manipulations, and Mumble could use her potentially very powerful bite with great delicacy.

  I learned that a bird’s tongue has a bone in it, and taste buds at the base (though relatively far fewer than in humans). Even though Mumble often yawned I have no note of ever having seen her tongue; this was shaped like a willow leaf, and she must have kept it pressed down inside her beak. Birds have a larynx, but, unlike that of mammals, it is not used for producing sound. Mumble’s voice was produced by an organ called the syrinx, much further down her respiratory tract, and when her beak was closed there was a direct connection between her windpipe and her nostrils – thus, presumably, her apparent ability to ‘sing with her mouth closed’.

  Birds have no sweat glands in their skin, and when a tawny is feeling hot or stressed it sometimes seems to pant, with its bill half open and its throat feathers rising and falling. I noticed this in Mumble only at moments of high excitement, such as imminent combat.

  * * *

  I knew from my reading that Mumble’s ability to engage acutely with the world around her depended as much upon her ears as her eyes, but their extreme refinement was even less visible from the outside.

  The Tawny Owl’s ear cavities are holes in the lower part of large, slightly banana-shaped trenches set vertically into either side of the skull behind the edges of the facial disc. The textbooks explained that the eardrum is linked to the cochlea or inner ear – and thence to the auditory nerve – by a single complex bone in the middle ear called the stapes, a relic of birds’ evolution from reptiles. This amplifies the sound vibrations by a factor of about sixty-five – three times the efficiency of the three bones of our own middle ear. The membrane in the cochlea of an owl’s ear is relatively enormously long, with huge numbers of the hair cells that transmit pressure waves to the nerve that carries the signal to the auditory centre in the brain, so owls can detect much quieter sounds than other birds can. In mainly nocturnal owls like the tawny, this auditory centre is itself several times larger than those of daytime birds of comparable size, such as crows; it is also relatively larger than those of less nocturnal species, such as Eagle Owls and Little Owls. (This obviously makes sense: if you hunt in better light conditions you can usually rely upon your eyes, so you don’t need magic ears.)

  The owl’s brain can register the minutest differences in the timing of the arrival of sounds in each of its widely separated, asymmetric ears – to within about one 30,000th part of a second (about fifteen times better than our ears can manage, despite their being far wider apart). Owls have an innate ability to identify the angle of a sound’s origin precisely, to within less than 2 degrees of the compass. If a sound is repeated, they can then estimate the distance of the source, though this skill seems to take practice to perfect – it is a learned behaviour rather than instinctive, and seems to depend on their familiarity both with the type of sound and with their surroundings. Once acquired, this ability enables an owl to triangulate – to judge accurately both the direction and the range of whatever is making the sound.

  In conditions so dark that they must rely entirely upon their ears, a first sound for direction-finding, followed by one repetition for range-finding, is enough to guide a Tawny Owl right in. It doesn’t make the confident pounce of an attack on something that it can see, but glides in more tentatively, with legs extended and swinging and toes spread widely, to feel for the prey in the place to which its ears have guided it. In one indoor experiment carried out in artificially complete darkness, a mouse was released on a smooth floor with a leaf attached to the end of its tail; the owl’s first strike hit the rustling leaf. Importantly, however, owls only seem willing to attempt this sort of blind kill in an area that they know intimately, and when they do so it has been recorded that they then follow an exact reverse bearing when carrying the prey back to the roost – which must mean that they are relying upon their memory to guide them home.

  As with their eyesight, their sound-location is enhanced by the long, flexible neck that allows them to move their head through wide angles in any direction without moving their bodies. They constantly check, update and compare the stream of signals they are picking up, by bobbing and twisting their heads to vary the position of their ears. Incidentally, there is no evidence at all of owls using echo-location like bats – that is, of them making a sound themselves and gauging distance by the delay before its echo is reflected back to them. However, while sharing my flat with Mumble I did notice that she sometimes seemed to mistake the origins of a sound from close range – she might look in quite the wrong direction, even at 180 degrees from the true source. It occurred to me that she might be picking up ricocheting instant sound-reflections from the enclosing walls; perhaps her ‘computer’ was cluttered by these short-range echoes inside a confined space?

  The soft crown feathers over most of Mumble’s head stood up in a continuous ball-like surface, light brown with a fore-and-aft pattern of dark brown curving lines. I knew that she had feathered flaps of skin along the front and back of the ear trenches just behind the edges of her face, the front flap being larger than the rear one and coinciding with the ruff of stiff little feathers that surrounded the facial disc, but these flaps were completely invisible in the fluffy ball of her head. Occasionally, when I was watching her at rest, I saw subtle movements among the feathers on the sides of her head, and I knew that she was focusing these ear flaps to amplify sounds – for instance, raising the front flaps improved her backwards hearing, as if you were cu
pping your hands in front of your ears.

  Once, when we were having a mutual preening session, she rubbed her head sideways against my nose, and the dense feathers parted for a moment. Squinting down, I could see inside her ear: it looked alarmingly big, as if it nearly bisected the side of her skull. It resembled a gently curved trench walled with smooth pinkish-grey plastic, and seemed to have an almost cylindrical ‘pipe’ passing sideways across the bottom, finely webbed with white filaments. (My knowledge of owl anatomy is still distinctly patchy, and I don’t think I could bear to attend a dissection. Could this have been the conduit carrying the optical nerves linking her eye to her brain?)

  * * *

  It is clear that Mumble had wonderfully efficient eyesight at low light levels, and perhaps even more efficient hearing. Nevertheless, in the present state of scientific knowledge it is impossible for us to appreciate the full range of her capability to perceive and make sense of her world. Apart from our very imperfect knowledge about her sense of smell, we can only guess the ways in which the input she received from all her separate senses and memories was integrated – that is, how it all came together in her brain.

  Imagine this: you wake in the middle of the night, and visit the bathroom without turning on a light. How do you do this? (Yes, of course you occasionally – and memorably – stub your toe; but that’s usually when your awakening has been sudden, and you start moving before getting yourself mentally centred. When an owl is suddenly startled into night flight, it too may collide with branches.)

  Your brain has stored spatial memories of the layout of your home, allowing you to anticipate each step. Your sense of distance covered is imperfect, but your bare feet tell you when you are crossing from one floor surface to another with a slightly different texture. Your eyes are almost useless, but not quite: if the slightest light is seeping in around a curtain, you are aware of dim reflections off pieces of furniture, confirming your mental map. Whether or not you are conscious of it, your ears are picking up sound clues – the quality of echoes from surfaces, the lack of them from empty spaces, the faint sound made by water in central-heating pipes. Perhaps there is even the sound of a dripping tap, and the faintest smell of perfumed soap from the open bathroom door ahead of you (and if the bathroom is tiled, the difference in sound quality will certainly be detectable as you approach it).

  Each of your separate senses is providing your brain with an absolute minimum of input, but their integration builds a mental picture of your surroundings that may allow you to move in the darkness with reasonable confidence. If you were an Australian aborigine, a Kalahari bushman, a member of a remote Amazonian tribe – or your own fifty-times-great-grandparent, anywhere in the world – you would still be able to do this out of doors, without consciously thinking about how you were doing it. Well, an owl can do it, with laughable ease.

  There even seems to be a possibility that owls have access to information from one sense that we do not have. Recent research into other bird species suggests that their ability to orientate themselves by day and night may owe something to a perception of the Earth’s magnetic field. Studies of this capability in birds – which have naturally concentrated on migratory species – are in their infancy, but have already yielded some remarkable suggestions. It has been established that not only pigeons, but also some non-migratory birds such as chickens, have minute deposits of microscopic crystals of magnetite (a type of iron oxide) around their eyes and in their nasal cavities. Separate experiments with European robins also suggest that a chemical reaction triggered in the left side of the brain by light entering the right eye is connected with their ability to navigate. The implication is that these parallel perceptions may be comparable to a sort of magnetic compass and a magnetic map of the bird’s surroundings. And a significant minority of owl species – including, in Britain, Long-Eared Owls – do make seasonal migrations. (Again, I stress my ignorance of ornithology; but it makes you think, doesn’t it?)

  * * *

  Mumble had an astonishing ability to change her appearance, which was due to the mismatch between her actual body and her loose, elastic suit of feathers. Nowhere was this more surprising than on her head and neck. The best way to describe this area of the outer Mumble is as an extremely extendible and compressible toque – one of those woolly tubes that outdoor types wear around their necks, which can also be stretched up over the back and top of the head like a balaclava, while the lower end stays stacked around the throat in folds. Mumble’s toque began at the dark edge of her facial disc, and ended in an in visible merging with her upper torso. It was a while before she revealed to me just what she could do with it.

  She made it clear from an early age that she hated and despised pigeons. On the fairly rare occasions when one of these urban scavengers landed on the balcony rail, she would always explode into action straight out of her daytime doze. She would hurl herself at the wire mesh as close as she could get to the intruder, and for some time after the pigeon had exclaimed ‘Oh, ****!’ and fled, she would cling there silently with fanning wings, staring eyes and half-open beak. When she was free in the flat at weekends I would occasionally hear a sudden flapping and the scrape of claws, and knew that she had spotted one of these (in her estimation) avian guttersnipes getting too close to her territory.

  One afternoon Mumble was sitting quietly on the long western windowsill on a favoured perch – a large ceramic keg with a solid top. I happened to point my camera at her at exactly the moment when a pigeon must have arrived on the balcony, and so I saw through the viewfinder her transformation, over a period of about five seconds, from fat, contented owl to thin, suspicious owl. It was as marked as the difference in appearance between, say, a cabbage-shaped lettuce and a cos lettuce; some books say that this response is an automatic attempt by a roosting owl to appear more like a part of the tree trunk it is sitting next to.

  First, her head turned towards the intruder, and she fixed her eyes on that bearing with utter intensity. Then, the outline of her body visibly changed: without (on this occasion) extending her legs and standing tall, she compressed her rear shawl feathers so that she grew thinner. Her toque seemed to slip downwards, and a complete change came over her scalp and face. The round ball of her head shrank and altered shape, as the feathers on the back flattened and the frontal crown feathers stood up sharply in a partial ‘Mohican’. The feathers above and between her eyes dropped and stuck forwards horizontally, like bristling eyelashes, and her eyes slitted. Simultaneously, the planes of her facial disc on each side seemed to flatten backwards, giving her a distinctly hatchet-faced look. In those few seconds Mumble’s whole aspect had changed from benign boredom to unmistakably hostile suspicion. She was suddenly an owl on whose wrong side you definitely would not want to get.

  * * *

  When she was in repose, the feathers on the top and back of Mumble’s head seemed to run back seamlessly, in a single hood, down into the thick shawl of light brown scapular feathers covering her shoulders and upper back. Except for the outer edges, which were delineated here and there with white feathers barred with dark brown, it was almost impossible to see where each mottled shawl feather met the next, but there was a slight contrast between the whole mass and the darker contour feathers that clothed her lower back.

  Birds have many more touch-receptor cells in their skin than mammals, and it is believed that a layer of hair-like filoplumes growing beneath the body feathers gather information about pressure and vibration. These pass messages to the brain about the relative positions of the various feathers, and thus enabled Mumble to ‘adjust her clothing’ more or less unthinkingly. Consider this ability in human terms – and be envious. You wake from a nap, and only after you happen to pass a mirror do you realize that you have been walking around with mad hair. If you were an owl, you wouldn’t need a mirror; you would somehow be conscious mentally that your hair was in disarray – and much more acutely conscious of it than your present dim awareness of the pressure of your
clothes against your skin. An automatic mental message would pass to muscles in your scalp (admittedly, it would have to be a fairly loose-fitting scalp), and these would shrug your hair back into place and settle it. Who knows, you might even be able to lift a stray forelock out of your eyes without using your hand.

  * * *

  The whole front of Mumble’s body was covered with thick, fluffy, creamy-white feathers each with a central vertical streak of dark brown. (When she moulted, I could see that in fact only the ends were white and brown – the greater part of each feather was made of loose dark grey filaments, but her plumage was so thick that these were completely hidden from the outside.) These insulating layers were deep and very soft, designed to keep owls warm during long winter hours spent motionless on their roosting branches. Birds have a significantly higher body temperature than we do, and a tawny’s luxurious clothing is a built-in duvet. These fluffy feathers continued down her belly, and back between her legs, becoming plain white in colour where they covered the bottom cone of her body beneath her tail. This cone was an extension of her pelvis, not her vertebrae.

  Growing on the separate end of her spinal column, above the cone, were Mumble’s twelve long tail feathers or retrices (rudders), their bases reinforced and thatched in above and below by smaller covert feathers. The central four rudders were narrow, of almost constant width, and plain donkey-brown apart from a small off-white tip. On each side of these were four broader feathers, patterned with bars like the flight feathers of her wings. When in sustained flight she spread out all twelve side by side into a broad, rounded fan; as far as I could tell from snatched glimpses, they seemed to be arranged not in a flat plane but in a very shallow arc, with the central four feathers highest and the others slanting away on either side, each overlapping the one below and outside it. When Mumble was settled she swivelled the patterned outer feathers inwards into a single neatly interlocked stack under the plain central feathers, like the folded vanes of a lady’s fan.