The Owl Who Liked Sitting on Caesar (12 page)

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Because even owls’ ability to see in darkness has its definite limits, hearing is actually at least as important to them as eyesight, and much more important when the darkness is at its deepest.

An owl’s highly developed ears are located in two vertical ‘trenches’ in its skull located just behind the edges of the facial disc. The shape of the facial disc gathers sound, because the dense ruff of feathers around the edges forms a dish, and there is some evidence that the consistency of the tiny face feathers also plays a part in this effect. The pitch or frequency of sounds is measured in units of kilohertz; human ears (when young – an important qualification) can detect sounds within a wide range of between 2 kHz and 20 kHz, but are most efficient at around 4 kHz. Tawny Owls’ hearing is also at its most acute at medium frequencies, between 3 and 6 kHz. It has been estimated that within certain given frequencies an owl’s ears are ten times more efficient than ours, although this varies from species to species; for instance, Barn Owls have an optimum frequency of 7 to 8 kHz. Hearing in owls has been estimated to be perhaps 300 times more acute than that of daytime birds, but – as with their eyesight – its
superiority is nothing like that great when compared with either humans or cats. (And as with eyesight, there are important qualifications to any headline figures, to take account of variables like background noise. Hunting by ear is obviously far more difficult on a windy night in the woods than on a still night in the middle of a cropped field.)

An owl’s range of aural perception coincides with the sort of noises that a rodent makes when rustling through grass or leaf-litter, and if the potential meal is foolish enough to squeak then the owl’s job becomes very much easier – as the pitch of a sound rises, the owl’s ability to pinpoint it in space improves. (Shrews are extremely quarrel some creatures with high-pitched voices, and their ‘sound discipline’ at night is stupidly lax; we might guess that it is only their vile taste that has stopped owls wiping them out long ago.)

In addition to acute hearing, the more nocturnal species of owls have a highly developed ability to process the information that reaches their ears, filtering out the distracting background clutter and drawing conclusions from the sounds that interest them. Their brains include a sort of ‘target acquisition computer’, which calculates the angle and range of whatever is making that attractive rustling or squeaking noise. This capacity for fine judgement is enhanced by the fact that some species – including Tawny Owls – have asymmetric ears, with one slightly higher than the other and oriented at a slightly different angle, so that even when the head is motionless a sound reaches each of the two ears after slightly different time
delays. In tawnies this asymmetry only affects the soft outer flaps rather than the actual passage through the bone; in some other owl species the difference is more pronounced, and one ear trench is also noticeably larger than the other, giving the skull a slightly uneven shape.

As well as equipping them superbly for night-time hunting, their all-round vision and sophisticated auditory equipment naturally make owls, in their turn, extremely difficult to sneak up on. While it is far from true in other parts of the world, in Britain an able-bodied adult of the larger species of owls has very few natural predators to fear. (There is one report of a Tawny Owl being taken from its daytime roost by a buzzard, at a time when rabbits were particularly scarce in that area; but the owl fought to the death, inflicting such serious damage on its killer that this must presumably be a rare event – predators will always prefer to go for an easy kill.)

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Because Tawny Owls are so relatively plentiful in Britain, and so attached to permanent territories, ornithologists have been able to make some quite thorough studies of their way of life. This applies particularly to their rearing of families, during a time of the year when, necessarily, they stick close to home and follow repetitive patterns of behaviour.

Tawny cocks and hens first seek mates around the turn of the year, when they are perhaps eight months of age. By this time they have survived the initial shock of their first
early winter in the territories that they established during the autumn. Courtship among all territorial carnivores must certainly be a nervous business, since their instinct is to challenge, drive off or attack all strangers. Tawny Owls show little if any difference in appearance between the genders, but are clearly able to recognize each other’s sex and individual identity by means of calls. (Some species of owls, though not tawnies, sing formal duets together at a distance before approaching one another.)

It is often said that cock tawnies give their familiar wavering hoots, which are answered by the hens with sharp ‘kee-
wikk
’ calls. This does happen, but the distinction is not rigid; both cocks and hens make both sounds, though not during the same conversation. Although Mumble might suddenly exclaim ‘kee-
wikk
!’ if she seemed to hear some distant hoot, her initial long-range calls were hoots; the hoot most often seems to be the question and the ‘kee-
wikk
’ the reply, from either sex. (This means that the traditional rendering of the call as ‘
tu-whit … tu-whoo
’ merges both question and reply, and puts them the wrong way round – it should be ‘
tu-whoo … tu-whit
’.)

If all goes well at what we might call the ‘e-mail and phone-conversation’ stage, the male flies closer to the female and, after a certain amount of eager chasing through the trees, the pair tentatively agree to meet. From that point on body language plays the major part in their exchanges. Once a male and a female Tawny Owl have, as it were, agreed to lay aside their weapons and discuss this situation like adults, they settle on a branch for
face-to-face negotiations. Some courting cock birds have been seen bringing the hen a gift of food, to break the ice. The cock utters a variety of quiet grunts, croons and clucks while sidling forwards and back again, swaying and nodding, alternately raising his wings and puffing out his body feathers, and then sleeking himself down again. He will sometimes be allowed to get close enough to nibble at the hen bird’s beak.

With luck, this performance will eventually earn him a softly repeated invitation from the hen; the cock then mounts her from behind, and Nature takes its course. As with many bird species, while the drive to mate is strong the actual moment seems to be a fairly brief and mechanical affair, distinctly short of ecstasy. To us the process anyway looks frankly impossible, since it involves the alignment of two internal vents hidden by feathers, but it clearly works for them. However, when the climactic moment has passed the pair will then roost together, side by side. Their earlier mutual suspicion is forgotten; pressing closely together, they will spend long periods preening each other’s faces, heads and necks, in what certainly looks like highly pleasurable pair-bonding.

While we cannot tell whether or not they are invariably faithful, Tawny Owls are monogamous. There are differing opinions, but most ornithologists believe that tawnies mate for life, although the pair do not live together all year round. They often roost separately – notably during the autumn, when their annual brood of owlets have dispersed. Nevertheless, as soon as the pair-bond has formed they
establish a joint territory for hunting, and thereafter they will share it for life, working together to expel any competitors. A famous study carried out in the early 1950s over some 1,300 acres in Oxfordshire (led by Britain’s doyen of Tawny Owl studies, Dr H. N. Southern) estimated the pair territories at between 32 and 50 acres – smaller in close woodland, larger in mixed woods and open country. Size is determined by a territory’s richness in prey animals: further north in Britain territories of up to 80 acres have been recorded (and a German study in much less prey-rich conifer forest found pair territories that seemed to cover several hundred acres). The boundaries of this hunting range seem hardly to change from year to year, since both cock and hen defend it fiercely from rival pairs and from hopeful juveniles seeking a first territory in autumn.

In England, mating pairs of tawnies establish a nest in February or March each year, and may well use the same few convenient sites in their territory year after year. As in their eating habits, tawny homesteaders are extremely easy-going. They can’t be bothered to build nests themselves, and usually prefer to move into existing holes in tree trunks or stumps – often courtesy of woodpeckers. Alternatively, they may take over the abandoned nests of other large birds such as sparrowhawks, jackdaws, magpies and crows, or even old squirrel dreys. Unlike Barn Owls, they will not tolerate humans close by, but they may choose to set up home in a suitable corner of a derelict building, and they are perfectly happy to use artificial nesting boxes (though these have to be of a different design from those
provided for Barn Owls). In conifer plantations with plenty of ground litter, and in extreme areas of their geographical range such as the thinly wooded Scottish highlands, they may even nest on the ground. This casual attitude extends to the interior furnishing; tawnies make no effort to line a nesting hole with soft materials, since the hatchlings will emerge from the egg well protected by thick, fluffy down.

* * *

Usually the hen lays three to five white, spherical eggs over a number of days from about mid-March, and sits on them for just under a month until they hatch; during this incubation period she is fed by the cock bird. Depending upon region, climate, prey availability and other variables, the staggered hatching of the owlets may be completed during April or not until June. From the time when the last hatchling breaks out of the egg the cock bird needs to catch perhaps a couple of dozen prey animals each day, depending upon their size. Each of the owlets needs feeding several times daily; the cock also has to hunt for their mother, who remains in the nest with them, and to keep up his own strength for this exhausting effort. This often forces him to continue hunting from dusk until well into the next morning in order to satisfy his family’s endless demands (which is certainly no fun for him, but provides us with our few opportunities to see a Tawny Owl out and about by daylight).

The hatchlings remain in the nest with the hen bird for about three weeks before they achieve the strength and
confidence to start creeping outside and moving about. They grow very fast, and their ravenous appetite increases with their size. At this point the demands of feeding the whole family become more than the most dedicated father can handle alone. Thereafter both parents have to take turns in a busy hunting rota throughout this fledging stage, and the fledglings remain dependent upon their parents for all feeding for up to another twelve weeks. To satisfy their voracious demands the parents have to provide well over a thousand rodents and small birds during this period. Among daytime raptors the parents will usually break up the prey and feed their chicks with bite-sized chunks. Initially Tawny Owl mothers will also roughly butcher the prey – at least taking the head off, to get the owlets started – but before long the babies’ own claws and beaks are strong enough for them to manage on their own when a meal is too big for swallowing whole.

The fledglings are both fearless and curious; they test their strength and agility at first by exploring the immediate surroundings of the nest, and then by venturing further – a procedure known as ‘branching’. Their parents’ child-minding is complicated by the fact that the fledglings tend to go off on expeditions in different directions; this perhaps has survival value, so that their loud demands for food do not attract a predator that could kill the whole brood at once. While they are still covered with fluffy down, rudimentary wing and tail feathers are appearing through it and growing stronger every day. At first the owlets can only make hopping jumps, but after perhaps a
week outside they get more ambitious. Over about two more weeks their attempts develop from ‘parachute jumps’ to short glides, and then to true, flapping (though rather hit-or-miss) flights from point to point.

It is in this period of their growth that people may find ‘lost’ fledglings on the ground or among bushes. They usually aren’t lost at all, but simply exploring; unless they have been injured they are strong climbers, and are probably perfectly capable of getting home by themselves. Unless they are obviously injured or in a dangerous spot, would-be ‘rescuers’ should not ignore their touchingly brave, hissing displays of defiance – even at this age they know what is best for them.

By about seven weeks after leaving the nest Tawny Owl fledglings are approaching the same size as their parents. For about another four or five weeks – so for April hatchlings, until say mid-July, but for May and June hatchlings, perhaps until August or even into September – the juvenile owls continue to explore their parents’ territory. Their instinct to look out for anything moving and to pounce on it seems to be innate. One would expect them to be practising finding and killing prey during this ‘adolescent’ phase, perhaps imitating demonstrations by their parents, and this may be the case. However, while studies are sparse, one published paper did report that during fledging the owlets observed were not actually catching prey for themselves, but continued to rely on their parents for food – for which they called, monotonously, from whatever perch they happened to have reached in
their wanderings. (Parents of teenagers will empathize.)

If this surprising report is true, then the youngsters must be confronted with a brutal challenge indeed when – about twelve weeks after they first leave the nest – their parents stop feeding them, and subsequently force them to disperse independently to seek their own territories. At this stage in late summer the family is disbanded; the exhausted parents separate for a few months, although both remain in their shared hunting territory. From that point on the year’s brood become competitors, and it is pretty much a case of every owl for itself. (However, there are anecdotal reports of adolescents and mother birds occasionally being seen together subsequently, sitting on adjacent perches and calling to one another in a conversational way.)