The tawny owl: night hunter

The tawny owl is most in evidence during the hours of darkness, when its exceptional hearing, sensitive vision and noiseless flight make it a particularly effective hunter.

Tawny owls are highly specialised nocturnal hunters. Although the head may seem dis

A tawny owl

Image via Wikipedia

proportionately big, inside the skull are two large, asymmetrical ears so sensitive that they can pick up the rustling and high-pitched squeaks of nearby prey after dark. They can pinpoint a moving target like a mouse with such accuracy that a miss is rare. In addition owls have unusually large eyes. These are forward-facing—like human eyes and binoculars—for three dimensional vision, which enables owls to judge distance accurately.

The owl can turn its head both left and right (like a radar scanner) to inspect a full 360 , so the bird can search for and locate its prey while keeping its body still. The ‘facial disc’ of rather stiff, bristly feathers serves as a reflector, collecting sounds and focusing them on the ears.

Silent hunter

The essence of effective nocturnal hunting is the silent approach—and again, in the tawny owl, evolution has come up with the necessary adaptations. The outer surfaces of the feathers have a velvety finish to deaden noise, and the feathers of the leading edge of the wing have a special comblike fringe to silence the wing as it cuts the air.

Tawny owls will usually sit motionless on a branch, waiting for some unwitting meal to pass below. The owl then drops silently on to its victim, seizing it in the fierce grip of large, sharp talons. If this does not kill the prey instantly, the death blow may be administered by a sharp bite at the base of the skull.

Food supply

Although the tawny owl is primarily a rodent killer (voles, mice and rats are all acceptable), shrews and small birds have good reason to be concerned by its presence, as their remains regularly feature in pellets. Owls often swallow their prey whole and the regurgitated pellets are made up of the in-digestible remains of its prey such as bones, fur and feathers. These left-overs can provide valuable clues to its diet. In the case of the tawny owl, rodents and birds occur prominently, but the wide variety of its diet (and thus the adaptability of the species) can be gauged by the regular presence of fish. Amphibian and reptile remains. Nocturnal observations show that invertebrates, particularly worms which do not leave easily recognisable remains in the pellets, also feature largely when more substantial prey is in short supply.

Family planning

In some uncanny way tawny owls seem able to assess the likely food supply at the start of the breeding season. In years when small mammals are low in number, clutches of eggs tend to be small; the number of eggs increases when mice, moles and small rabbits are more plentiful. Tawny owls usually have a single brood of young each year—and this occurs from mid-March onwards. Unlike small birds, which wait until their clutch of eggs is complete, the female tawny owl starts incubating as soon as she has laid her first egg, which is like a ping-pong ball in size, shape and colour. The chicks hatch at about two-day intervals, each egg taking 28-30 days to hatch. The chick waits fretfully in the nest for food—usually mice, shrews and sometimes even small birds. The first born tends to get more than its fair share of the food, the result being a considerable difference in size between youngest and oldest. If food is plentiful, then all is well. Should food fail, then the biggest chick eats the smallest one. It may sound unduly brutal, but for the survival of the species it is better that two chicks die to provide food for a third, than for all three to die of starvation. In exceptionally hard years when the shortage of food is acute, the tawny owl may not breed at all.

The owlets fledge (leave the nest) after five weeks, but for the next three months they continue to demand parental attention with hungry ‘ku-wek’ calls at their regular feeding stations, scattered through the woodland. After August, the parent owls begin to re-establish their territorial boundaries and the familiar calls, ‘hoo-hoo-hoo’ and ‘tu-whit’, are often heard. The youngsters finally move off or are driven away by the parent owls. This territorial activity increases in January and is probably at its height in February and March. Autumn and winter are the times when mortality is at its highest, particularly for the young birds, when cold weather and food shortages take their toll. Sadly, some also die in collisions with cars after dark on country roads, when the owls are dazzled by headlights.

Favourite nest sites are hollow trees, or cavities found in deserted buildings. One give-away sign of an owl’s nest—or roosting site— is pellets around the base of the tree. Occasionally, eggs are laid in old nests of other birds such as magpies and carrion and hooded crows. If there is a scarcity of trees, tawny owls will even nest on the ground, perhaps choosing an old rabbit hole. Tawnies also take readily to nestboxes, and a barrel with good drainage holes, if slung at an angle beneath a high branch sheltered from direct wind and rain, will often tempt a pair of owls. The best time to go out and see tawny owls is on a clear night and at dawn, when they are returning to roost for the day.

The tawny is Britain’s most numerous and widespread owl, though absent from Ireland; its place there is filled by a different species, the long-eared owl (Asia otus). We think of it very much as a woodland bird, and to a degree this is true. However, there are plenty of mice, rats and house sparrows in towns, plenty of parks and large gardens with trees large and old enough to have holes for nesting—and of course there are plenty of suitable buildings like churches in which to nest. Add to this the very catholic diet of tawny owls, and it becomes less surprising that these adaptable birds have taken to urban and suburban life so well.

15. November 2011 by admin
Categories: Ecology/Habitat, General Info | Tags: , , , , , , , , , , , | Comments Off on The tawny owl: night hunter

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