THE BARN OWL (Tyto alba) is widespread through much of the world, excluding only the far north and the far south. It is widespread in mainland Britain too, although its population at any one time is mostly guesswork. It is the most recognisable of our owls although the tawny owl is much better known (it’s the one that hoots). But the barn owl’s striking plumage – pale gold upper wings, back and head, often mottled with silver or bluish-grey details, and white face, breast, underwings and long dangling legs – make it impossible to mistake for any other species. But a variant, Tyto guttata, in mainland Europe has darker plumage and in some cases, no white plumage at all, and these occasionally turn up along our east coast just to keep birdwatchers on their toes.

The barn owl is primarily nocturnal although it is often visible at dawn and dusk, occasionally in daylight too. But it is supremely adapted to hunt at night with extraordinary eyesight, virtually silent flight, and (as with all owls) its ears are asymmetrically positioned on the side of its head creating a short time-lag between two pulses of sound, an arrangement that facilitates pinpoint accuracy in locating prey on the darkest night. Then, it looks supernaturally white in flight, an illusion assisted by its equally supernatural silence. In daylight, hunting when food is scarce or when it must service the demands of a large brood of chicks in the nest, the wings seem disproportionately long (85cm – almost three feet) for the compact size of head and body.

The barn owl is a fusspot with very specific requirements. The nest must be sheltered and ready-made, for it builds nothing at all (that matt of regurgitated pellets hardly amounts to any known definition of “building”). So it likes holes in hollow trees, recesses in caves, the roof spaces of old buildings like barns, church towers, belfries, broken down chimneys, but it also takes readily to well-designed and thoughtfully sited nest boxes.

But it is even fussier with its diet. Its wellbeing in any one year is inextricably linked to the well-being of field voles, its principal source of food. Alas for states of wellbeing, vole populations are notorious for chaotic fluctuations. In any period of three or four years there is likely to be a population crash and a population boom known as a “vole plague year”. Barn owl conservation is among the most inexact of sciences because the bird’s response is frankly perverse. When the voles crash, instead of saying, “okay, no voles this year, let’s hammer the pipits”, many birds (sometimes the great majority) simply decide not to breed at all, thereby eradicating the problem of feeding young mouths. Then, in vole plague years, the barn owls will start breeding early, lay big clutches (seven or eight eggs is not unusual), often try for two or even three broods, indulge in a little polygamy, and they can be found in the nest in every month of the year. All of which creates population earthquakes that nudge the upper reaches of the Richter scale, hence the guesswork when it comes to numbers.

A vivid illustration of the phenomenon occurred in 2013 (crash) and 2014 (plague). Surveys of traditional nest sites in 2013 suggested that as few as twenty per cent were occupied. In 2014, the figure was almost one hundred per cent. Thus, the only halfway-useful guide to population trends is to take an average figure of three or four years at a time, on which basis there may be around ten thousand pairs in Britain, with particular strongholds in the south-west of both Scotland and England.

THERE IS A DARK SIDE to human interaction with barn owls. A quick internet trawl shows how easy it is to buy a barn owl or two. The trade in captivebred birds is legal, or at least some of it is. A typical ad: “For sale, barn owls, breeding pair, reluctant sale due to illness. £250.” A cynic might read that and think, “Sale due to seller’s need for £250.” Legal or not, it’s not what barn owls are for.

Other facets of contemporary human lifestyle, notably road and rail traffic, kill thousands of barn owls every year. An environmental impact study for the HS2 high-speed rail link between London and Birmingham predicts the loss of the entire breeding population of barn owls within 1.5km of the entire length of the route. And ninety per cent of barn owls found dead on farmland contain rat poison. That is a lot of human predation on a bird we profess to love so much.

Yet love it we do. The centuries-old association with humankind and its architecture has accorded the barn owl a unique place in our affections and in our conservation endeavours. The Hawk and Owl Trust, the Barn Owl Trust, the Barn Owl Centre, the Barn Owl Conservation Network, the RSPB, the Scottish Wild Trust, and many if not all of the county wildlife trusts in England have practical projects to help barn owls. For example, after the desperately low breeding performance in 2013, the Somerset Wildlife Trust launched a campaign to erect a nest box in every one of the county’s 330 parishes.

And surely we have turned to the barn owl more than any other creature (except perhaps swans) to embroider the hodden grey cloth of folklore. It’s the bird of wisdom, its unexpected appearance is an omen of good luck – or death (it was Wordsworth’s “bird of doom”), it’s the guardian of the night world (in Gaelic it is cailleach-oidhche, the old woman of the night) and a beacon to guarantee safe passage through the underworld, its call summons bad weather but its call during bad weather heralds the end of bad weather. And a barn owl broth is a cure for whooping cough (don’t try this at home: apart from anything else, I’m pretty sure it’s illegal).

Poets have reached for the barn owl as long as there has been poetry, none more knowingly than Thomas Gray in his matchless Elegy Written in a Country Churchyard:

If you are unmoved by the flaky nature of folklore whenever it dabbles with the natural world, then there is always this simple and essential truth: the barn owl, unlike all other night-flying owls, is the one that we can see in the dark, that its unarguable beauty is layered with mystery, and that all of us have a place in our hearts and minds for mysterious beauty. I have known that to be an an essential truth since I was about eight years old.