BARN OWLS

Although they are mainly nocturnal and can be extremely unobtrusive, the pale, almost ghostly, form of a Barn Owl floating silently over a meadow in the soft light of dusk or dawn can hardly fail to excite the birdwatcher. Sometimes known as "Hushwing" for its silent flight, this charismatic and beneficial species has not always enjoyed the popularity it has today, at times having been thought a bird of ill omen.

The Barn Owl is, in fact, one of the most widely distributed birds in the world, occurring, like Peregrine, in every continent except Antarctica. In the UK, we have the northernmost Barn Owls in the world, which are only able to survive here because of the ameliorating effects on our winters of the Gulf Stream. They are absent from the central parts of North America and most of the central Eurasian landmass where harsh winters would deny them access to the small mammals that are their main prey. On the very edges of their range, some birds are semi-migratory in response to weather conditions.

We know more about the diet of Barn Owls than of most birds, thanks to their helpful habit of swallowing most of their prey whole and then having to regurgitate pellets, the densely compacted remains of the indigestible fur and bones, in order to have room for their next meal. They bring these pellets up regularly at their roost or nest sites, where they can easily be collected for analysis. Unlike Tawny Owls, which will eat anything from worms to Rabbits and will take birds up to the size of Stock Dove and even Magpie, and whose pellets are much harder to find as they do not reliably bring them up in the same place, Barn Owls are almost entirely specialists on small mammals, which they catch in rough, often damp, grassland areas. Fortunately their prey can quite easily be identified from their characteristic teeth, and a large pellet may contain as many as six skulls, as well as a large quantity of other bones. In the UK, the most common prey are Short-tailed Field Vole, Wood Mouse and Common Shrew (the shrews are easy to identify, not only from the distinctive skull shape, but also from their red teeth) but all mammals up to about the size of Rat have been recorded. A few Barn Owls have learned to catch birds as well and in years when the numbers of small mammals are low a few more may be forced to learn. Juvenile Starlings seem to be particularly vulnerable, but even Skylarks can be taken.

The clear insight into the species' diet provided by pellet analysis has given us a good understanding of their habitat requirements, an essential pre-requisite to any conservation action. Such action certainly became necessary in the last century in response to a significant decline in numbers. In 1932 one of the first single species surveys was conducted by George Blaker, revealing around 12,000 pairs of Barn Owls in England and Wales. In the mid-1980s Colin Shawyer repeated the survey for the Hawk and Owl Trust, using basically the same methodology but including Scotland and Ireland, which showed that the population had dropped to around 3,750 pairs in England and Wales, with another 650 pairs in Scotland but very few pairs in Ireland. Another survey conducted in the mid-1990s jointly by the Hawk and Owl Trust and the British Trust for Ornithology, using a different but more easily repeatable and statistically rigorous methodology, produced a figure of between 4,000 and 4,500 pairs for the UK, suggesting that the population had at least now stabilised.

To what can we attribute this decline? As a minimum, all species need adequate habitat to feed in and somewhere suitable to breed. For Barn Owls, both these were under pressure for much of the last century. Rough grassland disappeared under the plough or more intensive grazing, the sort of stackyards that had sustained large numbers of small mammals gave way to more efficient and less wasteful grain storage methods and the countryside generally, under pressure from society to produce more food, became less diverse. At the same time as their habitat was under pressure, so was the availability of nesting sites. Barn Owls need quite large cavities to nest, either, as their name implies, in buildings (before there were buildings, the equivalent was cliffs and caves, and indeed there are still a few pairs using such natural sites), or in trees. Old barns, unfortunately, either make desirable conversions into houses, or deteriorate and are replaced by modern ones lacking nooks and crannies. Old trees, the only ones likely to have large enough cavities, get blown down, or cut down for health and safety reasons.

Other factors may have played a part as well. Weather clearly affects Barn Owls and there was a cold spell before the current warming. Rodenticide residues have been found in dead birds and, as they are at the top of the food chain, they must remain vulnerable. With probably some 3,500 Barn Owls killed on roads each year, any recovery in numbers may be slowed, but careful design of new roads can lessen the likely mortality.

Fortunately, at least the two major factors, habitat and nesting sites, are amenable to our efforts to influence them. Rough grassland is returning, aided in part by agri-environment schemes; sympathetic mowing regimes can enhance the attractiveness to small mammals. Field margins, either 2 metres or 6 metres wide, are becoming a common feature of the countryside and are likely to benefit not only Barn Owls but also a wide range of species. Habitat, however, is not much use without nesting sites. Fortunately Barn Owls readily take to boxes and there are tried and proven designs suitable for the inside of barns, the outside of buildings, trees and poles. There are also a number of local conservation groups and experts able to advise on putting them up and siting them. Indeed, perhaps as many as 80 per cent of all the UK's breeding Barn Owls now nest in boxes provided by man. Certainly the use of pole boxes in intensely agricultural areas such as around the Wash, where there are few barns and fewer large trees, has enabled them to exploit the banks of ditches and dykes which are rich habitats for their prey. The species is specially protected from disturbance at the nest site by virtue of being on Schedule 1 of the Wildlife and Countryside Act and monitoring of boxes should only be undertaken by properly licensed and experienced workers.

How have Barn Owls responded to the increase in habitat and nesting sites? In good years, when prey is abundant, they can have broods of seven chicks (even nine has been recorded) and they can move quite substantial distances (ringed birds have been recovered 100 kilometres from where they were born only three months after fledging), so they can colonise areas that have newly become suitable, or re-colonise areas from which they had been lost, quite quickly. Although no formal survey has been undertaken since the mid-1990s, it seems likely that the population has now increased to somewhere between 5,000 and 6,000 pairs.

More information on this beautiful bird can be found on the website of the Barn Owl Conservation Network, www.bocn.org

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