Monday, 15 September 2008

The silent hunter

I have sometimes heard the Barn Owl referred to as ‘the silent hunter’, a particularly apt description for what is one of our most engaging birds. Many years ago I undertook a study into the habitat associations of various small mammals, the favoured prey of the old white owl, and this involved spending many hours on my knees measuring and sampling grassland habitats. The study area was part of the hunting range of a pair of Barn Owls and in some years the birds were joined by a neighbouring pair as they hunted over the ground. The birds were often to be seen quartering back and forth across the meadow, their slow flight designed to help them detect small mammals in the sward below. Every now and then one of the owls would fly right over my prostrate form, the bird completely silent as it passed within three or four feet of me. I guess that I was such a regular feature on the meadow that they had come to accept me as part of the landscape.

Silent flight is obviously important for this active hunter, allowing a close approach to the mice, voles and shrews that form the bulk of its diet. The silent flight also increases the effectiveness of the owl’s already exceptional hearing, reducing any unnecessary noise that might interfere with its efforts to secure prey. If you have ever handled a Barn Owl then you will know just how soft the plumage is, beautifully contoured to cut down on drag as the bird moves through the air. The individual wing feathers also show modifications to help reduce noise. Each of the primary feathers has a fine comb-like fringe along its leading edge and a velvety texture to its upper surface. Collectively, these features reduce turbulence as air rushes across the surface of the wing, which means less resistance and less noise in flight. The wings themselves are broad and fairly long, enabling the owl to perform its buoyant flight with surprisingly little expenditure of energy.

With the fieldwork finished I no longer see Barn Owls on such a regular basis and close encounters are now a ‘red-letter day’. However, there are a few breeding pairs in this south-western corner of the county and I still get a real buzz from seeing them. Just the other morning, a very pale individual (probably a male) was quartering a wet meadow near the village of West Stow. As it moved across the field, periodically dropping down to snatch at some hidden prey item, I felt very tempted to hunker down in the vegetation to see if it would make a close approach.

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