Country: Nature Notes

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A FOUR-YEAR survey by the Mammal Society has exposed a "worrying decline" in the abundance of field voles and common shrews. The data was obtained by analysing the pellets of fur and bone regurgitated by barn owls. The remains of over 50,000 small mammals were examined by volunteers, and the conclusion reached was that since the Seventies owls have largely gone off voles and switched from common shrews to the smaller pygmy shrews.

Experts point out that the owls would only go for smaller targets out of necessity: the relative scarcity of common shrew and field vole remains in the pellets shows that the two species must have gone downhill.

The decline of voles is attributed largely to the diminution of rough grassland, in which they thrive. The British population is still thought to be about 75 million, but the Mammal Society believes that the number is too small, and that any further fall will have serious effects on the survival of the predators - kestrels and weasels beside barn owls - which live on them. The society is therefore launching new research to develop techniques for monitoring further population changes.

Voles might have better survival rates if they could learn to make less noise. As it is, the squeaking and chittering of territorial disputes betray their presence to owls, which hunt with ears as well as eyes.