IS THE woodland birdsong quieter this spring? Are the bluebells sparse? Don’t be surprised: ravening beasts are wiping out much of our woodland wildlife. You may see them drift silently through the trees, liquid-eyed and elfin-faced. Don’t be fooled by their darling looks — deer are on the rampage.

The march of red deer in upland Scotland has been matched by roe deer in lowland England. The roe deer, extinct in England and Wales 200 years ago, now numbers about 700,000.

Various factors have encouraged the revival: more woodland, less hunting, more cereal farming — deer just love to munch wheatfields — and warmer winters. Two non-native species — the fallow and muntjac — have also benefited and are now widespread in England.

The sight of a big roe buck leaping across farmland thrills the heart. We are glad for its wild spirit, unfettered by hedges, fences and roads. Unfortunately its freedom is increasingly at the expense of other plants and animals.

This spring the Royal Society for the Protection of Birds and the British Trust for Ornithology will begin monitoring birds in 350 woods. The study follows startling declines in many woodland species. Since the 1970s willow tit numbers have fallen 78 per cent, woodcock by 74 per cent, and song thrushes by more than half.

“Birds such as nightingales and warblers need low, dense vegetation like brambles to nest in,” says Dr Rob Fuller, the trust’s director of habitat research. “Deer remove this. We also think food resources are affected. By chewing off buds and flowers, they reduce the amount of seed and fruit available to birds in autumn and winter.”

Deer can change a wood drastically. They nibble back ash, bramble, hazel, honeysuckle and sallow, leaving less palatable species to flourish. They eat shoots and saplings, so preventing woodland from regenerating. Gradually they reduce the plant variety which is crucial for the diversity of other woodland wildlife.

The effects of deer on woodland birds have been studied at Wytham Wood, near Oxford. Detailed records of its bird life have been kept since the 1950s and these show that many species declined as fallow deer multiplied — from a dozen in the 1960s to more than 250 by the late 1980s. The birds which suffered most include the blackbird, bullfinch, dunnock, nightingale, song thrush, woodcock and four types of warbler. All nest in low vegetation like bramble. Meanwhile, the great tit, chaffinch and mistle thrush, which nest high in trees, show no marked decline.

Nigel Fisher, the wood warden, hopes that by using professional stalkers to cull the deer the lost birds can be lured back. “This year we should have numbers down to about 90 animals over 1,000 acres of woodland,” he says. “That includes some roe and muntjac. We will check the condition of the wildlife over the next three years to see if that’s a sustainable level of deer.”

Deer, especially the muntjac, eat wildflowers. This dog-sized species, introduced from China early in the last century, is now the most common deer in parts of eastern and southern England.

Dr Arnie Cooke has studied the muntjac’s predilection for bluebells, orchids and other wildflowers in Monks Wood, Cambridgeshire, since the 1980s. “In the case of bluebells, muntjac eat the flower and the leaves,” Cooke says.

“By eating the emerging leaves in early spring they weaken the resistance of the bulb, so you tend to get smaller plants that don’t flower. And those that do flower get clobbered in April and May when the flower spikes are likely to be nipped off. “If you put up a fence to keep the muntjac out it’s amazing what comes up — bluebells, orchids and wood anemones. And beyond the fence you won’t see them at all.”

Although muntjac are now being managed in Monks Wood, Cooke worries that it may be too late to reverse the effects of overgrazing. “The seed source disappears and grazing encourages grasses which compete with traditional flora. Dog’s mercury once grew over one third of the wood. Now it covers just 1 per cent. I doubt it will ever fully recover.”

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