The importance of hedgerows for farmland birds

Hedgerows: the countryside's overlooked wildlife highways

A hedgerow is really a strip of woodland edge left stranded in the middle of a field. For farmland birds, that thin ribbon of thorn and leaf is often the difference between a landscape they can live in and one they merely pass through. In the most intensively farmed parts of the UK, hedges, their grassy margins and the ditches beneath them hold a remarkable share of our remaining birdlife: dunnock, yellowhammer, linnet, whitethroat, song thrush, bullfinch and, in the right places, tree sparrow and grey partridge. In winter, redwing and fieldfare strip the berries from them in noisy flocks.

Because hedges run in lines, they do something a lone copse cannot. They connect. A bird can move from a wood to a damp corner of a field, and on to the next farm, without crossing open ground where sparrowhawks and cats have the advantage. Get the hedges right and a lot of other wildlife follows — insects, small mammals, bats and, along the wet ditches at their feet, the sort of damp habitat that is increasingly hard to find.

What makes a hedgerow good for birds

Not every hedge is equal. Height, width, density and the number of native shrub species all matter, and so does what sits alongside them. The best hedges tend to be 2 to 3 metres tall, at least 1.5 to 2 metres wide, and dense from the ground up, with a domed or A-shaped profile that keeps rainfall off the base.

• Native, mixed shrub species — hawthorn, blackthorn, hazel, field maple, dog rose, guelder rose, spindle and holly. More species means more insects and a longer run of berries.
• A thick, bushy base — this is where most nests are built and where birds shelter from wind, rain and predators.
• Occasional hedgerow trees — oak, ash or willow left to mature provide song posts, nest sites for stock dove, and food for tits and nuthatches.
• A rough grass margin of 2 metres or more, ideally with tussocky, seed-bearing grasses and weeds.
• A damp ditch at the foot — a genuine wetland edge, valuable for invertebrates, amphibians and birds such as snipe and reed bunting on wetter farms.

Food from one end of the year to the other

Birds need hedgerows in every season, and for different reasons. From April to July, hedges are the larder for growing chicks: caterpillars, sawfly larvae, aphids and spiders, and the more shrub species present, the more of these there are. A pair of blue tits can take hundreds of caterpillars a day from a good hedge.

From late summer, the emphasis shifts to fruit and seed. Hawthorn haws, hips, sloes and ivy berries are taken by thrushes, blackcaps and bullfinches through autumn and into hard weather, with ivy especially important in late winter when little else remains. Below the hedge, seed heads of knapweed, teasel, vetches and grasses feed linnets and goldfinches right through to February. Tall, thick hedges cut on rotation also hold more over-wintering insects, which is what dunnocks, wrens and even yellowhammers pick through on frosty mornings.

Nesting, shelter and safe travel

Most farmland birds nest within a hundred metres or so of where they feed, and the hedge is usually both. Dense thorn gives cover from magpies and crows, and the tangle of stems keeps nests hidden from above. In winter the same structure acts as a windbreak and a roost: on a cold night, dozens of birds may pack into a single thick hedge for warmth.

Hedges also work as corridors. Whitethroats and yellowhammers will move along a continuous hedge, feeding as they go, in a way they will not risk across a bare field. Where farms have lost their hedgerows and only isolated fragments remain, these species simply disappear, even when the habitat looks suitable from a distance.

Managing hedgerows with birds in mind

The single most damaging practice is the annual flail cut, which trims every hedge to the same height and leaves a thin, hollow shell with little nesting value. A few simple changes make a big difference:

• Cut on a two or three year rotation, and leave a proportion — a tenth to a fifth — uncut each year so some hedges grow tall and berry-heavy.
• Cut in late winter, ideally January or February, after the berries have been eaten but before birds begin nesting in earnest.
• Avoid cutting between March and August, when nests are active; all wild birds, their nests and eggs are legally protected during this period.
• Trim to an A-shape so the base stays thick and sunny, and raise the cutter height a little each year to let hedges gain height.
• Lay or coppice overgrown hedges in rotation rather than flailing them hard for years, and gap up with native whips, using guards where rabbits are a problem.
• Keep spray and fertiliser out of the margin, and avoid cutting hedgerow trees.

Small changes, real gains

The pleasing thing about hedgerow work is how quickly birds respond. Widen a margin, leave a hedge to grow tall for three years, and yellowhammers, linnets and whitethroats usually return within a season or two. Old, leggy hedges brought back by laying can take four or five years to thicken up properly, but the nests come back with them.

It also pays to think beyond the field boundary. Cluster your hedges with neighbouring farms where you can, link them to woodland edges, ponds and damp ditches, and you build a network rather than a series of isolated strips. Walk the farm in late spring and listen: a hedge full of song is the simplest measure of whether the management is working. Given a little patience and a lighter touch with the flail, these old boundaries will keep doing what they have always done — feeding, sheltering and carrying our farmland birds across the countryside.