© 2014 by Barbara Copperthwaite.

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The hedgerow: A winter refuge

 

At first glance the land may seem bleak and empty at this time of year, but look closely in the hedges and you will find a refuge for all creatures great and small.

The hedgerow is a particularly rich habitat because it has characteristics belonging to two other habitats – woodland and open field – attracting animals and plants from each, as well as containing its own particular species. It offers a haven to all sorts of wildlife, especially in winter when the surrounding landscape is bare and exposed. Predators such as stoats and foxes use hedges as cover for stalking; rabbits and wood mice make short trips into fields to feed; birds take shelter and gorge in one of nature’s larders; insects hibernate.

   Hedgerows, especially of hawthorn with its tangle of twigs, were planted primarily to contain livestock and offer them some shelter from bad weather. At the heart of an old hedgerow lies a deep shrub layer, often a mixture of hawthorn, blackthorn, elder and dogwood. At intervals along this strip, trees such as elm, oaks and ash create a broken canopy.

   You can estimate the age of a hedge by counting the number of shrub species in a 30m (100ft) stretch. On average it takes 100 years for a new species to become established, so a hedge with four shrub species is likely to be roughly 400 years old.

   Although now farmers are increasingly chopping down hedges, they are vital to the survival of much wildlife in both the countryside and also in parks, particularly in winter. A small hawthorne thicket may accommodate several hundred Starlings and lesser numbers of Fieldfares, Wood Pigeons, Stock Doves and Magpies, as well as a host of other smaller birds such as Tits and Wrens. A dense hedge offers them protection from ground predators and also from wind which causes greatest loss of heat and therefore energy during long winter nights.

   At ground level, an herbaceous border hugs the hedge bank along the edge of fields or parks. This is made up of a mixture of well-known countryside plants such as Nettles, Lords and Ladies, and Jack-By-The-Hedge (incidentally, this is also known as Garlic Mustard, and makes a very tasty sauce! It is also curious because its leaf shape changes as it matures. For the first year of its life the leaves are rounded, and after that they become more elongated and spikey). These three layers – tree, shrub and field edge – are not distinct, however, for swags of honeysuckle, wild hops, clematis, bryony, bramble and dog rose climb riotously between them, knotting the whole together.

   As hedges often radiate out from woodland edges, they also create a strip-like continuation of the woodland food supply. Plants which cannot spread across open fields often ‘travel’ along the base of a well-grown hedgerow. Shade-loving woodland plants such as bluebells and primroses take advantage of the damp and overhanging conditions similar to that of a wood. The seeds of fruit-bearing plants are dispersed along the hedge bank by birds and small mammals often far away from the parent plant. Most berries are eaten for their fleshy outer coat. The hard seed passes through the animal undamaged, so a solitary blackberry bush can be the source of several other clumps of bushes along a hedge over a period of time.

A huge variety of food, particularly berries, are in hedgerows

The Mistle Thrush is one of the many birds which feast on the glut of food in hedgerows

   It is this special plant community, unique to a mature hedgerow, which makes it such a magnet for wildlife - it offers a wider range of foodstuffs than most deciduous woodlands. Migratory fieldfares and redwings join blackbirds, thrushes and starlings from home and abroad, and flocks of finches, buntings, sparrows and tits to exploit the seasonal succession of berries and seeds. After glutting on the autumn harvest of elderberries and blackberries, birds turn to rosehips and hawes, then sloes, and finally to ivy berries. Hips and sloes are taken mostly by thrushes, while agile tits collect the fruits of spindle, honeysuckle and bryony.

   In winter, voles, mice and squirrels bury caches of seeds and nuts. Wood mice and bank voles are good climbers and so can get at the berries high up in the hedge. A typical winter menu would include rosehips, haws, hazel nuts and acorns. With practice, we can learn from seed remains who has been eating them. Wild mice eat only the hard centre of haws, discarding the fleshy coat, while bank voles do just the opposite.

   This bounty of vegetarian food allows quite a number of mammals to remain active throughout the winter. But the predators such as weasels and stoats have to be versatile to survive. In winters when the hedgerow fruit crop is poor (hawthorne in particular is very variable), and the rodent population correspondingly low, predators alter their diet to include roosting birds or even move into nearby woodlands and fields to search for other foods. They use the shelter of the hedgerow’s undergrowth to move safely, stalking their prey or simply moving across a wider hunting area without having to put themselves in danger by going into the open. Badgers, too, will come out of a wood to root along hedge banks for whatever they can find.

   With the onset of winter many insects also seek nooks and crannies in the interior of the hedge to hibernate. A few invertebrates also manage to stay active throughout the winter, notably slugs, which tunnels deep into the hedge bank soil if freezing weather sets in. Snails are less adventurous, sealing their entrance off with a mucus plug and staying put for the duration of winter often in company with others. Hawthorn is a particularly good place for finding active invertebrate in winter because it favours growth of lichens and slimy algae called Pleurococcus, both of which provide food for springtails, barklice, and woodlice.

   A select band of moths – winter moths, spring ushers, pale brindled beauties and mottled umbers are also active in winter, laying their eggs at this time. The most striking feature of the group is that the females are small, wingless, bug-like creatures, scarcely recognisable as moths at all. The ones we see flying around the hedgerows are the amorous males, seeking females on the trunks of trees. If there are clumps of holly or ivy in the hedge then there may even be a brimstone butterfly hibernating within, protected throughout winter.

   In fact, a careful examination of any parts of the hedge will yield insects: ladybirds dormant in thick beds of lichen and crevices in and under bark; earwigs huddled together in the hollow, dead stems of hogweed; the larvae of holly leaf-miner flies inside the blisters on holly leaves.

   All of these dormant insects are, of course, vulnerable and supplement the vegetarian diet of roving mammals. Shrews take their toll of buried pupae; wrens, custom-built for the labyrinthine hedge habitat, mop up spiders’ eggs; tits puncture the blisters on holly leaves to extract the larvae of the leaf-miner fly.

   Given its sheltered conditions and the fact that it is a great reservoir of wildlife, the hedgerow is one of the best places to look for early signs of spring. From January onwards, the territorial song of the great tit is increasingly heard, soon accompanied by the more lyrical mistle thrush. In February, elder leaves begin to unfold and a sunny day may coax out an early brimstone butterfly. Blackbirds have been known to start nesting in February and some rabbits may give birth to their new generation of the year. All this thanks to the mini-ecosystem created by the humble hedge.

Slugs love lichen

As well as being regular garden visitors, several hundred starling can shelter in the average hedgerow.