Nature's Pathways and Highways
As they travel in search of food, mates and shelter, animals follow their own 'highways', the hedgerows, walls, fences and rivers that thread the countryside of Britain.
A patchwork of fields and field boundaries occasionally interspersed with natural features such as woods, rivers, and lakes make up the British landscape. However, a closer look reveals that a wide variety of animal paths also dissects it. These paths range from a few centimetres wide (made by small animals such as mice, voles and shrews) to several metres wide (made by larger mammals such as badgers, deer and foxes).
These animal highways serve the same function as our roads and tracks in allowing animals to move quickly from place to place,
However, animals have to choose their highways with some care since they are susceptible to predation, unlike humans. Therefore, they must travel by the most sheltered routes available, although this may necessitate going further— around the edge of a field, for instance, rather than straight across it.
Field boundaries offer some shelter, and they are exploited as relatively safe highways by an abundance of wildlife. If you look carefully beside a hedge or wall, fence or river, you may see a small but well-trodden path running alongside it; furthermore, in a hedgerow, you may see well-worn runs through the hedge where animals have crossed from one side to another.
Above: An English patchwork of fields, woods and hedges. Where the hedges, walls and fences form a continuous, countrywide network, animals are reasonably safe in their travels. In places, however, they may have to venture across open land (fields or heathland), taking refuge and finding food in thickets and woods where available.
Animal Travel Routes
Animals exploit animals travel routes for a variety of reasons. First and foremost, they offer a sheltered way for animals to travel from one point to another.
Animals need to move about the countryside in search of the resources necessary for survival. Food is a vital resource; animals move along their highway's in search of food, which they find en route or in adjacent land. However, travelling out in the open is a hazardous business; small animals are in danger from many different predators, while large ones often have man to fear.
Furthermore, nature's path frequently forms territorial boundaries, and animals travel along them to define and defend them. Scent marking (those of foxes and badgers, for example) at frequent intervals are used to mark territory but need regular replenishment.
Movement in search of a new home is called dispersal and typically involves juvenile animals (young foxes and weasels, for instance), expelled from their natal range at the end of summer and forced to until they find a vacant area in which to settle. Solitary species, such as hedgehogs and squirrels, also travel long distances searching for a partner with whom they can mate.
Nest sites
Field boundaries provide sheltered locations for nests. Numerous birds and small and large mammals build their nests in hedgerows, walls or banks for food, shelter and easy access to other areas that they provide.
Regular hedgerow-nesting birds include the robin, blackbird, chaffinch, dunnock, yellowhammer and whitethroat. Still, the birds most dependent on field boundaries for nesting are both our native species of partridge, the grey partridge and the imported red-legged partridge. They prefer hedgerows adjacent to woodland or farmland, and so the number of partridges that breed each year successfully depends on the amount and type of field boundary available.
These ground-nesting birds are highly susceptible to nest predation and choose a nest site in a well-protected spot with thick ground cover wherever possible. They also use the boundaries, together with adjacent farmland, as a food source, taking green leaves of grasses and cereals in addition to weed seeds and insects.
Small mammals, such as bank voles and field mice, build their nests in hedgebanks, within hedges or in-wall crevices, while larger mammals, such as feral cats and foxes, have resting sites and permanent dens in hedgerows or walls along with their regular patrols. The resting sites are used as temporary refuges for part of the night or during the daylight hours. In addition, such insects as bumblebees and wasps build their nests in hedgebanks, and numerous other insects lay their eggs on hedgerow plants upon which the larvae subsequently feed. In all cases, the nests are positioned in sheltered places with easy access to food either within the boundary itself or in adjacent land.
Below: The dunnock is a typical hedgerow dweller, depending on the habitat for shelter and food. It feeds on grass, chickweed, and plantain seeds. One pair will defend about 100m (330ft) of the hedge.
Dispersal Routes
Dispersal routes nature's highways are used as dispersal routes by a whole host of animals, but the overall distance travelled varies with the species. For example, a dispersing juvenile fox travels up to 17km (10 miles) per night along field boundaries or paths, searching for a vacant area in which to settle. By contrast, a young water vole dispersing along a river or stream only swims a few hundred metres each night, searching for an uninhabited stretch of water. A young grey squirrel, on the other hand, may move anything between 300m (1000ft) and 8km (5 miles) along to nearby copses or woods, but a blowfly greenbottle will disperse up to 500M or so in search of a corpse on which to lay its eggs.
Amphibians and reptiles make great use of nature's highways. Reptiles, for instance, are found in hedges sunning themselves on a south-facing bank soon after emerging in the spring and before dispersal. Lizards eat the insects and spiders readily available in field boundaries. The slow worm lives in limestone terrain, dry-stone walls or stony hedge bottoms, and common lizards on woodland edges and hedgebanks. Grass snakes and vipers also use nature's highways and hibernate in small mammal burrows in field boundaries.
Territorial boundaries
Once an animal has established itself in a territory in a previously uninhabited area or after dispossessing a previous owner, it must defend the territorial boundaries against other intruders.
These boundaries frequently follow natural or man-made land features because they are more prominent and more accessible to define than an arbitrary area of open land. Birds, for example, advertise their territories by singing from fence posts or hedgerow trees along the boundary. Badgers use field boundaries to delimit their territories and mark them with piles of faeces deposited in shallow scrapes or pits called latrines. Members of a badger clan regularly travel along these boundaries warding off intruders and deposition fresh faeces in the latrines. Prominent latrines in prime positions along the territory borders are visited at least once a day during the breeding season, whereas less important sites are visited every few days.
Food sources
Animals traverse their highways specifically in search of food or during some other activity, such as dispersal when they take the opportunity to feed as they travel. In addition, the highways themselves are essential sources of food, either directly by animals feeding upon the associated plant materials or indirectly by larger animals feeding upon the smaller animals living among them. Small rodents, for example, sometimes live entirely within a hedgerow, making their runs under the leaf litter and foraging on the invertebrates they find there.
The larger the predator is, the greater the length of field boundary it will patrol to find sufficient prey. By radio-tracking feral cats, it is possible to follow their hunting excursions. A small radio transmitter is attached to the animal, and its movements are monitored by picking up radio signals with a particular radio receiver and aerial. A male cat may patrol an area of up to 80 hectares (200 acres) in rural farmland, while a female will only hunt over 10-25ha (2560 acres). One young male followed on a hunting trip concentrated at least 80% of his activities along field boundaries, moving several kilometres in total but often spending long periods sitting and watching a rodent burrow, waiting for the animal to emerge.
By contrast, a radio-tracked hunting fox travelled about 12km (7} miles) in a single night along hedgerows and other field boundaries, catching small rodents and birds, taking fruit and berries as it came across them, and foraging for earthworms in nearby pastures.
Weasels and stoats also concentrate their hunting along field boundaries. Weasels favour dry-stone walls, which scour for the small rodents living in the crevices, whereas stoats hunt the same prey in their runs among leaf litter and under vegetation. A male stoat travels about 600m (2000ft) during one hunting trip. Brown rats move equal distances along hedgerows when food is fairly abundant.
The Future
Removing traditional field boundaries is highly detrimental to the survival of resident plant and animal communities. It has been catastrophic for hedgehogs, for example. Many birds prefer a woodland environment, but they can exploit the field boundary system of hedgerows if no woods are available. However, there is a limit to the abuse that nature can take before populations plummet.
Widespread removal of field boundaries results in isolated habitat patches with no connecting highways and, therefore, no immigration or emigration routes for animals. Animals cannot easily disperse along field boundaries to new areas, so stay in their natal ranges or take more significant risks in attempting to distribute across open land. As a result, many animals are confined to small patches of suitable habitat, unable to colonize new areas, and potential food sources, shelterbelts and nest sites would also decrease. Species diversity would therefore have declined, and our countryside would be the poorer.
References
The Living Countryside Series (1984) The Living Landscape. Eaglemoss Publications Ltd & Orbis Publishing Ltd (Readers Digest)