Birds Nests in Fields and Hedgerows
Field boundaries provide sheltered locations for nests. Numerous birds and small and large mammals build their nests in hedgerows, walls or banks for the food. shelter and easy access to other areas that they provide. Regular hedgerow-nesting birds include the robin, blackbird, chaffinch, dunnock. yellowhammer and whitethroat. but 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 successfully each year 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 their regular patrols. The resting sites are used as temporary refuges for part of the night or during daylight hours. Such insects as bumble bees 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 these cases the nests are positioned in sheltered places with easy access to food either within the boundary itself or in adjacent land.
Nature’s highways are used as dispersal routes by a whole host of animals, but the overall distance travelled varies with the species. A dispersing juvenile fox travels up to 17km (10 miles) per night along held boundaries or paths in search of 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 in search of an uninhabited stretch of water. A young grey squirrel, on the other hand, may move anything between 300m (1000ft) and 8km (5 miles) along highways to nearby copses or woods, but a blowfly or greenbottle will only disperse up to 500m (1600ft 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, frequently hibernate in hedges, walls or banks and can often be seen sunning themselves on a south-facing bank soon after emerging in the spring and prior to dispersal. All three species of lizard found in this country eat the insects and spiders readily available in field boundaries. The slow worm is particularly abundant in limestone country, living in dry-stone walls or stony hedge bottoms; the sand lizard prefers sandy banks: and the common lizard can be found on woodland edges and in hedgebanks. Grass snakes and vipers also use nature’s highways and hibernate in small mammal burrows in field 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 obvious and easier to define than an arbitrary area of open land. Birds, for instance, 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 depositing fresh faeces in the latrines. Important latrines situated 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.
Animals traverse their highways either specifically in search of food or during some other activity, such as dispersal, when they will take the opportunity to feed as they travel. The highways themselves are important 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 in order 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 special 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 (25-60 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 (7.5 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 they 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 comparable distances along hedgerows when food is fairly abundant.
Very little is known about the overall effect of removing traditional field boundaries, but it obviously eliminates the resident plant and animal communities. For the mammals the impact is unlikely to be catastrophic: few species are confined to field boundaries and the majority can live in alternative habitats. Similarly, many birds prefer a woodland environment but, if no woods are available, they can exploit the field boundary system of hedgerows.
Widespread removal of field boundaries results in isolated patches of habitat with no connecting highways and therefore no connecting immigration or emigration routes. Animals which disperse along field boundaries to new areas would be forced either to stay in their natal ranges or to take greater risks in attempting to disperse across open land. Many animals would be confined to small patches of suitable habitat, unable to colonise new areas, and potential food sources, shelter belts and nest sites would also decrease. Species diversity would therefore decline, and our countryside would be the poorer.