Wildlife Corridors - vital habitat links

Different types of corridor

Continuity of hedges is important to enable some species to move between different areas. Many species of butterfly move along hedge-lines and the edges of woods rather than crossing open fields. They will also breed and feed in hedgerows if they contain the right food plants for the caterpillars and nectar plants for the adult butterflies. Speckled wood butterflies will find their way along the hedgerow quite rapidly but gatekeeper butterflies, for example, are specific to hedgerows and are reluctant to cross open ground, so that large gaps in hedgerows can limit their spread.

Our small mammal studies at Denmark Farm have provided fascinating evidence of the movement of wood mice and, to a lesser extent bank voles, along extremely wide, bushy hedgerows. These hedgerow corridors are up to 5 metres wide from the centre of the hedge and fenced out either side from livestock. Some wood mice travelled over 300 metres from the heart of the woodland into and along these corridors to feed and breed.

Slow-moving animals that move between different habitats during the year often need the cover and microclimate conditions of hedgerows - warmth, shade, humidity and wind shelter. Toads use such corridors between breeding ponds and the dry ground where they hibernate. Similarly, snakes move between hibernation and breeding sites in banks or woodland and summer hunting grounds in damp grassland. Ditches can also act in the same way as hedgerow corridors, providing shelter and concealment from predators.

A hedgerow bordering grassland casts shade and influences temperature so that it may provide just the right conditions that allow a species to thrive. For example, bluebells can seed themselves slowly, but inexorably along hedgerows and reach suitable woodland sites if there is a connecting corridor.

Rivers and streams are important corridors for wildlife too, especially fish. Riverbanks act as both corridors and homes to water voles, otters and dippers. Streams and ditches provide a corridor for freshwater invertebrates and therefore a year round food source for insectivores such as water shrew. The presence of a ditch as a beneficial margin also increases the value of a hedgerow for wildlife. Some of the birds that often nest in hedges, such as song thrushes, blackbirds and robins find good feeding conditions along damp ditch sides. Similarly, some insects that pass their larval stages in the ditch will feed as adults on the hedgerow flowers. A ditch or earth bank running through woodland can support a distinctly different range of species from those found in the wood itself.

In relatively flat countryside, earth banks can provide areas of steeper gradient available to certain specialised plants. Animals such as badgers and birds like sand martins often rely on embankments in which to excavate their holes.

Even within managed broadleaf woodland, the presence of bramble and other dense scrub will offer breeding sites and feeding corridors for wren and dunnock. So, if scrub links are provided to this woodland from other areas, it will offer more nesting opportunities for birds that use the understorey.

The creation of long term set-aside and wildlife headlands within the farmed landscape offers great potential as marginal habitat and as another avenue for species distribution. Such headlands can have a beneficial effect on the main crop as they maintain populations of invertebrates that feed on many arable pest species - a form of natural biological pest control.

Our own studies of ground invertebrates on Denmark Farm and neighbouring intensively managed farmland show a marked variation in the population densities and range of species in grassland according to its management. Rough, 'unimproved' pasture has a diverse height and structure with clumps and tussocks, which provide microclimate and shelter for many ground invertebrate species. This type of pasture hosts many more species and in far greater numbers than the short, rye grass monoculture typical of much of our farmed grassland. Denmark Farm's habitat mosaic avoids isolated 'islands' of rough pasture and links it with hay meadows, woodland and wetland habitat, so that ground invertebrate populations can reach high levels over all of the site.

As well as these more traditional corridors, a number of other features can play a part in the overall wildlife distribution network. Railway lines and motorway verges offer security from human disturbance, with the wildlife quickly adapting to the noise and wind generated by passing trains and vehicles. Industrial sites can also provide vital links, through peripheral waste ground and overgrown run-off ditches, in what otherwise would be a wildlife 'desert'. As 'green field' sites are developed, gardens and school grounds can take on increasing significance as stepping stones for wildlife between areas of countryside.

Corridors can be non-continuous. For example, clumps of habitat not too far apart, such as copse, ponds, and standard trees in hedgerows. These enable some species to cross areas, which they would otherwise find difficult. Stepping stones can also create a more wildlife-friendly environment between patches of richer habitat. Some species may not need a direct link, or stepping stones of the same habitat type, but just a more friendly environment – one that at least provides food or shelter, even if it doesn't provide breeding habitat – over which to travel.

Any corridor which in some way helps species to move, feed and breed, and therefore ultimately survive, is of value. The scale can range from global – fragments of surviving rainforest are now being linked up across wide areas in south America – down to a short strip of hedgerow which links local woodland remnants.

Restoring corridors on your own land

In addition to the above, there are many more examples we could cite. Wildlife corridors can vary greatly in scale, area, structure, and suitability for different species. However, the principles are relatively simple and it only takes a more imaginative look at the potential for wildlife corridors on your own site together with some clear, longer term planning to identify opportunities to link up habitat. The more the merrier! If possible, this link up should extend to include adjacent land, so a key to success will be more farmers and landowners working together, to play their own part in a wider effort to enrich our countryside. (See our training pages or contact us for details of landowner forum and training events held at Denmark Farm.)