Fragmentation and Wildlife Corridors
Fragmentation
The lives of all birds are inextricably linked to the habitat in which they live, as it determines the availability of their food and shelter. Almost every type of natural habitat you can think of is threatened by clearance, fragmentation or other modification somewhere or other in Australia. This is the major conservation issue confronting our birds. Unfortunately, many of them cannot fly large distances in the open, searching for new habitats to move it when their current habitat is threatened or in order to find a mate and maintain a viable population. However, several smaller patches of habitat have the potential to act as one large patch, and support breeding populations of birds, as long as individuals can move between these patches.
Entire landscapes are seldom completely cleared these days, but in the past, vast swathes of forest and woodland were felled. Now, when clearing occurs there are often small patches of habitat left. Thus, where a habitat was once continuous, it is now divided into smaller fragments, which are separated by other, different habitats. This has all sorts of implications. Some species, such as forest owls like the Sooty Owl, require large areas of forest to hunt in. If the area of forest remaining is too small, the owls are simply unable to catch enough food, and die. When fragments of habitat are widely separated by very different habitats, such as patches of woodland separated by large areas of bare paddocks, movement between the patches is often difficult if there are no connecting corridors of vegetation. This situation is referred to as the 'island effect', as the birds living in one patch are as isolated from other patches as they would be if they lived on an island. For example, Rufous Bristlebirds living in a patch of dense vegetation near Port Campbell were apparently unable to move to another nearby patch of suitable habitat a few hundred metres away, as the patches were separated by an area of open farmland which they could not cross. This situation precludes the colonisation of new areas of habitat, or the recolonisation of previously inhabited patches if something happened to the existing population, such as burning of the vegetation.
How do wildlife corridors work?
Wildlife corridors can link areas connecting pieces of vegetation to each other, and allowing native fauna to move between the patches in search of food, mates or nesting sites. They also allow patches to become recolonised by new individuals following local extinctions caused, for example, by wildfire. Corridors are generally linear strips of native vegetation but can also be stepping stones of habitat scattered across a landscape. Roadside plantings, median strips, railway cuttings, windbreaks and hedges can all help birds to shelter and move around safely. Although birds can move around easily compared with mammals and reptiles, many bird species will not fly into human-dominated habitats without some form of cover.
Linear corridors
In order to maximise their usage and the success of corridors, a number of key elements must be taken into account:
- Their locations should be carefully planned, taking into consideration the placement of the remnants to be connected and the natural features of the landscape such as ridge lines and riparian strips.
- As a general rule when it comes to the shape of corridors, wider is better, with birds strongly influenced by both the width of the corridor and the habitat characteristics. Wider corridors tend to support a more bird species, particularly encouraging forest specialists (those that don't live in our suburban gardens) to move through them and live within them.
- To be effective in providing habitat for these forest specialists, corridors need to be wide enough to remove edge effects. Edge effects are caused by the boundaries of 2 different habitats (such as a simple suburban garden and a bushland remnant) and result in changes to the environment and vegetation at these boundaries.
- Given the availability of vegetation outside corridors that are scattered throughout the urban landscape in parks and gardens and can act as buffers, it is likely that narrower corridors would be used by these birds. Corridors should therefore be as wide as is possible in the space available.
- Current vegetation cover should be maintained and increased, where needed, to maximise the connectivity between remnants. This includes creating structural complexity utilising ground covers, shrub layers, a canopy (that retains live and dead hollow-bearing trees) and fallen logs and other natural debris. Where stepping stone type linkages occur such as with wetlands and isolated trees, the vegetated area should be enlarged and vegetation cover increased.
- Corridors that incorporate riparian habitat in the form of a creek or waterway tend to support more birds. Therefore the establishment and management of riparian corridors should be a priority.
- Structural and floristic diversity should be created as in other remnants and in gardens using locally native species.
- A mix of canopy tree species should be used in an attempt to reduce Noisy Miner invasion along the east coast of Australia. Areas where Eucalypts are the most dominant canopy species are more susceptible to being used by Noisy Miners - this can then impact on the rest of the bird community as these honeyeaters will exclude small birds from their territories.
- The overall aim should be to create a web of corridors throughout a region that connects high quality remnants with all other patches of vegetation and utilises a range of different habitats including riparian strips, linear bushland, streetscape vegetation, parks and suburban gardens.
Maintaining corridors
By maintaining tree cover in human-dominated landscapes, at least in key corridors between patches of remnant bushland, wildlife gardens can play an important role in keeping birds in the broader urban landscape. Some local councils have identified important wildlife corridors in their regions that should be the focus for habitat retention and reconstruction. Some councils will even provide free plants and advice to residents with gardens in these areas.
Gardens as buffer zones and beyond
If you are lucky enough to live near bushland your garden can act as a buffer zone to the bushland and can extend the places for birds to find food, shelter and breeding places. Plant locally native plants to supplement what is available in the corridor.
However even if you don't live next to a patch of bush, your garden can be a stepping stone, allowing birds to move across the landscape. Even if it seems as though your neighbouring gardens don't have much value for birds and so creating a garden yourself isn't worth it, your garden could connect to a nearby park or a suitable garden in the next street.
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