Habitat Clearance & Fragmentation

Home

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.

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.

In some areas, the clearance of the vegetation may not be complete, and may only refer to the removal of the shrubs of the understorey, or even fallen timber. Such habitats are uninhabitable for many woodland species, such as the Grey-crowned Babbler and Hooded Robin, both of which are threatened by these processes in southern Australia.

A few species are favoured by the fragmentation of habitats. Fragmentation increases the area of edge of the habitat, and aggressive birds such as the Noisy Miner thrive in these landscapes as they are able to vigorously defend a territory against other small birds, driving them away. Fragmented habitats that support Noisy Miners usually support few other species.