Habitat Management Principle 1: The bigger the better but small remnants are better than no remnants at all!
The minimum viable patch size for most bird populations is about ten to twenty hectares, but some species can only survive in patches that are larger than fifty or even 100 hectares.
Smaller patches are less able to provide the resources necessary to support some species; particularly those that normally live in large family groups (e.g. grey-crowned babbler). This is magnified by the length of time the patch has been isolated (see Principle 2) from surrounding vegetation. Some species may persist for many years in a small patch, but their population size will gradually decline to the point where they no longer breed successfully and eventually die out. This phenomenon is known as extinction debt (see “Key Concept” box).
Despite this, it is often surprising just how many bird species can be found in roadside or on-farm patches as small as one or two hectares. The diversity of birds in these smaller patches is often related to the structural complexity (see Principle 3) of the habitat available and how well they are connected to adjoining areas of bush (Principle 2).
- Maintain and/or reestablish large patches (10 hectares or more) of indigenous vegetation
- Protect small patches and strive to enlarge some of them
- Enlarge small patches by allowing regrowth to establish and remain around them
- Plant additional indigenous trees, shrubs and grasses adjacent to small patches
- Enhance the size of small roadside remnant patches by revegetating or allowing natural regeneration on your side of the boundary fence
- When managing regrowth, leave some patches for the birds
- Protect smaller remnants from serious disturbance like wild-fire, clearing and heavy grazing