Bushland reserves have been established in built-up areas as a means of conserving remnant flora and fauna. Recent fauna survey work allows for an assessment of the effectiveness of these reserves as conservation areas for native animals. Many bushland reserves are surrounded by houses and are subject to various forms of degradation, weed infestation and abuse. None are free of outside impacts. Therefore, it is likely that the composition of the fauna in the reserves will change in response to the pressures. If so, what animal groups will be most affected?
Fauna surveys have recently been carried out in three large bushland reserve areas. Large reserves are likely to be less severely impacted and may provide a useful picture of the changes in animal communities. The three reserves chosen also had detailed historic records of their original fauna. Thus, the current range of species in each reserve can be compared with previous species lists. The three bushland areas surveyed were:
- Kogarah Bushland Reserves – these are a series of reserves that occupy the headlands along the northern side of the Georges River.
- Rockdale Wetland Corridor – a large bushland area extending from Arncliffe to Sans Souci in the hind dune area of Botany Bay – around 200 Ha
- Burnt Bridge Creek Corridor- this is a long, narrow bushland corridor that extends from Seaforth to Balgowlah.
For these three large reserve areas, the average survival of species was as follows; Mammals 45%; Birds 70 %; Reptiles 40%; Frogs 47 %.
Bird species lost was less severe than for other types of fauna. The greatest loss of birds occurred amongst the ground-nesting species. The least affected were the tree-nesting species with generalised diets. Certain species were favoured by urbanisation such a currawongs, wattlebirds, magpies and noisy miners. These birds are aggressive, territorial users of open woodland.
Impacts which have lead to the loss of birds are:
- Loss of low ground cover (through clearing or too frequent burning). For ground-nesting birds this has resulted in an almost complete loss of nesting and shelter habitat.
- Loss of nesting hollows (through removal of old trees and dead branches; feral species also compete for the use of remaining hollows)
- Loss of mid-canopy layer (through removal of shrubs). This opens up woodland areas for aggressive birds to displace other species.
- Change in composition of flora (through dumping of garden plants, loss of native plants). Food plants may be lost (e.g. native grasses for finches).
The most severe impact recorded on any animal group has been on the ground dwelling mammals (such as Antechinus, bandicoots, wallabies and native rodents). In many reserve areas these animal have been completely eradicated. Grassland and wetland habitats appear to be the habitats that have been reduced the most. There was less impact on arboreal and flying mammals. Note: possum boxes provide hollows, but there is a need to monitor these to ensure they are not used by feral fauna.
Impacts which have lead to the loss of mammals are:
- Loss of ground cover (through clearing or too frequent burning)
- Increased predation by exotic and native predators (due to increased tracks through reserves and “edge-effects” in long, thin reserves)
- Displacement by exotics (such as foxes and black rats) in disturbed habitats.
Certain groups of reptiles have fared badly in bushland reserves. Marked losses have occurred amongst the vertebrate predators (such as goannas and snakes), large species (such as goannas, snakes and large skinks) and diurnal species (such as skinks and dragons).
Small reptiles and nocturnal reptiles have suffered much smaller losses.
Species which have benefited include the cavity dweller such as wall skinks, and the gastropod feeders (these include blue-tongue lizards – however, these may now be being lost due to hunting by dogs).
Impacts which have lead to the loss of reptiles are:
- Loss of ground cover and shelter. Protective shelter sites are lost through the removal of fallen timber or the burning off of dead branches and sticks. The broad- headed snake has been lost from many areas due to the collection of bush rock and from snake bashing.
- Increased predation by exotic and native predators (foxes, black rats and the high density of currawongs and kookaburras)
- Loss of breeding sites especially those which breed in loose sand (generally the first areas to be made into car parks)
Species adversely affected by urbanisation include riparian species (river and creek frogs) and ecospecialists (with highly specialised diets). Similarly, species that require thick, dense ground-cover have been adversely affected. Those species which have been positively affected include those that breed in still water, and species with some tolerance of water pollution.
Impacts which have lead to the loss of frogs are:
- Loss of water quality (through contamination of storm water by household chemicals, pesticides, fertilisers, petro-chemicals and detergents)
- Loss of breeding sites, especially ephemeral sites where water collects after rain. Low-lying ground is often filled in and levelled or drained.
- Increased predation by exotic and native predators (especially foxes and black rats)
How can bush regenerators help?
The over-riding reason for loss of fauna is the loss of shelter. It was suspected that loss of feeding areas would be more significant but it appears that most native animals are killed or driven out of bushland areas even if ample food is available. This has implications for bush regeneration. If regeneration involves the removal of the shelter provided by weeds, then replacement shelter must be provided prior to weed removal. Examples include the replacement of Wandering Jew by placing logs or other items of solid ground cover on the ground. In many reserves rubbish is often highly sought after as shelter sites because natural shelter materials have been depleted. Old fridges, car doors, rusting car bodies or boxes are often vital for a number of species to survive, and these should not be removed unless a replacement habitat is provided. For example, fauna refuge log piles can be easily built using scrap timber and branches – say about 5mx5mx1m high.
Clearing large areas is also extremely hazardous for fauna. Large clearings create large edge-effects and allow predators to quickly prey on remnant fauna. Smaller clearings permit the safer passage of fauna from site to site. The size of the area that can be cleared will vary from species to species but generally gaps of 5 to 10 metres are all that should be cleared at any one time.
The timing of bush regeneration, especially if it involves clearing and replanting needs to be addressed so that impacts on fauna are reduced. Similarly regeneration strategies are needed that allow for fauna recovery. This can be a difficult demand as clients (such as Councils) are often in a hurry to have regeneration completed in an area. However, the cost of hasty regeneration is an area containing native plants but devoid of native animals.
The size and shape of bushland reserves is clearly an important factor in animal conservation. Small reserves have a limited conservation role but are often important as stepping stones between larger, more secure areas.
Tools of the Trade
If fauna conservation is also to be an aim of bush regeneration, then bush regenerators need to add some tools to their tool kit. Ideally, a selection of artificial shelter boards and tubes are needed that can be laid down in an area prior to bush regeneration. These structures are not commercially available yet but you might want to get into the habit of carrying sheets of timber, or other temporary shelter objects that you can leave at each work site.
Councils that have bush regeneration teams should have these mass-produced and ready for use. The shelter boards may need to be labelled so that they are not taken away as rubbish.