The temperate woodlands of south-eastern Australia are highly productive and fertile agricultural landscapes that support a remarkable diversity of bird species. The Conservation and Landscape Ecology research group at The Australian National University has been conducting regular bird surveys at hundreds of sites on farms in this landscape for the past 18 years and in that time we have detected over 170 bird species.
While the richness of bird species remains high compared with some other landscapes, the temperate woodlands have been heavily modified from their original state and there have been steep declines in many woodland dependent bird species over the past 50-100 years. In response to this, a substantial amount of research effort has been dedicated to identifying ‘declining woodland birds’ (Box 1) and the processes that are driving these declines.
This resource is tailored to those landholders whose primary objective is boosting bird diversity on their properties. It aims to provide farmers with the tools and knowledge to most efficiently nurture the bird species that already exist on their farms and encourage the return of those species that may be absent. Birds bring with them a range of ecosystem services that contribute to increased farm productivity, such as pollination and pest control, and these will also be briefly addressed here.
The term ‘declining woodland birds’ is used frequently in the scientific literature. In the context of the temperate woodlands of south-east Australia, the term currently refers to 26 bird species whose populations are in decline. Most of these birds are insectivorous and forage on the ground. This group includes highly charismatic species such as the Grey-crowned Babbler, Diamond Firetail, Bush Stone-curlew, Regent Honeyeater, Jacky Winter and Red-capped Robin. While many of these declines may have gone unnoticed by the general public, some older landholders may remember hearing the mournful calls of the Bush Stone-curlew through during the night — a sound that has all but disappeared from this landscape. These woodland bird species will rely heavily on conservation efforts occurring on private land in order for their populations to recover.
There are a number of actions that farmers and land managers can take to arrest these declines and facilitate the recovery of this spectacular group of birds.
1. Retain existing vegetation – particularly hollow-bearing trees
One of the most important and achievable actions a land manager can take to promote bird conservation on their farm is to retain the native vegetation that is already present. This existing vegetation can be thought of as a head-start in the transformation of a biodiversity-poor farm into one that is rich in native birds. It is particularly important to retain large old trees and even more important to retain trees that have hollows, whether dead or alive.
Compared to other parts of the world, Australia has a very high proportion of birds that depend on tree hollows for nesting. There are several woodland parrot species of conservation concern that require hollows to breed, such as the Superb Parrot, Glossy Black-cockatoo, Gang-gang, Little Lorikeet and Turquoise Parrot. Perhaps surprisingly, many ducks also nest in hollows including the Australian Shelduck, Pink-eared Duck, Australian Wood Duck, Pacific Black Duck, Grey Teal and Chestnut Teal. Nocturnal bird species, such as the Barking Owl, Southern Boobook and Australian Owlet-nightjar, also use hollows. The Brown Treecreeper and Chestnut-rumped Thornbill, both of which are considered ‘declining woodland birds’, also rely on hollows to breed, as do the Laughing Kookaburra, White-throated Treecreeper and the spectacularly ornate Spotted Pardalote.
There are also many mammal and reptile species that rely on hollows for breeding and refuge.
Among the existing vegetation on farms, retention of scattered paddock trees is vital as they play a disproportionately significant role in promoting bird species diversity, particularly as a typical paddock tree is old and has developed hollows. Despite the multitude of benefits scattered paddock trees provide to biodiversity and productivity, they are vanishing from our agricultural landscapes primarily because of deliberate removal, fire and dieback. The loss of habitat through the disappearance of hollow-bearing trees is compounded by introduced species, such the Common Starling, Common Myna and European Honeybee, which compete with native species for the hollows that remain.
2. Facilitate natural regeneration
Given the importance of mature trees in the landscape, we need to look to the future and ensure that old, dying trees are continually succeeded by trees that have grown through to maturity. One of the most cost effective methods of revegetating an area is to reduce or remove the grazing pressure and allow seeds to germinate and seedlings to emerge naturally. This is only achievable where there is a viable soil seed bank (residual dormant seeds in the soil from when the area was vegetated) or in areas where nearby trees can cast their seeds.
The woodland landscape is remarkably resilient and, when given the opportunity, will often regenerate on its own. Areas of regeneration need to be temporarily excluded from grazing, but this may be for only 2‑3 years. This time will allow the seedlings to grow sufficiently tall that the plants’ key growth points are out of reach of animals allowed in for controlled grazing. In areas without viable seedbanks, paddock trees can be excellent focal points for natural regeneration as they produce large amounts of seed and will ensure that new paddock trees will be in development or in place when the existing ones eventually senesce and die. Areas of regrowth are often viewed as ‘rubbish country’, but it is this scrubby regrowth that is optimal habitat for a range of bird species of conservation concern such as the Grey-crowned Babbler and White-browed Babbler.
3. Planting trees for birds
Planting trees is an excellent way to create habitat for birds, as well as providing shelter for stock and pastures and numerous other benefits for farm productivity (see Native Shelterbelts). Like natural regeneration, plantings are important habitat for many woodland birds. Birds of conservation concern that readily use plantings are the Hooded Robin, Red-capped Robin, Rufous Whistler, Speckled Warbler and Flame Robin.
For nearly 20 years, the ANU research team has conducted long-term, intensive studies of the ways that birds use plantings in the agricultural landscapes of south-eastern Australia. There are 5 key evidence-based recommendations we can make based on the results of this work, including optimal size, shape and position of plantings for birds. It is important to note that every farm is different and not all plantings can meet all of the 5 criteria outlined below. Farmers should use these recommendations as a guide and incorporate each recommendation where it is feasible.
- Make plantings as large as possible: When it comes to the size of a planting for birds, bigger is generally better. Our research has demonstrated that large plantings support more bird species than small plantings. Additionally, breeding success is significantly higher in larger plantings and this effect is strongest for species of concern like Jacky Winter, Crested Shrike-tit, Brown Treecreeper and White-browed Woodswallow.
- Plant block-shaped or non-linear strips: Large, block-shaped plantings are the gold standard when planting for birds. Many of the birds that are thriving in heavily modified agricultural landscapes are well adapted to existing on the margins of patches of vegetation. These margins can be thought of as ‘edge habitat’, and the areas towards the middle of plantings as ‘core habitat’. By planting block-shaped, rather than elongated plantings, the ratio of core habitat to edge habitat is increased and it is this core habitat that supports many of the declining woodland bird species.
Of course it is not always possible to accommodate block-shaped or non-linear plantings on farms. Linear plantings are still highly valuable, particularly when used to connect existing patches. For linear plantings, the wider they are, the better they perform as bird habitat.
- Establish plantings close to other plantings or large patches of native vegetation and connect plantings with other vegetation wherever possible: Our research has indicated that bird diversity is highest in plantings that are located close to other plantings or large patches of native vegetation. We have also found that connected plantings support more species than isolated plantings and this effect is most pronounced in narrow, linear plantings. In particular, we found that the intersections of plantings were bird hotspots. This demonstrates that linear plantings, while not necessarily ideal, can still form crucial bird habitat when they are planned with biodiversity in mind, while simultaneously performing important functions for production (see Native Shelterbelts).
- Establish plantings around paddock trees: By incorporating paddock trees into a planting, their habitat value is increased for a range of bird species and gives your planting a 200 year head-start. It is also worth considering planting shrubs around isolated paddock trees that have been fenced off to allow natural regeneration.
- Plant in gullies and around watercourses: Plantings established in gullies or flat areas tend to support more species of birds than those in other areas such as on slopes or ridges. This can have the added benefit of contributing to riparian restoration, which brings with it a suite of benefits for production. Plantings that can incorporate standing water will also attracts a suite of wetland birds such as rails, ducks and waders.
4. Enhancement plantings
Enhancement plantings are also an excellent way to attract birds to your farm. Enhancement planting, or under-planting, involves planting within existing patches of vegetation. Typically, shrubs are planted as these are often missing in older plantings that have been grazed. Ongoing research by the ANU team has shown that replacing the understorey in remnant patches can be an effective tool for controlling the hyper-aggressive Noisy Miner, a native species that suppresses populations of other native birds by aggressively defending the food resources in their home range. Enhancement plantings can also be a great way of complementing areas of targeted natural regeneration, as understorey species are often depleted from the existing seed bank.
1. Limit or exclude grazing
There are conflicting views on whether to periodically graze plantings once they are established. For this reason, the ANU research team compared bird occurrence in plantings subject to uncontrolled grazing with planting where there was no grazing. We found that uncontrolled grazing undermines the biodiversity values of plantings. For example, White-plumed Honeyeater, Rufous Songlark and Superb Fairy-wren are all less likely to occur in a planting that has been grazed. As a result of this research, we suggest that wherever the objective of a planting is to enhance bird conservation, grazing should be limited or excluded.
2. Embrace mistletoe
Mistletoe is an extremely valuable resource for birds as it provides fruit and nectar, nesting habitat and it produces proportionally more leaf litter than other plants, thus forming the foundation for healthy invertebrate populations for woodland birds to prey on. Mistletoe boosts the suitability of plantings as bird habitat and should be left in place and allowed to flourish.
3. Leave large logs and fallen timber
Large logs and fallen timber also enhance the biodiversity value of plantings and other woodland patches. Landholders should resist the temptation to ‘clean up’ these patches and leave this timber as it has fallen wherever possible. In situations where logs and fallen timber obstruct the movement of farm machinery in cropping paddocks, they can be moved to woodland patches or plantings so that they can play a role as habitat for native fauna.
The ANU research team has accumulated a large amount of evidence on the topic of revegetating for birds. The information presented here summarises the central messages from this research. The recommendations made here can be thought of as the gold standard for creating bird habitat. Any attempt to promote bird conservation on private land based on any of the recommendations provided here is likely to result in positive outcomes for some birds and all landholders are encouraged to do what they can, however small the contribution may seem: a little goes a long way.