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By Bayley Costin, Heather McGinness and Linda Merrin Bayley Costin, Heather McGinness and Linda Merrin 22 March 2022 6 min read

Brolgas are iconic waterbirds found across tropical northern Australia (Image: BirdAsPoetry via Flickr)

The region spans about 40 per cent of Australia’s land mass. Across the north, there are floodplains, lakes, rivers, and both saltwater and freshwater wetlands. And these habitats teem with waterbirds.

Brolgas, magpie geese, glossy ibis, great egrets and masked lapwings all gather here.

As their name suggests, waterbirds are dependent on resources like surface water flow in wetland habitats for their reproduction and survival.

Waterbirds gather where they find suitable environments; environments with enough food, shelter, protection, and the preferred conditions for breeding. During breeding events, certain habitats in the north can support more than 100,000 waterbirds – an impressive sight!

Ruffled feathers: threats to waterbird populations

But while 100,000 might sound like a large number, the population of many waterbirds globally is in rapid decline.

Waterbirds are facing increasing threats, including water extraction, changes in water regimes (from dams to weirs), loss of inter-tidal habitats like mangroves and mudflats, an increase in human disturbance, and other anthropogenic impacts.

These threats have significantly increased mortality rates of waterbirds and deteriorated their habitats, both in Australia and internationally. For instance, the royal spoonbill relies upon freshwater habitats that are under serious threat due to a lack of inundation.

Because of these threats, waterbirds and their habitats are the focus of conservation efforts. For many years, waterbirds have been the subject of extensive research and in-depth analysis into their ecology and behaviours. This provides us with comparatively large datasets. These datasets can identify consistent trends in population and ultimately help with population recovery.

Magpie geese are found in large flocks across the north of Australia (Image: Matt Gilfedder)

Waterbirds are indicators of ecosystem quality

Waterbirds are important indicators of ecosystem quality. Their quick response to environmental changes helps researchers identify problems and risks that may impact a habitat’s integrity. Researchers monitor waterbirds’ presence, population, breeding and social behaviours on both an individual and community level to identify the stressors and variations of an environment.

Take the royal spoonbill, for example. This regal bird forms elevated nests over water in thick vegetation. For the eggs or chicks to have a maximum chance of success, the water level in the wetland must remain at an adequate depth. This depth protects the royal spoonbill against predators, maintains the birds’ growth, and provides an increased availability of food.

Unlike most other aquatic animals, waterbirds often relocate to different habitats[Link will open in a new window] – and even catchments – according to their needs and the availability of food and other resources. For instance, most people have seen extraordinary photos of 100,000 or more pelicans along the shores of Kati Thanda – Lake Eyre, following large periods of rain.

Waterbirds and water resource assessments

So how does all of this fit into the work CSIRO is doing in northern Australia?

CSIRO scientists and partners continue to undertake large-scale multidisciplinary water resource assessments across northern Australia. The assessments investigate risks and opportunities for water and agricultural development in the north. This includes research into how water resource development might affect different species and habitats. And a key part of this is investigating potential impacts to waterbirds.

Waterbirds are important to humans, too. Their unique characteristics and social behaviours have long influenced human culture. Waterbirds hold great cultural importance for First Nations people in northern Australia. Many species are used for food, and as part of traditional stories, dance, and other cultural activities. For example, magpie geese are an important food source for Bininj, who are working to bring flocks back to Kakadu National Park.

Waterbirds in northern Australia are highly diverse and species rich. So, for the water resource assessments, we grouped waterbirds into four functional groups.

Each functional group represents a range of species with similar ecological characteristics, such as the habitat they prefer, and how they nest and forage. We then chose the specific bird species within each functional group based on their significance for conservation, their cultural importance, and their sensitivity to impacts from water resource development.

The four waterbird functional groups

1. Colonial and semi-colonial nesting wading waterbirds

These birds have a high level of dependence on the timing and extent of floods, and the duration of inundation. Their breeding is stimulated by inundation, which supports fledging growth and survival. Species include ibises, egrets, herons and spoonbills.

Royal spoonbill is an example of a colonial and semi-colonial nesting wading waterbirds (Image: Stewart Baird via Flickr) ©  @2019 Stewart Baird

2. Shorebirds

These birds are migratory. They finish their migration in northern Australia after breeding in the northern hemisphere. Shorebirds are highly dependent on and large inland flood events that inundate sandflats and estuaries that hold large amounts of food to support extensive shorebird populations. They prefer shallow habitats to forage and roost, regaining energy to recommence their migration back north. Many shorebird species are of international concern and are listed throughout multiple bilateral migratory bird agreements. Includes curlews, sandpipers, godwits.

Eastern Curlew is a migratory shorebird (Image: JJ Harrison via Flickr)

3. Cryptic waders

These birds depend on shallow temporary and permanent wetlands with dense emergent vegetation, such a reeds and rushes. This kind of habitat requires continuous inundation to survive. There is a significant knowledge gap with this group compared to the other functional groups. But scientists can use their habitat requirements as surrogates to assess their vulnerability to changes in water. Includes crakes, snipes, rails, bitterns.

Buff-banded rail is an example of a cryptic wader (Image: Patrick Kavanagh via Flickr) ©  Patrick Kavanagh

4. Swimmers, divers and grazers

Swimmers, grazers and divers prefer open, deeper water environments, such as lakes, harbours, permanent ponds and other freshwater permanent waterbodies. They usually swim while foraging using methods such as diving, filtering, and grazing. All species within this group breed in Australia and some are partially migratory. Species include pelicans, cormorants, ducks, grebes.

The Australasian grebe and is in the 'swimmer, diver and grazer' functional group (Image: BirdAsPoetry via Flickr)

Why do we create functional groups?

All waterbirds depend on surface water flow, whether it is freshwater or saltwater. But each functional group requires different habitats and resources to survive and reproduce. Some birds like the Eastern curlew take refuge in estuaries and bays, and some birds like ibises breeding in flooded wetlands for protection against predators.

So, by grouping the birds, we can model how each of the four functional groups will likely respond to any water resource development. For instance, we model different hydrology scenarios (like the addition of a new water capture and storage options, such as a dam) and identify how the functional group would respond. To do this, we also use previous studies and local information about waterbirds and their habitats. This gives us an understanding on quantitative relationships between water flow, ecological responses, and outcomes for waterbirds.

Ultimately, with better information on how waterbirds function and rely on certain aspects of the environment, scientists can inform decision-makers on how to manage waterbirds when considering any agricultural or water development in northern Australia.

The CSIRO Northern Australia waterbird functional group team includes Bayley Costin, Heather McGinness and Linda Merrin. The ecology work in the current northern Australia water resource assessments is being led by Danial Stratford.

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