Flooding rains have brought large numbers of flocking birds to breed and feed in the rivers of Australia's Lake Eyre Basin, but numbers appear to have fallen compared to previous surveys because of persistent drought and lack of floods in the Murray-Darling river system.
Researchers from the University of New South Wales, Australian National University and Wetlands International have just completed aerial and ground surveys of the rivers, floodplains and lakes of the Lake Eyre Basin, where they counted colonies of breeding pelicans, ibises, cormorants and spoonbills as well as broods of pink-eared ducks and grey teal.
The floods around Mt Isa in north-western Queensland will produce a bird bonanza lasting six to nine months, according to UNSW Professor Richard Kingsford, who was part of the survey team.
"Up to 50 species of waterbirds from around Australia have arrived on the Georgina-Diamantina floodplain to feast on the boom in the supply of insects, invertebrates, frogs, crustaceans and fish," Professor Kingsford says.
He is encouraged by the amount of waterbird breeding, given that these rivers do not run every year and that many of the birds would not have bred for some time in the Murray-Darling Basin. The present floods were less widespread than big Channel Country floods about 10 years ago, which occurred in consecutive years, thereby enhancing the wetland breeding habitat.
However, he commented: "I had expected there to be more birds here, despite all this breeding. Also, we think that national populations of many waterbirds are relatively low, probably a result of many years without flooding in the Murray-Darling Basin.
"The prolonged drought and over allocation of rivers in the Murray-Darling has meant fewer and less extensive floods which are probably having continental effects on waterbird numbers. Without significant further floods in the channel country and good breeding conditions persisting in our northern wetlands, things could be a lot worse."
The Lake Eyre Basin measures more than a million square kilometres - including much of inland Queensland, large portions of South Australia, the Northern Territory and a part of western New South Wales - with about 70,000 km2 of wetland.
"None of the rivers and creeks of the Lake Eyre basin is permanent but in flood years they spill widely to spark a period of rapid growth and fertility. Long-dormant crustaceans multiply and flocks of waterbirds arrive in huge numbers to feed and raise their young before the waters evaporate."
The rivers and creeks of the Lake Eyre basin have been immortalised by Australian bush poets, and include the Finke River, the Georgina River, the Diamantina River and Cooper's Creek, where the explorers Burke and Wills met their deaths. The floodplains that have filled with this flood, principally the Georgina and Diamantina, are up to 30km wide and stretch up to 100km long.
The researchers surveyed from the wetlands at the top of the river catchment all the way down to Lake Eyre, a distance of up to 600km. They recorded a pelican colony of up to 30,000 to 60,000 nests and many colonies of ibises, egrets, spoonbills and cormorants in hundreds or thousands. As well, thousands myriad of pink-eared ducks, grey teal, hardhead and black-tailed native hens were breeding in the swampy channels that crisscross the floodplains. Based on systematic estimates of bird densities, many hundreds of thousands of waterbirds have been using the floodplains in the immediate post-flood months.
Most of the waterbirds are concentrated on the floodplains of Eyre Creek and the Diamantina, between the outback Queensland towns of Birdsville and Bedourie. At present, there are relatively few birds down towards the bottom of the catchment where Lake Eyre is filling. The Diamantina River is still running and so water is making its way into the Warburton River, filling Lake Eyre.
It takes months for water to reach Lake Eyre from the headwaters in the north. On the way, it fills channels, floodplains and lakes and tops up many permanent waterholes. Reconnection of waterholes is crucial for enabling re-colonisation of the system by fish and to help trigger breeding. The researchers estimate that 50 to 70 precent of the lake bed is now covered by water. Kingsford says: "Most of the water is extremely shallow and has only just managed to dissolve some of the salt crust and so is probably too saline for invertebrates, fish and most waterbirds to tolerate. More freshwater flows are needed to realise the boom in productivity. Where the freshwater is running in, the waterbirds are following."
Researchers estimate that there are currently less than about 5,000 waterbirds on Lake Eyre, mainly consisting of grey teal, pink-eared ducks, banded stilts, silver gulls and pelicans.
"The signs are still promising for numbers to build up a lot higher," Professor Kingsford says. "A pelican colony has just started of up to 1,000 birds and the banded stilts that traditionally breed on Lake Eyre have arrived with perhaps as many as 1,000 on the lake." Migratory shorebirds may also use the lake in large numbers in some years if the water remains when the birds return from Asia in the spring.
A colony of as many as 500 silver gulls was found to be breeding on one of the islands. Professor Kingsford says: "This may be a problem for management as breeding silver gulls are known to prey on young banded stilts. A key monitoring objective will be to determine when the banded stilts start to breed and protect the young chicks from being killed by silver gulls".
The biological boom is being almost matched by a tourism boom as many people in Australia flock to see the birds and the floods. Flights into Birdsville have doubled and there are non-stop flights from William Creek over the lake.
Kingsford thinks this provides another facet of rivers that should be considered in their sustainable management. "Protecting the flows of the Channel Country rivers has to be one of the most important environmental priorities for governments currently.
"This phenomenon throws into sharp relief the contrast between an ecological and agricultural collapse in the Murray-Darling Basin and this incredible Channel Country river system which has been fluctuating between natural flooding and drying cycles for eons.
"Australia has a great opportunity to lead the world in the protection of river flows within these wonderful river systems" says Kingsford. "There are few rivers anywhere in the world that are still free-flowing the way the Lake Eyre Basin rivers do. There is certainly sufficient science both on the ecology of these rivers and the damage caused by river regulation and unsustainable water use to know that protection of river flows is fundamentally important," he says.
In his 2007 book, Ecology of Desert Rivers, Professor Kingsford has revealed how birds and other organisms survive and thrive in an environment of such extreme swings in conditions. He reveals how human interventions, such as the creation of dams, is affecting desert, rivers and the animals and plants that depend on them for survival.
The current survey project is a collaborative effort with Wetlands International, the Australian National University and Wetlands International and is funded by the Australian Government and the governments of South Australia and Queensland.
Media contact: Dan Gaffney 0411 156 015