Drier conditions have led to waterbird numbers in eastern Australia plummeting by 50% compared with 2023, one of the country’s largest wildlife surveys has found.
Conducted annually since 1983, the eastern Australian waterbird aerial survey is one of the world’s longest continuous bird counts as well as one of the largest by geographical distance covered.
The survey spotted 287,231 birds this year – half the 579,641 birds recorded in 2023. The number of birds in the 2024 report was the 22nd highest in 42 years of the survey, well below the long-term average.
The director of the centre for ecosystem science at the University of New South Wales, Prof Richard Kingsford, who leads the aerial surveys, said there was a “wistful optimism” that after wet years associated with the triple La Niña there would be a sustained boost in bird numbers.
“In 2021 and 2022 there was a lot of flooding everywhere, and we know that there were a lot of birds breeding, but we just haven’t seen the same sort of recovery,” he said.
The survey, which tracks more than 70 species of waterbirds, covers a third of the Australian continent – an area measuring 2.7m square km, or 11 times the size of the UK. It comprehensively tracks the distribution and breeding of waterbirds as well as changes in the major rivers and wetlands of the Murray-Darling basin.
Three of four major markers of waterbird health – overall numbers, numbers of species breeding and wetland area – were down, continuing a trend of significant long-term declines.
The abundance of breeding birds fell to well below the long-term average and was one of the lowest on record.
“The areas that these birds breed in and rely on are floodplain areas,” Kingsford said. “So much of what we’ve done in building dams and diverting water has [affected] that flood water that’s so critical for the wetlands.
“We’re also increasingly worried about the effects of climate change in terms of the drying out of the south-east of the continent.”
The climate crisis is hastening the drying out of wetlands. This year’s total wetland area – 122,283 ha – was also well below the long-term average.
Kingsford said the Murray-Darling basin plan had been an important restoration initiative for rivers. “What our data are indicating is probably there’s been some decrease in the rate of decline, not necessarily a complete restoration. We’re definitely making a difference in terms of putting water back into rivers.
“But it’s the big floods that are very important for these systems and the biodiversity. We’ve got to think about that in terms of the next review of the Basin plan.”
Amid fears this year about the H5N1 strain of avian influenza, which has devastated wild bird populations internationally, the team also surveilled for instances of mass mortality as a sign of potential outbreaks. “We didn’t find any, which is always a relief,” Kingsford said.
Waterbirds were most abundant in the temporary wetlands of the Georgina-Diamantina river system in north-western Queensland, the scientists found. Lakes Mumbleberry and Torquinnie accounted for 17% – 50,000 – of all birds observed.
