Birds leave genetic clues in drinking water

Australian researchers have worked out how to trace an endangered bird species by analysing water samples from its drinking holes.

Using environmental DNA (eDNA), a team led by Karen Gibb from Charles Darwin University identified the movements of the stunning rainbow-coloured Gouldian finch (Erythrura gouldiae), a species native to tropical savanna woodlands in Australia’s north.

Once numbering in the millions, there are now just 2500 adults as a result of the illegal bird trade, altered habitat, predators and wildfires, and the species is listed as endangered.

eDNA is used to detect the locations and numbers of rare and threatened species from water samples and to date has mostly been applied to freshwater animals.

Gibbs and team, including colleagues from the University of Western Australia, saw an opportunity to track the Gouldian finch using water sample analysis, as it needs to drink several times a day.

To do this, they developed a test that can identify estrildid finches from a fragment of mitochondrial DNA, and a probe specifically designed to detect Gouldian finch DNA.

This was necessary to distinguish the colourful finches from masked finches (Poephila personata) and long-tailed finches (P. acuticauda) – other estrildid species that often flock together at the same waterholes.

“It’s a much more accurate test,” says Gibb. “By having primers that pick up other finches it tells us the eDNA is good enough quality to be amplified. If the Gouldian test is then negative, we can be confident that the eDNA test worked, but there just weren’t Gouldian finches at that site.”

First, they piloted it in wildlife park aviaries before doing field trials at the Yinberrie Hills in the Northern Territory, where scientists and rangers had good observation data to validate the tests.

With a 200-millilitre water sample they could successfully detect Gouldian finch eDNA from waterholes the birds had visited in the previous 48 hours, and where there were lots of birds, it was still measurable from the samples two weeks later.

“When it worked in the real world at the waterholes, even where the water was poor quality in places – where it was hot and looked a bit oily – we were really excited,” says Gibb.

The study opens new options for rangers and scientists to keep track of the birds’ movements by simply collecting small water samples during their explorations, which will help inform conservation efforts.

“People who are travelling around will be able to put a cup of water into an appropriate container and then into a car fridge, and be able to take a lot of samples,” Gibbs says. “We can cover a much larger area.”

The study is published in the journal Endangered Species Research.

Gouldian finches drinking among masked and mannikins at a waterhole.
CREDIT: Northern Australian environmental research hub