Endangered purple-crowned fairy wrens – tiny but striking Australian songbirds – could be at even greater risk from global heating after a study found that exposure to hot and dry conditions damages nestlings’ DNA.
Unlike the more tangible effects of global heating on species – such as a rising risk of bushfires, loss of habitat or lethal heatwaves – the scientists said the effect they had discovered was silent, pernicious and lifelong.
The wrens weigh less than 13 grams and live in pockets of dense vegetation along river systems in the Northern Territory and the eastern Kimberley region of Western Australia.
Research published in the Proceedings of the National Academy of Sciences found that as temperatures in the birds’ habitat rose above 31C during the dry season, this affected the length of a part of the birds’ DNA known as a telomere that is a marker for how well they can reproduce and how long they live.
As the climate warms, the study said, the birds were likely to be exposed to greater heat, further shortening the telomeres and increasing the risk of extinction.
The change was revealed after scientists took blood samples from veins in the wings of the birds living in a protected sanctuary in the remote Kimberley.
Dr Justin Eastwood, the lead author and a Monash University postdoctoral research fellow, said the shortening of the telomeres accelerated the ageing process, meaning the birds died younger and had fewer offspring.
Eastwood and his colleagues looked at climate models to see how the temperatures could change for the fairy wrens. “We found that even under relatively mild climate warming scenarios that the non-lethal effects on nestling telomere length alone could result in population decline,” he said.
The fairy wrens have been monitored at Mornington – Marion Downs sanctuary, which managed by the Australian Wildlife Conservancy, for 17 years.
Nestlings weigh just seven grams – not much heavier than a pencil – when the blood samples are taken and analysed.
Prof Anne Peters, a Monash University evolutionary ecologist who co-authored the paper, said the findings were concerning. “We have to be vigilant for these pernicious silent threats that research like this can uncover,” she said.
It was theoretically possible that natural selection could favour wrens with slightly longer telomeres, she said, and this could counteract the effect of the heat. But whether this could happen, or could happen quickly enough, wasn’t known.
Other species could also be at risk as conditions get hotter, Peters added, building on the existing threats faced by young birds.
“There’s never just one threat faced by a species,” she said.
While protected areas could reduce those other threats, she said, preventing DNA damage caused by rising heat was a much greater challenge.