A hidden threat facing one of Australia's most iconic birds has been uncovered in a new study led by researchers from the University of Copenhagen and The Australian National University (ANU).
The critically endangered regent honeyeater once numbered in the hundreds of thousands, but their population has dwindled to fewer than 300.
By analysing the DNA of museum specimens more than 100 years old and comparing it to modern samples, the team discovered that despite a population decline of 99 per cent, this has not been entirely mirrored by genetics. The bird has lost 9 per cent of its genetic diversity.
According to the authors, this disparity reflects a "time-lag" in genetic erosion- where genetic variation declines more slowly than population size.
"This delay might be hiding the looming genetic risks," Dr Ross Crates from ANU said.
"Our simulations show that diversity loss will continue and even accelerate, and the species is already likely experiencing diminished genetic health because of this process.
"With this information in hand, we can better protect the regent honeyeaters. We can identify priority habitats, optimise breeding programs, and closely watch for signs of inbreeding before it becomes a critical problem."
To better understand the challenges the birds face, the study also used environmental modelling. Based on historical records and projections of future climates, the authors found that ongoing habitat loss, urban development, and climate change have dramatically reduced the regent honeyeater's suitable breeding and feeding grounds.
Their models predict that conditions could worsen within the next few decades, especially for the species' remaining strongholds.
"This work shows how combining different datasets, such as genomic data and species distribution modelling, can provide a more complete picture of biodiversity decline," explained co-author Professor David Nogués-Bravo.
Associate Professor Hernán E. Morales, who led the study, added: "We must take the threat of genomic erosion seriously in the midst of today's biodiversity crisis. Although the regent honeyeater's genetic diversity looks relatively high, our findings show it's already eroding, and ongoing environmental threats only compound this risk.
"Loss of genetic variation can occur stealthily-and swiftly-after populations reach critically low levels. This gap between demographic collapse and noticeable genetic erosion is a hidden extinction risk."
The study is published in Proceedings of the Royal Society B.
