How the kākāpō got its colours

Aotearoa New Zealand’s adorable kākāpō comes in two colours, green and olive. Now scientists think they know why.

Once, the parrot only existed in one colour: green. The variation of an olive-feathered bird appeared around 1.93 million years ago, about half a million years after the evolution of two predators which killed kākāpō, the Haast's eagle and the Eyles' harrier, scientists assert in a paper in the journal PLOS Biology.

Waipapa Taumata Rau, University of Auckland biologist Associate Professor Anna Santure was a co-author of the paper. The lead author was Dr Lara Urban of Helmholtz AI, Germany, and the project involved collaborators including the Department of Conservation and Ngāi Tahu.

The kākāpō (Strigops habroptilus) is a nocturnal, flightless parrot endemic to New Zealand. It experienced severe population decline after European settlers introduced new predators.

By 1995 there were just 51 individuals left, but intense conservation efforts have helped the species rebound to around 250 birds. The two colours – green or olive –occur in roughly equal proportions.

To understand how this colour variation evolved and why it was maintained despite population declines, researchers analysed genome sequence data for 168 kākāpō, representing nearly all living kākāpō at the time of sequencing.

They identified two genetic variants that together explain colour variation across all the kākāpō they studied. Scanning electron microscopy showed that green and olive feathers reflect slightly different wavelengths of light because of differences in their microscopic structure.

Computer simulations suggest that whichever colour was rarer would have been less likely detected by predators, explaining why both colours persisted in the kākāpō population over time. The variation has remained even after the predators went extinct, around 600 years ago.

“We think the kākāpō population may have been swinging back and forth from a majority of green birds to a majority of olive, with birds being less likely to be detected by predators if they were the rarer colour of the time,” says Dr Santure.

The authors argue that understanding the origins of kākāpō colouration might have relevance to the conservation of the critically endangered species.

Co-author Andrew Digby, of the Department of Conservation, says, “Using genomics to understand the current significance of such characteristics is important as we seek to restore the mauri (life force) of kākāpō by reducing intensive management and returning them to their former habitats.”