Thousands of Years of Inbreeding May Have Saved This Flightless Parrot From Extinction

The Kākāpō had fewer mutations in its genome despite a small genetic pool and long history of isolation due to a previous near-extinction event

A close-up image of a kakapo. The bird has lime-green feathers, and a face that resembled an owl.
When comparing the genomes, the team found that the birds of Stewart Island had less genetic diversity than the mainland birds and had half as many mutations as the birds that dwelled on the mainland. Department of Conservation via Wikicommons under CC BY 2.0

The kākāpō (Strigops habroptilus)—a flightless bird with speckled lime-green feathers and endemic to New Zealand—is one of the most endangered birds on the planet. Also known as the owl parrot for its disk-shaped facial feathers, the nocturnal bird is currently listed as critically endangered by the IUCN Red List, and only 201 individuals remain today.

Most of the remaining population descends from a small gene pool, but a new study found that despite undergoing 10,000 years of inbreeding, the kākāpō has fewer harmful mutations than expected and may have lost them over time rather than accumulating them, reports Jason Goodyer for BBC Science Focus.

The results suggest that small populations without much genetic diversity can survive in isolation for hundreds of generations despite inbreeding. The study published in Cell Genomics may give more researchers insights into how genetic tools can conserve the kākāpō.

The island-dwelling birds’ population began to decline after they first met humans. Around 700 years ago, when the Māori arrived in New Zealand, they found that the kākāpō was not only easy to catch with its waddling gait, but a delicious meal too, per the Economist. Their numbers continued to decline after European settlers arrived and introduced cats, rats, and short-tailed weasels. By 1995, there was only one flightless parrot named Richard Henry left on the mainland and a total of 50 birds left on Stewart Island, located south of New Zealand’s South Island, Clare Wilson reports for New Scientist.

To understand the kākāpōs genome, Love Dalén, a geneticist at the Centre for Paleogenetics in Sweden, and his team of scientists in New Zealand and Sweden compared the genes of 35 live kākāpōs from Stewart Island to 14 museum specimens from the extinct mainland population, BBC Science Focus reports. One kākāpō included in the research was an individual bird named Richard Henry, who died in 2010 at 80 years old, reported Shireen Gonzaga for EarthSky in 2011.

When comparing the genomes, the team found that living Stewart Island birds had half as many mutations as the deceased New Zealand mainland birds, per New Scientist.

The find puzzled researchers because it was suspected the mainland population, which at one point held more individuals and in turn more genetic diversity, would have had less fewer mutations than the isolated birds residing on Stewart Island, the Economist reports. Steward Island kākāpōs had, on average, 18 genetic mutations per bird while the mainland parrots had 34 mutations, New Scientist reports.

Scientists suspect this discrepancy happened because of a near-extinction event 10,000 years ago when Stewart Island split from the mainland. This event made likely made Steward Island birds more resistant to mutations, in order to preserve the population, per the Economist.

The birds may have undergone a process called purging, where the individuals become so inbred that harmful mutations accumulated to the point that birds with two mutated copies of a gene had fewer offspring, which led to the removal of harmful mutations in the gene pool, per the Economist.

“The Stewart Island kakapo have been suffering from inbreeding for 10,000 years,” Dalén tells New Scientist. “Consequently, when the population size decreased even further in the last centuries, they were likely less affected than they would have been without going through this earlier purging of harmful mutations.”

For future studies, the research team plans on investigating other genomes of inbred animals to see if the results in the study were specific to the kākāpō or if the phenomenon can occur in other populations.