Norfolk Island morepork owl on brink of extinction due to genetic bottleneck

Conservationists are sounding the alarm about the critically endangered Norfolk Island morepork owl, warning that the species faces a genetic bottleneck that could lead to its extinction unless urgent action is taken.

The entire population of the Norfolk Island morepork owl, also known as the Norfolk boobook, is descended from a single female after the species nearly died out in the 1980s. About 25 owls are thought to survive on the island.

Monash University ornithologist Rohan Clarke said the window for action is closing. "I think it can probably be measured in years," Mr Clarke said. "I would be pretty confident that we're going to be in a substantially worse position in 10 years if translocations haven't happened."

In 1988, a male morepork from New Zealand, a close relative to the Norfolk Morepork, was introduced to the island to save the species. Norfolk Island science ranger Allie Andersen said the reproduction rate climbed after the first translocation nearly 40 years ago.

"Lots and lots of breeding was happening, nestlings were coming out of nests and that really restored the population," Dr Andersen said. However, Dr Andersen noted that due to inbreeding, the growth had stagnated.

"Probably the single largest threat would be their very small population size and high inbreeding," Dr Andersen said. "Every single owl that we have now is derived from just those two individuals."

Dr Clarke said infertility was common among highly inbred populations. "All of those reproductive challenges are classic signs of inbreeding depressions in populations that have gone through extreme bottlenecks," he said.

A 2021 study showed there were only about 26 owls left on the island, many of which experts believed to be part of the older generation. Dr Clarke said there may only be one single breeding pair out of 15 total pairs.

"Our knowledge is that the total number of young being produced is really small," he said. "If it's only one single with every loss of an adult bird and with the generation of more young from that single pair, the population continues to get more inbred because you've only got one female and one male contributing to the overall genetics of the population."

Another threat for the morepork owl is secondary poisoning through chemicals intended for rats and house mice. "If we lose even one owl to secondary poisoning that can have a real impact on the population," Dr Clarke said.

Dr Andersen said the community was worried about the future of the morepork owl. "I think we're all concerned," Dr Anderson said. "It's a beautiful species. It means a lot to the community."

The last hope for the Norfolk Island morepork is to increase genetic diversity by integrating more New Zealand morepork owls. Community consultations with the Norfolk Island community have already been completed. However, more work still needs to be done before the translocation can happen.

A Parks Australia spokesperson said "substantial ecological, genetic and practical challenges need to be addressed before it could proceed". Dr Andersen said the Norfolk Island community had not lost hope.

"While I think everybody is concerned, there's a lot of hope because we have such an incredible group of passionate people both on the island and off the island, a lot of researchers and a lot of wonderful research partnerships that have seen so much success in the past," Dr Andersen said.