Kakapo numbers have increased 20 per cent after the most successful breeding season in 25 years.

Just 126 of the critically endangered birds were left in July last year but the population has been boosted to 154.

in the mid-1990s fewer than 60 of the floor-dwelling birds remained and conservationists feared New Zealand's vulnerable flightless parrot might join the dodo in the ranks of extinction.

Department of Conservation (DoC) experts are still working towards the first artificial insemination of a kakapo from frozen sperm in an attempt to guarantee their long-term survival.

Advertisement

"DoC has not attempted artificially inseminating kakapo using frozen sperm since 2009. Cryopreservation of kakapo sperm is still in an experimental stage," Deidre Vercoe, DoC operations manager said.

"Despite the lack of success with artificial insemination, the 2016 breeding season was the biggest in the 25 year history of DoC's kakapo recovery programme.

"A total of 122 eggs were laid and 47 chicks hatched, of which 32 chicks are still alive. Fertility was typically poor with just 63 eggs fertile.

"The kakapo population currently sits at 116 adults and 38 juveniles."

Vercoe says a highlight of the season was the first successful breeding on Anchor Island and the first in Fiordland since the 1940s. An Indian bird expert has also been part of the preservation effort.

"Good progress was made in our ability to reliably collect high quality semen from males, assisted by avian artificial insemination expert Dr Sushil Sood from the Himachal Pradesh Forest Department, India.

"Further research is required to develop and refine AI techniques, which showed some success in limited trials in 2009."

It has taken years to figure out how to best preserve kakapo semen because the requirements of cryopreservation differ from species to species. One of the main hurdles with getting frozen AI working was figuring out how to stop, or minimise, the degradation process of the sperm.