A long-term kākā monitoring programme in Pureora Forest Park is proving its worth as results show a fourfold increase in kākā numbers following pest control in Waiapa Ecological Area, tipping the balance back towards a more even sex ratio.
The Waipapa kākā population has increased from 600 birds between 2000 and 2007 to around 2,600 birds during 2020 – an average annual population increase of 6.4%.
Female kākā sit on the nest for extended periods of time incubating eggs and tending to chicks and become easy prey for pests like stoats and possums. This results in the species’ sex ratios skewed towards males.
However, the new kākā population survey results show a significant improvement in the sex ratio of the birds. With pest management, Pureora has seen the previous 1:2.1 sex ratio (2.1 males for every one female) come back into balance and closer to 1:1.
“We can show comprehensively that populations which did not have pest control were highly skewed towards males because females are killed on the nest,” says Terry Greene, DOC Science Advisor.
Kākā are episodic breeders which means their breeding is linked to the availability of food resources. They sync their breeding cycles with mast events where trees produce and drop a significant number of seeds/fruit, providing ample food supplies for the birds.
“When there’s lots of food around, they’ll go for it, and even breed twice a year if they can” says Terry Greene, “We believe they live in the order of 40 years in the wild. They have variable numbers of chicks depending on the food crops available.”
But mast seasons can also spell disaster for native birds with an increase in ship rat numbers.
“Kākā breed the year seed is produced, and the pest populations expand after that,” says Terry Greene. “Rodents get stuck in, and numbers climb in winter and by spring, they breed and take off. Stoat populations follow behind in October and suddenly seed drops off and stoats start eating more birds.”
DOC has controlled pests within the Waipapa area since 1993 using various methods.
“We use a combination of 1080 dropped every three years and ground bait stations used annually,” says Jon Sadler, Te Kuiti Office Senior Biodiversity Ranger.
“We have more than 2000 bait stations on the ground, and the new kākā population results show the work is paying off.”
Annual monitoring of the birds is a coordinated effort and begins in October and runs for a week from 17 – 24 October 2021.
“A grid of about 130 points is laid over Waipapa Ecological Area and DOC rangers, contractors and volunteers go to the points with GPS units and stand there for 10 minutes. They need to know what the birds look and sound like and once detected, they use a laser range-finder to measure distance to the nearest metre. They go from point to point in pairs to maximise detectability,” says Jon Sadler.
“This study is the only one of its kind in the country,” says Terry Greene. “We don’t have density and abundance data like this because it’s difficult to resource long-term studies going and people move on. It’s fortunate the people who work in Te Kuiti have maintained it.”
“My great hope is that kākā become socialised and cherished in our wider landscape,” says Jon Sadler.
“And that they become more common in the remaining mainland forests and the population is maintained in Waipapa,” says Terry Greene. “It’s one of the great wildlife destinations in New Zealand at the moment. It’s one of those mainland forests that’s just extraordinary.”