DOC scientist Terry Greene on kākā and their remarkable recovery at Pureora Forest

DOC scientist Terry Greene has spent much of his career studying kākā. He has a soft spot for this boisterous, noisy, native forest parrot.

In 2020 he returned to Waipapa in Pureora Forest, 20 years after he first monitored kākā there, to see how they were doing. 

Previous surveys showed kākā numbers were slowly increasing.  What he found, to his delight, was a 400% increase in kākā—from 640 birds in 2000, to an estimated 2,600 birds in October 2020.

We asked Terry to explain this result and how he monitors this acrobatic and far-flying parrot.

What got you interested in kākā?

I have always liked parrots and kept them in aviaries as a child. My first up close encounters with kākā were on Hauturu/Little Barrier Island in the 1980s where great mobs of them were fed every day by the rangers. Some were tame enough to seek extra food from our hands and the kitchen if we left the door open. I admired their sociability and intelligence.

I wondered why it was increasingly difficult to find them in mainland forests, and whether anything could be done to improve their situation.  A small colour banding study on Hauturu in 1987 led to an interest in kākā that continues more than 30 years later.

What are some of your most vivid memories of monitoring kaka?

Something that sticks with me was climbing 25 m up a matai tree to my first kākā nest at Waipapa and finding a female quietly sitting on her clutch of four white eggs, completely unfazed at my presence. 

More recently, going back to Waipapa Ecological Area after almost 20 years and seeing and hearing kākā everywhere in the surrounding forest—that was amazing. Results of this survey showed an astonishing 400% increase in birds since predator control began.

Why did you start monitoring at Pureora?

The Waipapa Ecological Area had a sizeable patch of virgin podocarp forest and, what we thought at the time, a healthy North Island kākā population. Intensive pest control was just starting in the area and we wanted to measure the impact of these efforts. We radio-tagged birds to measure survival and nesting success and started surveys to track changes in abundance and density using distance sampling techniques.

How do you count them?

Most often kākā are counted using standard five-minute bird counts which gives us an approximate measure of abundance. At Waipapa we tried a different approach using a technique called distance sampling. This estimates the probability of detecting a bird and we use this to adjust our raw counts to calculate absolute abundance and density.

To do this we need to count the number of birds we see and hear and measure the distance to each bird seen to reliably model detectability. At Waipapa we count kākā on a grid of about 130 points at 300 m intervals over 1150-ha. We try and complete these counts as quickly as possible in September—within a single week if the weather plays ball.

Take us back to that first monitoring trip, what did you see?

My memories are hazy of that trip. I recall we were focussed on getting the counting technique right and were relieved to see and hear enough kākā to have our first go at calculating a density estimate that seemed to reflect what we were seeing on the ground. Phew.

Fast forward to 2020—how was it different?

Kākā were obviously more numerous. Early on in our surveys we may have seen one or two birds at a count station at most, with zero birds recorded at many stations. In 2020 we were seeing and hearing groups of six to eight birds at a station and it was hard to keep tabs on all individuals. The kākā seemed to be far noisier and more social than before.

There’s been a four-fold increase in kākā over 20 years. Were you surprised by this result?

Yes and no. Yes, because the change was so marked over what seems a relatively short space of time given kākā only breed every few years when the rimu trees fruit.

But, no, because this result is similar with improvements we’ve seen at other locations in Fiordland.

What’s behind this increase?

It’s simple. Effective possum and stoat control over prolonged periods. Remove these two significant threats and kākā will flourish.

Were there any points on this journey when you feared for the future of the population in this area?

I guess there was always the concern that if pest control wasn’t successful, particularly for possums and stoats, then eventually this, and the other remaining mainland kākā ‘strongholds’ would sooner or later blink out as they had already done over much of their former range.

However, we soon learned that we were improving nest and chick survival, so we were quietly confident, especially when we compared results with areas that weren’t getting good pest control.

Kākā live for up to 20 years—do you think some of the original birds you counted could still be alive today?

Quite possibly and it would be nice to think that our paths might cross again. Estimates of life span are always a bit of a guess for wild birds but I wouldn’t be surprised if they lived for longer than 20 years.

Have you seen this at other sites for kākā?

Yes, we have, in the Eglinton valley and Waitutu Forest in Fiordland where there has been sustained predator control. Also places such as at Zealandia in Wellington, Pūkaha National Wildlife Centre at Mt Bruce in the Wairarapa and Orokonui Ecosanctuary near Dunedin, where there have been release programmes for captive reared kākā.

What’s the future for kākā at Pureora?

The future is very bright for this kākā population, provided pest control is ongoing. We don’t know if the population will keep growing. I would like to think it will, but we have very little understanding of what carrying capacity of our mainland forests for any of our native bird species looks like.

We know from historic records that kākā were once found throughout forested areas in Aotearoa. The results at Waipapa show we can turn the fortunes of kākā around.

https://www.doc.govt.nz/news/media-releases/2020-media-releases/kaka-monitoring-reveals-four-fold-population-increase/