Since the first translocation of kākāriki karaka in the Brook Waimārama Sanctuary, we've been doing an annual population survey. This species is critically endangered and there is a requirement to monitor progress post-reintroduction. Normally this is done in May or June, but we had to delay it for various reasons (personnel availability being the main one) and this year the survey was conducted on September 1st and 2nd. We covered the Sanctuary in twelve teams of two people per team playing a recording of kākāriki karaka at designated points and attempted to count every member of this species present. An accurate population estimate would require all birds to hear the playback, respond to it, and then be detected by the surveyors either visually or audibly. The survey is conducted twice, on consecutive days, with teams swapping and doing different lines on Day 2 (this helps to reduce surveyor bias).
Prior to the survey, anecdotal evidence indicated a steady increase in population density in areas where kākāriki karaka have been regularly recorded, and continued spreading of the species into areas where they were either not previously detected or perhaps only occasionally spotted.
In the past couple of years it had become clear to many of us that some birds were simply not interested in the playback. They did not come in to investigate. Many of the counted birds were randomly detected in between playback points (spaced at about 200-300m centres). It seems clear to me that as the population increases, the birds have less reason to respond to playback. I.e., most of the birds will hear other kākāriki karaka many times per day and there is little reason to expect them to react every time they hear one. I have watched kākāriki numerous times when other kākāriki pass by or chatter some distance away, and the birds I'm watching do not react.
During this playback survey, there were a few occasions where we were walking between stations, and we'd hear a chirp, or minor chatter. We'd stop, and if we were unable to observe anything further we'd note it as one bird (one unidentified parakeet). However, on occasion, we'd look in the direction of the chatter, find the bird, then shortly after would see the bird's mate. Then nearby would be another pair, or more. So one chirp could indicate one bird, or four, five, six etc.
Overall, the lack of interest in the survey by some (many?) of the birds, and the conservative counting, means the number of birds detected is likely to be an undercount, possibly significantly so. This is of course partly offset by the small number of birds counted twice (if they've flown from one site to another and been counted again).
On day one we counted 285 birds, on day two it was 229. My view is that 285 is safe as an absolute rock bottom conservative minimum. Any other use of numbers will involve guess work. Counting small green birds in a large green forest is not an exact science! Even that rock bottom number indicates steady year-on-year population growth. If a fudge factor is added for the uncounted birds then it simply indicates an even higher growth rate.
It is worth noting that in ideal conditions, kākāriki karaka are capable of rapid breeding. They can begin breeding within a few months of fledging, have overlapping consecutive nests, and large clutches. Note the pair Trixie and Nacho at the Isaac Conservation and Wildlife Trust have produced 55 chicks over the last two seasons, with 33 in the last season alone. This is not typical, but it is easy to see how rapid population growth could occur in the ideal conditions of the Brook Waimārama Sanctuary (original beech forest with an absence of introduced mammalian predators).
Anyway, with a gun to my head, what would I guess is the likely population in the Brook? I would probably go for something in the high 400s, with rather wide error bars, perhaps +/- 200 birds. What if we only detected half of the birds? You do the math.... Anyway, it's all good news.
Here's a photo of a kākāriki karaka we detected on Day 2 of the survey.
...and here's one detected on Day 1.
Healthy birds reflecting a healthy population with healthy population growth.
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