Fiordland Kiwi Diaries: A New Hope

Results from the Wet Jacket Peninsulas 1080 Operation

We’re on the front lines of the Save Our Iconic Kiwi initiative. Our ranger Tim and his team have been studying the population of kiwi at Shy Lake to find out how to best protect them from predators like stoats.

In the last episode, we described the planning that went into the recent 1080 operation to protect kiwi chicks at Shy lake and beyond.  The next step was to monitor the results – how successful were we at controlling stoats?  Time to run some tracking tunnels.

Time to What?

Tracking tunnels are the tool DOC uses most commonly to monitor the levels of stoats and rodents in an area.  A card is placed in the base of a plastic tunnel, with a patch of ink in the middle and a tempting bait.  If you’re looking to track rodents, it’s peanut butter – in Fiordland we use the high-quality stuff, as this is more attractive to rats.  Apparently only the best will do!  For stoats we use chunks of rabbit meat.  The rats and stoats will run through the tunnels to get to the bait and leave telltale inky footprints on the card.  Roughly speaking, the more cards have tracks, the more stoats and rats there are running around the bush.

The tunnels are spread through the bush in lines of ten, 50 m apart.  The lines are then usually placed in sets that run from “ridge to river,” meaning that there’ll be a line in the valley bottom, a line a couple of hundred metres further up the hill, and so on all the way to the tussock tops.  We want to be confident that our index of stoat abundance is representative of the changing forest types and conditions at different altitudes.  Altogether we have 250 tunnels in 25 lines across the huge Wet Jacket Peninsulas 1080 block of nearly 40,000 hectares.  Every three months, a group of keen beans wears out their boots and their knees bashing through the scrub to put fresh cards in the tunnels and collect them again.

How did we do?

Shortly before the Wet Jacket Peninsulas 1080 drop, teams of hardy contractors ran the tunnels and found that 71 of the 250 tunnels tracked a stoat, across 60 % of the lines.  This is higher than usual for the area and reflects the widespread increase in stoat numbers following the 2019 beech mast.  We had already seen in previous seasons that 20 or 30 % of lines tracked still meant zero survival of our kiwi chicks.

After the drop, our post-op monitoring painted a very different picture.  None of our tunnels tracked a stoat.  We also tracked zero rodents in the areas where 1080 was applied. 

As a comparison, we also ran a set of lines just outside the predator control area.  All of the lines were visited by stoats, and of those lines, 78% of the tracking cards within them had stoat prints.  This gives us a lot of confidence that the 1080 operation was the reason for the drastic stoat reduction inside the control area.

This is a great result and as good as we could hope for from an ambitious and complex operation, and we’re all excited about what this could mean for hundreds of kiwi in the area.  We do need to be a little bit cautious, because we know that tracking tunnels aren’t always great at detecting stoats that are present at very low densities.  Furthermore, we need to sustain this result for a year to allow the kiwi chicks to grow big enough to be safe from stoats.  It doesn’t take many of these ruthlessly efficient predators to kill all of the kiwi chicks in an area.  So the acid test, of course, will be how many of our chicks survive.  It’s not about how many stoats we kill, but how many kiwi we save.

A few weeks ago, we headed in to Shy Lake to find the first nests of the season.  After a few months away from the hills in lockdown and at my desk over winter, it was a tonic to be out in the wilds again after a fresh snowfall, tracking kiwi to their nest and installing a trail camera outside the entrance.  And we’re off a really good start as so far, we haven’t seen any stoats on the trail cam footage from kiwi nests.  This is a huge difference from previous years, when up to 90 % of nests were visited by stoats.  At the moment I couldn’t ask for better and I’m looking forward to seeing how the chicks fare.

This is the twenty-seventh in a series of posts about Tim’s work, follow the Conservation Blog to keep up to date on his progress.