Fiordland Kiwi Diaries: Changing radio transmitters

Department of Conservation —  25/06/2018

We caught up with Tim, a ranger on the front lines of the Save Our Iconic Kiwi initiative. This is the thirteenth in a series following the work he’s doing to save the Fiordland tokoeka (kiwi). 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. They have captured a number of kiwi and put transmitters on them, and are now monitoring them through the breeding season to find out how well the adults and chicks survive without pest control. 

It’s autumn and we’ve been monitoring the southern Fiordland tokoeka at Sky Lake for a year now. In between trying to catch new adults to monitor, we need to recapture the birds we caught last year. The radio transmitters (known in the trade as “tx”) worn by each bird contain a wee lithium battery that lasts about a year, and so they need to be changed for fresh ones. This is the only time the adults are handled all year and so we take the opportunity to measure the weight and bill length.

Weighing kiwi. 📷: Em Oyston.

Weighing kiwi. 📷: Em Oyston

Mostly we work in teams of two as it is often handy to have a second person to help corral a running kiwi, to pass a bird to when upside down in a burrow, or to make it quicker and easier for handling when fitting the transmitter. Each of us carries a telemetry set consisting of a foldable aerial to gather the radio signal, and a receiver that converts that signal into audible beeps. As we swing the aerial from side to side, the volume and timbre of the beeps changes; where the signal is strongest, that way the bird lies.

Radio tracking. 📷: Vaughn Filmer.

Radio tracking. 📷: Vaughn Filmer

Of course it’s not as simple as that, as the basin is full of towering rock walls that mask the signal or cause it to bounce around. The signal can change wildly as you move only a few metres, and interpreting it is more of an art than a science. In many cases our clamber through the scrub is rewarded with kiwi sitting in an accessible burrow, and it’s just a case of reaching in to pull them out. But sometimes the roosts are pretty impregnable. When rangers Em and Sanjay go to visit Cake and Candles they are found roosting together, tucked up at the back of an underground palace, way out of reach and smirking at the humans a couple of metres away.

Em and Tahi. 📷: Sanjay Thakur

A few days later we try again. This time they are apart and as we approach Cake, the signal suddenly gets weaker. It looks like we’ve spooked him and he’s snuck off. We’re in thick, steep leatherwood and stunted scrub country where the kiwi can move much more easily than we can, so we decide to use four of us to embellish the standard technique of a pincer move. We fan out and two people take a wide line to hopefully loop round in front of the bird. The idea is that when Cake moves away from the sound of a person crashing through the scrub, he will hopefully move towards one of the others. He springs our trap a couple of times and we need to track him down again. At the third attempt, we are in a better position when suddenly he squirts from the centre of our ring down a rocky gut. Em makes a great dive to grab a leg and gathers him up, kicking but unharmed. Em gets a gold star for commitment to conservation, as in his dive he landed on a rock and cracked a rib.

Cake is weighed, his bill measured with callipers and a new transmitter fitted. The transmitter harness is switched to the opposite leg to mitigate rubbing on the skin. I’m pleased to see that although a few of our birds carry small scabs under the harness, there are no serious or painful looking injuries. The transmitter is probably more of a nuisance for the kiwi than anything, and when this study is over they will be removed.

Measuring the bill. 📷: Em Oyston.

Measuring the bill. 📷: Em Oyston

Most of the other captures are more straightforward as we split into two teams and work back to the bivvy. We even get a bonus in the form of a new bird: T-rex is roosting with his hitherto uncaught mate. I decide to fit a transmitter to her as well and name her T-regina. Over the next few days we work our way through all twenty-two birds needing a transmitter change. One interesting finding is that a couple of them have grown their bills by a millimetre or two. If they’re still growing then they’ll only a be a few years old. We knew that this year’s 10/10 chick mortality couldn’t be completely representative – there have probably been stoats here for a hundred years or more, so if no chicks survived then there wouldn’t be any kiwi left. But here we have direct evidence that at least the odd chick is still making it to adulthood. It makes me hopeful that this year one or two chicks might sneak through before the toxin operation (that must wait for next year’s beech mast) does its job in protecting them.

Measuring the bill. 📷: Em Oyston.

Measuring the bill. 📷: Em Oyston

This year we’re changing the way we monitor the early part of the nesting season by utilising some flash technology. The transmitters give us information on the kiwi’s daily activity levels which help us pick when they start nesting (see “The Perils of Nesting” episode for more details). Last year, with little known about the breeding behaviour of southern Fiordland tokoeka, we collected this data manually and graphed it to look for the lower activity that showed the birds were sitting on an egg. Now we know that their activity patterns look similar to those of the Haast tokoeka, and so this year our males get transmitters with an extra level of complexity: the transmitter itself analyses the data and when it detects the tell-tale consistent drop in activity, it will start counting the days from that point and tell us that running total. That means that we don’t have to be in there every fortnight through winter counting beeps, to make sure we get the point that incubation began and so predict hatch date. Instead we can arrive in mid-August and the transmitters will tell us who’s nesting and how long they’ve been doing it, thus saving a lot of time and even more money on helicopters. This technology has been tried and tested with other kiwi taxa around the country and I’m optimistic that it’ll work for us.

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

2 responses to Fiordland Kiwi Diaries: Changing radio transmitters

    Daryl J Neal 26/06/2018 at 7:17 am

    Good work guys.
    First time blog reader here. Seeing Sanjay (nz born or not) is kind of a gentle kick in the butt for NZ’rs to get off their own and take care of our heritage… maybe contribute by at least showing interest.
    Well done everyone.

    Kim Brandon 25/06/2018 at 6:23 pm

    Loving this blog. Thank you commited Kiwi team.