Northern Ruahine rat monitoring trip

This is a special guest blog by Anthony Behrens, content creator and conservationist at Swampthing, sharing his recent experience following DOC Rangers in the Northern Ruahine rat monitoring programme.

“When I last worked in the Ruahine, I thought the bird life was desolate. Now I reckon it’s awesome…and I’m saying that having just come back here from Pureora Forest, New Zealand’s bird mecca” said DOC Ranger Pete Bird as we sat waiting for our chopper ride home.

Pete, who has just returned to the area after eleven years away, ranger Tamara Friedmann and I had flown in to Ikawetea Hut the previous day as part of the Northern Ruahine rat monitoring programme. Rough weather had meant a late start to what should have been a fairly straightforward schedule, but the two fit rangers only had enough time to set three out of five lines of tracking tunnel the previous afternoon.

They may have been in a hurry, but as they went about their work placing peanut butter and inked up tracking pads into plastic tunnels, the abundant bird life was impossible to ignore.

There were good numbers of the usual suspects – grey warblers, fantails, tui, kereru and tomtits. But we were all impressed with the not-so-common bird life. Pete saw a kārearea circling above the hut. A male whio called from the river below as we ate tea. The impatient call of robins was a constant accompaniment to our work on the second day, while riflemen peeped about occasionally too. At one stage Tamara and I walked through a large flock of raucous whiteheads and Pete met a similar group elsewhere.

“I reckon there were about 100 of them. They come together at this time of year before they pair off for breeding,” he said as we tallied up our observations. 

The area’s birds have just had a pretty good winter – mast years are great for birdlife, and the huge mega mast of the 2018/19 summer seems to have resulted in a really good breeding season. In a mega mast, many different plants produce unusually large amounts of fruit and seed that would have meant plentiful food throughout winter. As a result, the birds of the Northern Ruahine were up to some serious family planning.

But what’s good for birds is even better for fast-multiplying rats who had an absolutely massive breeding year over much of New Zealand. As we walked to and from the monitoring lines, a large proportion of the traps we passed contained dead rats. There is a network of about 1400 DOC 200 and A24 traps in the northern Ruahine Forest Park, and the volunteers who look after them have been reporting unusually high numbers of kills throughout the year.

Tracking tunnels set in August showed overnight rat activity at 74%. Generally, a 20% visitation rate is enough to cause serious concern and a 1080 drop in areas that are considered to have valuable-enough biodiversity.

While most of the trap-based predator control in the area targets stoats, who are particularly deadly to remnant populations of whio and kiwi, it’s an overwhelming population of rats that is the major threat to the other birds. 

In a “normal” year a female rat’s territory is about one hectare (males will roam up to 300m) – which could feasibly be controlled by a well-placed and maintained trap. The problem that the vulnerable native fauna of the Northern Ruahine have is that the area covers 32,000 hectares of prime rat real estate. This neck of the woods is not only too vast to effectively trap for rats, but it’s also isolated and made up of steep mountain climbs and deep river valleys. Access to traplines is often only by helicopter and only then in good conditions. Winter’s heavy rains, freezing rivers and deep snow make effective trap maintenance for rats even more unfeasible.

In 2017 there was a Battle for Our Birds 1080 drop after a smaller mast in the same area. In a day and a half two choppers and their ground crew successfully treated the rugged territory. Monitoring after that drop found rat numbers at near undetectable levels. 

The bountiful birdlife we witnessed as we worked around Ikawetea Hut in early September 2019 is testament to the effectiveness of that programme, but the silence Pete had witnessed in the area all those years before was a warning of the destruction that introduced predators, especially rats, can bring.

As climate change causes temperatures to increase it is expected that mast years will become more common. Without effective control measures the Ruahine Forest Park could again fall silent.

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