Predator-killing aerial 1080 poison drops planned across the country will be shrunk by 100,000 hectares, and cost millions of dollars more, because of the severity of this year’s mega mast.
That’ll come at a cost. The two-year budget for DoC’s predator control programme, Tiakina Ngā Manu, including ground trapping, is expected to rise from $38 million to $41 million. But the greatest cost will be to the native species – such as rare and threatened birds, bats, frogs, lizards, and snails, many of which are at risk of extinction – in areas that will now not be treated.
“They’ll be seriously impacted through predation this season,” says Peter Morton, DoC’s predator control boss. “This is an exceptionally bad year in terms of rodent numbers across most of New Zealand’s native forests.”
Half a million hectares exposed
A whittling down of potential treatment areas has left exposed half a million hectares of native forest – about 6 percent of the conservation estate.
Initially, 1.4 million hectares of high-risk forest was narrowed to 1.15 million hectares. Based on potential weather interruptions and the pace of operations, the treatment area was only expected to reach one million hectares by June next year. Now, with more intensive treatment, the figure will likely be 900,000 hectares, Morton says.
The most vulnerable species, that only occur in the wild in relatively small pockets, are the top priority. DoC’s biggest push for a single species is the orange-fronted parakeet (kākāriki karaka) in Arthur’s Pass, nestled in the Southern Alps between Christchurch and Greymouth, where it will drop 1080 bait over about 100,000 hectares.
However more than 120,000 hectares has been pared from a planned 300,000-hectare drop in the Kahurangi National Park, at the South Island’s rugged north-west tip. Vulnerable species in the park include great spotted kiwi, kākā, kea, and rock wren.
Morton says mohua (yellowhead) are vulnerable to rat and stoat predation in the mega mast. “But we’ve moved from protecting 13 populations, which we’d hoped to be able to do, down to protecting 10.”
The strategy, Morton says, is to trim bits off lots of treatment sites rather than writing off whole sites – and potentially losing the threatened species populations present in them. “It’s not easy, but then that’s our job.”
“There’s a huge amount of food in the system.” – Peter Morton
A “mast” year typically refers to when beech seeds coat forest floors, proving a boon for some native species and introduced pests alike.
A so-called mega mast is heavy seed or flower production across multiple tree or plant-types at the same time. This year, on top of the huge increase in beech seeds, there’s also podocarp (cone-bearing plants) fruiting, on rimu and kahikatea, for example, and, perhaps, as with this year, high levels of tussock seed.
“There’s a huge amount of food in the system,” Morton says. “What that’s meant is that rodents, and a whole lot of native species, are having a really good year in terms of food availability.”
The best way New Zealand has to protect vulnerable native species right now is by poisoning predators – mainly possums and rats, but also, by virtue of their rat-eating ways, stoats – with 1080, or sodium monofluoracetate.
It’s mixed in tiny amounts into cereal bait and dropped by helicopters equipped with special buckets that run lines on a GPS grid. At a rate of 2kg per hectare, the “sowing” rate for bait used this year, a hectare of forest receives about three grams of poison, according to Dave Hansford’s book Protecting Paradise.
It was only in August that DoC realised its initial sowing rate of 1.5kg/ha wouldn’t cut it with the mega mast. Nearly 20 percent of rats survived its drop in the Cobb area of Kahurangi, which is far too high.
Given the abundance of food, it’s thought predators were keeping to a ridiculously small home patch, of perhaps 20 square metres. The solution, Morton says, was for helicopters to make two passes, ensuring every single piece of ground is covered twice. He compares it to mowing a lawn.
“Normally you mow whatever the width of your mower is and then you step across that area and mow the next bit. What we’re doing is instead of going the full width across, we’re only going halfway across, and mowing half the same area twice.”
Yes, it’s more costly
Before changing its methodology, DoC weighed its options.
It couldn’t throw money at the problem to employ more skilled helicopter pilots, rangers, and contractors. It had already mobilised pretty much everybody who knew what they were doing.
Another key issue is weather. Operations can only happen when there’s not a great deal of wind, no cloud, and not much rain forecast. “Everything has to be compressed into those weather windows,” Morton says.
A less intense programme wouldn’t be effective at knocking down predator numbers, so that was unpalatable. Pushing their luck by operating in more marginal weather conditions was ruled out for the same reason – it doesn’t kill as many predators.
“We’ve wound up with having to run a slower, more labour-intensive methodology, and spreading that as far as it’ll go. But it’s not going to stretch as far as we’d hoped.”
DoC’s new numbers show how some 1080 operations have shrunk by large amounts since initial plans were made.
The biggest loser, if you like, is Kahurangi, which drops from 303,641ha to 180,000ha, a 41 percent loss. Areas to lose more than 10,000ha include West Coast sites Abbey Rocks-Matakatake, Landsborough, Hollyford, Mokihinui/New Creek, and Te Maruia, the Catlins (Southland), and Makarora-Wilkin (Queenstown-Lakes). (See table below.)
Thousands of hectares earmarked for treatment in Southland – in the Clinton/Eglinton, Dart/Caples, and Kepler – will now not be. Wet Jacket Peninsula, an almost 40,000ha drop planned for the Fiordland National Park, has been kicked to next year because rodent numbers didn’t reach trigger levels.
DoC’s shrinking operational area for pest control might please some anti-1080 campaigners, some of whom continue to threaten DoC staff and contractors. “We certainly had to call the police on several occasions,” Morton says. “Basically, if there’s a threat to harm or kill people then we contact the police.” (This year, the Government allocated DoC $11 million over four years for staff safety.)
Aerial 1080 drops aren’t completely safe for native species. Some, like short-tailed bats, are particularly vulnerable to the toxin, and keas often eat the poison bait because of their curiosity. Morton says there haven’t been any reports of non-target deaths from the programme so far.
Former Parliamentary Commissioner for the Environment Jan Wright wrote in a 2011 report it’s understandable that scattering poison from the sky feels bad. But she concluded: “It is my view based on careful analysis of the evidence that not only should the use of 1080 continue (including in aerial operations) to protect our forests, but that we should use more of it.”
Morton says for all the difficulties of 1080 work there are some good results in places where predator control has been maintained for a long time. Places like the Landsborough Valley, Waitutu, or the Eglinton Valley.
Kākā monitoring in the Eglinton Valley, near Te Anau, a couple of weeks ago, showed record numbers. Morton: “If we put the effort in and manage predators on an ongoing basis we can turn our threatened species populations around.”