The Pig's Back

Forest and Bird, Issue 313, 1 August 2004, Page 20

The Pig's Back

of Origin Natural History

Media is a photo-journalist based in Wellington.

DAVE HANSFORD

—DAVE HANSFORD

finds wild pig numbers are on the

rise again, and no One KNOWS WNat TO GO aDOUT IT.

ld pigs are posing a growing WV for conservation projects in several parts of New Zealand. Community objections to their control by poisons, and illegal releases by hunters, are blamed for the surge in population. Rising pig numbers are a serious concern to conservation scientists trying to bring back several native animals from the brink of extinction. On the Chatham Islands, Graham Taylor recently tracked a typical incident by radio signal as he followed the return to the land of a critically endangered taiko, or magenta petrel. The signal came from one of his oldest charges, a bird first caught in 1982. The radio signal faded and surged as he

pursued it through the scrubby margin of the island. As a Department of Conservation scientist, Graham Taylor knew every taiko burrow by heart, and he realised the transmitter was drawing him to a new nesting attempt. But the signal peaked at a scene of devastation. ‘The burrow had been rooted up; the ground all around it was bare . . . big, foldedover chunks of soil. I found the transmitter and some feathers amid what looked to be the remains of the burrow, which been completely destroyed. We think the tracked bird may have survived, but we don’t know whether it lost its partner. Only one predator leaves such a catastrophic signature. Linnaeus called it

Sus scrofa. We call it razorback, te poaka, the porker, kuhukuhu or Captain Cooker — the wild boar. As omnivores, pigs will devour pretty much anything they find. On the main Auckland Island, says Graham Taylor, they’ve been seen to walk up to nesting whitecapped albatrosses and kill and eat them where they sit. Last decade, he had an entire shearwater colony — 20 to 30 burrows — destroyed by pigs on the Chathams, an attrition that continues. ‘We're still losing bird colonies to pigs, and blue penguins are suffering too. There’s good evidence that pigs exterminated six of the known Hutton’s

shearwater colonies in the Kaikoura ranges. The two surviving colonies owe their existence to a steep bluff that pigs can’t traverse, but Graham Taylor prays that a slip or heavy-snow year won't grant them access. ‘Once they got in there, they would just cause havoc? t Te Paki Farm Park in the Far North, a DoC technical-support officer, drea Booth, has witnessed that kind of havoc. She’s overseen efforts to protect what’s left of the region’s local flax snails from pigs, which include a series of exclosure plots ringed by pig-proof fences. ‘The land is totally devoid of vegetation outside the fence, she says. ‘It’s completely ploughed up. It’s horrific — there’s nothing regenerating. The snails are only hanging on in steep areas where the pigs can’t access. "Then, inside the fence, you've got healthy regeneration of coastal forest and lots of snails. They need the vegetation to feed on and the leaf litter to live in, and there’s none of that outside the fence’ Meanwhile, on DoC’s 1700-hectare ‘mainland island’ just east of Te Araroa on East Cape, a DoC conservation officer, Graeme Atkins, is trying to protect the country’s biggest surviving population of Dactylanthus plants, or ‘wood roses. These subterranean oddities — our only fully parasitic flowering plant — are among the world’s most prolific nectar bearers. In better days, they would have been pollinated by native short-tailed bats, but their powerful scent is more likely nowadays to draw possums, rats, mice — and pigs. Graeme Atkins says that when a possum or rat finds a Dactylanthus, the plant has an even chance of flowering again next season. When a mouse finds it, the plant may even benefit from the pollination. But when a pig comes to visit, the destruction is total. "They just tear it out. They’re our single biggest threat, he says.

our years ago, feral pigs were found with traces of brodifacoum (a popular rat poison marketed as Talon) in their livers. The discovery has forced DoC to change the way it deals with pests. As wild pork is a major item in the rural human food chain, the Department had no option but to withdraw the toxin from mainland aerial operations — it can now be used only in bait stations — and no effective alternative has yet been found for rats. So, for Graeme Atkins — and Graham Taylor — it means controlling the rodents by the time-honoured, but time-consuming, expedient of trapping. Graeme Atkins says if you set the traps at the right spacings, you can still get close to 100 percent kills, but it’s a very labour-intensive process for an operation that only has so many staff and so much money. In Marlborough, the impact of the brodifacoum problem has been more direct — and disastrous. The DoC area manager, Roy Grose, says because pig hunters can no longer sell wild pork (it was banned in 2001), hunting pressure has relaxed. Tl be quite honest, our 1080 operations have also compounded the problem, he says, ‘because pig hunters won't risk losing their dogs in the reserves we’ve treated.’ Consequently, he says, pig numbers are ‘rocketing. The problem is compounded by hunters ‘who feel it’s their mission to spread pigs as far and wide as possible, to the extent where we've had to remove pigs from islands in the Sounds, such as Pickersgill and Blumine; Roy Grose says. Releasing pigs on islands is usually a ploy to give the hunters an advantage in pig-hunting competitions — the island becomes a remote, secret ‘fattening pen’ — but the losers are the islands’ rare Powelliphanta snails. It seems pigs have an insatiable appetite for these carnivorous relics of ancient Gondwana.

Then there is the traditional hunting ethic of leaving sows with piglets to live another day. Roy Grose, a keen pig hunter himself, says he routinely finds sows carrying 10 or 11 piglets. There are other worrying things. ‘In the hill country around here, we have these giant native earthworms — they’re as thick as your little finger and about 25 centimetres long, says Roy Grose. ‘T caught a boar a while back and opened it up, because I’m always keen to see what they’ve be eating, and its stomach was just full of these earthworms. Pigs present a threat to biodiversity — especially invertebrates — wherever they roam. But at a national level, DoC is virtually silent on the subject. They’re not even listed on its pests web page, and the Conservation Authority’s Pests and Weeds, a Blueprint for Action makes not a single mention of them. Instead, conservancies are left to try and find their own solutions — solutions that invariably boil down to a compromise. That’s because the too-hard basket is bulging with conflicts over pigs — with Maori iwi, with recreational hunters, with landowners and farmers. DoC relies heavily on good community relationships, and has an obligation to manage the public estate in consultation with Maori. Pigs come squarely between both ideals because while DoC sees them as the worst kind of pest, those same communities treasure them as a hunting resource, and iwi regard them as a traditional food item. Graham Taylor has to live with this paradox in his efforts to save taiko on the Chathams. ‘Pig hunting is a really big thing on the island. The whole community turns out for the annual pig hunt each September — it’s like a big show day. Even some of the DoC staff are keen pig hunters. Graham Taylor says he walks a ‘very fine line’ between trying to keep pigs away from his seabirds and staying on good terms with the locals, whose support is vital to the project. ‘We can’t afford to compromise benefits like community support, access to land -a lot of our conservation sites are on private property — by taking a hard line on pigs. ‘We encourage the locals to hunt in the area where the birds are, but we accept that this is just a problem we have to live with. igs also have the Animal Health Board in a bind. They’re known carriers of bovine tuberculosis. While they don’t transmit it directly to cattle or deer, pig carcasses can be scavenged by ferrets and possums, which do.

The health board’s spokesman, Nick Hancox, says the pig hunters’ tradition of releasing pigs in new locations puts the farming economy in jeopardy. A few years ago, a pig was killed near Kaeo, in Northland, that was infected with a strain of bovine tuberculosis formerly restricted to the Central Plateau. He blames a surge in tuberculosis infections in wildlife on illegal releases. ‘Certainly the spread of tuberculosis in wildlife east of Taupo recently has been much more rapid than we would expect through natural dispersion. So we suspect strongly that translocation has been happening there’ While nobody has any firm ideas about how to control pigs, most agree that using 1080 is out of the question. Maori communities, like the ones with an interest in the East Coast Dactylanthus reserve, are precisely the sort of stakeholders DoC needs to keep onside. "They simply wouldn't tolerate it) says Julie Black, manager of Nga Whenua Rahui, (a Government fund to protect natural values on Maori-owned land). "They would have issues about the use of 1080 around a traditional food source, and also with waterways and people’s diets. ‘It’s about traditional Maori beliefs and values about upsetting the natural system with introduced toxins. Furthermore farmers, who would be key players in any war on pigs, are not about to risk losing their farm dogs to 1080 poisoning. Quite apart from anything else, pigs are smarter than the average pest, and will simply regurgitate a 1080 bait the moment they feel its effects. That creates two new problems, says Landcare Research wildlife toxicologist Penny Fisher. ‘It increases the risk of them are getting a sub-lethal dose and becoming bait-shy. Also the vomit itself can become a non-target hazard. In North Canterbury, Landcare, DoC, Environment Canterbury and landowners have teamed up to try to find an answer. They’re looking for funding to hire Connovation, the company that manufactures and sells cholecalciferol and Feratox encapsulated cyanide, to register an effective pig toxin. Steve Hix, of Connovation, says the answer probably lies with an existing poison: ‘Getting official registrations is far easier for existing products. If another new product came along, we would certainly have a look at it, but there’s nothing on the horizon. ‘It’s about finding a bait that pigs will eat readily. They're pretty smart animals While Connovation has indicated some

success with cholecalciferol, the most likely candidate seems to be cyanide, which it has been testing on pigs in Australia. It’s a fastacting poison, which is crucial if pigs aren’t to become bait-shy. But Landcare toxicologist Penny Fisher says a major hurdle will be getting the pigs to take enough of the toxin to kill them. ‘They're much bigger than a possum, and a block of pig bait would need a lot more cyanide in it than a normal possum bait? Then there’s the problem of by-kill, which she says might be solved by using buried baits, or specific entry stations for pigs: ‘Something that the pig has to force its way into to get at the bait. In any event, she says, pre-feeding — loading the stations initially with non-toxic baits to get pigs used to the idea of taking them — will be a must. Steve Hix says any solution is still a long way off. ‘It all depends on how many people get interested in it. We'd have to do some bait acceptance trials — there’s a lot of work involved even before we get to the toxicology stage. In the meantime, conservation managers like Roy Grose will keep on hiring pig hunters with dogs, and encouraging clubs to concentrate on areas of high biodiversity value. But even that comes at a cost to wildlife.

In May, a pig dog was found wandering on Motuara Island in the Marlborough Sounds, home to the 14 surviving kiwi chicks evacuated from the Okarito Kiwi Sanctuary in South Westland after a disastrous stoat irruption. The dog’s owner maintained it must have swum the two kilometres to the island after it went missing during a hunt. Fortunately, the dog only spent a day or two on Motuara — killing and eating a penguin before it was discovered — but DoC programme manager Mike Aviss says the incident could have been a disaster for the threatened kiwi subspecies. ‘If it had been there longer it is very likely it would have killed kiwi chicks for food. Kiwi in Te Urewera National Park have not been so lucky. Pig dogs left in the park last year killed nine out of 16 monitored kiwi in the northern part of the park. The local DoC conservator, Peter Williamson, says the use of pig dogs in conservation areas can only be justified if ‘the benefits outweigh the cost. ‘Trresponsible hunters may jeopardise DoC’s ability to continue to support using pig dogs as a control method if the costs outweigh the benefits, he says. "Last year, we found kiwi carcasses half buried and covered in dog bites, and dog stools containing kiwi feathers. ‘We're hoping that last season’s kiwi deaths

were an aberration and the policy of allowing pig dogs in the park won't need to be re-assessed. Peter Williamson says the Department generally has ‘a very productive relationship with responsible pig-hunters’ and appreciates their contribution to pest control in the park. ‘Our staff have been well received when speaking to local pig-hunting club members about avian-aversion training for dogs, which is something we recommend.

"We also recommend that hunters use tracker collars on pig dogs to reduce the risk of becoming parted from valuable animals in a vulnerable environment. In the meantime, pig dogs have been banned from parts of the park, and restricted to a hunting season elsewhere in the Urewera National Park. Wild pigs are many different things to many people — pests, trophies or taonga. They seem to enjoy a degree of public

‘ownership greater than deer or thar. Wildlife managers must somehow curb the devastating impacts of pigs on biodiversity while accommodating their place in rural cultures. This delicate juggling act may yet prove one of the biggest conservation challenges.