Battle for the Murchison Mountains
Stoats, rats targeted in battle to save takahe
For almost half a century the takahe was thought to be extinct. Since their rediscovery in remote Fiordland, there has been a constant battle to ensure their survival. Neil Ratley flew in to help in the effort to save the takahe.
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The majestic Murchison Mountains are freshly coated in spring snow and rise up like frosted fingers clutching for the helicopter. The pilot evades their icy grasp and descends into the valley. A thick curtain of mountain beech trees drapes from the encircling mountainsides, moss-coloured velvet sliding down to the streams below.
In what is largely untouched and isolated wilderness, it is hard to imagine, in this pristine environment, nature locked in a battle with introduced pests. However, a war is being waged by the Conservation Department (DOC) in the mountains of Fiordland.
The sun glistens off the patches of exposed granite enclosing the Snag Burn Valley. The helicopter sinks down into a snow-covered clearing and I leap out with a party of rangers to join them on the frontline in the Battle for the Murchison Mountains.
In the remote and rugged terrain of Fiordland the fight to ensure the survival of the takahe, a native bird species once thought to be extinct, is an ongoing campaign that began nearly 65 years ago.
Between 1800 and 1900 there were only four recorded sightings of takahe, and then none was seen until 1948. In that year, the last takahe survivors were rediscovered in the alpine tussock grasslands of the Murchison Mountains by a small team consisting of well-known Southlander Geoffrey Orbell and Invercargill couple Rex and Joan Watson.
With only 260 takahe left in the world, and 110 of those in the Murchisons, DOC's efforts are critical to ensure their survival against predators that were introduced by humans and which have no natural enemies.
The stoats and rats are relentless and resilient and DOC is going on the offensive. The battle in the Murchison Mountains has intensified this year, as predator numbers soar to plague proportions and threaten the area's and New Zealand's takahe population.
In charge of DOC's Takahe Recovery Plan is takahe programme manager Phil Tisch. Tisch says the department's Takahe Recovery Plan, supported by Mitre 10 New Zealand, focuses on establishing self-sustaining populations in Fiordland and on predator-free islands. However, unprecedented rat and stoat numbers in the Murchisons are forcing DOC to step up its campaign.
"In a non-plague year in winter and early spring we have historically caught around 50 rats over 15,000 hectares. This year those numbers have soared. In the first two weeks of June we caught 270 alone . . . that signalled a problem and stoat numbers have equally increased," he says as we wade through fresh, knee-deep snow and ford an icy stream looking for a bundle of stoat traps dropped in by air a few days earlier.
The number of traps and the frequency of checking traps have been increased and the spacing between traps has been reduced, Tisch says. "We have tripled the number of checks on traps and the number of traps has been increased in some critical areas where takahe are known to spend winter and early spring before returning to the alpine grasslands. Additional traps will be located in these areas so that the inter-trap spacing along an existing trap line is 100 metres rather than 200m."
It appears the hard work is paying off.
DOC takahe ranger Martin Genet holds up an antenna and a series of beeps brings a smile to his face.
Fifty-seven takahe have been fitted with transmitters and the correct number of beeps means a wired-up bird is alive and well, says Genet. "Forty beats per minute mean a bird is on the move whereas 80 beats mean the bird or the transmitter have stopped."
Takahe numbers and their movements are monitored by fortnightly sky ranger flights and the data is collected back at DOC headquarters in Te Anau.
Earlier in the morning back at headquarters, Genet's computer screen showed a map of the Murchison Mountains overlaid with small black icons shaped like takahe, each with their own name. However, amid the icons representing living takahe, there were a few crosses.
"None of the birds we have lost were due to stoat predation," Genet explains. "Autopsies of the deceased birds at Massey University have shown expiration was due to old age, drowning by falling through frozen ice or [being] covered by an avalanche. If a bird dies of old age we see that as a success and while we can try to fight stoats we can't fight mother nature if she chooses time's up for a takahe."
Genet says while not every bird is fitted with a transmitter, it would seem that data from those that are indicate the stoat trapping currently in place is benefiting the takahe population.
The reason for the plague of stoats and rats is twofold and includes a mast - seed production - from the beech trees that thrive in the mountainous terrain, and an unusually mild winter, Tisch explains.
"A few seasons ago the beech trees had a particularly explosive mast. Every four to six years, sometimes less, beech trees produce far larger than usual numbers of beech seeds, known as beech mast. This causes an explosion in populations of rats and insects due to the abundance of food.
"The increase in rats and insects means a greater food source for stoats, which then have an extremely productive breeding season. When the beech mast year is over, the rat population crashes. The boosted stoat population then looks to additional sources of food - takahe. Both adults and their clutches."
With a visible sense of irony in the September snow, Tisch says the warm winter experienced in Fiordland also helped predators to survive longer.
"Normally by now the rat and stoat numbers are on the decline and while we are finding fewer rats in the traps, we are still catching too many stoats to reduce the intensity of the trapping."
History has shown it is crucial to be vigilant in the fight against stoats in the Murchison Mountains. In 2007, the takahe population took a dramatic hit from a stoat plague less severe than the one currently being experienced. "We lost about 45 per cent of the takahe population in the Murchison Mountains," Tisch says. "The population fell from 167 birds to 94, the lowest recorded wild population since takahe were rediscovered in 1948. The population couldn't sustain another crash of that magnitude."
Normally stoats don't go looking to attack takahe but the 2007 plague showed that when the stoats had eaten out the rats, they became desperate enough to take on much larger prey. "Quite a number of birds got killed by stoats," Tisch says.
Since then, DOC has spread the trapping programme from the initial 15,000 hectares in the southeastern corner of the Murchison Mountains to cover 50,000ha, called the Takahe Special Area.
With the aide of a GPS, we find, buried beneath the snow, the stoat traps we have been seeking. The wooden and steel rectangular crates are loaded on to the rangers' backs.
Genet leads the way, charging through the snow, skipping across streams and gliding through the thick forest like a veteran who has done several tours of duty. DOC rangers assigned with protecting the takahe spend a lot of time in the hills and valleys of the Murchison Mountains laying, setting and checking traps in areas that have been labelled "pretty challenging".
"Its really hard terrain," Tisch says. "It's steep, there are lots of rivers to cross and there are avalanche zones. Working out here has to be managed quite carefully. Especially with increased checks during a time of the year when you wouldn't expect to be out in the bush as much."
With wet feet and toes beginning to feel the onset of frostbite, I try to keep up with Genet, who is searching for a place to set a trap or tunnel. Among low-lying ferns he gets to work.
A simple wooden and steel mesh rectangular box with entry points at either end and fitted with two steel traps is the method of choice to take out the enemy. Enticing the stoats into the tunnel and into the traps' jaws is an irresistible menu of rabbit with a whole and intact egg. Genet demonstrates the power of the traps by dropping his hat on to the trigger. A loud snap echoes through the beech trees. "That is the end of the stoat," Genet says.
The tunnels are designed to exclude non-target species such as the ever-inquisitive kea, Genet says, as he resets the spring and bolts the top panel on to the traps.
He will now carry on up the valley preparing several more traps, checking existing traps and baiting those that need fresh meat. After a night in the mountains, he will rendezvous with other DOC staff further down the Snag Burn Valley.
But for me, my tour of duty on the frontline in the Battle for the Murchison Mountains is over. The approaching thunder of the helicopter blades reverberates off the granite walls and signals it is time to be extracted from the Fiordland wilderness. Despite failing to come face-to-beak with a takahe, it is reassuring to know, as I soar above the mountains, that far below, amid the beech forest, the war to protect and sustain one of New Zealand's most precious and unique birds is being won. Go to southlandtimes.co.nz for a video of Neil's trip into the Murchisons.
■ The flightless takahe – Porphyrio [Notornis] hochstetteri – is a colourful green and blue bird with an impressive red beak and stout legs.
■ A takahe looks similar to the common black and blue pukeko but is much larger and is green rather than black over the back.
■ Alpine grassland supplies its food and shelter, such as broad-leaved snow tussock, mid-ribbed snow tussock and curled snow tussock.
■ In winter, if snow cover is heavy, birds descend into the forest for shelter and feed mainly on underground starchy stems of the summer green fern.
■ After the snow clears in October, takahe often nest under the shelter of snow tussocks where each nesting pair builds up a raised bowl of grasses.
■ One to three eggs are laid, and of these 80 per cent hatch.
■ The 30-day incubation period is shared by the parents. They both also feed the chicks for three months.
■ Usually, only one chick will survive its first winter.
■ An adult stands about 50cm high and can weigh over 3kg.
■ Takahe have lived over 20 years in captivity but in the wild few birds reach this age.
■ Wings are for display only – such as courtship and aggression.
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