Up against rats, rabbits and costs

Lives in the balance … a light-mantled sooty albatross chick
in its nest on Macquarie Island.

Lives in the balance … a light-mantled sooty albatross chick in its nest on Macquarie Island.

April 12, 2007

Macquarie Island, a World Heritage area, is in the grip of vermin and the situation can only get worse as governments argue over a plan to save it, writes Andrew Darby.

LANDSLIDES poured the dark soil of Macquarie Island down on the king penguins at Lusitania Bay in a small, muddy natural disaster.

The kings, a colony of a quarter of a million regal birds, had settled again by the time the damage was discovered, even jostling for space on the tumbled earth. But it was clear from the extensive area buried, and the feasting under way by skuas and giant petrels, that many had been killed.

The landslides were but two of 20 that cascaded out of the hills of the sub-Antarctic refuge last winter, says a University of Tasmania ecologist, Dr Jenny Scott. Another cut into a once-verdant hillside beside a tourist staircase at Sandy Bay.

Almost all of the beaches at Macquarie accommodate tightly packed breeding colonies of birds and seals, and the windblown ridges above are dotted with albatross and petrel nests. If there is more heavy rain in the coming months, Scott says, more landslides can be expected.

This would probably mean more wildlife dies on an island that is designated a UNESCO biosphere reserve, World Heritage reserve and state nature reserve - all classifications meant to give it the highest level possible of bureaucratic protection.

Macquarie is the only place on earth where tectonic forces have raised oceanic crust rock to the surface at an active plate boundary. Its young landforms are being naturally reshaped over eons. But nothing in nature prepared it for the rabbit and the rat.

In an accelerating one-two hit, exploding rabbit numbers are denuding Macquarie's hills of soil-stabilising megaherbs and tussock fields, exposing ground-nesting birds and new seeds to the ravages of rats and mice.

Along with the flora, at least 24 bird species, 12 of them classified as threatened, are under attack.

The solution being offered is the world's largest rodent eradication program - if agreement can be reached on how to pay for it.

Scientists with the New Zealand Department of Conservation, who are experienced at restoring remnant wildlife taking refuge on their offshore islands, first came up with the radical approach of saturation bombing an entire landscape with poison baits.

In 2001, with 20 island successes behind it, the department tackled a severe, longstanding infestation of Campbell Island by Norwegian brown rats. The $NZ2.6 million program used helicopters to carpet the island's 11,300 hectares with 80 tonnes of poison-laced baits, and two years later the island was declared rat-free.

Like Campbell, Australia's Macquarie is blessed with some stunning polar wildlife, and has been cursed with introduced pests since 19th-century sealers brought their vermin with them.

The island quickly lost a unique parakeet and a flightless rail before the predatory Maori hen, or weka, was removed, and it took decades to kill feral cats. In a trapping and shooting program conducted during the freezing Macquarie winter, the last 315 cats cost the Federal Government $1.2 million to kill before the island was declared cat-free in 2003. Then the numbers of rabbits and rats took off.

The cats were killing tens of thousands of burrowing petrels annually, but also preying on the rodents. Myxomatosis was introduced to Macquarie in 1978, but over time rabbits developed an immunity to it. And something was happening to the weather on the island, too.

A sentinel for climate change in the Southern Ocean, Macquarie's weather trends are confusing.

Total annual rainfall has increased from about 900 millimetres in the 1970s to 1050 millimetres in the past decade, the Bureau of Meteorology's Ian Barnes Keegan says. "Even so, it's possible that the rain is falling at different times of the year, or in short, sharp showers. There are big complications to the picture."

In any case, the Tasmanian Parks and Wildlife Service, which manages the island, believes that successive warmer and drier winters could be helping to extend rabbit breeding seasons.

Since 2000, the landscape changes caused by pests have become more dramatic. Before the landslides, many of the deep tussock and megaherb fields died away under browsing pressure, a Parks and Wildlife Service study found.

With no native grazing fauna, the flora has developed no defence against grazing. Instead of lush herbfields featuring the Macquarie Island cabbage plant and waist-deep tussocks, there are brown stumps on open ground.

Petrels that were previously hidden among these plants had their burrows, and fledglings, exposed to rapacious skuas. The growing numbers of rats and mice are eating exposed seedlings, as well as birds' eggs and fledglings. By the end of last year, 21 severely damaged areas of ground dotted around Macquarie's coast could be clearly blamed on the pests.

How then to clear a 12,800-hectare island? The Parks and Wildlife Service developed an eradication plan that draws heavily on the New Zealand experience.

It would rely on up to four helicopters to work for weeks through a winter season spreading 250 tonnes of bait that would carry five kilograms of the highly toxic poison Brodifacoum. An anticoagulant toxicant, it effectively works like household rat poison by promoting internal bleeding.

The plan calls for a 90 per cent knockdown of all rabbits and rats in its first application, and up to 9 per cent in the second. Teams of hunters with dogs would work for several years afterwards, to kill rabbits faster than they could breed.

There are some dangers to the native wildlife. The Parks and Wildlife Service says skuas, kelp gulls, black duck and giant petrels could be at risk, either from consuming the poison or feeding on its victims. In winter, most wildlife would have left, and species such as skuas and kelp gulls could bounce back.

Balanced against that are species such as the grey-headed albatross, whose sole Australian population of 80 pairs on Macquarie's Petrel Peak faces immediate risk of extinction as the peak slides seaward.

Then, despite the urgency of the problem, there was trouble over the bottom line. The $16.5 million cost was to be shared by the state and federal governments. The Tasmanian Environment Minister, Paula Wriedt, wrote in February seeking confirmation that the Commonwealth would pay its half.

Soon afterwards the expected cost ballooned to $24 million, and any co-operation between the two governments fell over.

Under the plan, the central weapons - helicopters and bait - would have cost about $4.6 million. The costs that blew out were another $11.7 million for personnel and wages, and a "contingency" cost of $4 million.

Tasmania withdrew its offer to share costs and, with an eye to the federal surplus, turned the eradication program into an election issue. "The commonsense solution is for the Australian Government to live up to World Heritage obligations," Wriedt says.

Tasmania would be seeking a commitment from the federal Opposition Leader, Kevin Rudd, as the alternative prime minister.

The federal Environment Minister, Malcolm Turnbull, is refusing to consider the idea: "Tasmania gets 40 per cent of all of the Australian Government's World Heritage funding. So this notion that the Australian Government should fund all of the cost of Macquarie Island because its a World Heritage area is absurd. It is without precedent."

Tasmania will send some workers south this winter to fence off areas of the island, and send shooters in spring. But eradication is at a stalemate.

"I don't care who pays," says Scott. "I feel continued desperation at this problem not being addressed."

