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Removing cats to protect birds backfires on island

BANGKOK, Thailand - Tuesday, 13 January 2009
By Michael Casey - AP Environmental Writer

It seemed like a good idea at the time: Remove all the feral cats from a famous Australian Island to save the native seabirds.

But the decision to eradicate the felines from Macquarie Island allowed the rabbit population to explode and, in turn, destroy much of its fragile vegetation that birds depend on for cover, researchers said Tuesday.

Removing the cats from Macquarie "caused environmental devastation" that will cost authorities 24 million Australian dollars ($16.2 million) to remedy, Dana Bergstrom of the Australian Antarctic Division and her colleagues wrote in the British Ecological Society's Journal of Applied Ecology.

"Our study shows that between 2000 and 2007, there has been widespread ecosystem devastation and decades of conservation effort compromised," Bergstrom said in a statement.

The unintended consequences of the cat-removal project show the dangers of meddling with an ecosystem, even with the best of intentions, without thinking long and hard, the study said.

"The lessons for conservation agencies globally is that interventions should be comprehensive, and include risk assessments to explicitly consider and plan for indirect effects, or face substantial subsequent costs," Bergstrom said.

Located about halfway between Australia and the Antarctic continent, Macquarie was designated a World Heritage site in 1997 as the world's only island composed entirely of oceanic crust. It is known for its wind-swept landscape, and about 3.5 million seabirds and 80,000 elephant seals arrive there each year to breed.

The cats, rabbits, rats and mice are all nonnative species to Macquarie, probably introduced in the past 100 years by passing ships. Authorities have struggled for decades to remove them.

The invader predators menaced the native seabirds, some of them threatened species. So in 1995, the Parks and Wildlife Service of Tasmania that manages Macquarie tried to undo the damage by removing most of the cats.

Several conservation groups including the International Union for Conservation of Nature and Birds Australia said the problem was not the original eradication effort itself but that it didn't go far enough. They said the project should have taken aim at all the invasive mammals on the island at once.

"What was wrong was that the rabbits were not eradicated at the same time as the cats," University of Auckland Prof. Mick Clout, who also is a member of the Union's invasive species specialist group. "It would have been ideal if the cats and rabbits were eradicated at the same time, or the rabbits first and the cats subsequently."

Liz Wren, a spokeswoman for the Parks and Wildlife Service of Tasmania, said authorities were aware from the beginning that removing the feral cats would increase the rabbit population. But at the time, researchers argued it was worth the risk considering the damage the cats were doing to the seabird populations.

"The alternative was to accept the known and extensive impacts of cats and not do anything for fear of other unknown impacts," Wren said. "Since cats were eradicated, the grey petrel successfully bred on the island for the first time in a century and the recovery of Antarctic prions has continued since the eradication of feral cats."

Now, the parks service has a new plan to finish the job, using technology and poisons that weren't available a decade ago.

Wren said plans to eradicate both rabbits as well as rats and mice from the island will begin in 2010. Helicopters using global positioning systems will drop poisonous bait that targets all three pests. Later, teams will shoot, fumigate and trap the remaining rabbits, she said.

Some of the earlier critics are now behind this latest eradication effort, saying it should help the island's ecosystem fully recover because it would remove the last remaining invasive species.

"Without this action, there will be serious long-term consequences for the majestic seabirds which nest on the island including the four threatened albatross species, and for the health of the island ecosystem as a whole," said Dean Ingwersen, Bird Australia's threatened bird network coordinator.

"We believe that the process they are going to follow uses best practice for this type of work," Ingwersen said. "And that all possible ramifications have now been considered."

From Wikipedia - Ecological balance

The ecology of the island was affected soon after the beginning of European visits to the island in 1810. The island's fur seals, elephant seals and penguins were killed for fur and blubber. Rats and mice that inadvertently introduced from the ships prospered due to lack of predators. Cats were subsequently introduced deliberately to keep the rodents from eating human food stores. In about 1870, rabbits were left on the island by sealers to breed for food. By the 1970s, the then 130,000 rabbits were causing tremendous damage to vegetation.

The feral cats introduced to the island have had a devastating effect on the native seabird population, with an estimated 60,000 seabird deaths per year. From 1985, efforts were undertaken to remove the cats. In June 2000, the last of the nearly 2500 cats were culled in an effort to save the seabirds. Although seabird numbers began to rise initially, the removal of the cats allowed a rapid growth in the number of rats and rabbits which together are causing widespread environmental damage.

The rabbits rapidly multiplied before numbers were reduced to about 10,000 in the early 1980s when myxomatosis was introduced. Rabbit numbers have grown again to around 100,000 on the island. The rodents feed on young chicks while rabbits nibbling on the grass layer has led to soil erosion and cliff collapses, destroying seabird nests. Large portions of the Macquarie Island bluffs are eroding as a result. In September 2006 a large landslip at Lusitania Bay, on the eastern side of the island, partially destroyed an important penguin breeding colony. Tasmania Parks and Wildlife Service attributed the landslip to a combination of heavy spring rains and severe erosion caused by rabbits.

Research by Australian Antarctic Division scientists, published in the 13 January 2009 edition of the British Ecological Society's Journal of Applied Ecology, showed that the success of the feral cat eradication program has allowed the rabbit population to increase, damaging the Macquarie Island ecosystem by altering significant areas of island vegetation.

On 4 June 2007 a media release by the Australian Federal Minister for the Environment and Water Resources, Malcolm Turnbull, announced that the Australian and Tasmanian Governments had reached an agreement to jointly fund the eradication of rodent pests, including rabbits, to protect Macquarie Island's World Heritage values. The plan, estimated to cost $24 million Australian dollars, will involve mass baiting the island similar to an eradication program on New Zealand's Campbell Island and is expected to take up to seven years.

Comment:  Wherever humans are, and that’s pretty well everywhere, there are problems.  With our exploding population nothing remains sacred and untouched for the other species.


Australia: The Unintended Consequences of Changing Nature’s Balance

February 17, 2009
Elizabeth Svoboda, New York Times

With its craggy green cliffs and mist-laden skies, Macquarie Island — halfway between Australia and Antarctica — looks like a nature lover’s Mecca. But the island has recently become a sobering illustration of what can happen when efforts to eliminate an invasive species end up causing unforeseen collateral damage.

In 1985, Australian scientists kicked off an ambitious plan: to kill off non-native cats that had been prowling the island’s slopes since the early 19th century. The program began out of apparent necessity — the cats were preying on native burrowing birds. Twenty-four years later, a team of scientists from the Australian Antarctic Division and the University of Tasmania reports that the cat removal unexpectedly wreaked havoc on the island ecosystem.

With the cats gone, the island’s rabbits (also non-native) began to breed out of control, ravaging native plants and sending ripple effects throughout the ecosystem. The findings were published in the Journal of Applied Ecology online in January.

“Our findings show that it’s important for scientists to study the whole ecosystem before doing eradication programs,” said Arko Lucieer, a University of Tasmania remote-sensing expert and a co-author of the paper. “There haven’t been a lot of programs that take the entire system into account. You need to go into scenario mode: ‘If we kill this animal, what other consequences are there going to be?’ ”

Seal hunters introduced rabbits to Macquarie in 1878, compounding the invasive species problem on the 21-mile-long island. By 1968, when authorities introduced the deadly Myxoma virus in an attempt to kill off the rabbits, the population had reached more than 100,000.

The strategy worked; by the 1980s, the rabbit population had fallen to less than 20,000. But that meant that the cats, which had depended on the rabbits as a food source, began eating seabirds instead.

To assess the consequences of the cat-killing initiative, the team of ecologists compared satellite images of the island taken in 2000, the year the last remaining cats were killed, with a set taken in 2007. When vegetation dies off, the sharp drop in chlorophyll content reduces near-infrared reflectance in a way that can be recorded.

“You can clearly see the difference between healthy and dead plants in our images,” Mr. Lucieer said. “The live vegetation shows up as bright red.” The scientists also closely studied ground plots to evaluate their plant species composition.

The later satellite images revealed a completely different landscape. The booming rabbit population had destroyed the lush grassy expanses on coastal hillsides, nibbling them bare. Exotic grasses and herbs began taking over the naked slopes, forming a dense network of leaves and stems that in some places prevented native seabirds from accessing suitable nesting sites.

The Macquarie debacle is not an isolated incident; several other species removal programs have inflicted damage on surrounding ecosystems. In New Zealand, conservationists decided to wipe out three introduced species in one go — rats, possums and stoats — by poisoning the first two.

The rationale was that the poisoning operation would eliminate stoat populations by association because rats were a critical part of the stoats’ diet. But when the plan was begun in the early 1990s, the stoats did not disappear. With the absence of rats, the stoats preyed on native birds and bird eggs.

Similarly, in the western United States, the removal of exotic saltcedar shrubs has threatened an endangered species of native songbird, the Southwestern willow flycatcher.

Saltcedar plants, which have nudged out much of the native vegetation, suck up so much water that they constrict river channels and make soil saltier, but they also provide an important nesting habitat for the flycatcher.

In 2005, Department of Agriculture officials began releasing defoliating leaf beetles to control saltcedar populations. In December 2008, the nonprofit Center for Biological Diversity struck back, filing a notice of intent to sue the department for failing to collaborate with the Fish and Wildlife Service to figure out a way to protect the flycatcher.

The scientists who studied Macquarie Island have added their findings to those earlier results and hope ecologists will approach future efforts more holistically, doing broad background work on the potential consequences of exotic species removal long before killing programs are started.

“There have been hundreds of invasive species eradication efforts, and the vast majority have resulted in clear conservation gains,” said Erika Zavaleta, an ecologist at the University of California, Santa Cruz. “But Macquarie Island is a new, clear example of unexpected side effects that can happen.”

To avoid worsening problems in trying to solve them, Ms. Zavaleta said, researchers need to make planning and monitoring their mantra. “Scientists need to ask themselves key questions, like how all the species on the island interact with each other.”

Macquarie Island offers a chance to do just that. A new eradication program being planned targets hundreds of thousands of rats, mice and rabbits. In theory, that should eliminate dire threats to local vegetation and fauna, because the rabbits mow down native grasses and the rats and mice eat seabird chicks. But this time, administrators are prepared to make course corrections if things do not turn out according to plan.

“This study clearly demonstrates that when you’re doing a removal effort, you don’t know exactly what the outcome will be,” said Barry Rice, an invasive species specialist at the Nature Conservancy. “You can’t just go in and make a single surgical strike. Every kind of management you do is going to cause some damage.”

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