From 300,000 rabbits to none: a Southern Ocean island is reborn
Invasive species on islands: Macquarie Island, a Unesco world heritage site, was being eaten alive until an ambitious eradication programme restored it
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Zoe KeanWed 10 Aug 2022 09.13 EDT
On a world map, Macquarie Island is a speck in the Southern Ocean, but for ecologists it is a beacon, illuminating a future for grand-scale environmental recovery projects.
Melissa Houghton first set foot on the 34km-long green streak as a dog handler in late 2011. Rabbits, cats, rats and mice had been introduced by sealers in the 1800s and were wreaking havoc on the world heritage site. At their peak, there were approximately 300,000 European rabbits and an untold number of black rats and house mice.
During their trip, Houghton and a labrador named Wags found what would prove to be the last vertebrate pests left on the island: an adult rabbit and her young. In 2014, Macquarie was declared pest free, the largest island to successfully eliminate rabbits to date.
Ten years after Wags sniffed out the last rabbit, the island has sprung back to life, and Houghton has stuck around to witness the change. She gave up dog handling, became a scientist and completed her PhD as part of the research team monitoring the island’s resurgence.
“Seeing it rebound, knowing it’s got a long way to go, and that we don’t know what else is going to happen, it’s so exciting,” Houghton says.
An all-you-can-eat buffet
Houghton remembers being “blown away” by her first views of Macquarie Island after a three-day voyage south from Tasmania in 2011. Its beaches were crowded with hulking elephant seals and raucous colonies of endemic royal penguins. But Keith Springer, who was leading the Macquarie Island Pest Eradication Project, warned her that beyond the beaches the once biodiverse and unique island was so damaged that it was “nothing but a pretty paddock”.
Attempts to rid the island of pests had already been under way for some years. The last feral cat was shot in 2000, poison drops were used in 2010 to kill the rats and mice, with rabbits also being targeted. But after the accidental poisoning of native birds, calicivirus (a rabbit haemorrhagic disease) was released in February 2011 to further reduce rabbit numbers.
Houghton and Wags were one of several teams sent to scour the island for surviving pests. “There are massive steep coast cliffs all the way round the island. There might be a few hundred rabbits, but it just seemed impossible [to find them],” she says.
Trudging through the landscape, Houghton saw the damage the pests had wreaked. Before the sealers, the largest creatures eating the island’s vegetation were insects. So for rabbits it was an all-you-can-eat buffet.
The island had been dominated by giant tussock grass and swaying forests of megaherbs, such as Macquarie Island cabbage, which can grow taller than a human. This, says Houghton, is “like celery, very delicious, so the rabbits just absolutely loved it and smashed it”, stripping the landscape and destabilising slopes where grey-headed albatross nested. “You’d have slime and lichen and landslips where albatrosses were trying to raise chicks and survive.”
Houghton was only able to see some plants in small fenced-off areas. These included two endemic orchids and a tiny herb called Huperzia australiana. “I couldn’t even envision what the island was meant to look like,” she says.
Birds such as blue and grey petrels, which had been hunted off the island by cats, were returning by 2011, says Dr Justine Shaw of the Queensland University of Technology and Houghton’s PHD supervisor. Shaw recently coordinated a 10-year project to assess the island’s response to pest eradication.
But life was still dangerous for the returning petrels. They nest in burrows, and rabbits had eaten the vegetation that hid and protected them, making the birds vulnerable to attack from skuas, a native predatory bird.
This one action, the eradication, has saved entire communities and species
Dr Justine Shaw, conservationist
‘The tussock is over your head’
Gradually, life for the island’s birds is improving. Antarctic prions and white-headed petrels, which also nest in burrows, had managed to cling on in some sites while pests were on the island. Their numbers are now increasing. “It’s fantastic and so exciting,” Shaw says.
As birds return to breed, they also poo. This adds nutrients to the soil, which in turn helps the plants to grow back stronger. Tall plants then help burrowing birds hide from predatory skuas. “It’s this wonderful feedback loop,” Shaw says.
Today, the “pretty paddock” that Houghton first experienced has been transformed. “The tussock is over your head, and you’re dodging all these penguin tunnels,” she says. The orchids and tiny herb that had been protected by fencing have started turning up all over the place.
Houghton’s PhD research has also tracked the response of invertebrates such as spiders, flightless flies and springtails. “It’s amazing that somewhere so isolated can have so much diversity of insects – there’s a lot of endemic species,” she says. Removing mice, rats and rabbits might not seem like a way to improve life for invertebrates, but many of them rely on the plants the rabbits were gobbling up. Also, “when mice are on an island they target juicy larvae, caterpillars, moths and spiders and beetles,” says Houghton. The change is palpable. “You go into a hut now and there’s cobwebs everywhere.”
Typically after an eradication scientists tend to assess how one charismatic species has responded to the pests’ removal. But Shaw is interested in how the island is responding as a whole ecosystem. “It’s not like someone turns the lights on and it’s back to normal. It’s actually quite a staggered response,” she says.
When Shaw talks about the legacy of the eradication she looks to the future. Understanding the intricacies of how Macquarie Island is recovering has informed island pest eradications on New Zealand’s sub-Antarctic Antipodes Islands, South Georgia and more. In July 2022 a project was announced to eradicate predators including possums, rats, feral cats and hedgehogs from New Zealand’s Rakiura/Stewart Island, an inhabited island.
Island eradication is not cheap – the Macquarie project cost Aus$24.5m (£14m) and would have been more if not for in-kind support from research facilities already on the island. But isolated islands are hubs for biodiversity, with each one often having its own unique array of flora and fauna.
“This one management action, the eradication, has saved entire communities and species, many of which are found nowhere else in the world,” Shaw says.
Houghton is grateful to have witnessed the island’s resurgence. “It’s one of the few instances where humans can permanently reverse some damage we’ve caused,” she says.