Macquarie Island’s Ecological Upheaval

Macquarie Island, a windswept outpost in the south-western Pacific Ocean between Tasmania and Antarctica, is a place of staggering natural wealth. Millions of seabirds once nested in its tussock grass and burrows, while seals crowded its beaches. But beginning in the 19th century, the arrival of a few stowaways and human introductions set in motion one of the most devastating ecological collapses in island history.

Macquarie Island was first sighted in 1810 by Australian sealer Frederick Hasselborough, who had been searching for new sealing grounds. His discovery proved fortuitous. The island teemed with wildlife, most notably an immense population of fur seals—estimated at between 200,000 and 400,000 individuals. The commercial response was swift. In just the first 18 months of exploitation, at least 120,000 fur seals were slaughtered for their skins. Within a decade, the once-abundant population had been driven to the brink of extinction.

Sandy Bay, Macquarie Island. Credit: Natalie Tapson

With fur seals no longer able to sustain the trade, hunters shifted their attention to elephant seals. Aside from their hides, elephant seals were also prized for their blubber, which was rendered into oil for widespread industrial uses. The elephant seals soon suffered the same fate. By the mid-1840s, their numbers had fallen by an estimated 70 percent.

Commercial exploitation then turned to the island’s prolific penguin population. While not as valuable as seal oil, penguin oil at least had the advantage of being relatively easy to get. At the peak of the industry in 1905, the plant established here could process 2,000 penguins at one time. Each penguin produced about half a litre of oil.

The ecological havoc unleashed by commercial exploitation was compounded by the introduction of animals never meant to inhabit the island. The first intruders were rats and mice, which disembarked from sealing ships. On Macquarie, where seabirds had evolved in the absence of land predators, their eggs and chicks became defenceless targets. Burrow-nesting species such as petrels and prions were hit especially hard, and colonies that had flourished for millennia dwindled within a few decades.

Penguins on the beach and the remains of the wreck of "The Gratitude", Nuggets Beach, Macquarie Island, 1911 (or possibly 1913). Credit: Frank Hurley

The rodents soon turned their attention to human food stores, prompting sealers to introduce cats as a form of pest control. But the remedy proved worse than the disease. The cats preyed directly on seabirds, killing them in staggering numbers. By the early 20th century, feral cats were estimated to be killing some 60,000 birds each year. Several species were wiped out entirely, among them the Macquarie Island rail (Gallirallus macquariensis), the Macquarie parakeet (Cyanoramphus erythrotis), and a still-unnamed species of teal.

The next wave of devastation came in the 1870s, when rabbits were released to provide sealers with an easy food supply. Finding lush grasslands and no natural enemies, their numbers exploded. By the 1970s, the rabbit population had swelled to more than 100,000. They stripped hillsides bare, gnawed vegetation down to the roots, and triggered widespread erosion. Soil slipped into the sea, seabird burrows collapsed, and vast areas of nesting habitat were obliterated.

By the late 20th century, Macquarie Island was in ecological freefall. Cats, rats, mice, and rabbits together had transformed it from a seabird sanctuary into a landscape of bare slopes and dwindling wildlife. In the 1980s, scientists attempted to halt the destruction by introducing the Myxoma virus, which causes the fatal disease myxomatosis in European rabbits. This caused the rabbit population to drop to 10,000. Attention then turned to cats. By June 2000, after an intensive culling program, the last of the island’s nearly 2,500 cats was removed in an effort to save the seabirds.

King Penguin rookery at Lusitania Bay. Credit: Wikimedia Commons

But this apparent success brought an unintended side effect. With one of their main predators gone, rabbits once again flourished. By 2006, their numbers had surged past 100,000.

Some researchers have questioned whether cats had ever exerted a meaningful check on rabbit numbers. They point out that, prior to the release of the Myxoma virus, at a time when cats were still abundant, the island still had an enormous rabbit population. This suggests that cats were not a significant controlling factor, and that the resurgence of rabbits was more likely due to the waning effectiveness of the virus.

The chain of events demonstrates the complexity of restoring nature's balance. It became clear that piecemeal approaches would not succeed, and only a coordinated campaign to eliminate all three invaders at once could save the island. Between 2010 and 2014, helicopters dropped 250 tonnes of poisoned bait across the island. The bait contained Brodifacoum, an anticoagulant that causes fatal internal bleeding in rats, mice, and rabbits alike. Following the bait drops, teams of hunters with specially trained dogs scoured the terrain, eliminating surviving rabbits by shooting, fumigating and trapping them.

The baiting was done in winter, when most bird species had left the island, reducing the risk of accidental poisoning. Against all odds, the project succeeded. By 2014 Macquarie Island was officially declared free of rabbits, rats, and mice—the largest island eradication project ever accomplished.

Bull elephant seals fighting over some females. Credit: Wikimedia Commons

Today, the island is healing. Vegetation is returning to slopes once stripped bare, and seabirds are reclaiming their nesting grounds. Dr Kris Carlyon, a wildlife biologist with Tasmania’s Department of Natural Resources and Environment, reported “extraordinary” vegetation recovery on albatross slopes.

“We were walking through tussocks that were twice my height,” she said.

“The albatross were nesting on pretty exposed slopes when rabbits were here. The tussock growth is really solidifying the slopes and means erosion isn’t such a problem for those species anymore.”

Dr Aleks Terauds, Program Leader at the Australian Antarctic Division, who spent years living in remote field huts on the island while studying the wildlife and was equally amazed.

“It was incredible to get back there and see the slopes that were once completed denuded of vegetation by rabbits, looking really healthy with lots of tussock and mega herbs,” he said.

“Some of us on this trip have been working on this wildlife monitoring program for many years and what we’re seeing now, 15 years on, is a really big improvement in the vegetation on the island, with important flow-on effects for the breeding sea birds.

“From a vegetation point of view, the island is in great shape.”

Similar tales of introduced species destroying the ecology of an island:

Waterfall Bay, Macquarie Island. Credit: Natalie Tapson

Macquarie Island base. Credit: Su Yin Khoo

Penguins on Macquarie Island. Credit: U.S. Department of Energy Atmospheric Radiation Measurement

King penguin rookery at the base of Gadgets Gully, Macquarie Island. Credit: Natalie Tapson

References:
# “Macquarie Island station: a brief history”. Australian Antarctic Division
# “Macquarie Island faces 'ecosystem meltdown' after conservation efforts backfire”. The Guardian
# “Cull upsets island's ecological balance”. The Telegraph
# “Macquarie Island’s astounding recovery, ten years on from rats, mice and rabbits”. Australian Antarctic Division
# “Plan for the Eradication of Rabbits and Rodents on Macquarie Island.” Parks And Wildlife Service
# “Up against rats, rabbits and costs”. The Sydney Morning Herald