The pest eradication program on Macquarie Island over the past couple of decades provides an informative story about human’s attempts of manage animal species. The story goes back to the early 1800s when Macquarie Island, in the Southern Ocean south of Australia was discovered by men hunting seals and whales. The first sailors who came ashore encountered thousands of fur seals, elephant seals (a large species of sea lion) and penguins. Some ships came to drop off gangs to establish whaling and sealing stations. Occasionally ships were wrecked on the rocks and shoals of the island and survivors sought refuge while waiting for help. Finding food on Macquarie Island was often challenging. Over the years, men arriving on Macquarie brought with them rabbits and weka (a bird similar to a small bantem chicken) to provide themselves a source of food. Some escaped into the wild. Some ships harbored rats and mice which came ashore and soon began to multiply. Domestic cats were introduced, presumably as pets as well as to catch mice.

Large Norway rats and smaller mice reproduced quite quickly, having found a ready source of food in the eggs of ground-nesting endemic birds (petrels and albatrosses). Wekas, which thrived in the wild, ate the eggs of other birds, such as ground-burrowing petrels. Rats clamored over the nests of albatrosses, poking for eggs under the adult birds, even as the female incubated her clutch. The population of rabbits exploded, with a practically unlimited supply of tussock grass. Feral cats multiplied, feeding upon baby rabbits. Before long, the impact of vast numbers of introduced species began to decimate populations of endemic species (resulting in the extinction of several, such as the Macquarie Island parakeet and a rail). The island landscape itself began to change. The number of rabbits grew so high that entire hills were denuded of grass, precipitating soil erosion and landslides. The ecosystem of Macquarie Island, which had developed gradually over 700,000 years (when the first rocky outcropping emerged at the surface from the ocean floor) had now been completely transformed in a geological blink of an eye.

People began to realize the sad consequences of introducing foreign species to the island and pondered what could be done. But Macquarie Island is a mountainous rocky piece of land twenty miles long and two miles wide. How could the population of rats, mice, rabbits, cats and wekas be controlled? Research teams in New Zealand and Australia began to work together to assess the situation more accurately and come up with a proposal for dealing with the pests. It was soon realized that simply trying to control the populations would never work in the long run. Rather, eradication, followed by strict policies to prevent further infestation would be necessary. Further, it became clear that a single eradication program targeting all the pest species together would be more cost effective and more likely of success than targeting individual species one at a time.

One early strategy to target the rabbit population was to use a naturally occurring virus (myxoma) that infected rabbits and caused blindness and weakening, eventually resulting in starvation (if predators did not prey on the rabbits first). Spreading the virus required a vector and the most natural was a flea that infected rabbits’ ears. The virus had the potential of reducing the rabbit population substantially but not eliminating it altogether.

Also it would have no effect on the rats or mice. A poison was available (Brodificoum) that was effective for killing rabbits, rats and mice, an anticoagulant that caused internal bleeding and resulted in death of the animal within 4-5 days. The first attempt to spread poison was hampered by inclement weather, and only about 10% of the island area was covered. A second virus, calisi was employed to suppress the rabbit population and thereby reduce the secondary effects on non-target species such as skuas, giant petrels, kelp gulls and ducks. The following winter the entire island was baited with approximately 300 tons of poison.

Biologists realized that the use of poison would inevitably have harmful secondary effects on non-target species such as the birds that preyed on poisoned animals and inevitably ingested the contents of the stomach. To minimize these unintended consequences, plans were formulated to collect and bury the carcasses of the poisoned animals. Also, the secondary effects would be reduced by scheduling the eradication to avoid times when migrating birds were on the island.

Wekas were eradicated by a combination of intensive shooting and predation pressure from feral cats. The cats faced a shortage of rabbits due to the effectiveness of the myxoma virus.

After several years of assessment and planning, an eradication program was developed. It involved injecting a virus into the blood of a few rabbits and infecting them with the fleas that would spread the virus from one animal to the next. These rabbits were then released at key points around the island. A large quantity of poison (the anticoagulant mixed into an oatmeal base and formed into small pellets) was amassed on the island and set up at loading stations that were accessible by helicopter. It was important to distribute the poison uniformly across the island, so helicopter pilots, using GPS sensors and computer systems, flew along carefully devised grid lines and released the bait uniformly from large buckets hanging from cables beneath the helicopter. On the first attempt, foul weather prevented the distribution of any more than 10% of the bait and the effort was postponed a year. The following year, the bait distribution went smoothly. It was followed up a few days later by individuals on the ground who collected carcasses. Then a second distribution took place to make sure that all pest infestation areans were reached.

Following the distribution of poison from helicopters, a team of hunters with rifles covered the entire island on foot, looking for evidence of live rabbits, rats or mice. They used traps, poison and rifles to eliminate any surviving pests they found.

The poisoning program on Macquarie Island was completed in 2012. As early as late 2012 the last rabbit was hunted and no sign of either rats or mice could be found. Even so, the island will not be officially declared rabbit and rodent free until late 2014 or 2015. At this time it looks like the program has been a complete success. The tussock grass, Poa foliosa and the megaherbs such as Stilbocarpa Polaris and Plurophylum hookerii have begun to grow back and cover the hillsides. Burrowing petrels and other native birds have been increasing in numbers. Macquarie Island seems to be returning to the condition it was in before men first introduced foreign species.

There are many places on Earth where people have been responsible for introducing new species into places where they reproduced so rapidly that they marginalized native species or forced them into extinction. Often once this has taken place, it is nearly impossible to restore the ecosystem to its original condition. Macquarie Island is one example of a place where it was possible to do so, but only at considerable expense.