Those Dirty Rats: Removing Invasive Species in the Pacific Islands

Invasive rat species have been responsible for crashes in many native bird populations in the Pacific Islands.(© Ray Pierce)

Have you ever wondered why the phrase “you dirty rat” is so popular in gangster movies? Or why betraying your mates is often referred to as “ratting” on them? It’s probably because although a few of the many species of rats — notably the brown (Norway) rat (Rattus norvegicus) and the black (or ship) rat (Rattus rattus) — are amongst the handful of “supertramp” species which have benefited greatly from the global distribution of Homo sapiens, they have hardly repaid the favour.

Rats have been vectors of some of the most devastating human diseases, including the Black Death of medieval Europe and typhus during the Crimean War — a disease which caused more soldiers’ deaths than the war itself.

In addition to being the primary carriers of diseases that have killed millions of humans, rats have had a far more damaging impact on other fauna. This is a serious problem on oceanic islands, where the endemic biodiversity has often evolved in the absence of any terrestrial mammals. In Polynesia and Micronesia, for example, Pacific, brown and black rats brought by vessels over the past several millennia — especially in the last two centuries — have single-handedly driven more bird species to extinction than in any other region in the world.

The team participating in this year's island restoration campaign. (Photo courtesy of Michael Donoghue)

This is still a clear and present danger. A few years ago, an Asian fishing vessel went aground on a reef at McKean Island, part of Kiribati’s Phoenix Islands. It may have been deliberately wrecked, thus allowing the owner to lodge an insurance claim far higher than the worn-out boat’s actual value — as well as being exonerated from the need to dispose of the hull when it was past its use-by date. Whatever the truth of the matter, Asian rats came ashore and discovered millions of seabirds from about 15 species. Within a few years, rat numbers had soared and the bird populations had crashed.

There is little doubt that without active intervention, rats would have consumed every last egg and chick on the island. Fortunately, thanks to a 2006 eradication campaign on McKean Island, this tragedy was averted. The effort was funded by the New Zealand Agency for International Development, with the support of the New Zealand Department of Conservation and the Kiribati Ministry for the Environment. Despite the numerous logistical issues involved, this mission demonstrated the feasibility of island restoration through protection of endemic biodiversity, even in such a remote location.

This year, an even more ambitious island restoration campaign — involving islands many thousands of kilometres apart — was completed by a multitude of partners, including the governments of Kiribati, the U.S. and the U.K.; a range of NGO partners who helped to organise the funding, including Conservation International, the Critical Ecosystem Partnership Fund (CEPF), Packard Foundation , New England Aquarium and the Pacific Invasives Initiative; and a group of dedicated rat slayers, including Ray Pierce, Derek Brown , Pete Garden and Graham Wragg — the folks who did the business.

The Endangered white-throated storm petrel is one species that could benefit from the eradication of rats in the Pacific Islands. (© Ray Pierce)

The voyage was made possible because skipper Kale Garcia decided that instead of taking time out to refit his boat, the MV Aquila — which fishes for crab in the Bering Sea in the northern winter — it was time for him to give something back to the ocean that has been so generous to him. Between May and August, the Aquila was the vessel used to carry out rat eradications on Palmyra Atoll in the North Pacific; two of the Phoenix Islands (Enderbury and Birnie) in Kiribati; and Henderson Island in the Pitcairn group.

The aim of the mission was to restore the native biodiversity of these remote and vulnerable islands, relying on a unique combination of funding from various government and NGO sources and drawing on an expert team from more than five countries. Using a large vessel that carried two helicopters for spreading the bait according to carefully predetermined GIS coordinates ensured adequate and efficient coverage of every ratty nook and cranny, and made the task of bait distribution infinitely easier than taking it ashore by small boat and spreading by hand.

Initial results indicate that the other islands were also successfully cleared of rats, although this cannot be confirmed for at least another year. Eradication of rats from critical breeding sites will give threatened species such as the Phoenix petrel (Pterodroma alba) and white-throated storm-petrel (Nesofregetta fuliginosa) another chance to defy extinction.

However, such voyages are expensive and are not without their risks, including extreme weather conditions and the dangers of working when it’s a five-day journey to the nearest hospital or landing strip. Securing the gains achieved and protecting bird populations in the Pacific Islands and elsewhere will require an ongoing commitment to repel those rapacious rodent invaders.

Michael Donoghue is executive director of CI’s Pacific Islands program. This year’s island restoration campaign would not have been possible without the support of Heli Otago, Pathfinder, Island Conservation, the Phoenix Islands Protected Area and the Royal Society for the Protection of Birds.