Few vertebrates have had greater impact on the biodiversity of islands than introduced rats. Three species
widespread throughout the Pacific are all originally from Asia, the Pacific rat; introduced by the earliest
Pacific voyagers, and the other two species unwittingly transported on ships in the last two-hundred or so
years. As a consequence rats are now found on almost every Pacific island. The impacts of these more recent
arrivals and especially the Black Rat (Rattus rattus) are particularly acute. In addition to their well-
documented impacts on island biodiversity, rats represent an on-going threat to human health spreading
bacteria such as leptospirosis and result in millions of dollars of damage to agricultural crops and food supplies
wherever they occur.
Rats prey on a wide range of plants, insects and larger animals, such as seabirds. Globally, the Black Rat is one
of the chief causes bird extinctions on Pacific Islands. Five species of birds disappeared from Taukihepa Island,
New Zealand, after the arrival of the Black Rat. On Lord Howe Island, Australia, five endemic bird species
became extinct following the arrival of rats from a shipwreck. In the Pacific a number of bird species survive
only where intensive rat control operations occur, or on islands free of Black Rats.
The Black Rat is also a threat to island people and economies. Throughout the world, vast quantities of
agricultural crops and food supplies are consumed or despoiled by rats each year. In Tonga it was estimated in
one study that 20% of the coconut crop was lost due to rats.
The Tuamotu Archipelago in French Polynesia is the home of many bird species such as the Polynesian
ground-dove and Tuamotu Sandpiper (Kivi Kivi). The continued existence of these species is threatened by
rats that predate on the birds, chicks and eggs. In 2015 Birdlife International and its local partner Société
d'Ornithologie de Polynésie (MANU), together with Island Conservation plan to eradicate rats from 6 atolls
and small islets in the Acteon and Gambier island groups of the Tuamotu Archipelago.
The Malau (Polynesian Megapode) is a critically endangered bird native to the Kingdom of Tonga. Ongoing
survival of this species is severely threatened by rats, and although it is not feasible to eradicate rats from the
entire Kingdom, it may be possible to eradicate them from some of their critical habitat such as Late Island.
This planned eradication, coupled with translocation of breeding birds from nearby island, can potentially
save this iconic species from extinction.
In cases where eradication is currently not deemed feasible for reasons such as cost or the presence of
vulnerable non-target species, specific actions can be taken to protect native species at risk. These may include
intensive control of rats and other predators. The Raratonga Monarch, for example, has been brought back
from the brink of extinction through rat and cat control, and the transfer of 30 young birds to Atiu Island
(known locally as the Land of Birds) in 2001-2003.
There are many projects in the Pacific region ready to be funded that would reduce the impact of rats on island
biodiversity and people. Fortunately, the tools and techniques necessary to reduce the impact of rats on
islands have advanced considerably in the past 20 years. Since the 1960s, rats have been successfully
eradicated from over 300 islands, and the number increases every year. The impetus of these past successful
eradications must be maintained to continue the battle to save the unique Pacific fauna and flora. An essential
part of the eradication process is ongoing biosecurity which is paramount in the fight to ensure that rat-free
islands are not re-invaded after successful eradication.