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Polynesian Rats Don’t Come From Polynesia

The Polynesian rat is distributed throughout the Pacific Ocean and is found on most islands. Early European naturalists thought that because the rat was already present it must be native to each island. However, taxonomists eventually learnt that the Polynesian, or Pacific, rat (Rattus exulans) in fact originally came from South-East Asia. Scientists working with National Geographic have even used the Polynesian rat to trace the original dispersal of Polynesians across the Pacific. And so here in Tetiaroa, in the furthest corner of the Pacific, we today find the diminutive Polynesian rat, which does not come from Polynesia.

A Polynesian rat and a hermit crab inspect one another
A Polynesian rat and a hermit crab inspect one another on Reiono, Tetiaroa (Photo by James Russell)

Although the focus of our current expedition to Tetiaroa is to document the ant fauna of the atoll, Dr Araceli Samaniego is also inspecting two motu (islands) of the atoll which have only Polynesian rats, and assessing their potential for rat eradication. Although the Polynesian rat is small, it is still a threat to island floras and faunas, and so by eradicating it from small motu in Tetiaroa we might be able to create more protected habitat for the current breeding seabirds, or the potential to reintroduce endangered land birds from elsewhere in French Polynesia.

An uncommon moon-lit perspective of Tahuna Iti/Bird Island
An uncommon moon-lit perspective of Tahuna Iti/Bird Island (Photo by James Russell)

In the course of our surveys of each motu with the Tetiaroa Society, it appears that Aie and Tahuna Iti (Bird Island) are also free of rats (and they have also effectively been eradicated from Onetahi). This makes eradication of rats from other motu such as Rimatu’u or Reiono even more important; to increase the total amount of rat-free island area, and to protect rats from colonising these rat-free motu. If rats arrived on Tahuna Iti it could be devastating for the birds nesting there. However, our surveys of the motu this week have given us confidence that rat eradication during the dry season would have a high probability of success.

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