The Polynesian or Pacific rat (Rattus exulans) was introduced during the expansion of the Polynesians across the Pacific. Henderson was abandoned but the rats, identified as a major predator on nestling sea birds, remained. Quoting from the Henderson Island News (Issue 5):
Rats have had a devastating effect on the island, killing over 25,000 petrel chicks a year and driving the Henderson petrel towards extinction. Seabirds, which would have numbered in the millions before rats arrived, have beenreduced to just 40,000 pairs. Rats have also been limiting the populations of other endemic bird species, altered the forest through seed consumption, and preyed upon marine turtle hatchlings and Henderson’s unique invertebrate populations.
The job of covering the island 43 square km in area with rodenticide (while capturing, holding (and breeding) Henderson rails in captivity until the exercise had been completed) while operating a long way from everywhere was a very great effort and attracted financial support from around the world, as well as from the UK government.
We visited Henderson on October 2010 on MV Clipper Odyssey during a Noble Caledonia Expedition Cruise from Easter Island to Tahiti. By the time we got to Henderson we had visited Ducie Atoll, also in the Pitcairns, now apparently rat free, with its incredible seabird colonies but no land birds. Henderson has its few land birds and some seabirds but in nothing like the numbers on Ducie. While looking in the undergrowth behind the beach we saw a rat and I managed to get a few seconds of video footage. It clearly had not read the information on this species stating that it is nocturnal.
I hope efforts to remove the rats will continue at this World Heritage Site and that those who provided financial support (including many individual RSPB members and expedition cruise passengers and the travel company Zegrahm Expeditions, as well as government and other charities) will continue to do so. Just seeing the contrast between Ducie and Henderson was enough for me to conclude: ...whatever it takes.