23 January 2009

Initiative to Restore Natural Ecosystem on Henderson Island

Planning is underway to eradicate rats and restore the natural ecosystem on Henderson Island, one of the four Pitcairn Islands in the southern Pacific Ocean.

North shore of Henderson Island. Picture courtesy of Angela K. Kepler, and available at the Pacific Biodiversity Information Forum.

The 3,700 hectare island - measuring 6 miles (9.6 km) long and 3.2 miles (5.1 km) wide - is one of the "world's best remaining examples of an uplifted coral atoll." In 1988 it was designated as a World Heritage Site by UNESCO, and given worldwide recognition for its unaltered natural character and variety of endemic species of birds, plants, insects and snails.

Birds: The flightless Henderson crake, Henderson fruit-dove, Henderson reed-warbler, and the especially rare Henderson lorikeet; these four species are listed as being vulnerable to extinction on the IUCN Red List. A few species have already been extirpated, including three doves and a sandpiper, as well as a shearwater species and the globally threatened white-throated storm-petrel, according to the kiore eradication feasibility report. An estimated 50,000-80,000 pairs of seabirds nest, representing a dozen species: Henderson petrel, Murphy’s petrel, kermadec petrel, herald petrel, red-tailed tropicbird, masked booby, red-footed booby, great frigatebird, fairy/white tern, blue-grey noddy, brown noddy and black noddy.
Plants: The flora includes nine endemic plant taxa, and five globally threatened flowering plant species
Snails: at least six of 22 land snail species disappeared because of the Polynesian impact, about half of those remaining are endemic, according to the feasibility study.
Insects: Some 20% of insects present today (ca. 180 species) are believed endemic.

These unique characteristics have brought the island special recognition as an Endemic Bird Area, an Important Bird Area, and an Alliance for Zero Extinction Site.

When Henderson Island was recognized as a World Heritage Site, there was a requirement to produce a Management Plan. The plan adopted includes an objective "to control or eradicate, where necessary and feasible, alien species that are already at Henderson Island."

This objective is one reason for the initiative to eradicate the Kiore, introduced hundreds of years ago by Polynesians which initially occupied the island early in ca. A.D. 700, and for at least the following six centuries, according to archeological findings. These people introduced the rats.

"… as long as Pacific rats remain on Henderson, the Henderson Petrel’s only known significant breeding site, the species is destined for extinction" - Feasibility study for kiore eradication on Henderson Island

"The subtle impacts of rats on plants and invertebrates are not known, but, based on other islands, undoubtedly bad," said Dr. Geoff M. Hilton, a principal conservation scientist, with the Royal Society for the Protection of Birds. "However, what we do know about is their impact on the nesting seabirds. Henderson is a global headquarters for the most oceanic of all seabird groups - the gadfly petrels. Although four different gadfly petrels still nest on the island, we now believe that they have been in slow, inexorable decline for hundreds of years, and that numbers were 10 to 100 times higher before the rats arrived. The rats kill and eat almost all of the newly hatched chicks, and so the petrels produce incredibly few fledglings.

"Of most concern is the Henderson petrel, known to nest only on the island, which we believe is facing extinction. Because they are such long-lived birds, they are not likely to disappear entirely in the next few years, but they are gradually heading down the slope. Removing the rats would restore normal breeding success at a stroke, and allow the seabirds to gradually recover to their former glory, averting extinction for Henderson petrel."

Planning is now underway for an expedition to the remote island.

"We are planning on having a five person team on Henderson Island for seven weeks in August-September 2009," Hilton said. "This team will include one of the very few biologists ever to have worked on Henderson before; one or two experts on island restoration and rodent eradication; and hopefully a Pitcairn islander."

"Organising this preliminary fieldwork trip is a pretty major undertaking, because Henderson is so remote, entirely without infrastructure and indeed fresh water.

"Their task will be to conduct a variety of bits of fieldwork that will pave the way for an actual eradication project in the future. It’s essentially clearing up the unknowns that the Feasibility Study threw up.

"Specifically, we need to know how much of a problem the land-crabs might be to a poison bait spread. In other tropical island rat eradications, it has been found that land-crabs very much enjoy rat bait. It does them no harm, but if they are present in really large numbers they could actually eat so much that there isn't enough left for the rats - potentially jeopardising the operation. We need to check how many land-crabs there are on Henderson, how much bait they will eat, and how much bait we would therefore need in order to kill all the rats.

"Another work area will be to work out how we will ensure that in the event of a poison bait drop using a helicopter, we don't cause any permanent damage to the native wildlife we are trying to conserve. So we will be looking at whether endemic snail species and endemic landbirds might take bait; whether (in the case of snails) it will do them any harm (we already know it will harm birds); how we can effectively keep them in temporary captivity until the island is safe again."

During the evaluation visit, special attention will be given to how the Henderson Crake might be affected by the poison baits. Tests using colour-dyed baits will be conducted to evaluate this risk. If necessary, plans call for trapping these birds and holding them in captivity until the poison spread about would no longer be a danger.

"The idea is that, if all goes well with these work areas," Hilton said, "the decks would be clear to plan an eradication. In all probability, it would take two years of planning to pull off such an operation - the logistics would be very complicated, and you only get one go at it.

"One major stumbling block of course would be funding. The actual operation is likely to cost in the region of $2 million USD.

"Although it is a United Kingdom Overseas Territory, the UK has not hitherto been a generous funder of biodiversity conservation in the Overseas Territories, so there is no certainty that we will rapidly find the money. However, we are absolutely determined that the money will be found somehow!

"We are already actively looking for funds for an eventual eradication, both from private foundations and through lobbying the UK government. It is important to be clear though that this island is part of the Pitcairn group and nothing will happen unless and until the Pitcairn community are in agreement. So far, they have been very supportive, and we hope to build a strong partnership with them as we go forward, so that they can be fully involved in this exciting venture.

The project would be especially costly due to the lack of local resources since the island is 3000 miles from the closest continent. Eradication efforts would be conducted from a ship loaded with supplies obtained in New Zealand, according to the feasibility report. This floating headquarters would contain everything needed to spread the poison, and provide logistics support for the people involved.

Following the eradication of the predatory kiore, the feasibility report recognized several positive and immediate benefits:

  • "Expansion of undetected relict populations of small petrels, perhaps storm-petrels.
  • "Flushes of regeneration of those species of forest plants susceptible to suppression by virtue of palatability of fruit, attractiveness of seeds or vulnerability due to reproductive strategy
  • "Benefits to fruit-dove and lorikeet from enhanced abundance of fruit and flowers, and possibly to warbler from enhanced invertebrate abundance. These benefits would be realised in increased populations sizes of the birds.
  • "Reappearance of hitherto rarely seen or even unknown species of large invertebrates whose populations had been suppressed by rats.
  • "Recolonisation by locally extirpated species of seabirds. For example on Raoul Island, these included blackwinged petrels (Pterodroma nigripennis) and wedge-tailed shearwaters (Puffinus pacificus). These two species and Christmas shearwater (Puffinus nativitatis) probably bred on Henderson in the past, and are therefore likely candidates for recolonisation. The globally Endangered Phoenix petrel (Pterodroma alba) is another possible (re)-colonist.

"To be involved in this programme is the sort of thing that conservationists dream about," Dr. Hilton said. "To be able to restore one of the world's great natural sites. This would not be the sort of damage limitation or finger-in-the-dyke exercise that we are so often forced into. There is no catch or trade-off here. This would deliver a genuine, major improvement in the fortunes of some highly threatened species. Creating a rat-free Henderson Island would truly be a wonderful contribution to the world’s natural heritage."


Map and information on Henderson Island

Henderson Island World Heritage Site summary

Henderson Island management plan published in 2004

The distinct avifauna of the Pitcairn Islands has been recognized by a number of commemorative stamps.

The endemic land birds of Henderson Island, southeastern Polynesia: notes on natural history and conservation

Bird remains from an archaeological site on Henderson Island, South Pacific: Man-caused extinctions on an "uninhabited" island

Extinctions and new records of birds from Henderson Island, Pitcairn Group, South Pacific Ocean

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