Forum News 35 article: Developing a plan for Pacific rat eradication on Henderson Island
A funding bid for rat eradication from Henderson Island is facilitated.
Analysis of the problem
Invasive alien species are the main current threat to the biodiversity of the UKOT's. Rats are the most widespread island invaders in the world, and are responsible for more extinctions in historic times than any other species except humans.
Henderson Island is a 37 km2 raised atoll in the South Pacific. It is one of the least anthropogenically modified islands of its size in the world, being uninhabited, and supporting undisturbed native vegetation communities and remarkably few invasive alien species. Consequently, it is a natural World Heritage Site, one of two in the UK OT's. The island is known to support several tens of endemic invertebrate species, nine endemic higher plant species and four endemic landbird species. There are 15 globally threatened flowering plant taxa, and six bird taxa. It is therefore an Alliance for Zero Extinction Site, one of seven such in the UK OT's.
The single major problem currently affecting Henderson's biodiversity is the presence of invasive alien Pacific Rats, Rattus exulans, which are abundant throughout the island. Evidence from fieldwork in 1991 and 2003 shows that rats depredate the chicks of the four species of Pterodroma petrels to such an extent that their productivity must be extremely low. Population modelling indicates that the birds cannot sustain such levels of depredation, and that their populations are in long-term decline. Henderson is one of the world headquarters for this group of species: the Endangered endemic Henderson Petrel, Near-threatened Murphy's Petrel, Kermadec Petrel, and Herald Petrel all occur in populations exceeding 1,000 pairs. The globally Endangered Phoenix Petrel also occurred early in the twentieth century, but appears to have been extirpated, presumably by rats. Prior to the arrival of Polynesians and the introduction of rats, populations of seabirds on Henderson were at least an order of magnitude higher than they are currently. The loss of such a major component of the community will have had profound effects on the terrestrial ecology of the site.
Elsewhere in its range, the Pacific Rat is known to have considerable effects on plant communities, by reducing recruitment of some plant species, and to reduce populations of some large invertebrates. It is highly likely that such effects are occurring on Henderson, but they have not been studied.
During recent years, technology and know-how for the eradication of invasive alien rodents has been developed. This has resulted in spectacular biodiversity recovery and ecosystem restoration at sites such as Campbell and Raoul Islands (both New Zealand) and many others. Consequently, island rodent eradications have become a major tool in attempts to reduce the rate of biodiversity loss worldwide.
Among the UK OT's, the major islands on which rodents are thought to have devastated globally important biodiversity, and where eradication is a plausible option (due to lack of a large human population) are Tristan da Cunha, Gough, and Henderson (the latter two being World Heritage Sites).
The draft 'Pitcairn Islands Environment Management Plan' has as an objective: "Funding sought to examine feasibility of increasing and continuing rat eradication efforts on Henderson." The Henderson Management Plan has as a principal objective: "to control or eradicate those alien species established on the island which pose a threat to native wildlife".
OTEP has funded (PIT401, TDC203 & 302), and RSPB has led, the production of Feasibility Studies and draft Operational Plans for the site since 2006. The essential message is that eradication of rodents at these sites is feasible and would deliver massive biodiversity benefits. At this stage, final areas of uncertainty for Gough and Henderson need to be resolved before moving on to fundraising and action.
However, the Feasibility Study for Henderson highlights two critical areas of uncertainty, which need to be resolved before an eradication could proceed. First, on tropical Pacific islands, land-crabs of various species are often extremely abundant, and will readily take rodenticide bait. The bait does not harm them, but in some circumstances the crab population can consume so much bait that there is insufficient left for all individuals in the rat population to consume a lethal dose. Substantial discussion and research is centred on this issue in the Pacific region, and other investigations into solution are under way. There is considerable potential to learn from these other investigations. However, density and behaviour of land-crabs seems to vary substantially between islands. An eradication operation on Henderson would cost in the order of £1 million. It would clearly not be prudent to risk such sums of money without examining the issue on Henderson itself; extrapolating results from other islands - especially when these are few in number and somewhat contradictory - would be unsafe.
Second, evidence for similar species from other islands suggests that the endemic Vulnerable Henderson crake population might be very vulnerable to non-target poisoning during a rat eradication operation on Henderson. This means that a proportion of the population would have to be held in captivity during an eradication, as an insurance. An eradication operation would be critically constrained by timing, because of the need for time-bound boat and helicopter charters. If it transpired that it is very time-consuming to catch good numbers of crakes in advance of the bait-drop, the ensuing delay could be fatal to operational success. Similarly, if it turned out that crakes cannot be maintained in relatively simple captive facilities on island during an operation, then the bait-drop would have to be cancelled. Evidence from related species suggests that capture and captive holding should not be prohibitively time-consuming or difficult respectively, but nevertheless, it is considered essential to test these issues in advance of an operation, rather than face the possibility of complete operational failure after major expense.
Complementary initiatives, and other relevant programmes/projects
RSPB is the UK partner of BirdLife International. BirdLife International's Pacific program is focusing on restoring islands in Polynesia and Melanesia. BirdLife Pacific is a partner organisation in the Pacific Invasives Initiative (PII)((See Link) , which is part of the Co-operative Islands Initiative under the IUCN Global Invasive Species Programme. The BirdLife partner in the closest island group - French Polynesia - is also active in island restoration work.
The Henderson programme has made strong links to these regional initiatives, sharing experience with similar environments and species - especially the land-crab issue, and discussing logistics and how to achieve economies of scale in eradication operations (e.g. in bait shipments, helicopter hire). The chief consultant used for the current OTEP project, Professor David Towns, is seconded to the PII.
Co-ordination with other agencies working in the country
By virtue of the current OTEP project, it has been possible to keep a dialogue open with the Henderson Management Committee, the Pitcairn Conservation Officer and Mayor, the High Commission in New Zealand, and other biodiversity stakeholders in Pitcairn (e.g. Steve Waldren at Dublin University). These stakeholders have been able to comment on successive drafts of the Feasibility Study, and thus on the work programme of this proposal.
How the new activities build on the previous ones.
This project is a direct follow-on from PIT401. The proposal has emerged from the feasibility study, which highlighted two key areas of uncertainty (described above), which need to be resolved before the Operational Plan can be finalised and fundraising begins.
- Report describing how to deliver poison bait on Henderson Island in such a way that bait consumption by landcrabs does not hinder the rat eradication objective.
- Report describing methods to efficiently capture and maintain a captive population of Henderson Crakes for the duration of a rat eradication programme.
- Modified and finalised Operational Plan for rat eradication, taking into account the information contained in these reports.
- Charter a vessel to take a fieldwork team to Henderson Island in approx August 2009.
- The fieldwork team will comprise a camp manager, bird husbandry expert, rodent ecology expert and general fieldwork assistant.
- The team will complete a 7 week fieldwork session, during which they will:
-Conduct experiments using toxic and non-toxic bait, to test bait densities needed to overcome bait consumption by land-crabs. In the experiment with toxic bait, the rats will be radio-tracked to determine mortality. The non-toxic bait will have a marker dye, and after distributing the bait, rats will be killed and their ingestion of the marker determined.
-Conduct a trial capture and captive holding operation for Henderson Crakes, to confirm that this species can be captured relatively quickly and maintained relatively easily.
- The project manager and Mike Brooke will then produce a technical report describing the outcomes and recommendations.
- The outcomes will be presented to a consultant eradication specialist, who will complete the draft Operational Plan for rat eradication from Henderson, such that all is in place for a funding bid and operational preparations.
- Pitcairn Island government and community:
The Conservation Officer and Mayor of Pitcairn has been consulted about the project proposal, but is currently incommunicado in New Zealand.
- The Henderson Island Management Committee:
This Committee is responsible for implementing the FCO-agreed Henderson Management Plan and co-ordinating conservation management of the island. The Committee has been consulted about the project proposal.
- Other biodiversity conservation agencies/people with an interest in the island & its species:
We have also discussed the project with the BirdLife International Pacific Regional Office, the BirdLife International Global Seabird Programme, the Pacific Invasives Initiative, MANU (BirdLife in French Polynesia) and various New Zealand eradication experts.
These stakeholders already form the basis for a communication and consultation group for PIT401, and this would be continued if the proposed project is funded.
Risk 1: Accidents or illness to staff on Henderson could have serious consequences for personnel and the fieldwork programme.
Impact: Personal risk to team members. Risk of reduced or incomplete execution of objectives if evacuation or reduced team capacity ensues.
Management: Prior medical examinations; ensure that a first aider is on the team; comprehensive medical supplies;
Insurance for evacuation, backup communication equipment; boat on standby for evacuation.
Risk 2: Failure to find funding for the eradication would mean that the wider goal is not met.
Impact: Project does not contribute to the wider goal. Eradication is an all or nothing activity.
Management: Developing an authoritative plan maximises probability of funding; funding possibilities, including major trust funds, already being tentatively approached.
Risk 3: Effective boat transport cannot be secured within budget.
Probability: Very low because quotes and availability have already been checked.
Impact: Fieldwork cannot be completed.
Management: See Probability.
The wider goal to which this project contributes is the restoration of Henderson Island by eradication of introduced Pacific Rats.
The current OTEP project PIT401 is producing a Feasibility Study and draft Operational Plan for rat eradication. The proposed follow-up project would remove the remaining obstacles to an eradication operation, which have been flagged by the current project, and thereby facilitate preparations and fundraising.
Removing rats from Henderson Island would complete the single major activity required to restore the World Heritage Site to an almost pristine state. It would prevent extirpation of several globally important seabird populations, and result in their recovery. It would be by far the major rodent eradication to take place outside New Zealand to date, and would signal UK and the OTs' intentions to undertake ambitious, high-profile restorations of their globally important islands. It would make a major contribution to the UK meeting its obligations under the CBD and World Heritage Conventions.
In the medium- to long-term, Pitcairn has opportunities to develop as an upmarket nature tourism destination. In such a scenario, Henderson would be a key site, as it is the most important site for biodiversity, has the World Heritage designation, is remote and exotic. Currently the depredations of rats on seabirds, and their general abundance, restricts this potential.
Funded by FCO/DFID Overseas Territories Environment Programme, 2008, project no PIT501
Multilateral Environmental Programme
World Heritage Convention
Henderson is a natural World Heritage Site, one of two such in the UK OT's. The other, Gough, also has as its major conservation issue the presence of introduced rodents. As part of the World Heritage inscription, a Management Plan must be adopted. The Henderson Management Plan has as an objective "to control or eradicate, where necessary and feasible, alien species that are already at Henderson Island." and notes that priority should be given to those species with greatest impact.
Article 5 of the Convention Concerning the Protection of the World Cultural and Natural Heritage notes that:
"To ensure that effective and active measures are taken for the protection, conservation and presentation of the cultural and natural heritage situated on its territory, each State Party to this Convention shall endeavor, in so far as possible, and as appropriate for each country: to take the appropriate legal, scientific, technical, administrative and financial measures necessary for the identification, protection, conservation, presentation and rehabilitation of this heritage;"
The inscription for the Henderson World Heritage Site notes that:
"Henderson Island, which lies in the eastern South Pacific, is one of the few atolls in the world whose ecology has been practically untouched by a human presence. Its isolated location provides the ideal context for studying the dynamics of insular evolution and natural selection. It is particularly notable for the 10 plants and four land birds that are endemic to the island. "
It is clear that the presence of rats is inimical to these values.
Convention on Biological Diversity
The project will help Pitcairn in meeting Article 8 (in-situ conservation) of the Convention on Biological Diversity, although this MEA has not yet been extended to Pitcairn.
In particular, Article 8. In-situ Conservation. "Each Contracting Party shall, as far as possible and as appropriate:.
(f) Rehabilitate and restore degraded ecosystems and promote the recovery of threatened species, inter alia, through the development and implementation of plans or other management strategies;
(h) Prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species;"
Actions to address invasive alien species are a 'cross-cutting issue' for the CBD and island biodiversity is one of seven 'thematic programmes'. A rat eradication on Henderson Island would reverse the loss of biodiversity on Henderson, and thus assist with meeting the 2010 biodiversity target.
The project will assist Pitcairn in meeting requirements under the Environment Charter. Pitcairn's commitments include "ensure the protection and restoration of key habitats, species, and landscape features" and "attempt the control and eradication of invasive species". The UK government commitments include to "promote-sharing of experience and expertise between Pitcairn, other Overseas Territories, and small island states and communities which share similar environmental problems." and "use UK, regional and local expertise to give advice and improve knowledge of technical and scientific issues".