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Good practice Imported

Palmyra Atoll Rat Eradication & Native Forest Recovery

United States of America · Palmyra Atoll · See the United States of America profile

Evidence: Observational / pre–post Top 81% 33/100 · Ask Evidence Copilot about this practice

A 2011 aerial rat eradication on Palmyra Atoll (Island Conservation/TNC/USFWS) preceded a peer-reviewed study showing native tree seedlings rose from under 150 to over 7,700 in five years - though it also triggered a coconut-palm rebound needing active management.

<150
Native tree seedlings (pre-eradication, all species)
>7,700
Native tree seedlings (5 years post-eradication) (5 years post-2011)
0
Pisonia grandis seedlings per 100m² (pre-eradication)
up to 688
Pisonia grandis seedlings per 100m² (1 month post-eradication) (1 month post-2011)
~26
Islets treated in aerial rodenticide broadcast (June 2011)
Palmyra Atoll Rat Eradication & Native Forest Recovery

Details

Maturity
Established
Promoter
Island Conservation / The Nature Conservancy / U.S. Fish & Wildlife Service
Period
2011-present
Keywords
invasive rodent eradication, native forest recovery, seabird nesting habitat, atoll restoration

Context

Palmyra Atoll, a remote National Wildlife Refuge in the equatorial Pacific roughly 1,600 km south of Honolulu, is jointly managed by the U.S. Fish & Wildlife Service and The Nature Conservancy, which owns part of the atoll. Black rats (Rattus rattus), introduced during the atoll's WWII military occupation, preyed on native seabird eggs and chicks and suppressed regeneration of native forest trees, including Pisonia grandis, a keystone tree that provides critical seabird nesting habitat.

Objectives

Island Conservation, The Nature Conservancy and USFWS aimed to eradicate invasive rats from the atoll to allow native forest and seabird nesting habitat to recover.

Activities

In June 2011, the partners conducted an aerial broadcast of brodifacoum rodenticide across the atoll's roughly 26 islets, successfully eradicating rats in what was, at the time, one of the largest tropical rat-eradication operations completed.

Results

A peer-reviewed 2018 study in PLOS ONE (Wolf et al.) compared pre- and post-eradication vegetation plots for five native tree species. Seedling counts rose from fewer than 150 individuals while rats were present to more than 7,700 individuals five years after eradication; Pisonia grandis, which had zero recorded seedlings pre-eradication, reached up to 688 seedlings per 100 m² within one month of rat removal.

Conclusions

An honest and widely cited caveat: removing rats also released the atoll's non-native coconut palm (Cocos nucifera, planted historically for copra production) from rat-suppressed seed predation, triggering unchecked palm recruitment that began crowding out the native Pisonia and Heliotropium forest the eradication was meant to help recover. The Nature Conservancy and Island Conservation began an active coconut-palm culling programme in 2019 to correct this cascading, second-order effect - now a widely referenced case study in island-restoration planning for anticipating indirect ecological consequences of predator removal.

Implementation
Indicative cost
High (€500k–€5M) — No specific budget figure is reported; a fully aerial rodenticide broadcast across ~26 remote Pacific islets, followed by multi-year monitoring and an ongoing coconut-palm culling programme since 2019, implies a sustained multi-organization funding commitment.
Time to results
Long (> 3 years) — Eradication conducted in June 2011; peer-reviewed outcome monitoring published in 2018; adaptive coconut-palm management ongoing since 2019.
Staffing & skills
Island Conservation eradication team, The Nature Conservancy site managers, U.S. Fish & Wildlife Service refuge staff, Wolf et al. research/monitoring team

Conditions for success

  • Complete simultaneous aerial rodenticide coverage across all islets to ensure full eradication (partial removal risks reinvasion)
  • Long-term post-eradication ecological monitoring (pre/post vegetation plots) to detect both intended recovery and unintended cascading effects
  • Willingness and capacity for adaptive follow-up management (e.g. coconut-palm culling) when eradication produces second-order ecological effects

Common failure modes

  • Removing an invasive predator can release a different non-native species (coconut palm) from suppression, triggering a new threat to the native forest the eradication was meant to protect
  • Without anticipatory monitoring, such indirect/cascading effects could go undetected and undermine restoration goals

Where it fits

Governance type
US federal agency (USFWS) + NGO partnership (TNC, Island Conservation)
Scale
single remote atoll (~26 islets)
Income level
high-income (United States)

Commonly funded by

National / regional programmes Philanthropic / foundation funding

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Data sources

Where this practice's information was retrieved from, and when.

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