Palmyra Atoll Rat Eradication & Native Forest Recovery

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.

In June 2011, Island Conservation, The Nature Conservancy and USFWS 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.

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.

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.

Read the full analysis: https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0200743

Read the full analysis: https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0200743