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Black rats (Rattus rattus), an exotic species introduced to the California Channel Islands before 1940, were a serious threat to the islands’ native species. The rats preyed on reptiles, amphibians, marine and terrestrial invertebrates, and the young and eggs of island-nesting seabirds. On Anacapa Island, part of Channel Islands National Park, these ravenous predators prevented two rare bird species, the Xantus’s murrelet (Synthliboramphus hypoleucus) and ashy storm-petrel (Oceanodroma homochroa), from nesting successfully.
The Anacapa Island Restoration Project is the effort of the National Park Service in conjunction with a partner, Island Conservation and Ecology Group, to restore the island’s habitat for native species. In November 2002 the second phase of the project got under way with the application by helicopter of the rodenticide brodifacoum on middle and west Anacapa islets; the treatment was modeled on the successful baiting of rats on east Anacapa Island in 2001. The project was developed with public and environmental input through NEPA (National Environmental Policy Act), a planning process that evaluated several management options. As part of the process, the National Park Service applied for and received an exemption from the Environmental Protection Agency permitting use of the rodenticide on the park’s natural areas.
Concern about the possible inadvertent poisoning of migratory birds, birds of prey, and native rodents prompted the National Park Service to implement a number of risk-reduction strategies. The project was designed around a specific biological window, November through December, when bird activity is low and the rats are more willing to accept the bait because other food sources are less available. The National Park Service also livetrapped native mice and birds of prey before applying the rodenticide; these animals were released after the threat of poisoning passed. A deflector attached to the bait hopper increased precision of the bait application on the steep hillsides of the island. Project staff conducted intensive search and removal of rat carcasses for 13 days after the baiting, followed by less intensive searches. Bird and wildlife populations were also extensively monitored before and after the bait application to assess efficacy and any unwanted impacts of the treatment.
Monitoring indicates that east Anacapa Island apparently is free of black rats a year after treatment. Researchers found an intact Xantus’s murrelet egg, which was notable because rat depredation of eggs had been repeatedly recorded in the past. Survival of juvenile lizards and salamanders on rat-free east Anacapa was double that on middle Anacapa. More than 150 native deer mice released on east Anacapa are breeding and their numbers had increased to approximately 1,000 by the end of the breeding season. Although years of monitoring will be required to determine if black rats have been eradicated on Anacapa Island, the project is already helping native species rebound from the crippling impacts of this voracious exotic species.
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