Balance Restored on Anacapa Island, California

Thousands of birds use Anacapa Island as a nesting area due to its natural lack of predators. But invasive, non-native black rats were inadvertently brought to Anacapa in the 1940’s aboard ships traveling to the islands. IC and other conservation groups began studying the impact of black rats on native seabird populations in the mid-1990s. Biologists discovered high rates of predation on murrelet eggs and found bird bands outside rat nests, evidence that rats were eating young birds. More than 96% of Scripps’s Murrelet (Synthliboramphus scrippsi, previously Xantus’s Murrelet) nests on Anacapa were being predated by invasive rats.

In 2001 and 2002, Island Conservation, the Channel Islands National Park, and the American Trader Trustee Council (comprised of the California Department of Fish and Wildlife, USFWS, and the National Oceanic and Atmospheric Administration) removed invasive rats from Anacapa Island, and subsequent monitoring confirmed the rats were gone. In the absence of these invasive predators, Scripps’s Murrelets rebounded almost immediately.

Just ten years after the removal of invasive rats, the ecosystem on Anacapa Island in the Channel Islands archipelago in California is showing profound recovery. The number of Scripps’s Murre­let nests, for example, has quadrupled, with a threefold increase in eggs hatched. Prior to the restoration project, invasive rats consumed approximately 90 percent of Scripps’s Murrelet eggs. This removal and the following ten years of successful reproduc­tion on an island free of invasive rats helped prevent the mur­relet from being placed on the U.S. endangered species list. In addition to the murrelet success, other species have prospered. Endangered Ashy Storm-petrels (Oceanodroma homochroa) have established their first-ever nesting sites on the island, and Cassin’s Auklets (Ptychor­amphus aleuticus) quickly colonized the island after rat removal.