Initial recovery of Xantus's Murrelets following rat eradication on Anacapa Island, California.

The catastrophic effects that introduced mammals have wrought on island-breeding seabirds are well known, often resulting in great population reductions or local extinctions (Moors & Atkinson 1984, Bailey & Kaiser 1993, Burger & Gochfeld 1994). In the 19th and 20th centuries, nonnative mammalian predators, especially cats Felis catus and rats Rattus spp., were introduced on many coastal islands used for breeding by Xantus’s Murrelets Synthliboramphus hypoleucus in southern California and northwestern Baja California, causing reductions in murrelet population sizes, restricted distributions and possible extirpations (Jehl & Bond 1975, Jehl 1984, Drost & Lewis 1995, McChesney & Tershy 1998, Keitt 2005). At Anacapa Island, California, the severe impact on the murrelet population of nonnative Black Rats Rattus rattus has been recorded since at least early in the 20th century (Collins 1979, Hunt et al. 1979, Carter et al. 1992, McChesney & Tershy 1998, McChesney et al. 2000, Whitworth et al. 2003a). Anacapa Island harbors abundant potential nesting habitat, but only a remnant murrelet population persisted in the 1990s by nesting in habitats such as sea caves, steep slopes and cliffs, although evidence of rats and rat-depredated murrelet nests were found even in those relatively inaccessible habitats (McChesney et al. 2000; Whitworth et al. 2003a; H. Carter, unpubl. data).