Recovery of a threatened seabird after eradication of an introduced predator: Eight years of progress for Scripps’s murrelet at Anacapa Island, California

Abstract

Eradication of introduced predators has become an increasingly important restoration strategy on islands since the 1970s, but the benefits for impacted seabird populations are seldom examined. Scripps’s murrelet (Synthliboramphus scrippsi), a small crevice nesting alcid, suffered severe impacts from introduced mammals at all breeding islands through much of the 19th and 20th centuries. From 2001 to 2010, nest monitoring was conducted to assess responses of the remnant murrelet population at Anacapa Island, California after black rats (Rattus rattus) were eradicated in 2002. Baseline (2001–2002) and post-eradication (2003–2010) monitoring in ten sea caves recorded a nearly 3-fold increase in hatching success (30% versus 85%), due mainly to a drastic reduction in egg predation. Post-eradication monitoring in caves was augmented with three plots in previously vacant “non-cave” habitats that were occupied within 1–3years of rat eradication. Nests increased 10% per annum in sea caves, 24% in non-cave plots and 14% overall. Murrelet nesting was limited mostly to remnant breeding habitats, consistent with recruitment of philopatric local cohorts as the major factor in colony growth. No nests were found during limited searches of suitable crevices on upper-island slopes and cliffs. Continued monitoring at Anacapa is needed to document the long-term progress and rate of colony recovery and detect nesting in currently vacant habitats. Better knowledge of the post-eradication responses of seabirds will assist development of more effective island restoration actions; thus, baseline and post-eradication monitoring should be essential components of more eradication programs in the future.