How Orange-crowned warblers reconcile conflicting pressures between avian predators and habitat destruction by feral pigs

PELUC, S. I.; SILLETT, T. S.; GHALAMBOR, C. K.

San Jose, CA

Congreso; 20th Annual Meeting of the Society for Conservation Biology; 2006

Introduction of alien species to islands can negatively affect native vegetation and animals. Our 2005 study of nest site selection and reproductive success in the Channel Island race of the Orange-crowned Warbler (Vermivora celata sordida) revealed potential conservation concerns resulting from feral pig disturbance to understory vegetation. We contrasted breeding ecology of warblers on Santa Cruz Island, where feral pig disturbance to understory vegetation is extensive and Island Scrub-Jays (Aphelocoma insularis) are common nest predators, vs. warbler populations on Santa Catalina Island, where feral pigs have been removed and avian nest predators are absent. Based on prior experimental results from Catalina Island, we predicted that V. c. sordida should nest on the ground in response to avian nest predators. Median nest height on Santa Cruz (0.25 m) was lower than on Catalina (1 m). However, feral pig disturbance on Santa Cruz could have forced warblers to nest above the ground, a stratum more exposed to visually-oriented jays. Daily nest survival probability was significantly lower on Santa Cruz (0.92 ± 0.02) than on Catalina (0.97 ± 0.005), as was annual reproductive success of warbler pairs. Our results indicate that V. c. sordida are likely to benefit from the feral pig eradication currently underway on Santa Cruz. We suggest that the warbler could be used as an indicator of understory vegetation health on the Channel Islands.