Nest site selection and reproductive success in Orange-crowned Warblers: a comparative study between Santa Cruz and Santa Catalina Islands

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

Veracruz

Congreso; IV North American Ornithological Conference; 2006

  We contrasted breeding ecology of the sordida subspecies of the Orange-crowned Warbler (Vermivora celata sordida) on Santa Cruz Island, where feral pig (Sus scrofa) 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, we predicted that V. c. sordida on Santa Cruz should nest on the ground in the presence of avian nest predators, as they do on the mainland. Median nest height on Santa Cruz (0.25 m) was lower than on Catalina (1 m). However, feral pig disturbance on Santa Cruz apparently forced some 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.