Adaptive plasticity in avian nest site selection in response to increased predation risk.

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

Congreso; 11th Congress of the International Society for Behavioral Ecology; 2006

Nest site selection in open-cup nesting birds is generally considered a conservative trait molded by natural selection in response to nest predation, the principal cause of reproductive failure for most open-cup nesting passerine birds.  Here, we provide clear evidence for adaptive phenotypic plasticity in nest site selection and nestling provisioning rates induced by experimental alteration of potential predation risk in a wood-warbler, suggesting a sophisticated ability to continuously track and assess different levels of vulnerability to predation throughout the reproductive period.  Almost all other Vermivora wood-warblers breeding on mainland North America, including orange-crowned warblers (Vermivora celata), are exclusively ground-nesters  However, orange-crowned warblers on Santa Catalina Island (V. c. sordida), where avian predators of nests are absent, nest at variable heights (0-8 m).  By altering the perceived nest predation risk within a breeding territory via the experimental introduction of a model avian predator, we demonstrate that warblers shift nest site selection to more concealed locations on the ground compared to controls.  We also found a decrease in feeding rates to nestlings in the presence of the model predator, and this response was enhanced at less concealed off-ground nests. Both the shift in site selection and the feeding rate adjustments constitute an adaptive response to an increased perceived risk of predation, providing convincing evidence that birds assess variation in the fitness costs and benefits of their behavioral decisions.