CONICET | Buscador de Institutos y Recursos Humanos

Avian foraging behavior may vary among years because of changes in the abundance and availability of prey. We therefore aimed to study the foraging behavior of White-crested Elaenia (Elaenia albiceps chilensis), a Neotropical austral migrant, in relation to interannual variation in its food resources in a mixed forest of Patagonia. During two summers of contrasting rainfall patterns, we recorded foraging maneuvers, substrate use, and use of forest microhabitat (plant species and heights) where birds capture their prey. We also evaluated the abundance of the main food items consumed by this species: Ripe fruit and arthropods. The first year was very rainy, when we recorded a lower supply of ripe fruits than in the second year, whereas the abundance of arthropods was similar throughout the study. During both years, the most frequent behavior of White-crested Elaenia was searching for food items while perched, capturing them from foliage using gleaning and sally-hovering maneuvers. Nevertheless, this species notably modified the use of foraging microhabitat between years. During the first year, elaenias used the canopy of the forest and foraged mainly in Nothofagus dombeyi trees, whereas in the second year elaenias used the entire profile of vegetation height and increased prey capture in shrubs of Aristotelia chilensis. Our results demonstrate the behavioral flexibility of this Neotropical austral migrant species and highlight the importance of considering the spatio-temporal variation of resources when evaluate the foraging behavior of birds.