Does predation drive Chilean Elaenia (Elaenia chilensis) nest-site selection in the temperate forest of southern South America?

Nest-site selection is a behavioral response that can provide protection for adults, eggs and nestlings, affecting fitness. Since predation is the main cause of nest loss worldwide, it has been considered as the main evolutionary driver in nest-site selection. Nevertheless, in some cases, nest microclimate may be the primary evolutionary force operating on nest-site selection. We aimed at determining at mesohabitat and microhabitat scales if Chilean Elaenia ( Elaenia chilensis ) selected the nest site and, if so, whether such selection was associated with a reduction in nest predation. Since nest orientation may influence nest microclimate, we also tested whether it affected the reproductive output. At the mesohabitat scale, the subcanopy cover (1.5–4 m from the ground) was selected by this species. At the microhabitat scale, elaenias preferred Schinus patagonicus to nest and oriented their nests preferentially to the north and eastern directions. These selected habitat features had no effect on nest success and reproductive output. Despite the risk of nest predation by several aerial (birds) and ground predators (rodents), both successful and predated Chilean Elaenia nests were close to the ground rather than at intermediate heights. Considering the hardness of S. patagonicus wood that can provide structural support to the nest against strong winds, and that nests were oriented to the opposite direction of prevailing wind, Chilean Elaenia nest-site selection might be related to microclimatic factors at nest sites rather than predation. Therefore, it is imperative to consider potential associations between nest microclimate and habitat features to advance in the understanding of bird nest-site selection.