Facing the heat: nestlings of a cavity-nesting raptor trade safety for food when exposed to high nest temperatures

Increasing temperatures due to climate warming may expose many species to thermally dangerous conditions, especially during less mobile phases of their life cycle when the chances of relocating to cooler sites are limited. We investigated how altricial nestlings of cavity-nesting lesser kestrels, Falco naumanni, respond to elevated nest temperatures. In the study system, nestlings develop in nestboxes placed on roof terraces. Before fledging, they often rest outside the nestbox, near the entrance hole, where they can be fed by parents and rapidly re-enter if threatened. This behaviour is similar to premature fledging observed in some species during heatwaves, which causes extensive nestling mortality. We experimentally tested whether high nest temperatures increased the likelihood of nestlings temporarily leaving their nest, thereby exposing themselves to higher predation risk. This may occur either because nestlings attempt to escape unbearable temperatures inside the nest or because ...