This article is taken from Les Indispensables de Sciences et Avenir #210 July/September 2022.
One can imagine the first flight of a bird as a particularly touching event. Undoubtedly, under the guidance of his parents, he learns to open and move his wings. And then a jump, that’s a big jump before hanging forever. This somewhat idealized view falls far short of the harsh reality of a chick’s often short lifespan.
So, in some species of songbirds, such as the blue warbler or tree sparrow, parents expel some of their offspring from the nest even before they learn to fly. In a 2020 study, researchers from the University of Illinois (USA) asked who was at the origin of this early eviction: chicks ready to break their necks to free themselves? Their parents?
Well proven scalable strategy
The answer is surprising: it is the parents who push them out of the nest, putting them at risk of dying sooner than if they had stayed warm with them. This seemingly cruel practice is actually the result of a well-oiled evolutionary strategy: by spatially separating their offspring, adults reduce the risk of the entire brood dying, which predators quickly deal with, increasing the chances that at least one of the young will survive to independence.
This phenomenon is especially observed in species with large broods and living in unprotected environments (meadows or shrubs), in those that nest in hollows, which, as a rule, delays the flight of their young.