How Do Young Birds Know When To Leave The Nest?

The age when young birds leave their nest is the evolutionary compromise between parents, who want their chicks to leave as early as possible, and offspring, who want to leave as late as possible.

Adult gray-headed junco, Junco hyemalis caniceps, enticing one of its youngsters to leave the nest. Parents hold food away from nest and tempt the young come out to get it. This picture captures a young bird that was just fed outside of the nest.
(Credit: T. E. Martin, doi:10.1126/sciadv.aar1988)

Major life changes can be dangerous, even fatal. Probably the most dangerous life transition is when young animals, such as fledgling birds, begin to move about on their own and to make their own decisions. Predictably, when baby birds -- nestlings -- transition from dependency to their new life as fledglings living outside of the nest, their first few weeks of exploring the landscape and learning to fly are fraught with extraordinary dangers.