There is a schedule, natural, instinctive, time to leave the nest. Only one baby still "at home", the Runt, the kid who's been walked on, sat on, last to get fed, last to hatch. Both parents calling to it, "Come, come. meet the world."
Runt is doing all the correct things... stretching, flapping, watching the world.
Meanwhile, sibling is very comfortable across the path in the bushes.
The nest is now empty. All three babies have fledged. Finding them is not easy. One has to follow the sound, "peep peep", and follow the parents with food in their mouths.