Asynchronous hatching
The situation in which all the eggs in a clutch do not hatch at (more or less) the same time, as is more usual among birds, but have their hatching spread over several days. It is well seen in the various types of raptor, and is an adaptation to a type of food supply which may fluctuate. During seasons when food is short the later hatched young will probably starve as the earlier hatched young, being larger and stronger, deprive them of food, and so the size of the brood is reduced to a level in balance with the available food supply. In years of plenty all the young may be able to survive. In 'synchronous hatching' all the eggs hatch at more or less the same time.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver