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Why do eggs in the same bird clutch often hatch at different times?

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A zebra finch (Taeniopygia guttata) with a bright orange beak, gray head, orange cheek patch, and black-and-white striped tail perches on a branch. — Bird A brightly colored zebra finch (*Taeniopygia guttata*) perched on a branch.

Many birds begin incubation as soon as they lay the first egg in a clutch, rather than waiting until the entire set is complete. This practice causes the eggs to hatch at different times.1

This strategy is often an adaptation to environments where food availability for the young may fluctuate significantly over a short period. By staggering the hatching times, the parents ensure that if food becomes scarce, only the smallest or youngest chicks are likely to starve, rather than the entire brood.1