The cruel, persistent bullying that older siblings display toward younger ones does not have lifelong consequences — at least among blue-footed boobies, a new study finds.

Boobies are marine birds that typically lay two eggs that hatch four days apart. During a four-month nesting period, the senior sibling is known to peck and attack its junior sibling incessantly until the younger bird becomes habitually submissive.

Senior chicks gain an advantage in size, strength and motor coordination over their younger siblings.

Younger siblings receive fewer feedings and less fish from parents, and during the first three weeks of life their weight is 11 percent lower. Younger chicks also suffer from elevated levels of stress hormones that are 109 percent higher than in senior chicks in the first 15 to 20 days of life.