Booby brothers and bullies

If you think your little brothers and sisters can be a pain, just be glad you don’t live with a baby brown booby. In an experiment, the little birds threw such fierce temper tantrums that they drove older, bigger chicks out of the nest—for good.

Brown boobies are seabirds that live near the Pacific Ocean. Mothers normally lay two eggs. But the chick that hatches first nearly always pecks at its younger sibling until the little one falls out of the nest and dies.

The older, larger chick pushes its younger sibling toward the edge of a brown booby nest.

J.L. Osorno

To learn more about the poor little chicks, scientists in Mexico took nine of the younger brown booby hatchlings from their own nests and put them in nests with older chicks of a related species called blue-footed boobies. Mother blue-footed boobies usually lay two eggs, too, but the siblings usually manage to get along and grow up just fine.

But when little brown boobies meet big blue-footed boobies, sibling rivalry takes on a whole new meaning, the researchers found. Four of the transplanted brown booby chicks went berserk. Even when their new big siblings were nearly twice their size, the little chicks delivered as many as 700 pecks per hour. One baby brown booby even shoved the older chick out of the nest.

So, next time you’re tempted to make fun of a younger sibling, you might want to think twice: The little ones might be capable of fighting back better than you think.