BEING a downtrodden younger brother or sister could pay off in the long run – at least if you’re a bird. Contrary to what you might expect, blue-footed booby chicks that are bullied by an older sibling become more successful parents than their abusive siblings later in life.
In a typical two-chick brood, the first booby to hatch is always dominant, cornering a bigger share of food and parental attention, and viciously pecking the younger nestling as soon as it hatches. Often the junior chicks don’t survive the abuse, and those that do grow much more slowly than their older siblings during their first two weeks of life. But surviving the trauma seems to pay off.
Hugh Drummond of the Institute of Ecology at the Autonomous National University of Mexico in Mexico City tracked the fates of more than a thousand nestlings on Isla Isabel off the country’s Pacific coast. He expected to find that younger siblings would fare worse in life. But during the first breeding season, older and younger siblings did equally well. Five and 10 years later, second-born chicks were successfully raising larger families than first-borns and giving their offspring a head start by nesting earlier.
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Drummond, a second-born sibling himself, speculates that adversity early in life may force younger chicks to adapt to harsh conditions, steeling them for adulthood. Alternatively, tormenting a younger sibling for three or four months could be a costly endeavour that catches up with older chicks later in life, he says.
Whether the same is true for people is less clear. But psychologist Frank Sulloway of the University of California, Berkeley, says it is significant that the effect can last a lifetime in birds, as there is also evidence from people that childhood relationships between siblings can have a impact on adult behaviour.
