Bullied booby chicks end up OK

Abuse doesn’t hamper younger birds’ fitness

WILLIAMSBURG, Va. — What does not kill them makes them successful blue-footed boobies.

Blue-footed boobies abuse younger and weaker siblings in the nest, but research shows that persecuted chicks turn out just fine, thank you. putneymark/flickr

Among seabirds named for their big, cornflower-blue feet, adversity early in life doesn’t necessarily put kids at a lifelong disadvantage, says Hugh Drummond of the Universidad Nacional Autónoma de México in Mexico City. Though older nestlings relentlessly peck junior ones and snatch away the biggest share of food, a persecuted younger chick often succeeds in life as well as its tormentor does.

In spite of chickhood trauma, younger sibs that survive end up having about as many chicks themselves over the course of their lives as their bullying siblings do, Drummond said July 28 at the annual meeting of the Animal Behavior Society. He speculated that evolution might have favored some kind of compensation for poor starts in booby life.

Listening in the meeting audience, Andrew Sih of the University of California, Davis, called the finding “a pretty striking result.” It’s startling, he said, because “there’s a long history of us assuming that nasty experiences early on can mess you up for life.”

Research in other animals, including humans, has certainly found long-lasting signs of a poor start in life. But testing how those effects translate into success or failure in the real world takes a lot of data spanning whole lifetimes. Having monitored blue-footed boobies for more than two decades, he has amassed records for thousands of birds on such features as aggression, reproduction and patterns of dispersal to new territories.

Life doesn’t start well for the younger chick or two in a booby nest. The oldest chick hatches almost four days before the second one, getting a head start on growing. It pecks any younger, smaller or weaker sibs, sometimes 60 times a day. The younger siblings grow submissive and by the end of their ordeal in the nest seem incapable of fighting back, Drummond said.

In the first week after hatching, for example, Drummond has found that bullied juniors typically lose out on about 17 percent of their fair share of food. But they generally experience a growth spurt later, catching up in weight with the oldest chick by the time they fledge.

If food gets too scarce though, the older sib becomes even more antagonistic and may kill the younger ones. Parents do not intervene.

Even without a food crisis, a younger chick shows high concentrations of the hormone corticosterone circulating in its bloodstream, a classic sign of enhanced stress. Yet so far, Drummond says, he has not found that a stressful start in life is anything a blue-footed booby can’t handle.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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