In “Abused Chicks Grow Up to Be Abusers” (Science, 11 October 2011), Virginia Morell reports,
It’s a scene that occurs daily among nesting colonies of Nazca boobies: A young adult bird struts over to a neighbor’s chick and begins biting and pecking it, sometimes causing injuries that lead to the nestling’s death. But if the chick survives, it’s likely to become just like its tormentor, attacking other nestlings when it reaches maturity and perpetuating this “cycle of violence,” researchers report. It’s one of the first times that the cycle, which is normally used to explain child abuse in humans, has been discovered in a population of wild animals.
It’s used to explain child abuse, all right, in the sense that everyone who host for Airhead TV knows that abused children grow up to be abusers. In reality, abused children may adopt one of a variety of strategies as parents, including passive parenting, overindulgent parenting, overprotective parenting, or just not having children. That’s one of the differences intelligence makes: Different people develop different responses to the same problem. Anyway, researchers have been trying to understand this unproductive behaviour among boobies.
The boobies’ behavior seems to be at least partly linked to the birds’ natural history. Boobies often lay two eggs, even though the parents can care for only one chick. If both eggs hatch, the nestlings fight each other to the death—a behavior that is governed by hormones.
Because the attacks by unrelated adults are similar to the sibling attacks, there may be a “maladaptive side effect” of something that makes evolutionary sense, says Scott Forbes, a biologist at the University of Winnipeg in Canada. Forbes agrees with Anderson that the boobies can provide a “useful model system” to study the causes of human child abuse. Others, however, are not yet convinced that the chick-abusing boobies and child-abusing humans are sufficiently similar to warrant using the birds as a model. “It is very interesting to see these intergenerational effects of early experience and hormones in an animal,” says Dario Maestripieri, a behavioral biologist at the University of Chicago in Illinois. “But what happens in humans is pathological,” he continues, “whereas the birds are programmed to attack each other as siblings,” because the parents can handle only one.
A reasonable possibility is that the survivor of the nest chick war later attacks chicks as a learned behavior that has no particular significance.