Thursday, August 12, 2010

Ball 11: Begging to Differ — New research challenges conventional wisdom about why animal babies grovel for food

Begging may be distasteful in polite society, but it’s a routine means of communication between animal offspring and their parents. Bird experts have assumed for two decades that they understood why chicks beg for food. But a group of scientists say the accepted theory is almost certainly wrong.

The prevailing view, solidly in place since the early 1990s, is that babies beg “to indicate how pathetic and needy they are,” says Douglas Mock, a behavioral ecologist at the University of Oklahoma. Their pleas signal parents to their most pressing desires—hunger to be sated—triggering a care-giving response that nature can’t ignore.

That theory resonated with our own cultural values,” Mock says. “We claim to love all of our children equally, we try to get everybody through by giving extra to the ones that need the most.

The problem, Mock says, is that the evidence doesn’t support the hypothesis.

I’ve been doing field work since 1970s and I seldom see it working the way these happy faced thoughts seem to be taking us.

Virtually any life form that features progressive provisioning of dependent offspring from birds to mammals, even insects and probably a lot more plants than anybody has contemplated, Mock adds

Researchers can’t measure true need in animals. After all, one more grub in the gullet is unlikely to improve a baby indigo bunting's prospects to a detectable degree, Mock notes. But the basic message that the chick is ready for another gulp is easy to test. And scientists can observe the way adult birds respond to the signals of their chicks.

Mock says:

If the signal of need idea is correct, then parents should do whatever they need to do to get food to the runts, but it turns out that parents more often than not bias deliveries of food to the bigger chicks.

Instead, Mock and his colleagues believe the true impetus for begging could be the opposite of a signal of need. Or, they say, it may be nothing more than a reporting of desire, like a child's letter to Santa.

In other words, he says, perhaps the only thing a begging baby bird communicates is the fact that it’s hungry. Yet the parents look at which baby is doing well and ask themselves, Is this a season that the family budget can support everyone, so I should shunt food to the runt, or is this a typical lean season when feeding the runt is a mistake?

Mock’s group, who presented its argument at a recent meeting of the Animal Behavior Society, takes another whack at the conventional wisdom about begging.

For a signal to be honest, the energy required to produce it can’t outweigh the potential upside. Consider the peacock, whose gaudy tail feathers boast of genetic fitness—yet serve as an “eat here” sign to predators.

Only a really strong male can carry around the drag queen paraphernalia. In effect, he's demonstrating that he can escape from predators even with the outrageous plumage. And that may indicate that his offspring will escape predators as well, Mock says.

For peacocks, the prospect of more frequent mating is worth the risks of ostentation, Mock says. But what’s the upside of a chick that so obviously advertises its need, in this case, hunger? Not much, he says.

The chick is supposedly announcing that it is weak and imperiled. It's giving a supposedly costly signal that it can ill afford to give, because it's so weak, but hoping to reap a disproportionate windfall.

Mock, who has spent his career studying siblicidal herons and egrets—sib-killing is also found in various hawks, owls, cranes, boobies and laughing kookaburras—says that for certain bird species, displays of weakness in the nest are death sentences.

If nothing else, one wonders why [a begging chick’s] stronger nest mates are suppressing their own, easily affordable signals, thereby stealing the spotlight and the meal. Sibling altruism certainly can evolve, but that cannot be assumed.

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