Meerkat pups grow fatter with extra adults.

Like children begging treats from indulgent grownups at a party, meerkat pups get fatter when they have more adult meerkats to pester for food.

That conclusion arises from a bit of managed foster care, explains Timothy Clutton-Brock of the University of Cambridge in England. He and his colleagues are studying the many cooperative behaviors within groups of the arid-land mongoose Suricata suricatta, which pokes around for beetles and other small prey in Africa.

Researchers knew that big groups of meerkats tend to raise hefty pups. However, it was unclear whether the advantage came from more care or lusher territories, Clutton-Brock says. He and his colleagues set up a test by borrowing pups from nine groups and adding them to foster homes. In the Sept. 28 SCIENCE, the researchers report that a crucial factor in pup growth turns out to be not territory but abundant adults indulging the youngsters' pleas.

"It was a clever method," comments Stephen T. Emlen of Cornell University, who studies cooperation in birds. The new meerkat findings parallel the booster effect from extra nannies that scientists have described in cooperatively breeding birds. "Compared with birds, we know much less about cooperative breeding in mammals," he notes.

Clutton-Brock rates meerkats as "fabulously cooperative." Their groups of 2 to 30 adults center around one breeding pair, although sometimes subordinates contribute a few pups. The many nonbreeding adults share child-care duties, fasting for a day as they babysit the newborns, carrying youngsters in their mouths, and bestowing prey on pups when they rush up squeaking.

In the foster test, the researchers round that a pup doubled its food intake when researchers created an adult-rich environment by sending three-quarters of the youngsters away to a foster home for a morning. In contrast, among pups in the receiving group, suddenly competing with extra mouths slowed their feeding to 55 percent of their previous rate.

In other experiments, the researchers found heavier pups more likely than their lighter siblings to survive the first year.

Clutton-Brock observes that relatives and unrelated adults work equally hard tending a pup, so he looks for more than kinship to explain cooperative breeding. It might arise when benefits of large groups are high and costs of cooperation are low, he speculates.

In only a small minority of mammals--including mole rats (SN: 12/2/00, p. 356), African wild dogs, and marmosets--do most of the adults in a group raise the young of just a few.

"People tend to think of meerkats as ground squirrels," Clutton-Brock says. "They're more like wild dogs."