If Mom chooses Dad, more ducklings survive.

A female mallard that gets to pick her guy has ducklings that survive infancy better than the offspring of a less happy coupling, according to a new test in Canada.

Pairing the female with her first choice, instead of with a reject, raised duckling survival by about a third, reports Cynthia K. Bluhm of the Delta Waterfowl Research Station in Portage la Prairie, Manitoba. She and Patricia A. Gowaty of the University of Georgia in Athens presented their results at the annual meeting of the Animal Behavior Society this week in Lewisburg, Pa.

What advantages come from a female choosing her mate "is a very basic question that we don't know the answer to," Gowaty says. She and an international consortium of collaborators funded by the National Science Foundation are striving to answer that question for fruit flies, guppies, mice, and cockroaches, as well as mallards.

Though Charles Darwin argued that female choice wielded great power in evolution, "nobody believed him for about 100 years," Gowaty explains. Even when researchers started testing the idea, she notes, their experiments focused on whether feminine fancy drove evolution of male fripperies such as the peacock's tail and whether such ornaments honestly identified males that would sire the healthiest young.

The new wave of female-choice experiments avoids any such assumptions about what constitutes irresistible hunkiness in another species and just lets females choose. These experiments should illuminate questions about how female choice helps shape an animal's social system, Gowaty predicts.

Mallards form pair bonds, but to human observers it's far from obvious why they bother, she says. The ducklings break out of their eggs essentially ready to swim to breakfast and hardly seem to need two parents. "The mothers build the nest, the mothers sit on the nest, the kids feed themselves, but the daddies hang around. We don't get it," says Gowaty.

Mallards also intrigued the researchers because a male often gives a female no choice in mating, even gouging her eye or snapping her leg in the struggle. "Mallard rapes are not nice," as Gowaty puts it.

Bluhm raised a colony of captive ducks from eggs she'd collected in the wild. She then showed each of about 70 females three different males. When females showed a clear tendency to hover near the enclosure of a particular male, Bluhm designated that fellow the preferred mate. She paired about half the females with their chosen drake and mated the rest with a rejected male.

"I didn't use any crummy drakes," Bluhm says. She also gave all the ducks what she calls "the spa treatment," protecting them from predators and keeping their eggs in an incubator.

"It was a very conservative experiment," Gowaty says. Seeing a greater duckling survival under such plush conditions suggests to her that the effects would be even more dramatic in the real world.

Why ducklings of preferred matings survived better "is a mystery," Bluhm says. Gowaty agrees. But she speculates that an aspect of compatibility, perhaps the mix of immune factors, plays a role.

John A. Byers of the University of Idaho in Moscow comments that the mallard study "comes closer than many people have to getting at the benefits of female choice." Byers, who studies how pronghorn antelope choose mates, calls for much more work on female choice in natural settings to complement the captive experiments.

"I think female choice is going to turn out to be really important," he says, "and it's going to have stronger effects than we expected."