Why the old alibi just won't fly for these unfaithful penguins - up front - infidelity may help breeding success

Emperor penguins are alone among colonial sea birds in their extreme and shameless infidelity. Oh sure, you could say they've got a ready excuse: they must choose a mate from a colony of tens of thousands of their kind by groping around for two weeks in the darkness and bitter winds of Antarctica's austral winter. Under such conditions, looking for a mate of seasons pas would seem downright featherbrained.

That alibi just won't fly, says Ann Bowles, a research associateat the Sea World Research Institute in San Diego and a graduate student at the Scripps Institution of Oceanography. She found that even when emperor penguins are allowed to choose their mates from among no more than 25 possibilities, they're still disloyal. What's more, the unfaithful enjoy greater success as parents.

Emperor penguins spend most of their time in the open ocean. Then, around April or May, at the start of the austral fall, they congregate on rookeries on the fast ice -- the ice between the open sea and terra firma. When winter comes, they range through the crowded colony, sounding their trumpet-like mating calls. Couples pair off, isolate themselves, and mate.

Two weeks later, the female lays her egg, shoves it across the ice toward the male, and makes for the open sea to look for fish and krill. The male balances the egg on top of his feet, keeping it warm with his giant roll of belly fat. He stands like this for 64 days, losing weight and waiting for his mate's return.

Finally she returns to the fast ice, with a crop full of chewed fish and krill to feed the chick that has hatched during her absence, and searches out the half-starved father, now shrunken by a third to a half in body weight. She takes over the baby-sitting for a few weeks while he trudges off to the ocean to eat. The parents switch back and forth like this, fattening the chick, until, four months after the birth, the fast ice breaks away from land and starts floating to sea.

Given this manner of chick rearing, fidelity would seem preferable for emperor penguins. After all, incubating an egg and raising a chick is a commitment that shouldn't be entrusted to a stranger, and the parent that goes out to seek food must be a reliable sort -- both the other parent's life and the chick's depend on it. Besides, says Bowles, the parents seem genuinely at- tached. They lie around on the ice after they mate, with their flippers wrapped possessively over each other, she says, and ''become distressed if they lose their partners.''

Based on these signs of affection and trust, scientists have long assumed that emperor penguins would be loyal to their mates if only they could find them. But after watching emperor penguins' mating patterns in the colony of fifty birds at Sea World in San Diego, Bowles decided that ''they may be actively selecting new partners.'' She found that about 30 per cent of the San Diego birds were faithful from season to season -- only a slightly higher percentage of faithfulness than in the wild.

Moreover, unlike other marine birds, emperor penguins that were disloyal had a better chance of raising their chicks to adulthood. Why? Bowles speculates that ''birds that have new partners are more motivated and involved in the breeding,'' particularly if they've had to fight for their mates, and therefore their eggs are more likely to hatch. In other marine bird species, mates who stick with each other from season to season have ''less overhead in terms of courtship and more breeding success,'' she says. ''But for the emperor penguins, there's obviously a good biologi-

cal reason for changing partners: novelty is exciting.''

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