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ANIMALS

Divorce, Sea-Gull Style : Sometimes Two Birds Just Can't See Eye to Eye Over Brooding Privileges

February 22, 1987|WILLIAM JORDAN | William Jordan is a Long Beach-based science writer.

Most of the year, sea gulls use a system of male dominance. But when they pair off to mate, they switch over to an entirely different one in which they work out differences not on the basis of size or strength but on the basis of wants and needs. Rather than resort to aggression, they resolve their conflicts through communication: The gulls' choking is actually a ritualized display that showed, after three bouts, that the female would not be denied. Judith Hand terms it "egalitarian behavior." In contrast to pure dominance, in which the dominant individual wins 100% of the time, with egalitarian relationships each of the participants wins roughly 50% of the time. This is true for the two gulls. Choking works both ways, and there are times when the male "persuades" the female to relinquish the eggs so he too can get his share of the pleasure.

There is an intriguing aside to egalitarianism among the gulls, however, and it has to do with what can only be called divorce. Many gull species are described as monogamous; they're supposed to mate for life. So much for descriptions. It turns out that, depending on the species and the location, more than 25% of young, newly paired gulls split up after their first attempt at raising a family. These broken marriages often result from excessive squabbling. Enough energy is wasted on disagreements that it interferes with the purpose of mating in the first place, and the pair does not succeed in fledging their chicks. But life goes on, and the next year the divorcees show up with new mates, fully intent on giving it another go. And this time they often succeed. It probably comes down to temperament. "Both gulls," Hand says, "can have a high drive to incubate the eggs--say that each wants to do it 70% of the time--and in pairs like that it's probably not going to work. What you need is someone to complement your drives. If you want to incubate 70% of the time, then you'll probably get along pretty well with someone who wants to do it 30% of the time."

It's nice to know, though, that not everything is confrontational on the home front. It is now 4 1/2 hours later, and the female gull is still incubating. But it is no longer the pleasure it was at first. A normal sitting lasts about three hours, and she has already had to leave the nest briefly to relieve herself. Hunger is also making demands--and why doesn't the male get his brood patch back here so she can leave?

Finally, an obstreperous landing call blasts out overhead-- he has arrived--and this time there is no dawdling around with tufts of grass and emotional displays. The male, sassy and content after 4 1/2 hours of R&R, wants nothing more than custody of the eggs. The female, hungry and frustrated after being forced to sit for an extra hour and a half, craves relief from domestic bondage. She gets up immediately and relinquishes the nest. Without pause, he walks over and prepares to settle down. For some reason, Oscar Wilde comes to mind: "If two people get along perfectly, one of them is . . . unnecessary." The male, whose eyes are closing in ecstasy as he sits on the warm, round eggs, would agree--for the next three hours. The female, who is flying off hungrily in search of food, would not.

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