By Sandi Doughton,The Seattle Times

SEATTLE – Some of Rich Osborne’s killer-whale pictures aren’t suitable for children. But among adults, the director of the Whale Museum in the town of Friday Harbor in Washington state sometimes brings out the censored shots: Young males engaging in what might be described as a ribald form of fencing.

“We try not to impose values on these things,” said Osborne, who has studied orcas for three decades. “But it looks pretty homosexual.”

From whales to buffalo to Caspian terns, an abundance of animals exhibit behavior that in humans would be called gay.

In his book “Biological Exuberance: Animal Homosexuality and Natural Diversity,” Seattle biologist Bruce Bagemihl estimates 450 species display some form of homosexuality, which can include same-sex courtship, displays of affection, sexual activity, long-term pairings and parenting.

• Up to 15 percent of Western gull pairs are females. The birds woo each other with gifts of food and form bonds that last for years. They build joint nests and tend clutches of unfertilized eggs. Occasionally, one or both females will mate with males, but they always raise their young together.

• In some penguin species, males form lifelong same-sex partnerships – especially in captivity. A pair named Roy and Silo in New York’s Central Park Zoo incubated rocks until keepers gave them an egg of their own.

• Male giraffes spend most of their time in bachelor groups, where they entwine necks and rub against each other for up to an hour at a time. These “necking” sessions often culminate in mounting, and can outnumber heterosexual encounters 9 to 1.

It’s rare for animals to be exclusively homosexual, Bagemihl said, but bisexuality is common. While male orcas seem to relish their same-sex romps, they mate with females, too. Virtually all bonobos, or pygmy apes, are bisexual.

None of this is surprising to field biologists, but many omit or gloss over homosexual behavior in their scientific reports. Others have tried to explain it away as a form of aggression or confusion.

In species like bonobos, same-sex behavior seems to help cement relationships and defuse conflict, said University of California biologist Marlene Zuk, author of “Sexual Selections: What We Can and Can’t Learn About Sex From Animals.”

Though it’s tricky to impute motives to animals, the fact that homosexuality is so widespread shows it is not unnatural or biologically aberrant, she said. “But I’m leery of trying to use animals for models of our own behavior.”

If the animal stories hold any lesson for human societies, Bagemihl said, it could lie in the dazzling variety of sexual behavior nature offers.

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