Female Galápagos birds mate with dozens of males before choosing a partner

On the Galápagos Islands, female Nazca boobies are rewriting the rules of seabird romance. Over 74 days of observation, researchers documented something ornithologists rarely see: females openly mating with multiple males—sometimes as many as 16—before eventually settling on a breeding partner. And the males seem entirely unbothered by it.

This behavior upends what scientists thought they knew about seabirds. Swans, geese, and albatrosses are famous for their monogamous bonds, and researchers have long treated seabirds as the gold standard for studying pair-bonding in animals. But the Nazca boobies' "freewheeling" approach suggests that image was incomplete.

"You don't expect to see females just running back and forth trying to copulate with so many males," said David Anderson, a biologist at Wake Forest University who led the study, published in PLOS One. "That's a huge surprise."

The twist: genetic testing showed none of these casual encounters resulted in offspring. The females were essentially "shopping around," as Anderson describes it, but only their chosen breeding partner actually fathered chicks. Once a female began ovulating, her outside encounters stopped almost entirely.

This is only the second documented case of female birds exercising such complete reproductive control—the first being lek-mating birds, where males gather to compete for female attention through elaborate displays. For a seabird species, it's unprecedented.

So why do male Nazca boobies tolerate this behavior? The answer hinges on a simple power dynamic. In most bird species, males are larger and stronger, which lets them control female sexuality through intimidation. Male Nazca boobies are the opposite: they're noticeably smaller and weaker than females.

"The males are afraid of the females, and also won't risk alienating a female since there are so few of them," Anderson explained. With fewer females available, males can't afford to be territorial or aggressive. They accept the arrangement because they have little choice.

But one question remains unanswered: Why are females doing this at all if it doesn't lead to fertilized eggs? The researchers are still searching for the evolutionary advantage. It could be practice, genetic sampling, or something else entirely. For now, the Nazca boobies are keeping that secret.

The findings challenge the assumption that seabirds are models of monogamy—and suggest that animal behavior, even among species we thought we understood, still holds surprises.