Mating for life may seem romantic, but for some animals it could be deadly.

New research has revealed a surprising link among mammals living on reserves in Ghana: Those with fewer mates are at higher risk for extinction. The finding suggests that conservation efforts might be better focused on those more vulnerable animals that stick to one or a few mates.

It could also mean that monogamy, which is already rare in the wild kingdom, may be a fading trait.

"In avoiding extinction, it pays to be promiscuous," said Justin Brashares, a conservation biologist at the University of British Columbia in Vancouver, Canada, who published the study in the recent issue of the journal Conservation Biology.

Fate of the Faithful

Brashares analyzed the population levels of large mammals in six reserves in the savannas of Ghana, where rangers have kept careful records of animal populations for more than 30 years. In that time, 78 species became locally extinct, largely due to human factors including hunting and loss of habitat.

He found that most of the lost animals shared at least two traits — their populations were isolated and the males mated with one or just a small group of females.

Among the fated faithful were species of duiker, a small, monogamous antelope, which died out within 10 years after each reserve was established. Also doomed were many species of colobus monkeys, which stick to one or a small group of two or three mates.

Meanwhile, African buffalo, whose males preside over harems of about 15 females, are still thriving, as are green monkeys and baboons, which are highly polygamous.

"We often think of large-bodied animals as the ones that are most endangered," said Brashares. "But species like elephants and buffalo are doing better."

Brashares says his work points to the need to focus conservation efforts on animals that keep their sex lives simple.

"We barely have the resources to monitor just a few species, so I'm always looking for traits of species that can help direct our resources," he said.

It’s a Polygamous World

Extinction rates aside, monogamy is already a rare trait among animals.

Among the some 4,000 species of mammals, fewer than 3 percent are considered truly monogamous. The short list includes duikers, the colobus monkey, and the snuggle-loving prairie vole.

Wolves and African wild dogs are also monogamous, but mostly due to their unusual pack social structure in which only the alpha female and male mate.

And although some scientists reject comparisons between human and animal behavior, recent surveys suggest people also have trouble sticking with one partner.

About 40 percent of men and 30 percent of women in the United States acknowledge having had at least one extramarital affair, and more than 80 percent of human societies throughout the world practice some forms of polygamy, according to David Barash and Judith Eve Lipton, authors of The Myth of Monogamy.

"People have all the fingerprints of a mildly polygamous species," said Barash, a psychologist at the University of Washington in Seattle.

Scientists have recently discovered that even birds, which were once held up as widely monogamous creatures, appear to copulate on the sly with mates other than their social partners.

"We started using biochemical techniques to do paternity testing in birds and the results were flabbergasting," said David Westneat, a biology professor at George Mason University in Virginia. "Species that were socially monogamous sometimes have 10 to 55 percent of their offspring sired by someone else."

The discovery of pervasive promiscuity and Brashares' findings suggest there must be advantages — at least in the wild kingdom — to having several sexual partners.

Risks of Monogamy

Some explanations are clear: Male birds that furtively mate with other females can improve their chances at siring more offspring with little biological effort. And even though reproduction is often a costly endeavor for females, polygamy may offer them more chances at scoring superior sperm.

In the Ghana preserve, it's still uncertain how monogamy or even having fewer mates may make animals more vulnerable to extinction, but Brashares has some ideas.

It's known, for example, that hunters generally kill more males than females. This might lead to a shortage of available males for monogamous or small harem mating.

Animals living in large harems protected by one male may also be better able to spot nearby predators. Species like the colobus monkey that have one or a small number of mates tend to spend more time in isolation, leaving them more exposed to predators.

Still, Westneat points out that monogamy exists for a reason. Often monogamous animals are either parents to offspring that require a lot of attention to survive or they live in areas where food is scarce.

He suggests it may be these factors that are placing animals at risk — not their sexual lifestyles.

"There are a lot of factors associated with monogamy that could lead to a higher death rate," he said. "I'm not sure you can blame it all on monogamy."