In case you haven’t noticed, humans are a little bit obsessed with pandas’ sex lives. Every year, mating season will inevitably bring forth, if not panda cubs, then at least cringe-inducing headlines littered with phrases like “care bears” and “caught in the act!”
To be fair, our collective obsession is well-intentioned, even if it is a little creepy: Pandas have the unfortunate luck of being both a threatened species and one that’s notoriously bad at sex. Frustrated zookeepers have even tried methods like pornography and Viagra to get the animals to mate, with limited success. Conservation biologists have generally blamed this on a combination of factors, including females’ extremely short fertile period (once a year for 24 to 72 hours), the stress of captivity, and even the possibility that they just don’t know how. But a study from March suggests that for all their efforts, the experts trying to make these panda couplings happen may have been overlooking one of the most fundamental parts of mating and attraction: personality.
Most scientists now accept that animals have distinct personalities, traits that endure over time and differ between individuals of a species. Researchers have found evidence of personality in practically every species they’ve examined, including sea anemones and insects. We also know, from studies and just from being humans in the world, that personality plays a huge role in whom we’re attracted to.
Which makes it somewhat surprising that this study, published in the journal Biological Conservation, is the first to examine personality compatibility and reproduction in any large mammal in captivity. Using a combination of behavioral tests and caretaker surveys, researchers developed personality profiles for 19 female and 10 male giant pandas, rating each one on a combination of traits reminiscent of the “Big Five” in humans, including aggressiveness, willingness to explore, excitability, fearfulness, and general activity.
The study authors then paired off the pandas based on personality, sometimes bringing together two animals that scored similarly on a given trait and sometimes adopting an “opposites attract approach,” testing each combination in males and females They found that some specific combinations had more sexual encounters and produced more cubs than others: Sometimes similarity enhanced mating success and sometimes it impeded it, depending on the trait.
“We are starting to realize some of these things that affect human mating and mate choice are at work in the animal world as well, and that’s opening our eyes to a lot of things,” says lead study author Meghan Martin-Wintle, the executive director of PDX Wildlife, an organization that works to improve breeding programs for threatened animals in captivity. (Although pandas and giant turtles have perhaps the worst reputations in that regard, mating in captivity is an issue for plenty of other species.) In addition to suggesting solutions, the study results provide insight not just to the role of personality in attraction, but also into the evolutionary origins of personality itself.
For the pandas, the traits that mattered most in terms of attraction were aggressiveness, excitability, and fearfulness, with each having a different effect on compatibility. Excitability appeared to be a case of opposites attracting: Highly excitable males and females each did well when paired with a more chill partner, mating about 90 percent of the time (more than twice the rate of similarly excitable pairs) and producing cubs just under 70 percent of the time. Couples in which both partners scored low on fearfulness had a similarly stellar success rate for sex. Fearful females and low-fear males were also a good match. A somewhat similar pattern emerged with aggression: High-scoring males and low-scoring females were the most successful match, followed closely by couples in which both the male and female scored high on aggression. Alas, fearful and low-aggression males didn’t have much luck with anyone.
The researchers used their results to develop a list of guidelines for matchmaking, including pairing highly aggressive males with less aggressive females, a suggestion that runs counter to the current standard operating procedure in most zoos. Traditionally, aggression “is one of those things that we actively try to avoid in mating in captivity,” Martin-Wintle says.
But couldn’t upping aggression in males harm the females by leading to forced sexual encounters? “No,” Martin-Wintle says. “Panda pensis are too small. Unless the female is cooperating, they can’t get in right position.” Female pandas have to physically back into the male in order to mate. (Martin-Wintle has seen female pandas reject males using a maneuver known as “pancaking,” or laying flat on the ground.)
That’s not to say females are the only ones shutting things down. “Both males and females can exercise rejection,” Martin-Wintle says. In fact, males are generally the limiting factor in captive panda mating situations. “Females are typically interested in most males,” she explains, whereas males “have to be motivated” to want sex. It makes sense when you consider what pandas do in their natural habitat: In the wild, males compete against one another for a female’s attention, and so must decide if it’s worth putting in the effort. This mutual veto power likely contributes to why panda sex is the rarity it is.
David Powell, the research director at the Saint Louis Zoo, says that he isn’t necessarily surprised by the results. “Even if you think about people, there are personalities that you bond with and personalities that you don’t,” says Powell, who helped pioneer the study of personality in animals in the 1990s. He also authored a 2008 study examining what personality traits were associated with higher reproductive success in pandas, although he did not look at compatibility.
For pandas, at least, it’s not totally clear why compatible personalities matter to the animals involved — once the mating is over, the male and female go their separate ways. Panda cubs are raised by single mothers. “What’s interesting about pandas is they aren’t selecting a mate that is going to help them and be a part of a stable family unit,” Powell explains. “If personality mating is robust in these solitary species it suggests that the animal is using it as an assay or proxy for something else.”
Although Martin-Wintle’s study may be the first to examine personality compatibility and reproduction in captive mammals, the phenomenon has been studied in species of monogamous birds, as well as in insects. For example, in a 2016 study involving water striders (an insect that skates on top of ponds), physical compatibility accounted for some couplings — large bugs were more likely to get with other large bugs — but it couldn’t explain all of them. Personality, measured by water striders’ activity level, also proved to play a significant role, lending weight to the old adage that looks aren’t everything. Male and female water striders generally mated with individuals of similar activity levels, but when personalities approached the more extreme ends of the spectrum, the pattern flipped: more active females mated with less active males, and vice versa.
Taken together, the research shows that “behavioral diversity is probably just as important as genetic diversity,” Martin-Wintle says. Zookeepers and biologists have traditionally paired animals based on their genes, using a vast genetic database to promote health and avoid hereditary problems. But “most of our conservation breeding programs are pretty unsuccessful,” she says. Taking into account how animals naturally pair off in the wild, including the effects of personality and attraction, “may improve our success for all endangered species.”
But while there has been some movement toward matching animals by personality in zoos, it is mostly ad-hoc. And there are still significant barriers to turning it into a widespread, rigorous practice, not least of which is the complexity and mysteriousness of personality itself.
“Personality is multidimensional. An aggressive male has other personality characteristics, so you kind of have to match the whole constellation of personality,” Powell says. “Just like when humans are choosing partners. It’s not one aspect of their personality that attracts you to someone, it’s kind of the whole picture.”
