Love.
When bears are given the opportunity to chose their own mates, researchers reported in the journal Nature Communications, they were far more likely to copulate and produce a cub. Couples in which both members showed an interest in one another had an 80 percent chance of becoming parents. Even when only one partner showed outward signs of affection, the likelihood of reproductive success was pretty much 50-50.
But when neither animal was interested in the other, exactly zero babies were made.
The results probably won't come as a surprise to anyone who has ever been set up - or, you know, has a heartbeat. Attraction is a complicated, fickle thing, and it can't be boiled down to some zookeeper's judgment of genetic compatibility (the panda equivalent of your mom saying, "Nancy Shapiro's son is the nicest boy, and he's in medical school").
But apparently this is news in the bizarre world of panda breeding.
"Incorporating mate choice into conservation breeding programs could make a huge difference for the success of many endangered species breeding programs, increasing cost-effectiveness and overall success," Meghan Martin-Wintle, conservation biologist at the San Diego Zoo and a co-author on the study, told Reuters.
The study examined more than 40 pandas at a conservation center in China's Sichuan province. The bears were kept in open-air concrete enclosures with barred "howdy" windows and gates on either side, allowing them a peek at the bears adjacent. This enabled researchers to conduct dichotomous choice tests on each panda.
The bears were then monitored for signs that they were interested in their neighbors. For example, a female panda might signal her interest by sticking her tail in the air and walking backward toward the male. The dude might signal back by scraping his foot or performing a handstand against a vertical surface and urinating. All in all, there's a lot of bleating, chirping, rolling around and splashing of water, as well as some more R-rated behaviors that may be best left to the imagination.
During the females' short fertility period, the animals were paired up according to genetic recommendations from the panda species survival plan (these plans help direct captive animal breeding to preserve genetic diversity and a healthy population as a safeguard against extinction in the wild). Some bears got matched up with their preferred partners, others did not. Male bears were introduced to females' pens for anywhere from three to 75 minutes, then moved on to the next one whether or not they made it all the way, so to speak. Ultimately, each female panda saw an average of four suitors, though some had as many as nine. And after the nightmare speed dating session was over, every female was artificially inseminated as a fail-safe - the researchers would sort out the mess of paternity questions later using DNA tests.
During the mating sessions, female bears were roughly twice as likely to successfully copulate with their preferred partners. Surprisingly - dudes are generally seen as faithless philanderers in the animal world - the same was true for male pandas. They were also 100 percent more successful if they were courting a female they'd previously had cubs with.
At the end of the three-to-five month gestation period, only panda couples in which at least one member liked the other were able to produce a baby. If both members of the pair preferred one another, their chances of parenthood shot up to 80 percent. Larger, older males were more likely to produce offspring, but that may be a side effect of the fact that they were more attractive and likely knew what they were doing (unlike hapless Tian Tian). And moms that had been raised by their own parents, rather than zookeepers, were more likely to rear their own cubs.
The success of panda breeding programs is crucial because China is working to release some giant pandas back into the wild. Fewer than 2,000 of the black and white bears exist outside of conservation centers and zoos, according to the World Wildlife Fund, but they're needed for their role in their ecosystem, mostly spreading seeds and boosting vegetation growth. And, conservation scientists argue, pandas belong in the wild (for one thing, wild pandas are a lot better at procreating than their captive counterparts).
But life is risky for a captive panda brought back into the wilderness - last year, the only panda successfully released by China fell ill and died after just a month on her own. The program's first participant, Xiang Xiang, was reintroduced to much fanfare in 2006 but was found beaten to death by a wild panda one year later. Three other reintroduced pandas seem to be doing well.
In order to keep up the reintroduction program, and keep the population of captive pandas large and diverse, zookeepers need to make sure that pandas reproduce as often and as successfully as possible.
Co-author Ronald Swaisgood, also of the San Diego Zoo in California, said that the findings from the study can help breeding programs pursue that goal.
"The pay-off will be higher reproductive rates and more baby pandas," he told the New Scientist. "When a zoo is struggling to get its pandas to breed, it might be possible to switch out one of the pairs to see if a behaviorally compatible pair can be found."
