Edinburgh Zoo has tentatively announced that Tian Tian, its female giant panda, may be pregnant. This is exciting news, as the species is one of nature’s most endangered creatures and only a handful have been born in captivity. Wildlife experts say that there may be as few as 1600 giant pandas in their natural habitat, and a further 300 in zoos around the world, most of which are in China.
Edinburgh officials are not saying anything definite just yet, however, as the notoriously difficult-to-breed panda often shows ‘pseudo pregnancies’ in which the signs are similar but false. All the zoo will say is that they are "not ruling out that female panda Tian Tian may be pregnant,” and that it may be a few more weeks before there is any certainty about the happy event.
Nevertheless, the signs are highly promising. Tian Tian has begun nesting, and her protein and progesterone levels have changed significantly in the past few days, though it should be noted that neither of these indications is conclusive. Last year, she displayed similar signs despite not mating.
After two unsuccessful attempts to mate Tian Tian naturally with the zoo’s male, Yang Guang, she was artificially inseminated in April with a concoction of fresh and frozen sperm from Yang, topped up with a frozen sample taken from Bao Bao, a male who died last year at Berlin Zoo.
This practice is becoming increasingly common as giant pandas are extremely reluctant to mate in captivity, and they don’t seem to fare much better in the wild. The females have an extremely narrow window of opportunity to get pregnant each spring – no more than 36 hours – although males may show sexual interest for a few weeks beforehand, performing scent marking behaviour and recording hormonal changes. Once summer arrives, however, it’s all over for another year and the pandas have no further attraction for each other.
Sexual activity between giant pandas is also rather awkward and aggressive. The male uses his superior weight to pin down the female, using one paw to push her head towards the ground while the other raises her back end. All the while, the female attempts to bite and attack her mate – perhaps it is no wonder that mating doesn’t seem to rank too highly among pandas. In any event, the whole affair is usually over within one to two minutes.
As if this wasn't enough of a difficulty for would-be-breeders, giant pandas in captivity often require special training to get ready for the mating season. Yang Guang, for instance, was given exercises designed to strengthen his back legs.
Recent research, however, has suggested that the main obstacle to panda breeding – especially in captivity – is a failure to understand what prompts the male sexual response. Although the females are on heat for a very short time and are extremely picky about potential mates, two studies have indicated that it is the male behaviour which may be turning her off.
San Diego Zoo in California has found that male pandas are not great listeners, and that they often need repeated cues that a female is interested. As females come into heat they begin to make bleating noises to attract males, and they proudly display their anogenital region. Unfortunately, male giant pandas only respond to these rather obvious hints once the female is actually in heat, giving them a limited time to make the most of the female's advances.
A Chinese study has also found that males will react more assertively if there are other males around. In a test on 11 pandas in a breeding center, one group was exposed to dung and urine-soaked wood from other males, while a control group had only their own smells in each pen. The group which smelled rival pandas was much more determined to follow and sniff females in an adjacent pen than were the control pandas. Given the fighting and shows of dominance which occur in the wild at breeding time, this is perhaps not too surprising, and creating rivalries - even false ones - may offer a way that this dwindling species can be bred more successfully in the world's zoos.
A successful gestation lasts about five months, and twins are commonly born. A full-term pregnancy can vary greatly, however, as the fertilized egg can ‘float’ in the womb for several weeks before implanting. The reason for this curious behaviour is that births need to be timed precisely to coincide with the growth of fresh bamboo.
Pandas are as picky about what they eat as they are about other things, and although they have trouble digesting bamboo - their stomachs are more designed to eat meat - it makes up the vast majority of their diet. Unfortunately, logging and other human activities have encroached on China's bamboo forests and many pandas no longer have the resources to build shelters for their young or fill their bellies.
Many wildlife experts believe that the unusual reproductive cycle and narrow habitat of giant pandas leaves the species in a kind of "evolutionary cul-de-sac", doomed to extinction. They simply don't have the survival skills to cope with diminishing numbers. But If pandas are their own worst enemies, then humanity's progressive destruction of their living space surely runs a close second.
Now, however, there is a fresh belief that behavioral research and reproductive technology can encourage these astonishing creatures to keep on breeding for a few more generations. In the next few weeks, the talented team at Edinburgh Zoo will know whether Tian Tian has a part to play in the giant panda's ongoing struggle for survival.