Tian Tian keeps zoo staff waiting

Last year we reported on the efforts of staff at Edinburgh Zoo to encourage mating between their two giant pandas. Tian Tian and Yang Guang were brought to Scotland in 2011, and if they successfully breed it will be the UK’s first giant panda birth. Unfortunately, on that occasion Tian Tian’s extremely brief fertile period passed without successful mating, and so zoo staff resorted to plan B.

Using sperm from both Yang Guang and another male panda called Bao Bao (a resident of Berlin Zoo until his death in August 2012), Tian Tian was artificially inseminated in April this year. Since then, experts have closely monitored her hormone levels and behaviour to try and determine whether the procedure was successful. With humans, it’s easy for a doctor to tell whether a woman is expecting a child, but confirming panda pregnancies is much trickier. For starters, pandas are prone to having phantom pregnancies, in which they indicate they are with cub despite no conception having taken place. Even when fertilisation does occur, pandas experience something called embryonic diapause, in which the embryo stays dormant for an indeterminate length of time before implanting itself in the uterus, making it difficult to predict exactly when birth will take place. Ultrasounds aren’t much help either, since baby pandas are very small and easy to miss. And it is even possible for the mother’s body to reject or reabsorb the foetus midway through gestation. All this makes panda breeding a very difficult process, full of false starts and dead ends.

In Tian Tian’s case, the most likely window for a birth has now passed, but experts aren’t giving up hope yet. After reexamining the evidence, they say it could be another fortnight before they can categorically rule out the possibility of a new arrival at the zoo. Meanwhile, other enclosures are having more success with their equivalent breeding programs, with a giant panda named Mei Xiang giving birth to a healthy female cub on August 23 at Smithsonian’s National Zoo in Washington D.C. A spokesman for the zoo described the birth as “joyous news”, and both mother and baby are said to be doing well.