It is now virtually certain that Tian Tian,
the female giant panda at Edinburgh Zoo, is no longer pregnant.
Following artificial insemination in April,
the zoo has been tracking Tian Tian’s hormone levels. The one to watch is
progesterone. At around the time of ovulation, there is a small rise, with
levels remaining roughly constant for several months. At this stage, the embryo
is fertilized but is not developing. Then, some 60 to 100 days later,
progesterone levels jump again from around 250 ng to 2500 ng (per gram of
faeces) and the embryo begins to divide. In a
press release, tantalizing entitled “Panda update: definitely maybe!”, Edinburgh
Zoo told us that this second rise occurred on 15 July.
According to the
latest study of pandas whose pregnancies went to term, a female will give
birth, on average, 38.8 days later. There is a large variation though, with the
swiftest female giving birth just 26 days after the jump in progesterone and the
slowest female 55 days after. If Tian Tian were on the pacey side, she’d have dropped a
month ago on 10 August. Even if she were more ponderous, she’d have given
birth by now. She has not.
On Friday, Edinburgh Zoo’s chief executive
issued a blog post that talked of “a flurry
of new births” but made no mention – not even in passing – of Tian Tian’s
pregnancy. Today, after much badgering, the zoo finally issued a brief update, saying that “we’re not out of
the game.” It goes on:
We are continually analysing hormone
and protein samples and, based on the latest results, our external experts now
believe Tian Tian may have experienced her secondary progesterone spike two
weeks later than the results previously available suggested.
I’m a journalist not a panda biologist,
but looking at the graphs of what progesterone does in a pregnant panda, it is
somewhat baffling that the zoo could have mis-identified such a massive change
in progesterone. They do say that “Tian Tian is a panda whose behaviour and
physiology appears to be more complicated than most!”
I suppose it’s possible
that she’s still pregnant. Or, more likely I’m afraid, she’s not.