Weird isn’t it, but we still don’t know how many giant pandas there are.

So it’s time for another census of this curious beast. The final figure, when it comes in a few years time, is really rather important. For it’s this estimate that will inform where the giant panda sits on the IUCN’s Red List of Threatened Species and this matters to a lot of very influential people.

Last week, for example, Chinese Premier Wen Jiabao (the most powerful man on earth?) confirmed the imminent arrival of giant pandas to Edinburgh Zoo, trading on the pull that their Red List status has on our emotions. Although (as I argued in a brief discussion with Jon Snow on Channel 4 News) this kind of panda politics may not be as effective as it once was, the panda is still a more appealing ambassador for modern China than the wooden-miened Wen (and he knows it).

But what if it wasn’t really endangered?

At the last count, completed in 2001, China’s State Forestry Administration arrived at the figure of 1596 adult pandas, curiously specific when you consider this was reached by counting poo. Don’t get me wrong; since it’s virtually impossible to see the pandas themselves, it is eminently sensible to look for another way of counting them and poo is the perfect proxy: the bamboo-munching bear gets through so much of this prolific but nutritionally poor plant that its dung lies everywhere and, unlike the animal, its excrement doesn’t run away long before you reach it.

But it doesn’t take a genius to spot the drawback of using faeces to estimate the population size of pandas. You see one poo, then another, but how do you know whether they came from the same panda? It would be completely stupid to assume that one poo equals one panda – you’d end up with a rosy figure in the tens of thousands. At the other equally ridiculous extreme, would be the idea that all faecal chunks of mulched bamboo must come from one rather incontinent animal. Obviously, the reality lies somewhere in between, but where?

Between 1974 and 1977, when China carried out its first “national survey” of its “national treasure”, some 3000 people were sent into the countryside to tot up sightings and spoor. The search for pandas was divided between the three provinces with pandas – Sichuan, Gansu and Shaanxi – and further broken down within each province to the county level.

What happened next is hard to believe. With each county keen to boast more pandas than the next, it seemed as though the panda population was incredibly healthy. In Sichuan, for example, the sum of all county-level counts came to around 4000 animals. At the same time, however, China wanted to the international community to get behind panda conservation so told the world there were only 800 left in the province.

When conservationist John MacKinnon arrived in China in 1987 as chief scientific advisor to the Worldwide Fund for Nature, he confronted forestry officials with this bizarre discrepancy. “All the numbers were politically decided and not scientifically decided,” he told me over lunch in a quiet Beijing restaurant in March 2010. “They were surprised that I was so naive as to imagine the numbers should add up.” With 150-200 for Shaanxi and a further 100 for Gansu, the first national survey came up with an official estimate of 1050 to 1100 pandas. Period.

The second census, conducted between 1985 and 1988 with WWF’s input, took a more scientific approach, a small and stable team of 35 people moving methodically from one county to the next. Their mission was to work out the distribution of pandas, estimate numbers but also to collect data on the forest, the bamboo and the people. The figure they came up with was 1,120 plus or minus 240. A straight comparison from the first to the second survey would suggest that panda numbers were going up, whereas everything indicated the opposite. “The range had shrunk and the bamboo area had shrunk and the number of bamboo patches had shrunk,” says MacKinnon. The two censuses were so different that comparing them is meaningless, but at least the second survey had set a figure that would be used to gauge conservation success over the coming decades.

Or had it? In the third national survey, carried out between 1998 and 2001, the methodology changed again, this time with a dedicated focus on panda poop. Data collected by the Chinese panda expert Hu Jinchu (presented in a paper published in 1987) suggested that the size of faecal deposit and the length of the bamboo fragments it contained could help distinguish between the poo from a cub, juvenile, adult or senile panda. So measuring the length of bamboo bits inside panda droppings could indicate whether several piles of faeces lying nearby had come from just one or more pandas. With this unsavoury methodological twist, the survey team dissected some 3,800 scats into that strangely precise figure of 1,596 pandas.

This is, at best, a very rough estimate. If you’re in any doubt about this, just look at a paper published in Current Biology in 2006 and the controversy it whipped up. The authors explored the possibility of improving on the existing size-and-content-method of working out which panda laid which turd. Surely, a DNA profile from each scat would be both cleaner to obtain and yield cleaner results? When they did this in the Wanglang Reserve in Sichuan, they found DNA from 66 different pandas, more than double the 27 adults that appeared to be resident in the third survey conducted just five years earlier.

They reached a bold conclusion: “if similar disparities between traditional and molecular census estimates are found for the other key giant panda reserves…it seems likely that many more individuals are extant in the wild than estimated in the Third National Survey,” they wrote. Just to ram home the implications of these results, they added that “there may be as many as 2,500–3,000 giant pandas in the wild.” That is almost double the 2001 estimate of 1596!

Not everyone appreciated this suggestion. In a response published in the bear journal Ursus (a PDF of which is archived here), several experts acknowledged that extending the bite-size method “to separate individuals was probably beyond the rigor of the technique” but questioned whether the DNA-based approach “was necessarily more accurate”.

They had two main problems. One was that the Wanglang faeces had been collected over the course of a year, so represented “the cumulative total of pandas that ventured into and defecated in the reserve, even if they only resided there for a few weeks.” Pandas, they presumed, had been coming and going with gay abandon, resulting in an exaggerated figure. DNA profiling is also not error-free, they pointed out, and “Genotyping errors may be another source of population overestimation.”

But, as with just about everything to do with pandas, this was about more than just numbers: “Over-estimation of panda numbers would not just be an academic error,” acknowledged the Ursus authors. For the population size is crucial in deciding how threatened the panda actually is. According to the Red List entry for Ailuropoda melanoleuca, the giant panda qualifies as “Endangered” because it meets the criterion C2a(i) in the 2001 Categories & Criteria (version 3.1). Put succinctly, the panda population is estimated at “fewer than 2500 mature individuals”, is experiencing “a continuing decline…in numbers of mature individuals” and “no subpopulation [is] estimated to contain more than 250 mature individuals”. If the extrapolation to 2,500-3,000 individuals were correct, the giant panda would have to be downlisted from the high-profile position of “Endangered” to the far less worrisome status of “Vulnerable”.

Since two of the Ursus authors – David Garshelis and Wang Dajun – are both members of the IUCN Species Survival Commission Bear Specialist Group that assesses the panda’s Red List status, it is understandable that they should have picked up on the extrapolations made in the Current Biology paper:

“For a politically-sensitive, conservation flagship species such as this, where the success or failure of conservation initiatives is gauged largely by periodic assessments of total numbers, scientists should exercise great caution and critical analysis when producing population estimates.”

Which is why, at their latest assessment in 2008, Garshelis and Wang (and colleague Lu Zhi) ruled that the giant panda should still be considered “Endangered”. In their justification, they argued that “there seems to be little doubt that there are less than 2,500 mature giant pandas in the wild; additionally each population is believed to have less than 250 mature individuals. At least until recently there has been a general population decline, although there is hope that this has been reversed by general habitat improvements — nevertheless, this remains an uncertainty.”

So will the forthcoming “Fourth National Survey” clear up any of this uncertainty? It seems unlikely. The plan, according to a story released through China’s Xinhua news agency, is to use the molecular method to count pandas through their poo. This will almost certainly get us closer to the “true” number of wild pandas but this figure has little significance to conservationists without the means of comparing it to the 2001 estimate. This will only be possible if the survey team also collects old-school data on bite size, a point stressed by the authors of the Ursus paper. Only then would we be able to get a feeling for the direction in which the panda population is going and the success or failure of conservation measures implemented over the last few decades.

As there are plenty of scientists involved in carrying out the forthcoming census, we can be pretty confident that everything will be done to facilitate this comparison. Still, it’ll be really interesting to see what happens if the evidence suggests the giant panda should no longer be classified as “Endangered”. Call me cynical, but with such vague baseline data and so many influential folk keen to keep the world’s attention on the panda (modern China and the Worldwide Fund for Nature for starters), there will be plenty of pressure to keep things just as they are.

Additional note (added 2 August 2011): In the “supplemental experimental procedures” of the Current Biology paper, the authors describe how they “sampled twice, first October – December 2003 (47 feces and one blood sample left on snow in Wanglang, 7 feces in Baima), and second, February – August 2004 (254 feces in Wanglang, 27 in Baima, 25 in Wujiao, 13 in Huanglong).” This tots up to a collecting period covering ten months, which is presumably why the Ursus authors reached the conclusion that “the fecal collection in Wanglang was conducted over nearly a year”. Mike Bruford (senior author on the Current Biology paper) informs me, however, “We collected samples from Wanglang in October-December 2003 and then broke for the winter, finishing in April. The samples collected in August were from Jiuzhaigou and Huanglong.” Collection in Wanglang was therefore either over three months (October to December) or six months (if they broke for the winter, returned to Wanglang in February and finished there in April).

Is the panda really endangered?
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