From the AP:
How do they know this? They took genetic profiles of poop. And it had to be fresh.
SHANGHAI, China - Scientists using DNA samples have doubled their estimates of the wild panda population in a nature sanctuary in China, a finding they say bodes well for the survival of the endangered species.
The researchers believe between 66 and 72 pandas are living in the Wanglang Nature Reserve — more than twice the previous estimate of 32, said Wei Fumin, a zoologist at the Chinese Academy of Sciences.
What a job.
[Study author Michael] Bruford said the field work, carried out by graduate student Zhan Xiangjiang, was arduous, not only due to the mountainous terrain but also because of the need to obtain fresh samples for DNA analysis.
"Once panda feces change from green to brown, we know we've had it," he said.