China's successful giant panda conservation efforts have seen the extinction risk of the species downgraded from endangered to vulnerable in 2016, with the population of giant pandas in the wild growing steadily from around 1,100 in the 1980s to nearly 1,900 as of last year.

Against that background, giant panda lovers around the world have cheered the growing tribe of China's national treasure.

However, an article in The New York Times earlier this month voiced some concerns. Citing comments made by experts in 2006 and 2010, it said the methods used by China to survey the wild panda population were "not ideal" and that "China keeps its methodology a secret".

Chinese experts have responded by noting that assessing the population of pandas in the wild is by no means easy, although various complex and reliable methods are employed to enhance the accuracy of the count.

Futhermore, there have been four giant panda censuses since the 1970s, with the most recent being completed in 2015 — a full five years after the 2010 comments were made by the sources cited by The New York Times.

"Population assessment is a challenge in wildlife conservation research, especially for forest dwelling animals like giant pandas, which are often difficult to directly observe and count, and can only be assessed through collecting relevant trace information," said Xu Weihua, vice-president of the Institute for National Parks.

The nation's protected area for giant panda habitats has expanded from 1.39 million hectares in the 1980s to 2.58 million hectares today.

The establishment of the Giant Panda National Park in 2021, spanning the provinces of Sichuan, Shaanxi and Gansu, ensures the protection of about 70 percent of the pandas' wild habitat. Thanks to careful monitoring, the number of giant pandas captured on camera and encountered in the wild has increased, according to the National Forestry and Grassland Administration.

In the third national giant panda survey, which began in 1999, and the fourth survey, which began in 2011, researchers set up survey lines every two square kilometers in key areas within the panda distribution range. In areas with fewer pandas, survey lines were set up every six sq km.

"This is high-intensity information gathering. Surveyors collected data on panda feces and bite marks, and used distance and bite mark differentiation methods for a comprehensive analysis to evaluate the population of giant pandas nationwide," Xu said, noting that both methods are scientifically validated and effective for conducting surveys on wild populations.

The term "bite marks" refers to the undigested bamboo stem fragments found in pandas' feces.

The distance differentiation method involves calculating the distance between panda trace points obtained during field surveys, such as feces, footprints and fur, to determine if they come from the same panda, thereby confirming the number of pandas in the area.

Regarding the counting method involved, Xu said: "Giant pandas are solitary animals, and except during mating and seasonal migration periods, their movement within a certain time frame is limited and stable. By determining the home range and dispersal ability of giant pandas, we can confirm whether trace points belong to the same panda. If the distance between two trace points exceeds the normal activity range of a giant panda, it is preliminarily determined that there is more than one panda in the area."

When the distance between two trace points falls within the potential activity range of a single panda, further identification using bite mark differentiation can be applied to enhance the accuracy of the census.

"Ninety-nine percent of a giant panda's diet consists of bamboo, which they cannot fully digest.... Due to variations in individual digestive capabilities, there can be significant differences in the average number of bite marks in feces," Xu said.

"By comparing characteristics like bite mark length, we can determine if the feces in an area was left by the same panda," he added.

In the article in The New York Times, some foreign experts proposed using infrared cameras and DNA analysis to assess the panda population.

However, Chinese experts have argued that due to the similar appearance of pandas, it is challenging to differentiate individual pandas by examining photos from infrared cameras. In addition, DNA analysis requires fresh panda feces, making it impractical for large-scale operations and unsuitable for reflecting the total panda population nationwide.

"The survey methods used by Chinese giant panda experts have a complete process flowchart and calculation method, and are currently the most reliable among existing methods," Xu said.

"We are also exploring new technologies for giant panda population assessment and individual identification. With advancements in technology, especially the application of artificial intelligence, big data and the emergence of new equipment, future panda surveys will be more efficient, and population assessments will be even more accurate," he added.

yandongjie@chinadaily.com.cn