"In the northeast, it is really cold in winter and snow can sometimes reach to our knees," An said. "However, it can make it easier to see the tracks of wild animals, including their feces and footprints."

After retirement from the military in 2005, An returned to his hometown and became a ranger.

"At the beginning, it was difficult for me to distinguish the different feces of animals," he said. "Every year, the bureau held training courses for us, and we have learned a lot from the forestry experts."

Years of field work have brought abundant practical experience. "Taking Siberian tigers as an example, their feces always contain the hair of their prey," he said.

The Northeast China Tiger and Leopard National Park, which spans an area of over 1.4 million hectares in Jilin and Heilongjiang provinces, is the most important habitat and breeding area for wild Siberian tigers and Amur leopards in China.

The latest data from the park shows that there are more than 50 of the tigers and about 60 of the leopards, including more than 17 cubs, in the park.

The survival rate of Siberian tiger cubs has increased from 33 percent before the establishment of the park in 2016 to the current 50 percent.