LANZHOU, May 4 (Xinhua) -- Infrared cameras in a nature reserve located in northwest China's Gansu Province captured nearly 30 images of leopards from January to the end of April.

Researchers from Longdong University recently collected videos and photos caught by 30 infrared cameras they set up at the Ziwuling nature reserve.

"Based on the size, hair color and patterns of leopards in these images, we conclude that there are about 10 leopards roaming in an area of 120 kilometers in the reserve," said Zhou Tianlin, head of the college of life science and technology of Longdong University.

Two adult leopards were caught walking together, which is quite rare as the big cat usually walks alone, he added.

Leopards are under China's highest national-level protection and are listed as vulnerable on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.

"The images show that there might be a leopard population in the reserve that is on the rise thanks to an improving ecological environment after years of efforts," Zhou said.