Monitoring data show that Cao Cao, a 16-year-old giant panda raised in captivity, has mated with a male in the wild - a rare occurrence for the endangered species - according to a panda research center in Sichuan province.

Cao Cao was released in the Liziping Nature Reserve in early February in time for mating season from March to May.

In March, researchers reported seeing several males fight for the right to mate with her and began checking data sent by the GPS tag on her neck - which is fitted with a recording device - every five days.