Male giant panda Yang Yang mates yesterday with Su Shan at the Bifengxia base of the China Conservation and Research Center for the Giant Pandas in Ya’an City in southwest China's Sichuan Province. [Xinhua]

Two captive giant pandas at a breeding base in southwest China's Sichuan Province mated naturally yesterday.

A female panda named Su Shan and a male panda, Yang Yang, mated at the Ya'an base under the China Conservation and Research Center for the Giant Pandas yesterday morning.

So far, 15 out of 26 female pandas selected for this year's mating plan have finished mating, said Zhang Guiquan, director of the base.

Five-year-old Su Shan was initially supposed to mate with 10-year-old male panda Yi Bao. However, Su Shan and Yi Bao ignored each other while sharing a den and made noises indicating their rejection of the arranged pairing.

Zhang selected another male panda, Yang Yang, to replace Yi Bao, though 17-year-old Yang Yang is already considered old for the species.

"Male captive pandas capable of natural mating are extremely rare, accounting for less than five percent of the whole population," said Zhang. "So female pandas do not have much choice."

To help Su Shan become interested in Yang Yang, breeders played Yang Yang's sounds to her before they were placed together.

Breeders then used a pole to touch Su Shan's tail, stimulating her desire to mate. Soon, Su Shan and Yang Yang were congenial with each other and mated successfully.

Panda experts said Su Shan is very likely to get pregnant, but they will not know if she is for about two months.

There are only two or three days each year when they are likely to get pregnant, and their eggs only live for 36 to 40 hours, making conception even more difficult.

Panda experts have to find the "right" male panda within 36 hours. If they miss the window, even successful mating will not result in pregnancy. Because of this, experts often resort to artificial breeding, according to Zhang.