After their arrival at the San Diego Zoo, Bai Yun and Shi Shi settled into their separate exhibit areas, and the crowds of adoring visitors flocked to see them. The panda team researchers and keepers were watching Bai Yun closely for signs that she might be interested in breeding, and in the spring of 1997, they saw what they had been looking for. The team carefully planned out an introduction for her and Shi Shi, hoping to see mating behavior. In the wild, giant pandas are largely solitary, and males and females only find each other for breeding, and the Zoo panda team was copying this pattern.

Bai Yun was let into Shi Shi’s area, and she approached him. Things seemed okay at first, but when she got closer, he began giving her “back off” vocalizations. If she persisted, he swiped and bit at her. The encounter was not turning out as everyone had hoped. Bai Yun was eager to mate and did her best to get Shi Shi’s attention (left), but to no avail (above).

As it turned out, even upon subsequent tries, Shi Shi would not respond to her advances—in fact, he was aggressive with her. It was determined that he was actually quite a bit older than originally thought, and apparently reproducing was not on his agenda. This was a conundrum that the researchers now had to address: if Shi Shi would not breed naturally, was artificial insemination possible with giant pandas? Reproductive physiologists at the Center for Reproduction of Endangered Species (CRES) went to work to find out.