Sunday, March 18, was a great day at the San Diego Zoo’s Panda Trek, with three copulations achieved between panda adults Bai Yun and Gao Gao (see post Sunday: Persistence Pays Off). Despite the rain and wind, our bears had been paired five times.Toward the end of the day, however, Bai Yun had shown reluctance to drop her shoulders to the ground into the posture we call lordosis, and this made things more difficult for Gao Gao. It is an absolute necessity for her to get low so that Gao Gao has the access he needs to ensure a copulation.
On Monday morning, March 19, we assessed Bai Yun at first light to determine if there was a possibility of pairing them again that day. All of her behavioral signals still looked good: she bleated frequently, gave us a ready tail-up when touched, and walked backward toward us. When we put her out into the exhibit to assess Gao Gao’s response to her across the howdy gate, her behavior remained strong, and she began chirping at him.
An interesting side note: Bai Yun reserved her chirp for her mate this year. She was almost never heard emitting this vocalization outside of his presence. Our past research has demonstrated that males can ascertain a female’s breeding readiness from the structural content of that chirp, and it seems Bai Yun wasn’t wasting her efforts on chirping at any of us! It’s as if she knew that only Gao Gao could decipher the message.
For his part, Gao Gao was in fine shape. We might have expected him to be a bit sore and slow on Monday, given his high level of physical exertion the day before. Certainly that had been the case in recent years. This time around, he seemed to suffer no ill effects. He was at the gate right away that morning, and although he wasn’t initially showing signs of high motivation to pair with Bai Yun, he was nonetheless interested in checking her out. He stood at the gate in the rain and mud and watched, sniffed, and vocalized.
After a half hour of assessment, Gao Gao decided she was still ripe for his attention. With rain buffeting us, we opened the howdy gate. The bears moved toward each other right away. In a few minutes time, the two were tucked inside the passageway between the two exhibits, attempting to achieve the correct position for mating.
We’ve always been quite lucky in San Diego, at least since Gao Gao arrived. While pandas can take quite some time to achieve the mating position in a manner that allows copulation, our pair has typically been very efficient. We have never had to wait more than a few minutes, perhaps half an hour, before they succeeded. Having watched mating introductions in Wolong, I know that it isn’t always so easy. Sometimes staff observes for an hour or more before a mating is accomplished, particularly if the breeding pair involves one or more inexperienced animals.
On Monday, I felt like I was back in Wolong. As each attempt to achieve the correct posture failed, Gao Gao would push and pull and nibble on Bai Yun, coaxing her into shifting a little to allow him a different angle to work with. However, on this muddy, wet day, Bai Yun seemed very reluctant to leave her sheltered spot in the passageway. Not only was she out of the rain there, but she was also on a cement pad, out of the mud! Could this possibly make a difference for a panda? She is a bear, after all! In the wild, pandas mate in snow and rain and mud and all kinds of conditions. But Bai Yun has apparently become something of a princess during her time in San Diego. She seemed reluctant to give herself over to getting that dirty and wet. Unbelievable.
We watched as the minutes ticked by: 30, 45, 60 minutes passed. Gao Gao was getting a little tired from his efforts. He’d pause briefly to sit beside her, panting heavily. But after a breather, he returned to his duties, trying to force her to move her body so that he could gain access. As time wore on, she seemed to be tiring, too, and she moved into the low, lordosis posture less frequently.
After about an hour and 15 minutes, we decided to try to reset the bears and get them out of the tunnel passageway. If we could get them back to Bai Yun’s exhibit area, then perhaps they could find the slope that had facilitated their copulations in the past; with Bai Yun head-down on the slope, Gao Gao seems to have better access. So we called them apart, closed the howdy, and let them line up once again. They weren’t ready to quit and were anxious for us to reopen the door.
After about 15 minutes apart, we gave them access again. Unfortunately, Bai Yun moved straight for the passageway. Once again, she parked herself on that cement pad and refused to budge. Gao Gao worked hard to get the job done, but Bai Yun was no longer getting into lordosis, and she wouldn’t allow him to drive her out of her sheltered spot. Finally, after a cumulative effort of about two hours, Gao Gao gave up.
He walked away. But she followed. She turned her backside to him and chirped away. He walked away again. And she followed. She was not ready to give up, apparently. But neither was she willing to drop her shoulders for him. And Gao Gao was tired. He finally let her know he wanted to be left alone. At that point, staff intervened, and we separated the two into their respective enclosures. The howdy gate was closed between them, most likely for the last time.
Although we would have liked to see another breeding on that day, we were pretty happy to have accomplished three copulations during this breeding season. As Bai Yun’s estrus behavior waned throughout the week, life returned to normal at Panda Trek. And now, our focus shifts to what lies ahead. I know you’ll be with us on the journey toward the possibility of a new panda cub in San Diego.
Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research.