Today marks a milestone for our fourth panda cub, Zhen Zhen: her weaning window has opened. A necessary step in the life of any young animal, weaning an infant from its mother involves an end to nutritional dependence on her. In the case of Zhen Zhen, as with many other species in general and with pandas in particular, this also means an end to extensive social contact with Mom as well.
We aren’t entirely sure how the weaning process proceeds in the wild. No one has been fortunate enough to track a mom with dependent young carefully enough to document the changes that occur at this dramatic time in a cub’s life. Even so, there are some things we know to be true about pandas that allow us to make educated guesses about how weaning is accomplished.
Here are some facts:
1) The inter-birth interval in wild pandas is typically two to three years.
2) A female entering the den to give birth does not bring her previous offspring with her. It doesn’t take a scientist to do the math in this equation!
We know panda moms gradually increase the time they are absent from their offspring throughout the period of mother-cub association. Starting from early in the denning period, she must leave her cub to forage on bamboo and find water. As the denning phase ends, the female moves her young into lairs and ultimately into the trees, where cubs are safe while Mom is gone for an entire day or more while feeding. In some cases we can imagine that Mom just walks away one day and never reunites with her cub…hence, weaning is accomplished.
Here is something new that we know: female subadults are very likely to be the bears to migrate out of their home range of birth and establish new ranges for themselves. Our work in Foping, China, has documented the case of a young female that moved about 12 miles (20 kilometers) away from her natal range to set up her new homestead. Thus, leaving Mom is quite a final prospect for some female pandas as they embark on their own lives. With that kind of distance between mother and offspring, a panda might be trying to ensure that she does not breed with any male sibling that might not have dispersed.
There are other things we know as well: young pandas have been seen in the trees at breeding sites, presumably watching from high as their mother engaged in mating with males during her estrus. Unfortunately, this is not a scenario we can allow in the zoo setting. Unlike the abundant space allotted to wild animals, a cub in a tree would be unable to escape an exuberant male that might misinterpret the presence of a youngster as a threat. For Zhen Zhen’s safety, we cannot take the chance that she would get hurt if she were hanging around her mother during breeding.
And so it is that we will follow what we believe to be the natural course of weaning as much as is possible in a managed-care environment. In a zoo setting, nature cannot be allowed to take its course, because there are hurdles to accomplishing these objectives that a wild panda does not encounter. If Bai Yun wanted to walk away, where would she go? If Zhen Zhen wanted to disperse, where would she go? There are walls around our bears that prevent them from acting on their natural weaning instincts. And so we must facilitate this process.
Today, we will begin the process by giving Bai Yun and Zhen Zhen access to both of the exhibits. They will spend about a week acclimating to both sides of the public area. The door between the exhibits will remain open so that they can move freely between the space they have been occupying for more than a year and the adjacent exhibit. Then, early next week, we will begin to close the door between them.
Our experience with weaning three previous cubs has taught us that a gradual, step-wise approach to separations is the best way to go. We anticipate very little stress from either bear in the early phases of this process. We first close the door between them for about six hours. After a few days, we lengthen that to about half a day. Our third step is to separate them for about 75 percent of the day, and finally, a total separation occurs. The whole process from acclimation to separation takes two to three weeks. We adjust our timeline based on the response we see from the bears and will lengthen or shorten each step as we deem appropriate.
“Bear” in mind that in the latter stages of the weaning process we are very likely to see some anxiety on the part of Zhen Zhen. This is common and normal. No baby likes to say goodbye to its mother, even if Mom is ready to move on. We will do for Zhen what we have learned can help alleviate such anxiety: provide her with lots of fun enrichment and extensive keeper-panda social interactions. These help to keep her in good humor. Additionally, once final separation is achieved, we will remove Zhen from the main viewing exhibits and take her to the classroom exhibit, so that her mother is not sitting on the other side of a door from her after weaning. This will help her to adjust more smoothly to the new life she will be embarking on.
Soon Zhen Zhen will be a solitary little panda, and we have no doubt that she will prove as robust and healthy as her siblings have been. Please feel free to come and see her over the next few weeks, as once weaning is accomplished she will be off exhibit for a while. I cannot give you any firm dates as to when this will happen, because we will be adjusting our schedule based on the bears’ response to the weaning process. In the meantime, you can witness an important transition in the life of any panda: the transition to independence.
I will update you throughout the process as we progress through the weaning protocol.
Suzanne Hall is a senior research technician at the San Diego Zoo. Read her previous post, Wider World for Sun Bear Cubs.