Monday was an exciting day for North American zoos holding giant pandas! We are thrilled for our colleagues at Zoo Atlanta, who welcomed not one but two panda cubs as their hero mother Lun Lun gave birth. As a twin birth had not been witnessed in the US in a while, this occasion is especially momentous. We have our fingers crossed that things continue to go well for the Atlanta bears and staff in the next few critical days.
Twinning in giant pandas is an issue of interest to us, because although females give birth to twins nearly as often as they have singletons, the giant panda mother appears unable to successfully care for two cubs simultaneously (see Pandas: Are Two Better Than One?). While there are a few anecdotal accounts of finding panda twins of significant age in the wild, in most cases these reports are not well substantiated. A female in a Japanese zoo several years ago successfully reared twins, but she was the fortunate beneficiary of a lot of support from the zoo staff. Keepers hand-fed her at times or took her cubs to an incubator from time to time to allow her to rest. While her case offers a glimpse into the possibilities for twin rearing in panda mothers, it is not comparable to the solitary effort required by a free-ranging wild panda mother.
Panda mothers in Chinese breeding centers have allowed us to watch a variety of their responses to a twin birth. Many mothers initially do try to care for both cubs, cradling and grooming their twins for a few hours or days before ultimately giving up and rearing only one. Some females don’t put any effort into caring for both cubs and instead focus on one from the very start. It would be interesting to follow those mothers through multiple years to see if their strategy changes with each twin birth or if you can predict that a female who has attempted to rear twins once will do so again in the future. As of this writing, I do not know the answer to that question. What we can say is that at some point, a mother of twins has to make a choice about which cub she will care for and which will be abandoned to its fate.
The San Diego Zoo’s Giant Panda Conservation Unit has invested considerable time in trying to understand what factors play a role in determining which twin cub a panda mother selects for nurturing. Is it the birth order that matters most? Or do mothers choose larger, more robust cubs? Perhaps they prefer a specific gender of cub? Is the mother’s decision influenced by whether or not she is a first-time mom? Our work is using data compiled from Chinese breeding centers and twin births around the globe throughout the known history of giant pandas in captivity. Soon we will be able to answer several of these questions.
Our Chinese counterparts have demonstrated repeatedly that with twin swapping and good nutrition, a rejected panda twin is not necessarily fated to die but instead can embark on a healthy, productive life. We know that Lun Lun’s offspring will be offered great care, whether from mother bear’s embrace or from their well-trained staff while in an incubator. With a little luck, we may all get to watch a charming pair of panda cubs grow up right here in North America—and that would indeed be a milestone for our panda population.
Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Xiao Liwu: Meeting those Milestones. Watch our pandas daily on Panda Cam.