To Breed or Not To Breed, part 1
Posted at 6:29 am May 11, 2006 by Suzanne HallSome of you have noticed that at some institutions in China, panda females often give birth yearly, rather than every other year (or less often) as our female Bai Yun has done. A few questions have arisen as to the natural state of the panda on this matter.
In the wild, pandas nurse their young for 18 months to two years. This long lactation period generally prevents the occurrence of an estrus the year after a cub is born, something we refer to as " lactational suppression of estrus." Lactation (aka, milk production) prohibits the hormones responsible for estrus and fertility from taking hold, thus preventing the female from being sexually receptive and getting pregnant again while her offspring are very young and dependant on milk. This means that wild panda females rearing young will not give birth every year.
Why would a panda need to avoid giving birth yearly? One of the driving factors for the spacing of births seems to be the development of the cub. If the young were to become separated from their mothers at six months of age, before they are able to sustain themselves on bamboo (many of their bamboo feeding teeth have yet to come in at that age), then they will not survive. Lactational suppression seems to function on a timescale that allows the cub to fully develop the teeth and the skill set necessary to support itself on bamboo before being weaned.
The fact that female pandas can get pregnant more often than every other year tells us something about their biology. It would make sense that in a year in which a female gave birth to a cub or cubs, but was not able to ensure their survival, she should be able to breed again soon. From an evolutionary perspective, if you aren't raising cubs, you should be working on creating some new ones. Wild animals are often brought into estrus upon the death of their dependant offspring: think of lions, for example. Females in the pride will begin cycling if a new male takes over the pride and kills their young. This ensures that each lioness is in a constant state of " getting her genes into the next generation." We have every reason to expect that this same logic applies to the panda.
In captivity, animals are exposed to many factors which have an impact on their well being and daily life. We provide them with highly nutritious food, veterinary care, and safety from predators, disease, and injury. Captive managers can also manipulate aspects of an animal's life to promote specialized breeding. Those of you who breed dogs or cats know this firsthand. In China, they also manipulate panda mothers by removing their offspring and thereby promoting a rapid cycling of breeding and birth.
Since the Chinese-born panda cubs are reared by human hands, they will survive their early weaning from their mother. From their mother's perspective, however, the cubs are gone, and her body then sets its sights on the next crop of baby pandas. Interestingly, not all females have been able to get pregnant yearly. It is very common for a first-time mother to be unable to get pregnant in the year following the birth of her first cubs. Why this is remains unclear; perhaps her body is still maturing and needs more time to develop a rhythm like older females have. Perhaps the first pregnancy is especially taxing and drains the female of nutritional reserves that require more time to replenish. In any case, many females take two years or more from the birth of their first to second litters, regardless of what human intervention occurs.
Hua Mei was one exception to that trend. Why was she capable of having cubs two years running right from the start? We cannot say. Perhaps she had a better nutritional start in life because she was mother reared for 18 months and was never given formula; this might allow her to avoid being completely nutritionally depleted between pregnancies. Or perhaps she just beat the odds. In any case, she will likely continue to breed each year that the Chinese allow her to, and her cubs will continue to be raised by the competent staff of the Wolong nursery.
Next week I'll discuss this further, anticipating some of the questions I will receive on this topic.
Suzanne Hall is the senior research laboratory technician for the San Diego Zoo's Office of Giant Panda Conservation.
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May 11th, 2006 at 8:02 am
Thank you, Suzanne. As always, you seem to have answered my question, all that you are saying makes a great deal of sense. But I sure hope they don't expect Hua Mei to repopulate the pandas all on her own
May 11th, 2006 at 9:01 am
Thank you Suzanne for this blog… I suppose I was one of those people that felt a bit upset and concerned, thinking that maybe Hua Mei was being treated like an incubator for babies. But really, I've come to the conclusion, thanks in part to your blogs, that the most important thing to remember is that everyone is trying to save these beautiful animals from extinction. That the only reason that Hua Mei is even alive is because of this. I'm happy that she is so successful in bringing healthy cubs into the world - and that one day those cubs will also breed… I feel better thinking that some day, these animals will be thriving in the wild, and that some day they won't be on the verge of being lost forever. Many, many thanks to everyone for saving these amazing creatures - I'm sure the world is a better place with them in it!
May 11th, 2006 at 11:51 am
Wow Suzanne, great information! This makes me feel so much better about Hua Mei. I still think it would be nice if she had a year off just to be a Panda though, and do what Pandas do - eat, sleep, play, eat, sleep, play - hee hee. But I understand the logic and the need.
Do you think little Su Lin is in for the same " adventure" ? After all, at this point in time, she and Mei are the only offspring of Gao Gao, correct? I would think his genes are important too, as he was born in the wild. Or have they tracked Gao's genes to other wild Pandas?
Anyways, thanks again for the wonderful insight and I'm looking forward to " Part 2" .
May 11th, 2006 at 4:42 pm
There seems to be a transition taking place with Su Lin and Bai Yun. Su has been coming down from the trees more, exploring and working with bamboo. It was so sweet to watch this afternoon (thank you camera person). She circled playfully around her mom, the way Mei Sheng used to. She knew enough to scamper out of Bai Yun's reach after nursing to avoid the dreaded bath, but was eventually caught and cleaned.
May 11th, 2006 at 7:41 pm
Thank you Suzanne for such a wonderful article !
May 12th, 2006 at 8:53 am
Thank you, Suzanne. I do understand the biological imperative that drives all creatures to push their genes into the next generation. And it is comforting to know that Hua Mei's body has the option, if overly stressed, to refuse to conceive. I guess sometimes you have to relax and let nature decide what is best.
May 12th, 2006 at 9:24 am
Very entertaining information. What kind of unusual behavior is she speaking of in relation to the girl pandas? We saw a clip from Wolong that had some crazy activities. Sliding down snowy hills, rolling around in the snow, flipping upside down, etc. Wish I hadn't lost the clip on the Tivo.
May 12th, 2006 at 10:22 am
Suzanne, thanks for another very interesting and informative blog. It would be interesting if Bai Yun were to have twins. Would the Panda Team then need to set up the newborn nursery as seen at Wolong, and rotate the cubs between Bai and an incubator? Do pandas have the first milk that is high in substances to promote immunity in the cubs, as humans do for their newborns? And when cubs are weaned early and put into a " kindergarten" , how do they develop all the skills they will need as adults? Do they learn certain skills from the short time that they observe their mothers? Or are these skills innate, and the cubs just need time to physically mature and will gain the skills by just plain practice? Is it possible that keepers can also help the cubs to learn behaviors that they might not have observed, as the pandas are trained for behaviors that help with medical care? Finally, I'm done with questions (for now–lol!)
May 12th, 2006 at 1:18 pm
Very interesting. I pretty much figured that, in wild, female would go back on estrus when she loses her cub. I hope Hua Mei's getting all the goodies and yummies in Wolong so that she can be healthy.
Because panda cubs are born so tiny, I have a feeling that nursing may be more burdensome to the mother than actually giving birth. And I understand that the nursing continues until the cub is weaned at 18 months - 2 years.
So, how long are pandas capable of reproducing? Bai Yun is 14 going on 15. How long is she capable of having babies? Is there any age record of panda birth in captivity?
May 12th, 2006 at 2:58 pm
Thanks for the fascinating information. I wondered why the " kindergarten class" was taken from their mothers before they were weaned and this entry explains some of it.
We are watching Mei Xiang at the NZP starting to wean Tai Shan. From a human perspective it seems rather harsh when she pushes him away and he settles for chewing on some bamboo. Tai is 10 months old now, so how long does this weaning process last typically?
s.
May 12th, 2006 at 3:10 pm
Hua Mei's body should be given a rest once in a while. Maybe let her raise her own cub to weaning sometime. Still sounds like a panda machine to me. Besides, why have so many babies if they can't all be released into the wild? There's not enough room for that. Maybe they need to slow down. They don't have to repopulate in 10 years (just a random #)
May 12th, 2006 at 3:25 pm
Can Bai Yun go inside her air conditioned bedroom during the afternoon? I have seen her hugging her outdoor water cooler at times.
May 13th, 2006 at 1:21 pm
Excuse me for posting again, but I just wanted to suggest putting out some small blocks of ice in the afternoon for Bai Yun and Su Lin. With Bai Yun nursing, she would probably appreciate it and it would be fun to watch Su Lin's reaction to it.
May 15th, 2006 at 9:03 am
Rita #12,
The temperature in the exhibits is monitored by the keepers. We have a protocol in place to respond to any high-heat situations. To cool the bears, we would turn on cool zone fans (like the NFL uses to cool players on the sidelines) or open up the air conditioned bedrooms.
I should mention that the temperature in San Diego over the last few weeks has been rather cool, as we are experiencing the " May Gray" cloud cover regularly. We have had a few glimpses of sunshine here and there but for the most part the weather has been highly favorable to the bears' comfort.
May 16th, 2006 at 9:58 am
I understand that the survival of the species is so important that accelerated breeding may be considered necessary in China, and that the pandas there are given excellent care, attention, and nutrition.
At the same time, I do wonder if there is any research on the long-term developmental effects of weaning the cubs at such a young age, and on the physical and perhaps psychological stress this may cause both the mothers and their cubs. How long are the young pandas given milk and formula after their weaning? Does the loss of their mother's milk, nearly a year before they would stop nursing in the wild, affect their overall levels of nutrition and growth (including brain development)? How are they affected in terms of learning how to be adult pandas and obtaining the skills they would learn in the wild?
I know the kindergarten group is intended to help the cubs develop their " panda" skills and provide stimulation, socialization and enrichment (and it's lovely) — but can it compensate for such an early disruption in the natural cycle of panda development?
Any input would be welcome, thank you so much.
May 17th, 2006 at 8:49 am
Suzanne , do you think there is a chance one day we might have one of Hua Mei's offspring
in San Diego? I would like to see if he is like his mother.
May 18th, 2006 at 3:30 pm
Hi Suzanne, here is another off-topic question. Are some of Bai Yun's attempts to bathe Su Lin in part her trying to get Su to practice play fighting, rather than always heading up a tree? They really had a wrestling match this afternoon.
May 30th, 2006 at 10:10 am
Hi Suzanne, here's another question. I was wondering whether mother giant pandas recognize their offspring after they have been weaned. So, if at some point in the future, Bai Yun were to come into contact with Hua Mei again, would there be any recognition between the two?