panda pregnancy


News about Zhen Zhen


Zhen Zhen relaxes after her 3rd birthday festivities in 2010.

Back in February, we reported with excitement that panda Zhen Zhen had bred for the first time and was the first female at the Bi Feng Xia center in China to do so in 2013 (see post Panda Zhen Zhen). For newer panda fans, Zhen Zhen is Bai Yun and Gao Gao’s youngest daughter and moved to China in September 2010. Well, it is with some sadness that we share the latest news on Zhen Zhen: On May 6, Zhen Zhen gave birth to a single cub; however, the cub died soon after birth.

Of course, we know that Zhen Zhen, who will be six years old this August, will have many more opportunities to breed and have cubs in the future, and there is no reason to doubt that she will be successful down the road. An early May birth is very unusual for pandas, with most of the births being recorded between July and September, after a variable period of diapause and a 50-day period of gestation.

Megan Owen is a conservation program manager for the San Diego Zoo Institute for Conservation Research. Read her previous post, Our Pandas in China.


Panda Pregnancy Watch in Full Force

Bai Yun has been sequestered behind the scenes at Panda Trek for some time now in order to provide her the solitude and environment most conducive to a successful pregnancy and cub-rearing experience. Surely many of you are wondering: is Bai Yun showing any signs of pregnancy? Until about a week ago, the answer was “no.” During most of the time since breeding in spring, she has been her normal, hungry, and active self.

We have been tracking many behavioral and physiological parameters that could give us a clue as to her pregnancy status, one of which is her appetite for bamboo. A decline in bamboo feeding is one of the first reliable behavioral indicators that something is happening with Bai Yun. When we see that she has begun leaving the leafy greens behind at a meal, we know that we are about three to four weeks from a potential birthing window.

Guess what? She started falling of her bamboo feeding late last week.

But hold on. Bamboo feeding generally gives us a broad idea of a birthing window, but it does not actually tell us if she is pregnant. Pseudopregnant females also experience similar changes in feeding patterns. So while we might have a picture of when a birth might occur, we cannot say for sure that a cub is on the way.

Bai Yun has been sitting for regular ultrasounds and thermo-imaging procedures, and we are collecting urine for hormone assays as well. I can tell you that her hormone profile is in full swing, and the ultrasounds have shown some positive changes indicating the hormones are having the desired effect on Bai Yun’s uterus. But again, all of this is consistent with pseudopregnant females as well.

As a result of these changes, we have given her access to her birthing den. In it, she has begun building her nest with bits of bamboo. She occasionally takes short naps in the den. She is showing us more positive pregnancy—and pseudopregnancy—behavior.

And so we wait. The days ahead will be telling. If we are able to visualize a fetus via ultrasound, we will know this is a true pregnancy. Keep your fingers crossed!

Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, The Bears Thank You.


Bai Yun: Hero Mother

Bai Yun rubs fragrance on her face.

As you know, we have watched giant panda Bai Yun closely over the last few months to see how she progressed throughout this birthing season. This effort involved keepers recording daily information about changes to her eating habits, behavior, and physiology. It involved San Diego Zoo veterinarians, who performed several ultrasounds a week to document the changes in Bai Yun’s uterus. It involved our reproductive physiologists, who monitored her hormone changes and used thermal imaging to assess the heat profiles of her abdomen. And it involved behavior researchers assessing the daily check sheets and watching time-lapse video of her denning activities.

In the end, our Panda Team has come to the conclusion that Bai Yun will not be giving birth this year.

We did see some positive signs in July, when there was evidence of uterine changes via ultrasound, and Bai Yun slowed down and left large portions of her daily feed untouched. She started using the den and built a small nest. As time wore on, we were not able to visualize a fetus or fetal heartbeat, and this left us to wonder: Was there a fetus in there somewhere that we just weren’t able to capture on ultrasound? Or was there a pregnancy somehow thwarted before it even got going?

At this point, Bai Yun’s hormones have returned to baseline. Her uterus is declining from its swollen state. Her appetite is on the increase, and her time spent in the den has become minimal. She will obviously not be giving birth this year. And we will never really know why. Bai Yun is, after all, on the outside edge of the range of known breeding ages for female pandas. Perhaps she is done, for good, and is physiologically ready to experience “maternal retirement.” Or perhaps her body simply needed to take a year off. Either way, we are okay with that.

In the next few days, you can expect to see Bai Yun given more opportunities to roam the area as she chooses. For the moment, she hasn’t seemed to want to stretch her legs very much, but we know that will change soon. She will want to climb trees and eat for hours and will become more responsive to the keepers’ attempts to shift her. Look for her atop the climbing structure in the north exhibit, or drinking from the pond in that yard, in the next week or so.

What’s in store for Bai Yun? In the short term, cub or no cub, you can be sure that our staff will continue to dote on her and meet all of her needs. She still is, after all, our own “hero mother.”

Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Panda Pregnancy: Detection.


Panda Pregnancy: Detection

After a successful breeding season in which we are fortunate enough to realize one or more breeding sessions between Bai Yun and Gao Gao, we then shift into “wait and see” mode. During this time we wait out the period of embryonic diapause (see post, Panda Pregnancy: Embryonic Diapause).  Then, once progestins begin to rise, and Bai Yun’s behavior begins to change, we start to look for clues that help us determine if our female is pseudopregnant or will, in fact, give birth (see post, Panda Pregnancy: Pseudopregnancy).

In the past, there was only one tried-and-true method to distinguish between the two: witness a birth. If a female had a cub (or two), then obviously she was not pseudopregnant. So it was that staff at a panda facility would spend quite a bit of time observing a female, watching for signs of labor to confirm that a cub was imminent.

I recall sitting in a darkened observation area in the middle of the night for months on end back in 1998. We had artificially inseminated Bai Yun earlier in the year, and we had no idea if she was pregnant. We were also uncertain about the timing of any potential birth. For six months staff rotated through the area, and there was always someone whose job it was to watch Bai Yun. It was a 24-hour-a-day assignment. Alas, you know that Hua Mei was our first-born cub (in 1999), so I don’t have to tell you how those intense six months ended.

Things have improved quite a bit since then. The biggest change over the last decade has been our ability to visualize a panda fetus via ultrasound. Once our veterinarians are able to see a heartbeat in utero, it becomes quite clear that we are not witnessing a pseudopregnancy: the female obviously conceived, implanted, and began to grow a new little panda. Hua Mei provided our very first in-utero cub photo just three days before she was born. That was a very exciting day, and it’s one I will always remember very clearly! Where were you when the first panda fetal image was obtained?

Since then, our vets have been able to get visuals of our fetal cubs with great regularity, charting their development in utero much as an OB-GYN might do for a human patient. But there has been another exciting development in panda pregnancy detection: the advent of a ceruloplasmin test.

Ceruloplasmin is a protein that recently has been shown to be a positive indicator of pregnancy in pandas. And I mean recent: research on this detection method has been published only in the last few weeks, it’s that new! There are many promising things about this new test, but the most exciting is that it provides us with a way to distinguish pregnant from pseudopregnant bears. It may also help us make that distinction early on in a pregnancy. In the future, it should become a powerful tool for panda facilities to utilize.

So where are we with Bai Yun in 2011? We aren’t able to run her ceruloplasmin yet, as the test is so new there are some logistical issues to deal with in getting the results in a timely fashion. So we can’t tell you what is happening on that front. Our vets have been doing ultrasounds with Bai Yun for some time, and, to date, they have yet to confirm a heartbeat in utero. This means we are still waiting.

And I know you are, too. Until we have definitive information either way that Bai Yun will—or will not—be delivering a cub this year, we will all just have to get used to waiting. Just like the old days!

Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research.


Panda Pregnancy: Pseudopregnancy

Why is pregnancy in pandas such a complex affair? On Friday, we reviewed embryonic diapause as a factor in adjusting the length of panda pregnancies (see post Panda Pregnancy: Embryonic Diapause), and today I’ll describe another interesting aspect of their reproductive strategy: pseudopregnancy.

First, a definition: what is pseudopregnancy? Sometimes known as a “false pregnancy,” a pseudopregnancy occurs when a female exhibits the signs and symptoms of pregnancy when in fact she is not experiencing one. Like embryonic diapause, pseudopregnancy is not a phenomenon limited to pandas; it has been observed in mice, dogs, and even humans.

In pandas, the signs and symptoms of pregnancy that also occur in a pseudopregnancy include a decrease in appetite, a decrease in activity level, and even physiological changes to the genitalia. The onset of these changes in a pregnant female follow the rise in progesterone noted after the period of embryonic diapause, when the blastocyst implants in the uterus. But here is where it gets tricky: pseudopregnant females also experience a rise in progestins. It is what is driving their behavioral changes, too.

In many animals, the way to detect pregnancy is to look for the presence of progestin byproducts in the urine, feces, or blood. In a panda, if you find progestins in the urine of a female you can only say definitively that she is either pregnant or pseudopregnant. So far, we haven’t been able to identify a way with progestins to tell for sure if she is gestating a fetus.

Over the years, panda researchers have puzzled over this. What is really going on here? Is it possible that pseudopregnant females were actually bears that had, indeed, gotten pregnant but miscarried before the birth? That is certainly possible, and Bai Yun has shown us via ultrasound that she has three times carried twins only to give birth to a singleton. Clearly there is fetal death occurring in utero from time to time. It is entirely possible that many “false” pregnancies would retrospectively be classified this way, had ultrasound technology been more available in the past.

However, it is also true that in some cases, pseudopregnancy has been noted in females who had not even had the chance to breed. Thus, for those females, there was no possibility of a pregnancy (or miscarriage), and they went through the behavioral motions anyway.

Why would a female panda experience the signs and symptoms of pregnancy even if she didn’t give birth? We aren’t entirely certain, but here is one theory: because it doesn’t cost them much to do so. From an energetic perspective, it doesn’t take much effort to slow down and allow your body to become physiologically primed to gestate a panda fetus. Cubs only grow for about 50 days, which doesn’t require a long-term commitment. And if you are a panda, which only mates once every two to three years while raising a single cub in between, it is important to have that pregnancy “take.” If you miss a year, it’s a big loss to your lifetime reproductive output. When the typical lifespan of a wild panda is no more than 20 years, and a female isn’t fertile until at least 5 years of age, she can only rear about a half dozen cubs in her lifetime. Losing one has a big impact on her overall reproductive success. In the end, it could be as simple as a little cost-benefit math equation: pandas can’t afford to lose the chance to reproduce, and it doesn’t cost them much to be prepared.

Embryonic diapause makes it difficult to assess when we should expect a birth in the time shortly after breeding. Pseudopregnancy insures that we must interpret our progesterone and behavioral indicators with caution. How, then, do we actually confirm a pregnancy in pandas? I’m sure you have some idea, but there is also some new and exciting research on that front. That will be the topic for my next entry. Stay tuned!

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.


The Waiting Game

Bai Yun

In pandas, the period of fertility for females typically occurs in spring. Bai Yun routinely experiences her estrus in spring, and all of her breeding dates for those years she has given birth are lumped into a 33-day window beginning in late March. A betting person would have put money on March-April for this year’s estrus, as well. We are nearly all the way through March at this point. Bai Yun, for her part, has shown very little indication that a breeding date is near. Changes in the size and color of her external genitalia indicate that she is in the early stages of estrus, but we may yet be a few weeks away.

We do not yet have any way to know if she will have a fully expressed, fertile estrus in 2011. Some pandas experience weak estruses, in which the behavioral signs are muted or the hormone profiles are not quite as dramatic as those that have strong estruses. These weak profilers typically don’t succeed in getting pregnant. It is probable that they don’t quite get to the point of ovulation. Young females experiencing their first estrus often show weak profiles, but as they mature, their behavioral changes grow stronger. Some older females also experience these weak profiles, presumably as their aging bodies senesce and they put their reproductive days behind them. Thus far, Bai Yun has never had such a weak estrus, although she has had a truncated behavioral estrus in 2007 and 2009. Due to this change in pattern over her last two fertility windows, we anticipate another truncated estrus from Bai Yun this year. She’s very healthy for her age, but it is possible that she could have a weak estrus, or even no estrus at all. Only time will tell what this breeding season has in store for her.

Fortunately, Gao Gao is also very healthy and is clearly responding positively to the season. His changes in genitalia and behavior are right on track, and he has been seen climbing high in his exhibit and wandering about in a manner consistent with a male hoping to cross paths with an estrus female. If Bai Yun is willing, Gao Gao will be ready. We’ll just have to wait and see.

Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research.


Pandas: Getting Closer

Bai Yun continues to progress toward her birthing window in a predictable fashion. Part of this progress means she is “denning up” in preparation for the birth. Over time, she is spending more and more time in the den resting, eating, and nest building inside. In the last 24 hours, she spent 680 minutes (over 11 hours) in that den, but soon enough it will be 1,440 minutes (a full day!).

For now, when she is not in the den, she can typically be found sleeping just outside the den entrance. She no longer makes trips out to the large outdoor space she had available, so the keepers have closed off that area. She has even stopped visiting the garden room and resting atop the platform there. From this point forward, it’s den, bedroom, and sun room…but increasingly just den.

We can’t tell you exactly when Bai Yun will give birth. We can say that all signs point to early August. Our various signs and indicators do have some predictive value for us: How far out did she reduce her bamboo intake? When did she begin spending time in the den? What do the fetal measurements tell us about how developed the cub is? I can tell you that all of these factors are aligning nicely with regard to a predicted birth date, all pointing to windows within a few days of each other. There is enough variability, however, that we won’t be brash enough to predict for you exactly when the cub will be born. You could say we are watching her overnight…

Cub, not cubs. Did I mean to type that? We have good evidence that one cub (gestating in the right uterine horn) is developing beautifully. You may have seen it on the ultrasound pictures, curling its head and moving its paws. The vets have been able to see mineralization of the bones and tiny claws. This cub looks strong and healthy so far. What about its twin?

Last week we saw a heartbeat from the cub in the left uterine horn. It looked smaller and less developed than its sibling. Since that heartbeat sighting, we haven’t had a chance to see Left Cub. We have not seen its heartbeat stop or its placenta degrade as Mei Sheng’s uterine roommate did in 2003. But staff is becoming increasingly suspicious that Left Cub will not survive the pregnancy.

If this makes you unhappy, you’ll have to take it up with Bai Yun. This is her call. But you’ll have to wait for some time, because it looks like she’s going to be busy for the next few months!

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.


Pandas: Are Two better than One?

We have been excited to discover that Bai Yun is pregnant with twins! Our veterinarians confirmed via ultrasound that there is a fetus in each of her uterine horns (the panda has a bifurcated uterus, shaped like a Y). When they were first discovered, vets could see that one fetus was well developed, with a robust heartbeat, and the other was smaller with a well-developed placenta but no heartbeat yet detected. A subsequent ultrasound revealed a fetal heartbeat on both sides. This morning, only the more developed cub could be seen. Does this mean that the other embryo is lost? Or was it just hidden from view? We can’t say for sure either way.

Dr. Meg Sutherland-Smith performing the ultrasound procedure this morning.

Dr. Meg Sutherland-Smith performing the ultrasound procedure this morning.

This is not the first time Bai Yun has been pregnant with twins. Veterinarians also saw two fetuses when looking in 2003, the year of Mei Sheng’s birth. Amazingly, they were also able to document the resorption of one fetus prior to birth. We were left to wonder if that fetus was somehow less viable than the other, and therefore died prematurely, or if Bai Yun’s body selectively pruned her litter of two down to one. Although Bai Yun herself was a twin, she has never given birth to twins. Will she prune her litter again this year?

Why would a female prune her litter? We know that raising one panda cub is an extremely difficult and labor-intensive task for a female. She invests a lot of energy in holding, suckling, cleaning, and protecting her young. We know from our comparative studies with other bear species that pandas are far more attentive mothers than American black bears or brown bears, and even the active sun bear isn’t quite as diligent as a panda. As demanding as raising a panda cub is, rearing twins is even more of a feat, so much so that it has been very rarely documented that a female might rear more than one cub in a natural setting. To save energy, it may be a good evolutionary strategy for a female panda to avoid putting herself in this position in the first place, and so she might have natural biological mechanisms in place that ensure a singleton birth.

Even in the event of a twin birth, panda mothers routinely make choices about how to rear their litter. In birth centers in China, females sometimes reject one of their cubs immediately upon their birth, deciding from the get-go that she will only raise one of the offspring. Others may choose to attempt to rear two for a few hours, but ultimately set one cub down to attend to the other. We don’t yet know what factors go into making the choice between cubs, but we are actively looking at this as a research project and hope to have the answers soon.

In the final analysis, a panda mother seems incapable of rearing twins on her own. There have been a few spotty reports of wild twins located in tree nests or wandering about in China. This suggests there might be a possibility of a panda caring for two cubs from birth. Certainly this is possible with most other bear species. However, to my knowledge there has been no confirmed case of a panda that gave birth to and successfully reared twins without support.

What would Bai Yun do if she did give birth to two? We don’t know. She’s never been put in that position before, and we aren’t sure how she might react. Bai Yun is an excellent, skilled, experienced mother; perhaps if she feels she’s up to the job of handling twins, she would try to raise both. She is also well-seasoned and knows just what’s involved in caring for the cubs, and splitting her efforts between two means neither one gets her full attention. For that reason she may reject the demands of rearing two in order to ensure the survival of one of her offspring. We’ll have to wait and see.

In a future update I will describe some of the conditions and considerations our staff will contend with in dealing with a twin birth. Stay tuned!

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.

Here’s a link to video of this morning’s ultrasound


Pandas: Reading the Tea Leaves

Things are falling into line in preparation for a possible panda birth this summer. Our camera system is squared away, other preparations are in place or are in final stages, and Bai Yun is being closely watched for signs of pregnancy. While there was a time when we could not easily discern what the signs she registered might mean, we have learned a lot over Bai Yun’s lifetime that helps us to better understand where she is at, reproductively speaking.

Ultrasounds started a few weeks back. The vets are looking for undeniable signs of pregnancy, like the appearance of a fetus. In past years, a fetus was first visualized 17 days before it was born. However, before seeing a fetus, there are other signs that indicate her body is getting ready for a pregnancy or a pseudopregnancy. These include the simple visualization of the uterus. It is usually difficult to see because of the gas in the gut and because outside of this season in her life the female’s reproductive tract is just less obvious. Hormones responsible for pregnancy and pseudopregnancy drive the enlargement of the uterus to make it more visible to our vets nearer to her birthing window. Thus far, there has been some indication of positive change of Bai Yun’s uterus.

Another indicator is her behavior. A significant marker to us is a decline in Bai Yun’s appetite for bamboo. She has begun showing this decline for the last few days, rejecting even her favorite species and leaving behind some fresh stems untouched. Her behavioral changes are also considered positive when she becomes sluggish and uncooperative, a change witnessed for the first time yesterday (July 14). Normally, a keeper might become frustrated by a bear that refuses to shift or won’t come when called or that generally seems noncompliant. This time of year, behavior of this sort from Bai Yun just makes us smile.

Is she pregnant? That we can’t answer with certainty yet. We can say that her body is getting ready and may already be gestating a fetus in its early stages of growth. Only time will tell us if this is not the dreaded pseudopregnancy we have seen with her before, in 1998 and other years we did not realize a cub. Perhaps due to her age we might expect her to be more inclined to have this false pregnancy this time around. On the other hand, Bai Yun is very healthy, at a good weight, and she has never missed with Gao Gao. So place your bets.

We’ll keep you posted as to her progress. In the meantime, back to reading her signs…

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.