My first day observing Chinook and Kalluk came chock-full with several moments of awe. The first was upon getting a good look at Kalluk. He’s a young male, less than half of giant panda Gao Gao’s age, and yet the size difference between them is astonishing. Kalluk, as a representative of the largest bear species on the planet, is a towering hulk. Despite his lean frame, I am told he weighs in excess of 850 pounds, or 380 kilograms (compare that to Gao Gao’s mere 160-pound, or 70-kilogram, weight). Resting on his backside in an erect seated posture, he is taller than I am. And when he stands on his rear legs to get a look at something placed up high…well, even NBA stars would have a run for their money looking big next to Kalluk.

I have spent most of my time over the last few years working with the (not so?) giant panda and the sun bear, the two smallest living bears. What factors might account for the great difference in size that we see in the spectrum from these smallish bears to the massive polar and brown bear species? One major contributing factor is the different environmental niches that these species inhabit.

The largest bears are cold weather animals, living in harsh, extreme climates much of the year. Coping mechanisms to deal with cold and its resultant food shortages include hibernation periods, insulating fat deposits to keep the heat in, and (in the case of the polar bear) translucent hairs which aid in conducting sunlight down to the skin to increase heat absorption. But increased size is also a fundamental way of coping with coldness, as the basic principle of surface-to-volume ratios indicates: the larger the body, the smaller the surface area relative to body volume. This reduced surface area ratio allows for a lower rate of heat loss.

Compared to the harsh, cold climates polar bears inhabit, sun bears enjoy warm, tropical habitats. The steamy rain forests from Borneo to Thailand and India were the birthing grounds of this species, and the bear benefited from a smaller size to aid in rapid dissipation of heat to avoid thermostress. But what about pandas? Don’t they typically inhabit snowy, cold mountain passes more closely resembling the habitat of a larger brown bear? Why aren’t they so large?

One answer to this question lies in the evolutionary history of the panda. Long before man came to be so populous in China, pandas could readily be found in the lowlands of southeastern China, at about 1,600 feet (500 meters) above sea level. The panda populations probably expanded and contracted in range many times as the temperature alternately warmed and cooled, with warm weather allowing expansion due to the increasingly favorable conditions for bamboo growth in warm seasons. Thus, at some points in the panda’s evolutionary history, this ancient bear species enjoyed warmer climates and survived well with a smaller size.

Of course, the question of size differences among bears is more complicated than the surface-to-volume picture I have sketched here, but it does provide a partial answer to the wide variety of sizes achieved across the eight living bear species. It even explains some of the differences seen between subspecies, such as the discrepancy between the warm summering grizzly populations relative to their colder cousins, the big Kodiak brown bear. Next time you have a chance to visit your local zoo and observe the bears housed there, maybe you will see their body sizes in a whole new light!

Suzanne Hall is a senior research technician with the San Diego Zoo’s Giant Panda Unit.

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There have been a few changes to the viewing areas. Trimming back branches, installing new tree guards, and some replanting helped make the areas ready. A change of scene is great environmental enrichment for any animal, and with the pandas, there’s the added enrichment of the scent of the previous occupant. This is always stimulating and exciting, at least for the four months that the scent will persist. As an added bonus, the keepers have been recycling to the greater good, using old firehoses from the San Diego Fire Department to craft cozy slings, installed in the trees to provide resting places for our growing cub. (Hose feeders, hammocks, and climbing structures are being used as enrichment in many parts of the Zoo with all kinds of animals, a great way to use what might ordinarily be discarded!)

Watching ZZ explore her new area is a hoot. There’s now a bit of water in the pool and, unlike her older sibs, she’s already plowed right in. And much to my surprise, not only was ZZ rolling in the soil beneath the pine tree but Mom was rolling and tree marking as well. Could it be that Bai is loosening up in her middle years? She actually appeared to be enjoying herself, getting dirty and playing with her cub, at least to me. It’s going to be fun watching them as the months go by. The elm tree will soon leaf out, but the slings are lower down and we can only hope that their allure will remain through the summer months, allowing ZZ to be seen more easily by her many fans.

And Gao Gao?? He, too, has settled readily to his “new home,” in the classroom area but that’s no surprise. He’s always been an adaptable guy, hasn’t he? For now he’ll remain off exhibit—think “Spring Break”—but eventually he’ll be rotated out to give his fans a chance to visit him in the viewing area as well. When this happens will be an animal care decision, but we’ll try to keep you all informed as we get more information.

Ellie Rosenbaum is a panda narrator at the San Diego Zoo.

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It appears from droppings left overnight that Bai Yun spent some of her time resting atop the cave-like lair in the exhibit during the evening hours. When staff arrived this morning, she appeared relaxed and was content to begin her morning routine. Little Zhen, or “Z” as many staff members call her, was high in the branches on exhibit. Keepers called Bai Yun into the bedroom area so they could clean and restock the exhibit, and Zhen climbed down and followed momma into the building. What a pro!

This happy adjustment stands a bit in contrast to the last time we moved Bai Yun to this area. In December 2005, we moved her, along with Su Lin, into this space. Bai Yun was less calm then, and for nearly two weeks she displayed some level of restless walking or door-directed behavior. This time, there has been little to none of this undesirable behavior. What accounts for the difference?

It’s hard to say. It could be that Bai Yun spent enough time in that area with Su Lin that she now feels very comfortable in that exhibit, making the transition seem like a move to a very familiar space. Perhaps Zhen’s boisterous personality has left Bai Yun more at ease. Maybe this is another indication of momma’s increased maternal experience, reinforcing the notion that Bai Yun no longer seems to sweat the small stuff. Or maybe the issue is cub age: Zhen is three months older than Su Lin was when she moved to this space, and in Bai Yun’s mind that may make all the difference in the world. Whatever the reason, we are very pleased at how well both mom and cub are doing.

Su Lin (pictured) is being housed in the adjacent exhibit, and she has noticed that there are some new neighbors nearby. She has been seen scaling trees to try to catch a glimpse of the goings on next door. She may well get a chance to see her little sister, who climbs up regularly and is beginning to feel at home in some of Su Lin’s old favorite perches. So far, Bai Yun hasn’t shown any response to Su Lin’s presence next door, and if she did, we would probably expect aggression on momma’s part: she still has a youngun’ to protect, after all. She definitely showed such aggression to other offspring when she encountered them post-weaning. Su Lin, though an important bear to Bai Yun in the past, could be perceived as more of a threat now.

Suzanne Hall is a senior research technician with the San Diego Zoo’s Giant Panda Unit.

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If, after a couple of days, they do not venture down on their own (which is very unlikely), the keepers have various techniques they can use to help encourage the twosome to make the journey. Most of these techniques involve food; we all know Bai Yun will do almost anything for a slice of apple! But the keepers also have such a close relationship with Bai Yun and Zhen Zhen that most likely all they’ll need to do is call them, and they’ll follow the keepers down to the exhibit. And Zhen Zhen is such an adventurous cub, I’d be surprised if she didn’t romp down the corridor and start exploring her new area just as soon as we open the door. That being said, we can’t give a definite date of when the two will be out on exhibit for public viewing. We let them go at their own pace, so it could be one day or it could take a week.

This process of shifting Bai Yun and cub from the bedroom/den area to the main exhibit area is the same process we have used with all of Bai Yun’s previous cubs when they reached this age. Therefore, we expect that Bai Yun will settle in quickly to this familiar location since she has raised all three of her previous cubs in this exhibit space. We also feel confident that Zhen Zhen will be comfortable with the larger, more consistent crowds that pass through the main exhibit area because, for the past few months, we’ve gradually been acclimating her to the presence of Zoo visitors by having her on public display for only a few hours in the morning.

Gao Gao and Su Lin are currently housed in the two main exhibit areas. But once this transition is complete, and Bai Yun and Zhen Zhen are on exhibit, we will begin a rotating schedule with Gao Gao and Su Lin. Starting this week, Su Lin will be in the main exhibit area adjacent to Bai Yun and Zhen Zhen, and Gao Gao will be in the off- exhibit area we call the Classroom. We will rotate the two of them so that they each have some time off exhibit for a little private time, and they each also have some time on display for their adoring fans.

We hope all of our Zoo visitors enjoy seeing Bai Yun and little Zhen Zhen out in the main exhibit area for longer viewing hours.

Pamela Crowe is a research technician with the Giant Panda Conservation Unit of the San Diego Zoo.

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Is it the chiming of the carillon in Balboa Park? I have seen her “cock an ear and raise an eyebrow” to acknowledge it before climbing up. Is it when we open the area to visitors each morning? She’s often awake for a bit of time long after. Is it the presence of visitors? Given that the pandas have just about finished their first fresh feeding of the day, I’d suspect that it’s being full and contented and ready to rest and digest. As an aside, though, with so many excited visitors in that small space, it has become noisy from time to time. Bai Yun has reacted to this by vocalizing with a honk, one of a panda’s 11 vocalizations, which appears to indicate mild distress. As the old saying goes, “If Mama ain’t happy, ain’t NOBODY happy”, and we’ve been quick to quiet the area.

The whole crew is doing fine. Gao had his annual physical earlier this week. He was not a happy boy when he had to fast to make his checkup safer for him and compensated the next day with a VERY hearty appetite. We all know how he enjoys his bamboo! Su Lin is following in her half-sister’s footsteps, though, and becoming, uhm - more particular about her bamboo. (Let’s hear it for the browse crew who dedicate their time to keeping the huge crop of bamboo browse growing and thriving and bringing in the pandas’ favorites!)

ZZ keeps testing that one tree guard and still isn’t big enough to cross it. She has found other spots to drape. They probably won’t last too long since these branches aren’t forked and she’s now weighing around 26 pounds (12 kilograms). She and Bai are spending the quality play/teaching time together that is appropriate to this age, although I couldn’t tell you when. With luck, Panda Cam viewers and visitors can watch this as time goes on. I personally can’t wait until dirt-bathing lessons begin!

Ellie Rosenbaum is a panda narrator at the San Diego Zoo.

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It now appears to be a familial trait. Little sister Zhen Zhen (pictured) found her way up over the tree guards in her and Bai Yun’s enclosure, napping in a spot that made her inaccessible to her mother should Bai decide it was time to nurse the cub. (And as any nursing mother can tell you, sometimes Mom has to make that call!) In an effort to solve this problem, new tree guards were installed to replace the old, giving the tree the appearance of bearing large green parasols on its trunk. But in the best family tradition (remember Mei Sheng in the poplar tree?), little Zhen Zhen mustered her 22+ pounds back up the tree and has been persistantly trying to breach the barrier. Creeping up the trunk, extending a paw to bend the flexible plastic toward her, the only thing holding her behind the “bear baffle” is her size.

Her technique will undoubtedly be successful with just a few more inches in length; it’s going to be fun watching her progress back up to the tree tops. Like it or not, she too will be back up there by summer, another panda cub sleeping in the tree!

Ellie Rosenbaum is a panda narrator at the San Diego Zoo.

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Why is it necessary to understand this stage of bear life? On the practical side, it is important because we know so little about how a female, tucked in a den, cares for and nurtures her young. Since six of the eight species of living bear are currently classified as either endangered or vulnerable to extinction, it is imperative for their survival that conservation managers take an interest in their situation. Learning as much as we can about their biology and natural history is a first step toward understanding the needs of each species so that conservation action plans can be tailored to serve the best interests of each bear.

Efforts at reproduction in zoos and other facilities can be more effective if the natural behavior of the species is supported. Bears in zoo settings have often been known to neglect to care for their young, sometimes killing or abandoning their young inexplicably, obviously defeating the purpose of any goals of increased reproduction. Knowing more about the normal course of healthy maternal relationships will aid managers in identifying bears that are in need of assistance in caring for their young and in providing an environment which promotes good maternal care in the first place.

Adding individual bears to our study has proved to be a bit daunting. First, the San Diego Zoo has a limited number of bears on site, since bears require large amounts of resources and cannot be maintained in large populations in any one place. Nonetheless, we are utilizing the animals we have on site to the best of our ability. As you know, our pandas have been studied intensively, and our sun bears have contributed to their own maternal care data set. We are thrilled to be expecting a few pairs of sloth bears in the future, which we hope will enable us to study many aspects of their biology. But most of our work with this project has depended upon collaborations with other zoos and institutions.

Our American black and brown bear data have come from collaborators inside the U.S. Andean (or spectacled) and sloth bear collaborations are in development, working with facilities ranging from coast to coast. However, we can’t get at all of those vulnerable species by sticking solely with collaborators in the U.S.

To that end, we have partnered with bear researchers as far away as China and Japan to study species such as the panda and, most recently, the Asiatic black bear. This species is classified as vulnerable but is currently not being bred by any AZA-accredited (Association of Zoos and Aquariums) facilities in the U.S., so we have had to look farther afield to include them in our research. As of this writing, I am pleased to report we have cameras currently installed in the dens of our first two Asiatic blacks. We are awaiting news that they may give birth to their cubs, and a new chapter in our research, sometime in the next month.

I look forward to sharing more updates about this aspect of our work with you as it develops.

Suzanne Hall is a senior research technician with the San Diego Zoo’s Giant Panda Unit.
Here’s information about the study, Mother-infant Relationships in Bear Species…

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With all the research going on and the careful observation and study of so many cubs in the U.S., it’s tempting to all of us to compare and contrast their behaviors, but “so many” is only six cubs so far; not a very large sample, by any standards, and even fewer by the same paternal line with the same mother, Bai Yun. There seems to be a tendency to hover and worry, if one cub doesn’t do “it” the way others have, whether crawling or climbing, eating or playing. Each of these little bears is an individual, growing and changing at his or her own rate. Yesterday, ZZ broke through her “glass ceiling,” making it all the way to the top of the fabled elm tree, where she spent the night just as Mei Sheng did after his first trip up there. Even after four cubs, they can still surprise us!

For all her napping in the same spot, however, ZZ’s been a busy little girl. We’ve seen a lot of oral exploration, putting and holding things in her mouth, including bamboo. Toddlers, whether human or animal, gain a lot of information about their world through this kind of feeling and testing. She’s also still cutting teeth, so a combination of these two things may be giving the appearance of bamboo eating at this point. While she may inadvertently ingest bits and pieces of whatever she has in her mouth, her primary source of nutrition is still milk. By 8 or 9 months of age she’ll begin sampling bamboo and other food items with more purpose, but panda cubs generally aren’t self-sufficiently feeding until 12 or 13 months of age.

Ellie Rosenbaum is a panda narrator at the San Diego Zoo.

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Wild male pandas have large home ranges in which they search for food and acquire information about other pandas that live close by. A single male can have several females with home ranges that intersect his. In this way, a male may have several different females for which to compete during the breeding season. However, these females are likely to come into estrus and be ready to mate at different times throughout the spring; thus, it is a male’s predicament to always be ready and be in the right place at the right time.

To this end, a male experiences some changes in preparation for breeding season. His testes enlarge, increasing seminal volume and quality in order to ensure better breeding success should he have the opportunity to mate. And a male must be mobile, checking and rechecking the status of females nearby by investigating the scents they leave behind. He has to pinpoint that small peak fertility window exactly in order to be a successful breeder.

Gao Gao may not have access to Bai Yun this year, but his body doesn’t register this artifact of captivity. He will gear up for the breeding season nonetheless. Already he has begun to show signs of increased restlessness, wandering about his pen more frequently. In the wild, this would translate into a strategy allowing him to keep a close eye on the girls nearby. In the zoo setting, he begins to wear paths through the turf in his yard. This physical exertion can lead to a weight loss, as calories are burned in the relentless pursuit of the perfect mates. Fortunately for Gao Gao, his keepers stand ready to provide him with extra food supplements to increase his caloric uptake should his weight begin to drop too far. This is something the staff is prepared for.

In the coming months, when Gao Gao is at his peak of breeding form, he will likely be electro-ejaculated so that his semen can be used for artificial inseminations either with other bears here in the U.S. or with future assisted reproduction with bears in China when Gao Gao returns home someday. In this way, a breeding season with a healthy, genetically desirable male will not be lost to Bai Yun’s anestrus.

It’s easy to think of Gao Gao as the perfect breeding panda, a little-engine-that-could who stands ready to mate with any female who should cross his path. He has obviously produced some lovely, healthy cubs over the years. But how would he manage if he were actually a wild panda? He is a small male, by all accounts. And at the San Diego Zoo he does not have to contend with one major hurdle a wild male faces in the breeding season: competition. Would Gao Gao, for all his breeding prowess, be able to battle other males for the right to breed with a female in estrus? Would he challenge other males openly, or try a sneakier strategy for finding his way to a breeding opportunity? We have reason to believe that Shi Shi (our previous adult male) was seriously injured in a fight during a breeding-season encounter, and we know males can be very aggressive to each other under these conditions. We can only speculate about Gao Gao’s success should he have faced such obstacles. Fortunately for our Little Big Man, there is no competition for mates in San Diego. We just get to sit back and admire his handiwork in the form of Mei Sheng, Su Lin, and Zhen Zhen.

Suzanne Hall is a senior research technician with the San Diego Zoo’s Giant Panda Unit.

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