Pandas

Pandas

194

Xiao Liwu: Star Student!

Xiao Liwu now eats more bamboo than his mother does!

Xiao Liwu now eats more bamboo than his mother does!

Keeper Jen Becerra passed along some updates on the San Diego Zoo’s panda family, starting with Xiao Liwu, who will be two years old next month (how time flies!). Jen claims “Mr. Wu” has been the easiest of Bai Yun’s six cubs to train, and she marvels how each of her cubs has been progressively smarter, with Mr. Wu at the head of the class! Yesterday he began training for blood draws and blood pressure checks, done with the help of a metal sleeve. The panda is asked to put his or her arm in the sleeve and grab the bar at the end (see post Still Ga Ga for Gao Gao.) An apple slice is placed near the end of the sleeve for the panda to grab for, and after several weeks of this, the bear learns to grab the bar at the end of that sleeve to receive the reward. Well, Xiao Liwu stuck his arm in the sleeve on his first try AND grabbed the bar on the end, as if he’d been doing it all his life! Jen kept using the word amazing to describe how the first day of this training went. Just a few months ago, keepers were concerned that Wu would be challenging to train because he prefers bamboo to other food items used for rewards. But it seems that for Mr. Wu, interaction with his keepers is reward enough!

Xiao Liwu has broadened his food menu but is still rather particular about its presentation. Still a huge fan of bamboo and apples, he has added to his repertoire low-starch, high-fiber biscuits (only if they are soaked in water first), and sweet potatoes and carrots (but only if they are cut into sticks). And speaking of bamboo, he now eats MORE of it than his mother, Bai Yun, does. Yes, you read that right! Wu polishes off 11 to 13 pounds (5 to 6 kilograms) of bamboo each day, whereas Bai Yun eats 8 to 11 pounds (4 to 5 kilograms). Gao Gao is the biggest eater of the three, downing 15 to 17 pounds (7 to 8 kilograms) daily. Xiao Liwu’s current weight is 84 pounds (38 kilograms).

Our growing boy seems quite comfortable in the main viewing exhibit and doesn’t call to his mother or look for her in any way. The feeling is mutual, as these days Bai Yun’s attitude is “It’s all about me!” When not eating his bamboo, Xiao Liwu spends time in buckets of ice or in front of the mister fan but doesn’t play much with his enrichment toys. Jen says he’s like “an adult bear in a small body.” Wu is a fan of various enrichment scents, with wintergreen, peppermint, and cinnamon his top three fragrances.

Gao Gao continues his recovery from his surgery and is spending more time in the north yard, off exhibit to guests but where he may be seen on Panda Cam. He still prefers hanging out in his bedroom suite, where keepers are at his beck and call. Jen admits that Gao Gao has come up with a special vocalization used just for them—a sweet, light bleat that seems to mean “Come here, please.” When the keeper comes, there is Papa Gao, pressed up to the mesh for a back scratch. Who could resist that request?

Debbie Andreen is an associate editor for San Diego Zoo Global.

158

Pathologist’s Report on Gao Gao’s Tumor

On the left is the paraffin wax block containing the processed tumor tissue, which is then cut into thin slices (about the width of a human hair) by our histotechnologist. These thin sections are then stained by several different methods to allow microscopic evaluation of the cells in the tumor.

On the left is the wax block with the processed tumor tissue, which is then cut into thin slices (about the width of a human hair). These thin sections are then stained by different methods to allow microscopic evaluation of the cells in the tumor.

As most of you know, giant panda Gao Gao had surgery May 6, 2014, to remove his right testicle after a tumor was discovered by our veterinary staff (see Surgery for Gao Gao). Since that time, we have received a lot of questions about how Gao Gao’s diagnosis was made and what the findings mean for his long-term prognosis. In this blog I’ll tell you about our analysis of the tumor in the Wildlife Disease Laboratories of the San Diego Zoo Institute for Conservation Research and what we know about the tumor in giant pandas and other animals.

After we received Gao Gao’s testicle in the laboratory, parts of the tumor were processed and stained for examination under a microscope. From this, the veterinary pathologists gathered clues from the arrangement and distribution of tumor cells, features of individual tumor cells, and the frequency of tumor cell division and invasion into adjacent normal tissues.

This photomicrograph (taken through a microscope) shows the tumor on the right-hand side compressing the normal testicular tissue on the left.

This photomicrograph (taken through a microscope) shows the tumor on the right-hand side compressing the normal testicular tissue on the left.

We also used a specialized technique, immunohistochemistry, to determine if the tumor was making substances characteristic of one particular cell type or another. All of this information was synthesized to determine the tumor cell type and if the tumor was completely removed.

In Gao Gao’s case, the evidence supports a diagnosis of seminoma, which is a tumor arising from the germ or sperm-producing cells. In addition, there was no evidence in the surgically removed tissues of tumor spread beyond the testicle. In domestic animals, seminomas are common in older dogs, and they are usually completely cured by surgery. However, in other species such as humans, a higher percentage of seminomas will metastasize (spread) to other organs without additional treatment such as chemotherapy.

This high magnification photomicrograph shows a single tumor cell undergoing mitosis (cell division), a characteristic that indicates tumor growth. The dark purple material at the center of the cell is the nucleus beginning to divide.

This high magnification photomicrograph shows a single tumor cell undergoing mitosis (cell division), a characteristic that indicates tumor growth. The dark purple material at the center of the cell is the nucleus beginning to divide.

So what does this mean for Gao Gao? The answer is that we can’t tell for certain if his tumor has been cured by surgery or if there is a small chance that it could reoccur at a later time. This is a common problem for pathologists who work with endangered animals, because very few tumors will ever be observed in these species, whereas it is easy to gather information on tumor behavior in dogs and humans where thousands of cases can be studied over time.

Despite this uncertainty, we are very hopeful that Gao Gao’s tumor will behave more like a seminoma in dogs. In 1997, a seminoma was found in 26-year-old giant panda Hsing Hsing, from the National Zoo, and treated by surgical removal. Hsing Hsing died two years later from kidney disease, and there was no evidence of any remaining tumor at his necropsy. We have had an opportunity to compare the microscopic sections of Hsing Hsing’s tumor with the samples from Gao Gao, and they are very similar.

Allan Pessier, D.V.M., Diplomate, A.C.V.P., is a senior scientist (veterinary pathologist) for the San Diego Zoo Institute for Conservation Research. Read his previous post, The Last Ones?

Update May 23, 2014: Gao Gao seems to be enjoying his keepers’ attention in his bedroom suite as he continues his recovery. He has even been soliciting neck scratches from them.

49

Our Panda Conservation Program

Bai Yun has been a wonderful ambassador for pandas.

Bai Yun has been a wonderful ambassador for pandas.

When Bai Yun arrived at the San Diego Zoo back in November 1996, we all had great expectations for the San Diego Zoo’s panda conservation program. And we knew that these expectations rested squarely on Bai Yun’s beautiful black-and-white shoulders. In the years since, our panda conservation program has grown and has achieved a number of notable successes.

At the center of it all is Bai Yun. Of course, Gao Gao, too, has been extremely important to the success of our breeding program at the San Diego Zoo. Not all male pandas show appropriate breeding behavior, so Gao Gao’s arrival in San Diego in 2003 enabled us to fulfill our goal of studying giant panda reproduction, from breeding to maternal care. However, Bai Yun’s importance to our conservation program goes beyond her successes as a mother, as she has truly exemplified the role of conservation ambassador. Engaging and fascinating the public for the last 18 years, she is the quintessential giant panda, emblematic of the inherent beauty and value of wildlife.

Bai Yun will be 23 years old in September. For those of us who have watched her over the years, we are amazed at her consistent good health, youthful behavior, and appearance. However, this year, her estrous behavior has not been what it has been in the past. Can Bai Yun be heading toward reproductive senescence? Heading into her 23rd year, the answer, most likely, is yes; however, we won’t know for sure until next spring. As of this writing, Bai Yun has not shown more than a minimal level of the behavioral changes that are typically associated with estrus. Back in March, we saw a bit of scent marking and some water walking, behaviors that normally indicate that estrus is coming. However, the expression of these behaviors did not escalate, and soon after they began, they ceased. Since then, Bai Yun has been “quiet.” While estrus can occur into June, the vast majority of breeding, including for our bears here, occurs in March and April,

When Bai Yun gave birth to Xiao Liwu in 2012, it was widely noted that she was the second-oldest giant panda to give birth. While an impressive statistic, that notable milestone provided us with valuable information regarding the finite nature of a female’s biological capacity to produce offspring. Male giant pandas, like other male mammals, can theoretically sire offspring later in life, though for wild pandas, other factors may get in the way of this, including competition with other males for breeding access to females and choosy females that may not be interested.

Bai Yun has given birth to 6 cubs over the past 15 years. While some other females have given birth to 10 or more cubs, the number of litters a female has is typically no more than 6 or 7. For example, between 2004 and 2013, Bai Yun’s first daughter, Hua Mei, has had 10 cubs from 7 litters. While Hua Mei is 8 years younger than Bai Yun, it will be interesting to see whether or not she has more cubs in the coming years. These contrasting mother-daughter patterns are at the heart of one of our research questions: What are the limits of reproductive output in the species?

In some panda breeding facilities, cubs are weaned earlier in order to promote successive annual breeding opportunities. In other facilities, cubs are weaned at about 18 months, mimicking what we believe is the more natural timing of weaning. In these cases, females will only be able to breed every two years. Given this, we might expect to see females that breed every year producing 15 litters over their reproductive lives. However, this does not appear to be the case.

Understanding what governs female reproductive output in giant pandas has implications for both captive breeding and conservation of wild giant pandas, and we are currently analyzing a fairly large volume of data to address this question. Is reproductive output governed exclusively by chronological age? Or is it governed in part by health and vigor? And how does variation in inter-birth-interval (the time between successive pregnancies) influence a female’s lifetime reproductive output? We hope to have some answers to these questions in the coming months.

I have to admit that I never get tired of watching our giant pandas here at the San Diego Zoo. While the excitement of a new cub is undeniable, I know that I will enjoy watching Bai Yun and Gao Gao relax this summer, while young Xiao Liwu explores and plays, enjoying his first summer as a solo panda. Our panda family exemplifying their roles as ambassadors for conservation!

Panda Yun Zi in China.

Update on panda Gao Gao, May 11, 2014: Thank you for all the Gao Gao well wishes! He is doing well post surgery and is enjoying spending time in his back bedrooms. There he is catered to by his keepers 3 to 4 times a day, and he lets them know when he wants back scratches. Gao does have access daily to an off-view exhibit that has a panda camera in it, although he seems to prefer to enjoy the air-conditioned bedrooms, his black sleeping tub, and his keepers’ attention.

105

Surgery for Gao Gao

Get well soon, Gao Gao! Your bamboo awaits.

Get well soon, Gao Gao! Your bamboo awaits.

This morning, May 6, 2014, giant panda Gao Gao underwent surgery to remove his right testicle, due to the presence of a tumor. The surgery, which took about an hour, went well, and the San Diego Zoo’s veterinarians are hopeful that Gao Gao will make a full recovery. Unfortunately, due to the nature of the surgery, we do not know if Gao Gao will continue to be part of the panda breeding population. In addition to the surgery, veterinarians took the opportunity to do an ultrasound to follow up on his previously diagnosed heart condition. We are awaiting a review by experts for results of the ultrasound.

The San Diego Zoo’ Panda Team had been observing Gao Gao and Bai Yun for signs of breeding behavior over the last month.  No changes in Bai Yun’s estrous behavior were noted, and in the best interest of Gao Gao’s health, the decision to perform the surgery was made. Bai Yun has reached an age where it is likely she will no longer go through a breeding cycle, and the observations seen this spring are consistent with signs seen in other aging pandas.

The Ministry of Forestry for the People’s Republic of China has been fully informed regarding the status of Gao Gao’s health and gave approval for the surgery. Officials from San Diego Zoo Global and China are expected to discuss the future of the giant panda program in San Diego before the end of 2014. No changes in the panda population at the Zoo are currently expected.

Christina Simmons is public relations manager for San Diego Zoo Global.

Update May 7, 2014: Gao Gao is recovering from his surgery in his own private quarters at the Giant Panda Research Station. Keepers report he is starting to show an interest in solid food.

Update May 8: Keepers report that Gao Gao is resting comfortably in his familiar bedroom area and showing marked improvement. He is eating bamboo and taking his medicine, hidden in apple slices, without a fuss.

Update May 9: Gao Gao now has access to the north yard, an off-exhibit area, if he’d like to get some fresh air.

49

Still Ga Ga for Gao Gao

Gao Gao places his arm in a metal sleeve for a blood pressure check.

Gao Gao places his arm in a metal sleeve for a blood pressure check.

Just for our blog readers, the following is an advance look at an article that will be published in the upcoming June digital issue of ZOONOOZ magazine. To see this and all our digital issues, download the ZOONOOZ app for iPad or the web reader version for your desktop, FREE!

Keeping elderly animals comfortable and healthy can entail rearranging animal groupings to avoid individuals in their golden years getting inadvertently roughed up by younger animals, providing medication for aching joints and other age-related ailments, and monitoring potential health issues with noninvasive exams. The latter requires the animal’s cooperation and can take time to train and condition the animal to go along with it. For instance, tracking the blood pressure of Gao Gao, our 24-year-old male giant panda, requires collaboration between keepers, veterinary staff, and panda. The calm competency of the staff involved and the sweet trust of the black-and-white bear are impressive!

Equipped with apples cut into bite-sized pieces, a small bucket of biscuit balls and bamboo bread, and a blood-pressure monitor attached to an extension cord, keepers and veterinary technicians got into position while I watched the procedure. Gao Gao ambled past, dapper and darling all at once, heading into the squeeze cage and eager to get down to business with a series of enthusiastic bleats and neighs (excited giant panda vocalizations). A steel sleeve, with a cutout area on the top that aligns with the bear’s forearm, was secured to the sturdy cage. Knowing that this noninvasive medical procedure entails his favorite foods, Gao Gao plunged his arm into the sleeve, grasping the metal bar at the end. “We use this sleeve to collect blood samples as well,” explained Brian Opitz, registered veterinary technician (RVT) at the Zoo, “so he knows to hold onto the bar inside the sleeve. To get his blood pressure, we just wait a few minutes for him to let go of the bar and let us place the cuff around his forearm.” All the while, Gao Gao is being hand-fed his favorite snacks, peering at us from behind those big, black eye spots.

Gao Gao does this procedure willingly.

Gao Gao is amply rewarded with tasty treats for his cooperation.

Gao Gao is a senior bear (in the wild, pandas can live up to about 20 years and up to 30 years in managed care), and keepers and vets go to great lengths to ensure he remains healthy. “Keepers put in a lot of time in training for these procedures so we can stay on top of possible medical issues without having to use anesthesia to collect bio-samples,” said Jill Kuntz, RVT at the Zoo. Over time, the grinding action of chewing thick bamboo stalks can wear down a panda’s teeth, as is the case with Gao Gao. Hence, he is given tasty little homemade biscuit balls made of dried bamboo, which he devoured with great gusto throughout the procedure.

Keepers and vets have been gathering baseline data—no one really knows what a normal blood pressure range is for a giant panda—on Gao Gao since May 2013. A few other zoos are also participating in this blood-pressure project. Every 7 to 14 days, staff gathers to collect 3 blood-pressure readings from Gao Gao, which he is agreeable to doing on either arm. “We also trained Yun Zi [Gao Gao’s son] to do this before he left for China,” said keeper Liz Simmons, “but he grabbed the blood- pressure cuff and tore it up.” Undaunted, they continued the training process, rewarding the younger bear for placing his arm in the steel sleeve while keepers peeled the Velcro apart to get him accustomed to the sound of the blood-pressure cuff. Soon, he was going along with the procedure, a skill that will surely come in handy in his homeland.

More wit

The information gained from these weekly readings will help us care for our senior bear.

Accepting the blood-pressure cuff is one of many husbandry behaviors the pandas are patiently trained to do through positive reinforcement. They also present a paw, belly, or rump to keepers, which is helpful in monitoring the animals’ health. Bai Yun, our prolific female panda, will even allow ultrasound procedures so veterinarians can monitor her pregnancies. It’s clear that the keepers are deeply committed to their charges. “We do this training for their health,” said Karen Scott, senior keeper. “That’s what we’re here for. We don’t force them.”

As the bottom of the treat bucket becomes visible, and his blood-pressure readings have been duly noted, Gao Gao calmly looks us all over. A keeper puts a few drops of rubbing alcohol on the floor, and the bear happily rolls around on it. “Usually animals balk at the scent of rubbing alcohol, but Gao Gao loves it—it’s like catnip to him,” explained Brian. It’s the ultimate treat! Gao Gao continued to rub and roll in the acrid odor, then proceeded to scent mark with his own “cologne.” With the procedure completed, he was free to mosey back out on exhibit. “We are lucky to have such an easygoing, tractable panda who allows us to do these exciting and important health procedures as he ages,” said Liz. And we are all fortunate to share the noble journey of Gao Gao’s life, quirks and all.

Watch our pandas daily on Panda Cam!

Karyl Carmignani is a staff writer for San Diego Zoo Global. Read her previous post, With a “Headstart,” Local Turtles Make a Comeback. /

60

“Go potty,” Xiao Liwu

What a clever panda boy we have!

What a clever panda boy we have!

Many of you have wondered how we trained the San Diego Zoo’s panda youngster, Xiao Liwu, to provide a urine sample upon request. Teaching a bear to urinate on command takes a lot of patience and observation of the bear and his or her habits. We used a method called capturing a behavior.

We noticed that when “Mr. Wu” shifts off exhibit and goes into the tunnel, which has a concrete floor, he would, fairly regularly, go to the bathroom before he went into his bedroom. Urine is a very important tool for information about any animal to determine health or hormone levels. So, we started keeping a water syringe and extra apples with us when we started shifting him in at night. When we “caught” him going potty, we would say “go potty” and show him the syringe. When he was done, we would offer him his verbal cue, “Good,” and an apple reward.

After about two weeks of this, he started to go potty when we asked him to. We then use the syringe to collect his urine sample off the concrete floor, which is cleaned every day and night. No cup or pan needed!

Jennifer Becerra is a senior keeper at the San Diego Zoo. Read her previous post, Yun Zi Travels to China, Part 2.

70

Entertaining Panda Cub Xiao Liwu

Xiao Liwu relaxes in his off-exhibit bedroom next to his rocking "horse." See, he likes apples!

Xiao Liwu relaxes in his off-exhibit bedroom next to his rocking “horse.” See, he likes apples!

What has our panda cub been up to, now that he’s been on his own for a few weeks? Keeper Jennifer Becerra filled me in on all things “Wu,” and I’m eager to share what I learned with Xiao Liwu’s many fans!

Jennifer says Xiao Liwu, now 20 months old, is doing quite well. He is not as playful as his older siblings have been and instead has become a bamboo-eating machine. Now weighing 70.5 pounds (32 kilograms), “Mr. Wu” eats about 22 pounds (10 kilograms) of bamboo each day—a lot for a little bear! Shunning most non-bamboo food items, he is developing a taste for Fuji apple slices and applesauce. Lately, keepers have been blending steamed carrots, yams, applesauce, and banana-flavored biscuits into a mush for him. They serve the concoction in a metal pan, which you may have seen in his enclosure.

Lest you think Wu is all about food, don’t worry. He does enjoy playing in a long, plastic tray filled with ice cubes. He climbs all over a recycled plastic “rocking horse,” which is really in the shape of a whale, that is in his off-exhibit bedroom area. And you’ll be proud to know he is doing well with his training. He already urinates on command when he hears the words “go potty”! Being able to collect this vital fluid for periodic testing is part of our animal care protocol. Mr. Wu knows how to “target” or touch his nose to a target stick, and he knows to put his paws up, paws down, and to sit when asked to do so. He also enjoys his new bedding material, called excelsior hay, that is on top of the cave structure. This hay product was on his Wish List—thank you, donors!

Ice cubes feel good on a warm day!

This ice feels good on a warm day!

And then there are scents! Our pandas love to roll and anoint themselves with different odors. Their keepers found a fragrance company that provides a huge variety of choices. They all like the smell of cinnamon, but I found it interesting that each panda also has his or her favorites. For Mr. Wu, it’s wintergreen. Bai Yun enjoys those in the mint family: wintergreen, peppermint, and spearmint. Yun Zi, who is now living in China, loved honeysuckle and earthworm! And Gao Gao? He tends to lean toward more musky scents, but his all-time favorite is rubbing alcohol!

Debbie Andreen is an associate editor for San Diego Zoo Global. Read her previous post, Delightful Tasmanian Devils.

33

Yun Zi Travels to China, Part 2

Dr. Beth (at right) and Jennifer pose with their flight captain.

Dr. Beth (at right) and Jennifer pose with their flight captain.

Be sure to read Yun Zi Travels to China, Part 1!

Panda Yun Zi was a natural traveler in the van all the way to the Los Angeles Airport. He sat quietly in his crate and ate bamboo all the way. When we got to the airport, he decided to take a nap while we waited to get checked by security. We had to wait a short time before Yun Zi and all of his luggage was strapped down safely onto a pallet and ready to load onto the plane. The pilots were very kind to ask what temperature and light settings would make Yun Zi most comfortable in cargo during our long flight.

The time flew by, and before I knew it, Yun Zi, Dr. Beth Bicknese, and I were boarded onto the plane. Yun Zi was nice and calm all the way onto the plane. Not me! I was super-nervous, as this was my first flight overseas and flying on a large cargo plane. We met with all five pilots and introduced them to Yun Zi. He did extremely well meeting the pilots, and they even spoke a little Chinese (Mandarin) so he could practice.

Jennifer and Dr. Beth meet Yun Zi's new keepers upon arrival.

Jennifer and Dr. Beth meet Yun Zi’s new keepers upon arrival.

Our flight departed around 9 p.m., and we were off for our 22-hour journey. The airlines and the pilots were wonderful, as we all felt like we were in first class. They understood our needs and the care we needed to provide Yun Zi on his flight. Dr. Beth and I did not get much sleep on the plane, as we were making sure Yun Zi was as comfortable as possible. It was extremely easy to access Yun Zi, as he was only behind one door, and we checked on him every three to four hours.

I will tell you he was a much better flyer than I! Every time I checked on him, he was resting and calm. He enjoyed his biscuits, bread, and honey water in first-class style. I didn’t sleep much at all, wanting to make sure he was comfortable, and I was reassured every time I checked on him that he was calm. The flight was entirely at night as we flew up the coastline to Alaska and over the Pacific Ocean and landed in Shanghai two hours early, around 6 a.m.

When we landed, we were greeted by airline security, and the pilots quickly took us through customs so we could get back to Yun Zi. It was wintertime in Shanghai, and lucky Yun Zi had his fur coat on, as it was 40 degrees Fahrenheit outside. We waited for Yun Zi to be unloaded and noticed his small welcoming party (small because we landed two hours early!). Dr. Beth and I were immediately introduced to one of his new keepers (Mr. Strong) and veterinarians (Mr. Deng). They checked on Yun Zi and offered him a fresh apple. Yun Zi was polite but decided he would rather sleep.

And off he goes to his new home!

And off he goes to his new home!

Dr. Beth and I passed along Yun Zi’s training video (we had made a video for his new keepers to show them what he knows so far) and all his information to his new keepers. Mr. Deng asked several typical questions about Yun Zi: how much he eats, how much he poops in a day, his favorite scents, and favorite toys. We talked about his training and how he likes to see people.

I know Yun Zi is in good hands with his new staff and was ready for his journey to Wolong with them. I did leave a little piece of my heart in Shanghai that day, but I know Yun Zi will do well in China.

Jennifer Becerra is a senior keeper at the San Diego Zoo.

29

Yun Zi in China

Yun Zi arrives in the quarantine area.

Yun Zi arrives in the quarantine area. Photo credit: Wolong

Life is Good in Dujiangyan

We were all sad to see giant panda Yun Zi leave the San Diego Zoo and move to China, and honestly, we all miss him! However, we were not surprised to hear reports from keeper Jennifer Becerra (see Yun Zi Travels to China) that he traveled well, and it looked like the transition to his new life in China would be very smooth.

Yun Zi explores his new digs.

Yun Zi explores his new digs. Photo credit: Wolong

The changes a panda might experience when he or she moves to a new, far-away home include some changes in diet, new voices, different smells, and, for bears heading to China, the presence of a larger population of other pandas. Experiencing these novel stimuli for the first time may be both challenging and exciting for a young panda, and given Yun Zi’s generally spirited personality, I have no doubt that this was very exciting for him!

A good place to leave a scent mark?

A good place to leave a scent mark? Photo credit: Wolong

Yun Zi is now living at the Duijiangyan Base (part of the China Conservation and Research Centre for Giant Pandas), where there are 21 pandas, including 10 adults. Reports from our colleagues indicate that he is doing very well. Now 4½ years old, Yun Zi is approaching adulthood, but he is not yet of breeding age. That said, this breeding season could provide Yun Zi with some indirect experience, as he may hear the vocal communication of courting pandas at the facility and potentially catch the scent of a panda female in estrus. In a couple of years, he may be ready to experience panda courtship firsthand, but for now, he is simply enjoying spring in the Sichuan Province.

Megan Owen is an associate director with the San Diego Zoo Institute for Conservation Research. Read her previous post, Panda News: The Good and the Bittersweet.

40

What to Eat When There’s Nothing to Eat?

Bear ambassador Mi Ton Teiow finds relatively shallow snow, but no food, as the northern winter begins.

Bear ambassador Mi Ton Teiow finds relatively shallow snow, but no food, as the northern winter begins.

The answer? Nothing.

Most of us are familiar with the idea that some bears spend long periods of time in dens, inactive and not consuming significant amounts of food or water. Some bears in some locations survive eating nothing by doing almost nothing. They become inactive, which is sometimes called winter sleep or hibernation. Although you may be familiar with this aspect of bear ecology, have you thought about how incredible it is? These big mammals can go without eating or drinking for months, sometimes while birthing and nursing cubs, yet wake up without bedsores or weakened muscles! This is why the physiology of bears, including that of giant pandas and polar bears, has been a hot field of research.

The only way for a wild American black bear to survive for months without food in the northern U.S. is to save energy by hibernating in a safe, insulated den. The hole to the right of the tree trunk is the only obvious indication that there is an American black bear below the snow.

The only way for a wild American black bear to survive for months without food in the northern US is to save energy by hibernating in a safe, insulated den. The hole to the right of the tree trunk is the only obvious indication that there is an American black bear below the snow.

Although all female bears seclude themselves in dens to give birth to cubs, not all bears enter dens for long periods of time. There’s even variation within species in whether or not individual bears remain in dens or for how long. Researchers have found that in general, bears spend long periods in dens not to avoid cold temperatures, but to reduce their metabolic requirements when there is not enough food to survive environmental conditions. So, in the southern part of their range where their energy balance can remain positive, individual brown bears, Asiatic black bears, and American black bears may not den except to give birth. At last year’s meeting of the International Association for Bear Research and Management (see post, A Whimsical Bear Ambassador Arrives), Lorraine Scotson and Dave Garshelis reported that some sun bears might den for periods of time in the most northern parts of their range, meaning that non-reproductive denning may occur among at least half of the world’s bear species.

The holes melted in the snow are made by the black bear’s respiration.

The holes melted in the snow are made by the black bear’s respiration.

The giant panda is one bear species that has not been known to den in response to a relative lack of food, and perhaps it cannot do so. During the rare times when all the bamboo plants in an area have flowered and then died, the giant pandas have left the area in search of food; they have not entered dens. Perhaps this is because a bamboo die-off is unpredictable from the giant panda’s point of view, or perhaps this is because a giant panda eating bamboo cannot build up sufficient energy reserves to be able to wait out the lean time in a den, or maybe both factors play a role.

Adult polar bears also do not enter dens solely to avoid food shortages. Pregnant polar bears do spend prolonged periods of time in dens, but biologists think other adult polar bears don’t do so. However, polar bears in some populations regularly fast for extended periods when sea ice conditions don’t allow them to hunt. As for other bears, anything that causes a polar bear to expend more energy, whether inside or outside of a den, or to fast for a longer period of time, makes it less likely that the bear will survive. Climate change is doing just that by reducing the amount of sea ice available to polar bears: the bears expend more energy and go without eating for a longer period of time, creating a great challenge for the conservation of this species (see Polar Bears, Climate Change, and Mi Ton Teiow).

Hibernating bears often line their den with leaves, twigs, and grasses, insulating themselves from the cold ground and conserving additional energy.

Hibernating bears often line their den with leaves, twigs, and grasses, insulating themselves from the cold ground and conserving additional energy.

The Bear Specialist Group’s Ambassador Mi Ton Teiow recently made a visit to the northern US, where he found plenty of snow but little food for bears. After a short stay in this area, which receives an average of 45 inches of snow per year, the ambassador returned (fled?) back to sunny San Diego, where the last measurable snow fell on the city in 1967. The odds are good that Ambassador Mi will not be snow camping in San Diego any time soon.

Russ Van Horn is a scientist with the San Diego Zoo Institute for Conservation Research. Read his previous post, Courtship in Front of the Camera.