Spring 2009 Updates
It has been very quiet around the exhibit lately as the pandas and staff settle back into a normal routine. It will be almost a year before the breeding season and the possibility of a birth cycle come around again—that’s if Mei Xiang returns to a more typical March-to-May breeding time frame. Panda years are long, while the years of our lives just fly by.
About seven to ten days after Mei’s hormones return to baseline, her maternal behaviors gradually disappear. Last week we cleaned out her abandoned nest. The drain grate “cub” was returned to its proper place, which pleased our plumbers, who had to clear her opened drain of shredded bamboo. Mei’s Kong toy and plastic ball “cubs” were also returned to their place on the enrichment shelves in the keeper area.
Tian Tian has been very mellow. He is sleeping the early summer days away in the grottoes, often skipping a meal as his appetite is beginning to decline. Bamboo loses some of its allure around this time every year. Tai Shan still has a great appetite. He weighed in at 205 pounds this morning. It is getting even more difficult to tell him apart from the adult pandas.
Staff confirmed late yesterday that Mei Xiang is not pregnant but was experiencing a pseudo, or false, pregnancy during the past several months. Zoo scientists, veterinarians, and keepers were keeping a close eye on Mei Xiang, monitoring her hormone levels and behavior, as well as conducting weekly ultrasound exams in an attempt to determine if she was pregnant.
On April 20, Mei’s level of urinary progesterone (a hormone associated with pregnancy) began to decline. Upon reaching normal baseline levels, this decline would end in either the birth of a cub or the end of a pseudopregnancy. Based on this information, and not having seen a fetus during the ultrasound exams, Zoo researchers have determined that Mei experienced a pseudopregnancy.
As you may recall from previous years, female giant pandas almost always undergo a pseudopregnancy when they ovulate but fail to conceive. During a pseudopregnancy, hormonal changes and behaviors are identical to those of a true pregnancy, making it very difficult to determine if a giant panda is actually pregnant or not. This is the fifth time Mei Xiang has had a pseudopregnancy. She had her only cub, Tai Shan, in 2005. Giant pandas ovulate just once a year—Zoo scientists will determine whether Mei should be considered for breeding again in 2010.
We expect Mei to return to normal, hormonally and behaviorally (including an increase in appetite and activity level), in the coming days. The indoor part of the Giant Panda Habitat will reopen today at 10 a.m. It had been closed to provide Mei with a quiet environment in the event that she did give birth.
Yesterday, veterinarians anesthetized male giant panda Tian Tian so that scientists could collect semen to freeze and store as part of the Zoo’s collaboration with the worldwide giant panda breeding program.
Zoo scientists have detected the start of the decline in urinary progestin levels in Mei Xiang. This hormone decline indicates that her reproductive cycle will be concluding fairly soon. She has been spending more time in her den and cradles objects as she would a cub. We don't know whether or not she is pregnant or experiencing a pseudopregnancy, or false pregnancy, which is common in giant pandas.
FONZ volunteers are now monitoring Mei's behavior (and manning the panda cam) 24 hours a day.
Tai Shan had a physical and follow-up exam this morning. After being anesthetized in the transfer cage, he was transported to the Zoo hospital. Injecting the pandas with anesthetic always goes very smoothly and this time was no exception, thanks to the practice sessions with the keepers and vets leading up to the “big day.”
During a physical, Zoo animals receive a thorough check-up, which includes blood collection, radiographs, ultrasound, dental exam, and heart and blood-pressure monitoring. In addition, Tai had a follow-up exam with an endoscope to look at both his upper and lower intestinal tract. Gone are any signs of the irritated tissues we saw during his exam last September.
Tai Shan is now consuming large quantities of bamboo culm, or stalk, which is very tough and woody. It is still amazing to see proof that the toughest part of the bamboo plant passes through his digestive tract without incident. Tai’s stomach is honeycombed like the inside of a beehive, while his small intestines were described as being ridged like a cruller donut. All of his tissues from his esophagus to his colon were smooth, glistening, and pearly white to faint pink. Tai’s colon was clean and unremarkable. Well, there was still a bit of bamboo leftovers down there! Now we have to examine minute biopsies collected from along his digestive tract to confirm that everything is perfect at the cellular level. Tai also received his distemper vaccination today.
Mei Xiang has been spending a bit more time in her den. This morning she was up and eating yesterday’s bamboo when we arrived. She was fairly alert and cooperated for ultrasound. After she was done she chose to cradle her pear reward rather than eat it. She carried it under her chin just like a cub.
Since Tai Shan was otherwise occupied, Tian Tian did a great job of being the exhibit panda. With the building closed for Mei Xiang, the boys have to please our guests. Tian was the perfect panda ambassador—asleep, front and center by his grotto.
Mei Xiang decided to spend today, Earth Day, indoors. She was reluctant to move this morning and ate her bag of biscuits in slow motion before retiring to den two for most of the day. We knew this day would be a different when we arrived to find her bamboo uneaten. Mei did shred some bamboo in den three overnight to supplement her nest. She also interacted with her kong toy, picking it up and manipulating it for a few minutes this afternoon. This toy is provided as an object for her to cradle, however Mei will also cradle larger objects such as balls and spools and even the very dear drain grate.
These behaviors are our cues to begin one shift of the behavioral watch (4-7 p.m.) daily. We will not expand the watch until we see further behaviors, such as more nest building, cradling of objects, and further loss of interest in all the affairs of her world, except of course the state of her chosen den.
Mei’s elevated progesterone levels trigger all these maternal behaviors and get her ready for the (potential) main event, the birth of a cub. This hormone is elevated after insemination but then in pandas elevates again usually one to four months later. This first time frame, marked by lower levels of progesterone, is considered the time before the fertilized egg implants in the uterus, a period we note as the period of “delayed implantation.” Then a secondary surge in hormone levels occurs, which is believed to reflect the time when the egg implants in the uterus and begins to develop. The secondary hormone rise has been tricky to mark this year, as Mei's hormone levels have taken a different course from those charted over past years. This secondary rise provides us with a 40- to 50-day window for the end of a false pregnancy or the birth of a cub. Mei behaved normally just yesterday, lying perfectly still for an ultrasound and eating the training treats (bits of apple, pear, and biscuit) with gusto. Nothing significant was observed on the ultrasound. We are left guessing as usual as we create the right birth environment and hope for a sibling for Tai Shan.
Restless Tai Shan and Tian Tian continue to be influenced by their male hormone testosterone. Their days continue to be active ones of wandering, sniffing, scent marking, and consuming large quantities of bamboo culm. It is very impressive to watch them process those large stalks with a resounding crack. Tai and Tian are consuming 33 to 44 pounds daily. It is hard to believe that the low nutrition and energy content of bamboo sustains wild male pandas through the breeding season.
Mei Xiang had an ultrasound this morning, and nothing of interest was observed. Well, some people may find fluid and uterine folds interesting, but most of us who monitor Mei want to see a lot more. The larger shaved area on her belly really has helped to improve the quality of the picture on the ultrasound, even if the content is missing. Her progestin levels remain elevated, and she continues to be active, dancing at the door to go outside in the morning. She is also consuming a lot of bamboo, up to 40 pounds daily, and has started grazing on some of the young, tender grass in the yards. She continues to keep us guessing!
Tai Shan has been the wild man in the trees lately. He enjoys climbing right side up, and then upside down all over the new deadfall, much to the delight of our spring crowds. Tai shows some of the restlessness of his father, without quite the intensity.
Tian Tian appears to be in peak rut, and unfortunately there are no other females to focus his attentions and intentions on. In the wild, male pandas would wander through the three- to five-square-mile home ranges of their neighbors searching for females, congregating and sparring with other males along the way for access to them. Here at the Zoo, enrichment activities last a minute, before Tian is off on his quest again through the yards. He is currently spending most of his time in the big yard, in order to give him maximum room to wander, pace, and deposit his scent by rubbing his tail just about everywhere.
One day late last week, Tai Shan managed to catch a white-throated sparrow. Once in his grasp, he held it tightly to his chest and under his arms, rolling it around on his body and then his head. We have seen our pandas scent-anoint using rotten wood, but this time it was the poor bird. At one point he put it in his mouth and pulled out a few wing feathers before the bird managed to get away. We never saw the sparrow again, so it might have survived, hopefully a bit more wary from its ordeal in the panda yard.
It certainly has been an enriching two weeks for our pandas! Monday a week ago, they were plowing through the snow on their bellies, with the hills of their habitat providing the momentum for adding in somersaults and rolls. The excitement of the snow carried over into wild tree climbing and swinging, then down to the ground to get coated again. By Thursday, the temperature had shifted from below freezing cold to the sunny 70s, and snow-frosted pandas morphed into giant, dirty, mud sliders.
At the beginning of this week we added new logs to Panda Yard 1. Tai Shan got very excited as he watched the crane lowering the giant limbs into the exhibit. So far Tai is the first one to have the opportunity to explore these new furnishings. A bit shy at first, caution was soon replaced with exploration. The logs will provide exercise and resting places, and even a back rest for eating bamboo.
All the pandas continue to shred and consume bamboo at their maximum amounts typical of this time of year. Tian Tian takes time away from eating to show the typical breeding season or rut behaviors of pacing, investigating Mei’s scent marks, and marking over them. We are now seeing similar behaviors in Tai as he matures. Mei Xiang is in her own world, reminding the neighboring males that she is definitely not interested in their existence with her moans. We all watch Ms. Mei and wait expectantly for any change.
We want to say a special thank you to Pandas Unlimited for the funds to enrich our panda exhibits.
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