Pandas, Bears, and Pregnancy

Bai Yun’s ultrasounds have revealed a leg, spine, and heartbeat.

The giant panda diverged from the rest of the bear lineage some 20 million years ago, and it has developed some really unique traits not shared by other bears as a result. Dependence on bamboo for sustenance and the development of the pseudothumb to aid in bamboo acquisition are two examples of differences between pandas and other bears. However, when female pandas are pregnant (or pseudopregnant), they remind us of just how bear-like they are. Although pandas do not experience the hibernation-like state of cold-weather bears most of the time, the females still couple hibernation-like behaviors with the changes in their pregnancy-related hormones.

Cold weather bears like polar, black, and brown bears give birth while denned up in the winter. The females rear their young for the first few months in the quiet warmth of their den before emerging in the spring. During the denning period, females generally forego food and are largely inactive, producing milk to sustain their young while they themselves conserve energy by resting. Winter is a good time for females to slow down and fast, because they wouldn’t find much food anyway during the frozen months of that season. Springtime is a good time to emerge hungry from the den, because food abundance is on the uptick at that time of year, and the mothers leave the den with a long season of good eating ahead of them.

Panda mothers experience the same sluggishness and fasting behaviors, but their window for such behavior isn’t coupled with winter. This is probably because bamboo is not a seasonally available food source; it’s around them all year long. Pandas tend to den up in the summer months instead. Those are some of the warmest months in the mountain ranges in China, and caring for tiny, fragile neonates during warm months affords the mother the opportunity to keep her cub sufficiently warm even when she needs to leave the den to feed a few weeks after birth, as panda mothers do.

The San Diego Zoo’s giant panda female Bai Yun’s hormones are in full pregnancy mode, declining from a peak a few weeks ago toward a presumptive birth window. To that end, we have kept monitoring her hormones and behavior, and have been conducting thermo-imaging and ultrasound procedures. What do our results show thus far?

Her behavior is interesting, showing a slight increase in denning activity over a week ago. She is building her nest. She is sluggish and still declining her bamboo but has also become very finicky with respect to non-bamboo, too. She has begun insisting that keepers peel her apple slices during husbandry sessions; no skins for Bai Yun! Her hormones continue to drop toward baseline. And her ultrasounds have revealed a fetal heartbeat!

Yes, we are very excited to think Bai Yun is carrying what we hope will be her sixthcub. We are patiently waiting and crossing our fingers that she will carry this cub to term. I know you will be crossing your fingers with us!

Suzanne Hall is a senior research technician with the San Diego Zoo Institute for Conservation Research. Read her previous update, Panda Update: Seeking Seclusion.

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