Reproductive Behavior of Captive Adult Giant Pandas
With the wild population of giant pandas in serious danger of extinction, it becomes increasingly important that a self-sustaining captive population is established and maintained. Both female and male captive giant pandas exhibit behavioral problems that hinder the development of a self-sustaining captive population. In 1996, personnel from Chinese institutions housing giant pandas reported that most females did not display normal behavioral estrus, and very few males were breeding. The non-breeding males were reported to either lack sexual interest in or show excessive aggression toward estrous females. There was a need to identify the factors responsible for reproductive failure of both female and male captive giant pandas. The purpose of this study was to conduct urinary hormone and behavioral monitoring to determine whether captive females that failed to exhibit normal behavioral estrus were simply not ovulating or were showing “silent” estrus (i.e., ovulating but not showing the behavioral changes usually associated with ovulation). Behavioral and hormonal measures were also obtained from reproductively successful females to determine if there were significant differences between these females and those that were less reproductively successful. For males, behavioral and hormonal data were also collected to compare breeding season behavior with non-breeding season behavior and to compare the behavior of males exposed to estrous females with the behavior of males isolated from estrous females.
Subjects were 17 adult giant pandas (4 males, 13 females). This study also represents Zoo Atlanta’s long-term collaboration with the Chengdu institutions. Fifteen subjects were housed either at the Chengdu Research Base of Giant Panda Breeding or the Chengdu Zoo and two are housed at Zoo Atlanta. The pandas on loan to Zoo Atlanta are particularly important subjects in this study, because we have followed their sociosexual behavioral development from birth into reproductive maturity and can now compare their adult sexual behavior to that of other subjects in the study. The Zoological Society of San Diego (ZSSD) and Smithsonian’s National Zoological Park (SNZP) have also been valuable research partners for this study, because they assisted with hormonal assays.
Comparisons were made between females that were reproductively successful (i.e., copulated or gave birth) and those that were not. We found that females that copulated displayed lordosis significantly more than those that did not and, females that gave birth displayed tail up significantly more than those that did not. We did not find any significant differences in the estrogen concentrations of females that copulated and those that did not. However, we found that females that gave birth had significantly lower estrogen concentrations than those that did not.
Comparisons across females revealed that scent mark, bleat, chirp, tail up, backwards walk, urinate, rest, feed, and aggressive vocalizations toward a male changed significantly in the three-week period surrounding ovulation. We also found that estrogen concentrations changed significantly during the period surrounding ovulation. Within females, several behaviors were found to correlate significantly with estrogen concentrations, including scent mark, chirp, urinate, olfactory investigate, water play, observe male, aggression toward male, locomote, rest, and feed.
One of the males displayed behavioral changes associated with androgen changes. This was the only male that had contact with estrous females in the year that androgen concentrations were measured. Behaviors found to correlate significantly with androgen concentrations were scent mark, bleat, locomote and affiliative interactions with females. This male also exhibited higher levels of behaviors associated with olfactory investigation than the males that were not exposed to estrous females. No significant behavioral differences were found for the males between the breeding season and non-breeding season, but this finding might be accounted for by small sample size.
All 13 females in our study displayed estrogen profiles indicative of ovulation. Estrus was not “silent”, because all females also exhibited some behavioral changes associated with ovulation. Thus, the females in our study did not suffer from the physiological and behavioral problems previously proposed to account for reproductive failure in captive female giant pandas. We have followed the same group of captive adults over several consecutive years. This extensive examination led us to hypothesize that reproductive shortcomings in this group stemmed from insufficient opportunities for males and females to synchronize reproductively. To address this problem, we recommended facility modifications at the Chengdu Research Base and using a stepwise process to gradually introduce potential mates. As a result, loan money from Zoo Atlanta was used to construct a new complex of indoor and outdoor enclosures, which improved communication and reproductive synchronization among adults and allowed individuals to be introduced to multiple potential mates. Thus, the reproductive shortcomings experienced by a few members of this group have largely been overcome by these efforts in Chengdu. In 2004, 8 out of 10 females at the Chengdu Research Base copulated and 4 out 5 males copulated. The three individuals that did not mate in 2004 were just entering reproductive maturity at 4.5–6.5 years old, and will most likely mate successfully when they are older and more experienced.