Behavioral Competence of Adult Giant Pandas Exposed to Varied Early Social Environments
Both female and male captive giant pandas exhibit behavioral deficiencies that affect their reproductive competence, and one determinant of reproductive success is early social rearing experience. The period of mother rearing provided for captive giant panda cubs is usually significantly shorter than the species-typical duration. Our study of sociosexual behavioral development examines the ramifications of this by following individuals with different rearing experience from birth into adulthood. Because giant pandas are not sexually mature until 5 to 6 years of age, it will take at least 10 years for us to gather enough information on subjects in the ontogeny study to determine how rearing experience affects adult behavior. Thus, we also examined this question by determining how the duration of mother rearing affected mating behavior in the captive adult population. We hypothesized that the duration of mother rearing would be positively correlated with the likelihood of successful reproductive behavior. Thus, the earlier the animals were removed from their mothers, the more disturbed the reproductive behavior was expected to be. We also hypothesized that males would be more severely affected than females by shorter durations of mother rearing.
Subjects were 52 giant pandas (17 males, 35 females). Twenty-six of these animals (9 males, 17 females) were wild-born, and 26 of them (8 males, 18 females) were captive-born. Two of these animals remained with their mothers for one month or less, four animals remained with their mothers for 1–4 months, 20 animals remained with their mothers for 4–6 months, five animals remained with their mothers for 6–12 months, and 21 animals were separated from their mothers after 12 months of age. Twenty-one females and 9 males had copulated as adults. This study involved collaboration with 11 other panda holding institutions located in China, Germany, Japan, and the United States.
We first examined the effect of birth origin (i.e., captive-born vs. wild-born) on copulatory behavior. We found 62% of captive-born subjects and 54% of wild-born subjects copulated as adults. The difference in copulation rates between captive-born and wild-born subjects was not significant. Thus, captive-born individuals were as likely to copulate as wild-born individuals. Second, we examined the effect of duration of mother rearing on reproductive success. In this sample, duration of mother rearing ranged from 0–18 months. One hundred percent (two out of two) of subjects that remained with their mothers for no more than one month copulated as adults, 25% (one out of four) of subjects that were mother-reared for 1–4 months copulated, 70% (14 out of 20) of subjects that were mother-reared for 4–6 months copulated, 60% (three out of five) of subjects that were mother-reared for 6–12 months copulated, and 48% (ten out of 21) of subjects that were mother-reared for more than 12 months copulated. No significant difference was found for reproductive success under different mother rearing conditions. Thus, offspring that were removed from their mothers at an early age did not differ from those that remained with their mothers for a relatively longer period of time in exhibiting successful mating behavior. Finally, no significant sex difference was found within the relationship between early rearing experience and reproductive success. Thus, the effect of duration of mother rearing on reproductive success did not differ between males and females.
We found no significant effect for early rearing experience on adult reproductive success in this study. However, we have reasons to suspect the reliability of the findings. First, our sample had a biased distribution. That is, 50% of our subjects were wild-born, whereas only about 30% of the total captive population was wild-born. Second, according to the animal care staff, some wild-born animals were rescued and captured as adults because of illness or injury in the wild. Although these animals were assumed to have stayed with their mothers for a species-typical length of time (18 months), differences in their experience compared to that of captive-born animals might have affected their later reproductive behavior in captivity. For example, some wild-born animals that were captured as adults displayed extreme timidity toward other animals, which appeared to be a factor that contributed to copulation failures. Thus, the varied backgrounds of wild-born animals might have confounded our analyses. To eliminate the potential confounds brought in by wild-born animals, we analyzed data from captive-born animals separately. However, no significant effect of rearing experience was found among captive-born animals either. This may be because of the lack of variation in the duration of mother rearing for captive-born animals. That is, it has become a standard management practice in Chinese zoos that giant panda cubs are permanently removed from mothers between four to six months of age to allow their mothers to enter the next reproductive cycle earlier than the natural condition. In our study 69% (18 out of 26) of the captive-born subjects fell into the 4-6 months of mother-rearing group, which resulted in a lack of variation in the independent variable, hence decreasing the ability to detect a significant effect. Therefore, adding more captive-born subjects that remained with their mothers for a longer period of time (e.g., 12 months) will help us determine the underlying influence of early rearing experience on reproductive success.