How Behavioral and Endocrine Factors Influence Well-Being During Development of Captive Giant Pandas

Adult giant pandas are essentially solitary animals and rarely make social contact, except for mating, which occurs for only a few days each year. In captivity, young giant pandas are typically raised with peers from the time they are permanently removed from their mothers into adulthood or until aggressive interactions become prevalent. Because captive giant panda cubs are typically removed from their mothers one to two years earlier than is typical for the species, peer-rearing is used to provide socialization for young pandas. There is some evidence from other species that prolonged social housing of solitary species results in chronic stress, which may disrupt reproduction, or leads to habituation and loss of sexual stimulation from potential mates. Thus, extended social housing of giant pandas may be detrimental. However, there are no clear guidelines for determining the optimal time to change management from social to solitary housing. Separation procedures have been used to assess peer attachment in a variety of species, and so this methodology was adopted to assess attachment in young giant pandas. Specifically, the purpose of this study was to examine the behavioral and physiological effects of brief, periodic separations on a pair of subadult pandas to determine the optimal time to change from social to solitary management.

The giant pandas on loan to Zoo Atlanta were the subjects of this study. Endocrinologists from the Zoological Society of San Diego assayed urinary cortisol for this study and helped interpret the results. The pandas were separated for 24 hours once a month for seven months. Behavioral measures and urinary cortisol data were analyzed to assess the subjects’ reaction to separation and subsequent reunion.

After the first four separations, both animals experienced a reduction in cortisol during subsequent separations. The March 2001 separation was the first time both animals displayed lower cortisol levels in the separate condition. The female also began to vocalize aggressively at the male in March. Contact aggression between the pair was only observed in April 2001 when the female was in estrus. Thus, the cortisol patterns seem to correspond to behavioral changes between the pair that were related to sexual maturation of the female.

In general, the male responded to the periodic separations with more behaviors characteristic of social attachment and protest than did the female. The male spent less time feeding when his cortisol concentrations increased. He also locomoted more and engaged in more olfactory investigation over the course of the separations. Social behavior decreased for the female in the pre-separation and reunion phases over the course of separations. The results indicate that the female may have adjusted more quickly than the male to solitary housing and by the end of the study may have preferred solitary housing. The sex differences in behavioral reactions to separation might be related to differences in rates of sexual maturation. Females tend to mature at a younger age than males. The female in this study exhibited a hormonal profile consistent with ovulation in 2001, but the male did not have a hormonal profile like that of a mature male in 2001. Throughout this study, the male may still have been in a juvenile stage of development, and this may explain why he was more interested than the female in maintaining social contact.

Based on the results of this study, housing of the pair was changed in 2001 from continuous social housing (i.e., access to conspecific for 24 hours per day) to partial social housing (i.e., access to conspecific for 4 hours per day).