Development of Giant Panda Sociosexual Behavior
Standard management practices for captive giant pandas include permanently separating cubs from their mothers before 6 months of age, which enables the adult female to cycle every year, reducing the inter-birth interval and, presumably, increasing the number of offspring produced over an individual’s lifetime. This is one to two years before cubs would normally disperse from their mothers in the wild. This study examines the effects of early removal from the mother on behavioral development, particularly social play, and subsequent adult sexual behavior. Behavioral comparisons are made between young pandas reared with their mothers for 12–13 months and those removed from their mothers at 4–5 months of age and then reared with peers. This study also examines sex differences in giant panda behavioral development, because previous studies on other species have suggested that early social deprivation negatively influences resultant adult male sexual behavior more strongly than it does female sexual behavior.
Twenty young giant pandas (10 males, 10 females) are subjects in this study. Twelve of these individuals (7 males, 5 females) remained with their mothers for 12–13 months. Eight (3 males, 5 females) were separated from their mothers at 4 months of age and peer-reared.
Like the study of maternal behavior, this study is part of a long-term behavioral research collaboration with the Chengdu Research Base of Giant Panda Breeding and the Chengdu Zoo. All the subjects were housed at the Chengdu institutions or Zoo Atlanta. The pandas housed at Zoo Atlanta have been subjects in this study since their birth, and represent each of the comparison groups. The male was separated from his mother at 13 months of age and the female was separated from her mother at 4 months of age. One of the primary reasons these pandas were chosen for loan to Zoo Atlanta was because they were already included in this study.
Data from 17 cubs (9 males, 8 females) have been analyzed for the 6–12 month developmental period. Behavioral comparisons were made between 10 mother-reared (i.e., subjects that remained with a mother for 12 months) and 7 peer-reared (i.e., subjects that were removed from their mother at 4–5 months of age, and then reared with peers) cubs. Mother-reared cubs spent significantly more time locomoting, whereas peer-reared cubs spent significantly more time inactive. Peer-reared cubs engaged in significantly more reciprocal play-fighting with other cubs than did cubs that were raised with a mother and a sibling or unrelated peer. Similarly, cubs that were raised with a mother and a sibling or unrelated peer exhibited significantly more reciprocal and non-reciprocal play-fighting with the mother than they did with the other cub. Finally, peer-reared cubs exhibited oral stereotypic behaviors and mother-reared cubs did not. No significant differences were found between peer-reared and mother-reared cubs for self-motion play, object-examine bamboo, or self-grooming.
Comparisons were also made between male and female cubs. Males initiated significantly more play-fighting with other cubs than did females. Males also initiated more play-fighting behavior with mothers than did females, but this finding only approached significance. No significant sex differences were found for the other behaviors analyzed: reciprocal play-fighting, object-examine, self-motion play, locomote, inactive, self-groom, and nurse.
Our findings show that mother-reared cubs are significantly more active than peer-reared cubs. This may indicate that mother-reared cubs explore their environments more than peer-reared cubs. The presence of the mother might encourage cubs to venture further in their environment, because the mother is generally familiar with her surroundings and confident about moving throughout her enclosure. We have also found that mothers initiate play with cubs and will often awaken sleeping cubs to play. This may also account for the increased activity exhibited by mother-reared cubs. Another important difference affected by rearing condition is the development of stereotypic behavior. Only cubs removed from their mothers before six months of age were found to exhibit oral stereotypies. Young animals of other species exhibit similar behavior when they are removed from their mothers before the species-typical weaning age. We continue to follow the development of the subjects to determine if these behavioral differences persist into adulthood.
Our finding that twin cubs spend more time playing with their mother than with a sibling or unrelated cub is interesting, because young animals typically prefer to play with conspecifics similar to themselves (i.e., like-aged, like-sexed, like-sized). Our results suggest that even when a sibling is present, giant panda mothers act as the primary social agent in behavioral development of their young offspring.
Our finding that male cubs directed more non-reciprocated play toward peers and mothers than did female cubs is particularly interesting given we did not find sex differences in reciprocal play-fighting between mothers and cubs and between peers. It seems that mothers and peers respond equally to play initiation by male and female cubs, but male cubs continue to attempt play initiation more than female cubs. The sex differences found for social play do not seem to simply be the result of higher activity levels in male cubs, because we did not find significant sex differences for the other behaviors we examined. Our findings are consistent with those of other studies examining play in young mammals that have found sexual differentiation in play is most common in species with sexually dimorphic adult roles, particularly species exhibiting sex differences in adult aggression.