Because our studies are longitudinal and long-term, so far we have incomplete data for making definitive conclusions about the impact of early weaning and hand-rearing on long-lasting social and behavioural competency in the giant panda. It has been standard practice in Chinese breeding institutions to wean a giant panda cub permanently from its mother at least one year earlier than weaning occurs in the wild. Certainly, removing a cub at a younger age reduces the interbirth interval by enabling females to re-cycle (and potentially conceive every year), thus increasing total offspring number in the ex situ population. However, we would argue that depriving a young panda of a full and protracted social experience with its mother may have long-term detrimental consequences on its social competence and its eventual value and contribution to the population. To date, we know that allowing at least four months of mother-rearing does not appear to significantly compromise a female's later reproductive ability. However, weaning earlier in life appears to produce females that lack critical mothering skills. Nonetheless, if these females do reproduce, their offspring can survive by the remarkable ability of unrelated dams to accept cubs -often multiple offspring - through cross-fostering. Additionally, some behaviourally deficient females appear to be able to learn to become good mothers over time. The impact of early separation from the dam with the onset of the young's eventual reproductive ability is less clear and confounded by the usual practice of labelling an individual as a nonbreeder. These individuals have historically been ignored, with little chance to contribute to the gene pool. But when given a later opportunity to breed, many of these pandas reproduce. Finally, as yet, we have been unable to relate the severe problem of male hyperaggression to any early social deficiency. Rather, this behaviour may be a natural trait that is being misdirected to females because of inadequate captive management techniques. Regardless, we will continue to monitor the male cohort in our study (a few of which have now entered adulthood) for their reproductive proficiency in the context of their earlier life experiences.
Meanwhile, we continue to see value in exploring the vast amount of data available from other species on the influence of early rearing on later reproductive competence. This approach will be useful for identifying future research priorities for the giant panda. Our highest overall priority will continue to focus on determining the impact of longer periods of mother-rearing on an offspring's subsequent reproductive viability and parental behaviour. The latter appears especially important in an altricial species such as the giant panda.
More specifically and based on experiences to date, we would suggest that high priorities in basic research include:
1. additional studies on the significance of sex differences in play-fighting of cubs and its role in subsequent reproductive and social success;
2. identifying the earliest time (or window) of weaning that will allow offspring to become fully socially competent as an adult (in parallel, such efforts should closely monitor the potentially adverse health effects of premature separation from the dam on traits such as growth rate and disease susceptibility);
3. exploring the significance of size and sex of a cub's peer group post-weaning on subsequent development;
4. detailed investigations of the relationship between testosterone concentrations, behaviour and possible influences of social histories on male behaviours, especially aggression.
From an applied management perspective, our findings would strongly suggest that more attention be focused on providing 'learning opportunities' for breeding. This is relevant to both sexes, but especially for placing young males with older, experienced females. This indeed may require re-analysing the existing paradigm for most small holding institutions where two individuals is the usual number. Rather the management norm may need to be shifted to maintaining a small population, perhaps at least two experienced adults and one to two younger adults to be mentored by their older counterparts. In a related matter, it would be interesting to study further the ways to train behaviourally deficient dams to be better mothers. It is exciting to know that dysfunctional females can acquire these skills, but how can the process be made more efficient? Certainly another management-related research target should be investigating the value of allowing both males and females more opportunities to explore each other's scents, largely to improve familiarity, reduce aggression and promote safe breeding. Similarly, any technique that has proven useful for reducing antagonistic behaviours in other species, especially carnivores, should be tested in the giant panda.
Finally, there is value in being more diligent in recording individual animal behaviours and predilections, including adding this information to the studbook. Indeed, the studbook for this species should contain relevant information on rearing methods for every animal, data that will allow tracking the importance of mother-rearing on overall species' well-being in captivity. Eventually it will be necessary to assess the overall benefits (or detriments) of premature mother-cub separation. Although it makes sense that a practice that allows a cub to be produced annually (rather than every two to three years) is valuable, ultimately the questions need to be asked:
1. Are giant pandas biologically built to produce healthy cubs annually?
2. Even if so, are our management practices sufficient to ensure that prematurely weaned offspring can be raised into competent adults that will contribute to a successful, self-sustaining ex situ population?
The experiments to address these queries are ongoing, with answers expected in the near future.
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