Thesis: Family life: A comparative study of behavioural development and family social dynamics in captive gibbons (Hylobates moloch, Nomascus leucogenys and Symphalangus syndactylus)
Gibbons are commonly described as monogamous apes; however, recent research suggests that gibbon social behaviour is more complex. Gibbons, like many humans, tend to live in nuclear family groups consisting of mum, dad and up to 4 offspring, but blended families may form after a death or divorce. Gibbons are also very long-lived (20 to 40 years in the wild) and reproduce slowly (one offspring every 2-4 years). Recent evidence from field studies suggests that many gibbon groups contain more than two adult individuals; however, it is so far unclear whether this is due to delayed dispersal of mature offspring or whether gibbons form polygamous groups more often than previously thought.
The study of primate behaviour is increasingly focused on the flexibility of primate species in response to ecological and social conditions. If gibbons are not always monogamous, what causes the variation in group composition? The plastic responses of individual gibbons to their surroundings results in variation among and within species. Understanding the patterns of physical, behavioural and social maturation, dispersal and new group formation may give insights into the evolution of social structure. This is particularly true in “nuclear family” living species wherein the retention or expulsion of mature offspring show variation. Individual gibbons vary in the degree of investment in offspring or siblings. Studying subtle intra-group interactions in response to changes in group composition is possible in captive groups. The gibbon species in Australian and New Zealand zoos (H. moloch, N. leucogenys and S. syndactylus) represent three genera and allow a comparison of intra-group behaviour between genera. There is sufficient variation in the structure of captive gibbon groups in Australia and New Zealand to provide comparisons of activity by age groups and to determine how parental behaviour toward existing offspring may change with the advent of new offspring and the maturation of those existing offspring.
Why my research is important
All gibbons are found in SE Asia, from China down to Java. Studying them in the wild is extremely difficult because they occupy the highest part of the canopy in dense tropical rainforest. They are also extremely agile and fast and not easily habituated to the presence of human observers.
Naturalistically housed captive gibbon groups give researchers the opportunity to quantify subtle social interactions in a semi-controlled environment, using individuals of known sex and age. While of course, their behaviour will be dictated in part by their management (e.g. feeding routines etc) and their ability to alter their social interaction opportunities is limited (can’t leave enclosure), the observable patterns in how they do respond to their social and physical environment may reflect underlying behaviour patterns that allow investigation of gibbon life history. This is especially apparent when there are changes in the social structure of the group (e.g. addition of a new individual) and individuals’ responses can be compared before and after such an event.