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While the great apes such as chimpanzees, gorillas and orang-utans are familiar to many people, it just might be that humans can learn much from the smaller, less well-known apes of the gibbon family.

Like humans, gibbons usually live in family groups consisting of long-term, mated pairs and overlapping immature offspring. However, divorce, death and subsequent bonding can result in varying family groupings such as step-parents and half-siblings.

Anatomy and Human Biology postgraduate students Helen Dooley and Belinda Burns are extending their honours work on captive gibbons to investigate gibbon families using two behavioural ecology approaches.

Helen has been observing Kloss’s gibbons (Hylobates Klossii) in the wild over an 18 month period at the Siberut Conservation Program (SCP) field site on the Mentawi Islands in Indonesia.

Kloss’s gibbons are endemic to the Mentawai Islands and are unique among gibbons because humans have been their primary predators for at least 2,000 years.

Group sizes were larger at the Siberut site than in more southern populations and several of the groups had three (rather than the more common two) adult-sized individuals. For these gibbons, one advantage of extra adults in the group may be protection against predators.

Larger gibbon groups employed an anti-predator behaviour that included one adult acting as a ‘decoy’ by approaching and displaying to human observers while other group members fled quietly in various directions.

‘Decoys’ may risk their own safety to protect other family members from human predation. Helen Dooley hopes to use DNA analyses to examine the relationships of these individuals: are the extra adults mature offspring staying at home to help or are these groups polygamous (extra unrelated adults)?

Adult gibbons are also important role models for immature gibbons and pass on valuable skills such as foraging and social interaction.

Like humans, immature gibbons grow up slowly and exposure of young gibbons to varied social interactions may be important.

Detailed observations of social behaviour are difficult to obtain in the wild, so captive studies of the behavioural maturation of gibbons in differing social environments are also important.

As a result, Belinda Burns is studying the role of social context in the behavioural development of captive, immature gibbons.

Ecological variation is reduced in captivity where groups are managed in a similar manner, so behavioural differences between gibbon families are more likely to reflect underlying species differences or responses to social environments.

Family groups of gibbons housed in naturalistic enclosures in Australia and New Zealand include the silvery gibbon (Hylobates moloch), the white-cheeked gibbon (Nomascus leucogenys) and the siamang (Symphalangus syndactylus).

Cross-sectional measures are augmented with rare longitudinal measures of behaviour spanning the seven years since Dooley’s first honours work on gibbons at Perth Zoo – enough time to observe a baby gibbon growing up.

Burns’s study is the first to measure subtle social interactions between individuals of known sex and age to better understand the role of family composition in gibbon social maturation.