Cheating and divorce among gibbons

Brian Switek at Laelaps writes about the social and sex lives of gibbons, and how the social notions of scientists who are studying these animals had coloured our understanding of the behavioural patterns of these apes:

Habituation is a problem for zoologists, and many times a researcher will habituate themselves to one group of animals and study them in detail, but such an approach can have drawbacks. If there are other groups nearby that are not habituated to the researcher they may avoid contact with the study group when they would otherwise interact, and this seems to be the case with gibbons. In previous studies researchers would often habituate themselves to just one pair, other neighboring pairs typically avoid the scientists. The results? Mating outside of the pair that might normally occur was blocked as the non-habituated gibbon wouldn’t allow researchers to get close enough, running off through the canopy instead. Furthermore, many studies take place over the course of a few months or a year, these short studies mask what is actually going on in the Indonesian forests.

As I noted previously, it used to be thought that gibbon pairs formed when a subadult male and subadult female from two “families” met up and gained access to their own plot of forest, and this does in fact happen. What was unexpected, however, is that gibbons are much more opportunistic and do not stick with the same mate their entire lives. A longer 6 year study, undertaken by Ryne Palombit and others, showed that gibbons will often leave their partner if an opportunity arises nearby, i.e. a male might abandon his female partner if the male of another nearby pair dies or disappears. In turn, another male might move in when the 1st male leaves or the abandoned female might die, but it was a bit surprising to find that not all pairs were subadults that were in permanent, monogamous relationships. The realization that gibbons “cheat” and “divorce” leads us to a very important realization; there is a difference between social monogamy and reproductive monogamy, the presence of one not necessarily indicating the other. This illuminates the fact that reproductive monogamy is much rarer than previously thought, mating being a much more opportunistic affair than one dictated by social bonds. Indeed, there may very well be advantages to being socially monogamous that are distinct from reproductive monogamy, the pair bonding of gibbons perhaps having much more to do with defending a territory (and hence resources) than whatever sense of long-term affection was attributed to them previously.

A must-read piece. Take a look!

Tags: gibbons, Lar gibbon, monogamy, reproductive monogamy, sex life of gibbons, siamang, social monogamy, White-handed gibbon