Concept results project "Orangutan Cultures: A Comparison of Cultural Behaviour between a Sumatran and a Bornean Population"

1 december 2003

Behaviour can spread through a population when individuals invent the behaviour independently or when they learn it from others. In the former case there is no social transmission and following the definition of culture (i.e. culture is socially transmitted behaviour) used here, there is no culture. In the latter case, behaviour can spread both vertically, from members of one generation to these of another generation (e.g. mother to infant), and horizontally, between members of the same generation (e.g. peers). Which of the two takes place in orangutans remains to be established.
Characteristics of individual behaviour are the key to understanding nonhuman culture.
Individuals of a population will differ in the number of food related cultural behaviours expressed, how often these behaviours are employed and how efficient these are used.
Two hypothesis have been put forward to explain this variation: the necessity hypothesis and the social interaction hypothesis. The neces sity hypothesis assumes that ?necessity is the mother of invention?.
The social interaction hypothesis predicts that, provided some form of learning and/or teaching is important in acquiring novel behaviours, the time an individual spends in association with others skilled in cultural behaviours determines its opportunities to acquire and refine these behaviours. Since individual orangutans show a large variation in their time spend in association, they are very well suited to investigate this relationship.

Where?

Research is being conducted in two research stations. The first research area is the Ketambe Research Station (3o 41'N, 97o 39'E), Gunung Leuser National Park, Leuser Ecosystem, Sumatra, Indonesia. The second research area is the newly established Tuanan study area in the Mawas Reserve, Central Kalimantan, Indonesia (20 09? 06.1? S; 1140 26? 26.3? E).

Preliminary results

Since the Tuanan study site has only recently been established our first concern was to habituate orangutans. The orangutans at Tuanan show several of the cultural behaviours described in the list of van Schaik et al. (2003) and in addition show several that are not in their list and therefore ?new? possibly cultural behaviours unique for the Tuanan area.

Important for our development of models for the spread of cultural behaviours in an area is the fact that not all individuals show all these behaviours. This holds true for both sites. It is important to note here that certain individuals might simply not show a specific behaviour due to the fact that that behaviour only occurs at a low frequency and the fact that some individuals have not been followed sufficiently long. An important next step is therefore to calculate frequency?s per day for all cultural behaviours so that it can be assessed after how many observation hours each individual should in all likelihood have shown each behaviour. This will enable us to specify more realistically which individuals do and which do not show a particular behaviour.

At a later stage in this study we aim to correlate the variation in cultural behaviours between the individuals to association patterns, rank, sex, and also to genetic relatedness. At both sites faecal samples are being collected for further analyses of genetic relatedness.

Summary

In summary, the first few months have yielded several new behaviours at Tuanan that can be classified as cultural since they do not occur in other areas. In addition it is very likely that there are several differences in cultural behaviours between the two study sites (Ketambe and Tuanan).
The remainder of the project time (until July 2006) will be used to collect more data on more individuals in both sites. This will yield a more complete matrix for the cultural behaviours for all individuals at each site and also on more subtle differences between individuals. These complete matrices will then be used in subsequent analyses for the distribution of cultural behaviours at each study site.