Introduction

Chimpanzees express many behaviours towards each other, such as vocalization, aggression, copulation, drumming, amongst others. These behaviours carry different meanings, with vocalisations used for greeting and communicating, aggression to exercise authority or power, and copulation for reproduction purposes. Chimpanzees also use drumming for long distance communication, as well as to scare individuals from neighbouring communities. In some scenarios, chimps use drumming to show off their strength to fellow members of their community.

What is drumming? 

Drumming in chimpanzees entails hitting or slapping any object capable of producing sound, mainly using the hind limbs to hit the surfaces of the object. At times, they may also use their hands to hit the objects. The main surfaces hit by the chimpanzees in the Budongo forest are the roots of large trees, and more specifically of species of trees with large buttresses, for instance Cynometra alexandrii, Celtis zenkeri, Alstonia boonei, Ficus exasperata, Ficus mucuso, Celtis mildbraedii, Chrysophyllum albidum, Khaya anthoteca, and Ficus sur (capensis/vogelana). However, any trees with good and large buttress roots can be used for drumming, irrespective of the tree species. Chimpanzees may also use tree stumps for drumming. Chimpanzees know the location of these trees used for good drumming within their territory. In addition, when in communities neighbouring the forest or going through the BCFS camp facilities, chimpanzees may use the walls or doors of houses, empty drums or tins. Finally, chimps can also stump or slap the ground. 

Some signs can help identify when and how an individual is going to drum:

• Puffing: increasing body size by rising of the hair and muscles

• Charging: running towards the hitting surface

• Knowing the location of a drumming tree in the forest

Who performs drumming?

Most often, the males in the community are the ones that do the drumming. Females also drum but the sound produced is not as high as that of the males. By around 3 years, regardless of the sex, chimpanzees start trying to drum and exhibit this culture, though the sound produced is very low and without any rhythm. 

The sound produced from the drumming differs based on the size of the individual, though this does not always impact how loud the resulting sound is. Hierarchy plays a big role in drumming behaviour - if the alpha male drums, the response is high because most members of the community reply by drumming too and calling. It should also be noted that each individual produces a different rhythm whenever they hit a surface, hence it is easy for the other members of the community to recognize the alpha's drumming. This different rhythmic drumming can also be used to identify particular individuals: especially done by experienced field assistants. As well, there are preferences between individuals in terms of the structure of the buttress and the drumming surface selected (e.g., buttress, door, etc.). Musa, a male from the Sonso community, was even observed several times testing the surface of a buttress with his knuckle, to test how loud the drumming would sound.

Drumming is usually done in unique ways: drumming with no vocalization and then vocalize and do the drumming after. The vocalisations performed with drumming is pant-hoots (build-up and climax or only build-up). 

Why is drumming done? 

• To locate their fellow individuals – this is done by drumming, then sitting and listening for a response.

• In the context of patrols (where they travel quietly and in a vigilant way close to the border of their territory), they can drum at the end of a patrol to check whether the other community is present close by 

• To show their presence to other individuals

• To scare off other communities during inter-community encounters – males drum to indicate their number and their strength. During community encounters, the drumming is joined by pant hoots which, unlike drumming, is done by most of the individuals that are present and is also produced to indicate their number. 

• To confuse and facilitate the capture of prey like the black and white colobus monkey.

• To scare off humans (usually accompanied by charging) or other species (e.g., bush pigs) and protect themselves. 

• To show power or strength among themselves, usually performed when charging. Higher ranking individuals are more likely to drum when with lower rank. 

• Drumming can also play a role in bonding i.e., when an individual starts drumming, other individuals can join in to drum irrespective of which individual has started. Joining another’s drumming shows support towards that individual. 

Conclusion

Drumming is a very important behaviour in chimpanzees, with many different purposes, including showing strength or sealing social bonds. There are differences in drumming between individuals in terms of the loudness and the rhythm, for example, but also in terms of preferences for the structure of the buttress and the type of surface selected to drum. Though males are usually the ones to drum, the behaviour can also be observed (though less frequently) in females. Irrespective of these differences, drumming is usually performed to communicate something to others.