Well-digging, river walks and very wet feet

Different populations of chimpanzees across Africa exhibit different suites of behaviours and can even be said to have different cultures. One of the most interesting behaviours in the cultural repertoire of the Semliki chimpanzees is the practice of well-digging. The chimpanzees here are known to hand-dig wells in the riverbed that they drink from, and will occasionally use leaf or palm pith ‘sponges’ to better access water from these.

It is not known for sure why the Semliki chimpanzees dig wells in this way. Whilst they do often dig them when the river has dried up they are also found next to clear flowing water, suggesting that water scarcity is not the predominant driving factor in their manufacture.

The project that I am working on whilst here in Semliki aims to tackle some of the questions that arise when thinking about the wells. Why do the chimpanzees dig the wells, and why do they dig them where and when they do? Are there any patterns for the location of wells and are there preferred locations for digging? These are just some of the questions that I hope to answer.

As part of my investigations I have been surveying the Mugiri River that runs through the study area, mapping sections where wells have been found in the past in terms of sediment type and several other factors. When I find wells I take a series of measurements of their dimensions, location, surrounding sediment type etc and undertake bacterial testing of the water in the wells and of nearby flowing water for comparison. It is always exciting to find the wells and to think of the chimpanzee digging it and to wonder about what made it do this. It is also good to be able to put the odd collection of equipment that I lug around each day to good use.

To search for wells and to survey the river I plan to do a ‘river walk’ at least once a week, starting from today. The aim of these walks is to proceed along the riverbed for a few kilometres taking data on the river itself and on any wells that are found along the way. The walk inevitably involves getting very wet feet as many stretches of the water are deceptively deep, but for the sake of the data collected (and to be honest for the fun of it) I am happy to sacrifice having dry feet for one day a week.

I loved the first river walk this morning and it was great to get a change of scenery from the now familiar trails. I felt very intrepid wading through the river, clambering over logs and debris and pushing through overhanging vines with my notebook in hand.

The first walk yielded four wells, 3km of mapping and many interesting sights along the way, perhaps the best of these being the seemingly never-ending line of ants we encountered. The ants were in the process of moving to a new headquarters and so the whole colony was on show, from the tiny white grubs and the multitude of workers carrying these to the large and viciously-jawed soldiers that guarded the procession.

Overall I would regard my first river walk as a success and so I will not even think of complaining when I have to put on damp boots tomorrow, as unpleasant as this may be! I am looking forward to the river walks to come and hope that they will enable me to begin to unravel some of the mysteries surrounding the well-digging practice of the Semliki chimpanzees.

Written on Friday 23^rd July