From the field!
March 2022 (Sam Baker)
A Grooming Hand Clasp (GHC), as observed by the author at Issa (left) with straight-armed palm-to-palm GHC (the most common style) and on right, as drawn by Natasha Ereira-Guyer. The drawing depicts the same pairing during a second clasp moments later, and exemplifies a straight-armed palm-to-wrist GHC.
Habari! My name is Sam Baker, I’m a postgraduate from University College London in Bioanthropology. I travelled to the GMERC research station in the Issa Valley during the latter part of 2021 to collect data on the Grooming Hand Clasp (GHC) in chimpanzees – but saw so much more! My time at Issa didn’t just reward me with chimpanzee observations. The area is home to numerous mammal and bird species, and if fortunate – as I was – there is a chance to observe these species in their wild synchrony… more on this later.
But first, what is a GHC? It is best described as a social custom that is expressed between adult members of the community, individuals engage in a connection of arms overhead whilst they simultaneously groom one and other. The behaviour occurs across eastern, central, and western chimpanzee populations. The GHC differs between closely located groups and variation in the behaviour is not based on genetic or ecological differences (broadly speaking). Primarily, the GHC serves a grooming function, allowing both individuals access to certain portions of the partner’s body. It has been proposed to be a signal of rank within the group, strengthening the hierarchical backbone of chimpanzee communities. Numerous studies have examined the different clasping styles of E African communities - a GHC clasp contains two arms which provide a functional shape through angles at the elbow and wrist joints, this is accompanied by specific connection points where the arms meet; collectively we can refer to these elements as style.
For my study I investigated potential causes of intra-group variation responsible for the inter- community differences already identified in the literature. I suggest that the GHC reveals ‘who-is-who’ within the community, it alludes to the social variables (rank and sex) of claspers, certainly for human researchers, but perhaps for chimpanzees, too. I found that social variables account for stylistic variation observed in the GHC, and we can reasonably predict the clasping individuals’ rank and sex through specific stylistic combinations.
Beyond my investigation into GHC, I observed other unpredictable events, some enormously rare!
Chimpanzee colobus hunt
Chimpanzees are known to hunt red colobus monkeys, yet these events are impossible to predict and at Issa, are rare compared to other communities. In a moment of enormous luck, I observed this putative social hunting, including the vocalising, displaying, and shepherding of the prey the monkeys that is suggestive of cooperative hunting, as described elsewhere. The result was numerous captures, for chimpanzees a successful hunt, but which for me, was both extraordinary and distressing!
Corona catches galagos
Corona, a young adult female in estrus, had a uncanny ability of locating and catching greater galagos (Otolemur crassicaudatus) from tree holes during the day. I observed her do this twice, with a total of three kills observed during my time at Issa. She was the only member of the community to do this, interestingly, on both occasions she did not share the meat, even when consuming the meat near five (!) high-ranking males.
Two months among the community situated throughout the Issa Valley rewarded me substantial observations of clasping data, which when coupled with te events described above, made for an unforgettable field season. Issa is unlike other E African chimpanzees: smaller than other communities, comprising more males than predicted, and exhibiting less intra- and inter-group aggression (so far!). A final distinction that I propose is the distinctiveness of a unique GHC style (see photograph). This style differs from that of the closely located Mahale Mountain National Park (M group) community recorded by McGrew and colleagues (year)
Finally, an enormous ASANTE SANA to the GMERC team that supported me throughout this work.