Nambi, her daughters Nora and Night, and the young sub-adult male Zalu are travelling together in the south when they hear calls near by; immediately nervous, they stop and glance around. Suddenly two strange females appear: an older adult and a young sub-adult who is in swelling, a sign that she might be coming into her fertile period. Nambi and her daughters seem relatively uninterested, but Zalu is keen to check out this attractive young newcomer and moves over to sit near the younger female.

It’s quite unusual for a strange adult female to be found in another group’s territory without being in swelling; chimpanzees can be highly territorial – brutally attacking and sometimes killing strangers that stray across into their community area. To the local females any new female represents competition for them and their offspring; however for the males, new females represent a new chance to mate. Arriving with the large pink genital swelling that signals the oestrus period is a way of attracting the favour and, by association, the protection of the community males. Straying across territory lines without it is a very risky move.

While the younger female is quite relaxed, the adult newcomer is clearly nervous and pant-grunts submissively to Nora; this seems to be the wrong move and Nambi suddenly starts to pant-hoot and scream loudly – a sure sign she’s trying to get the attention of other members of the Sonso community, not something that bodes well for the strange adult. Sure enough, within a few minutes the top two males, Nick and Musa, arrive displaying energetically. They move immediately over to the new female, but show no signs of attacking and after she pant-grunts to them they both relax.

While so far Nambi hadn’t seemed particularly bothered by the adult female, the fact that when the males turn up they appear to be accepting of this new potential competition doesn’t seem to be at all what she had in mind. She apparently decides she’s going to have to do something about this unwelcome visitor herself. The top female in the Sonso group, Nambi is a force to be reckoned with and she now attacks the strange adult, biting her in the back and leaving her bleeding. The males are still sitting on the fence; they don’t seem keen to drive off this potential new addition to their group, but they seem equally unwilling to risk incurring Nambi’s wrath by doing anything to defend the stranger. After the attack the Sonso chimps start to move away, but although this gives the strangers a clear opportunity to escape they make the strange decision to follow the Sonso group. The young sub-adult female with her swelling gets plenty of attention and avoids any real hostility, but again the adult female is not so lucky. Another big male, Zefa, arrives and starts to attack her, this time everyone joins in and she is brutally beaten and dragged along the floor.

Over the course of the day other Sonso community members come and go – two more females Janie and Juliet arrive and the adult female is attacked for a third time. Not until 4pm, when the Sonso chimps are enjoying a last feed and starting to think about finding a nesting site for the night do the two strangers disappear back into the thick undergrowth.

While the male chimpanzee hierarchy has been well documented, we are only starting to get a glimpse of the complex social dynamics that govern female community structure. DNA based paternity research suggests that some females seem to copulate outside of their community on a regular basis and observational work has shown how peripheral community females seem to juggle membership of several communities. Days like this one highlight just how little we understand about the complex social lives of our forest cousins. What could have motivated the adult female to visit a neighboring group when she wasn’t in oestrus? And why stay after the first, or second attack? What was her relationship to her young companion? Why did Zefa (the gamma male) attack her when the top two males had not – was he trying to curry favor with the powerful Sonso females? The only thing we can be certain of is that more research is required, and that we are more than happy to keep searching for the answers!

Is culture uniquely human? Many people would instinctively answer yes, but there is now a well established body of research that questions whether we may be wrong to assume this. Over the years a number of behaviours have been proposed as the answer to the puzzle of what makes us human – planning, tool use – all have fallen by the wayside as observations of their use by other species ruled them out. In recent years some of the hottest scientific debate has centered around the question of culture. Frequently hindered by the lack of agreement over what exactly culture is, there is still no doubt that the debate has stimulated exciting observations and experimental research in species that range from chimpanzees to crows. Some primatologists argue that there are group-specific behaviours seen in chimpanzees that can not be explained away by ecological or genetic factors; these must be transmitted socially from generation to generation, and that this constitutes a form of culture.

Observations such as the nut-cracking in wild west African chimps inspired a body of experimental research – now Sonso PhD researcher Thibeaud Gruber has added to the debate with new evidence recently published in the journal Current Biology. He and his colleagues present the findings from a series of experiments conducted with two Ugandan chimpanzee communities: one in Kanyawara and here with our own Sonso group. Both groups are the same sub-species of chimpanzee and live in similar forest environments but show some interesting behavioural differences. Kanyawara chimpanzees regularly use stick tools to extract honey, a behaviour never seen at Sonso. When both groups were presented with the same controlled task of extracting honey from holes that had been drilled in logs, the Kanyawara chimps spontaneously manufactured stick-tools while the Sonso chimps used either their fingers or the leaf sponges that are normally used for collecting drinking water from tree holes. Given the absences of differences in genetic or environmental factors, the researchers concluded that the chimps must be relying on their local cultural knowledge to solve the new task.

For more information the full article is currently available in the online journal of Current Biology as: Gruber et al. 2009. Wild Chimpanzees Rely on Cultural Knowledge to Solve an Experimental Honey Acquisition Task.

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