The ability to flexibly produce facial expressions and vocalizations has a strong impact on the way humans communicate, as it promotes more explicit and versatile forms of communication. Whereas facial expressions and vocalizations are unarguably closely linked in primates, the extent to which these expressions can be produced independently in nonhuman primates is unknown. The present work, thus, examined if chimpanzees produce the same types of facial expressions with and without accompanying vocalizations, as do humans. Forty-six chimpanzees (Pan troglodytes) were video-recorded during spontaneous play with conspecifics at the Chimfunshi Wildlife Orphanage. ChimpFACS was applied, a standardized coding system to measure chimpanzee facial movements, based on FACS developed for humans. Data showed that the chimpanzees produced the same 14 configurations of open-mouth faces when laugh sounds were present and when they were absent. Chimpanzees, thus, produce these facial expressions flexibly without being morphologically constrained by the accompanying vocalizations. Furthermore, the data indicated that the facial expression plus vocalization and the facial expression alone were used differently in social play, i.e., when in physical contact with the playmates and when matching the playmates’ open-mouth faces. These findings provide empirical evidence that chimpanzees produce distinctive facial expressions independently from a vocalization, and that their multimodal use affects communicative meaning, important traits for a more explicit and versatile way of communication. As it is still uncertain how human laugh faces evolved, the ChimpFACS data were also used to empirically examine the evolutionary relation between open-mouth faces with laugh sounds of chimpanzees and laugh faces of humans. The ChimpFACS results revealed that laugh faces of humans must have gradually emerged from laughing open-mouth faces of ancestral apes. This work examines the main evolutionary changes of laugh faces since the last common ancestor of chimpanzees and humans.

Baboons are well studied in savannah but less so in more closed habitats. We investigated predation on mammals by olive baboons (Papio anubis) at a geographical and climatic outlier, Gashaka Gumti National Park (Nigeria), the wettest and most forested site so far studied. Despite abundant wildlife, meat eating was rare and selective. Over 16 years, baboons killed 7 bushbuck (Tragelaphus scriptus) and 3 red-flanked duiker (Cephalophus rufilatus), mostly still-lying ‘parked' infants. Taking observation time into account, this is 1 predation per group every 3.3 months - far lower than at other sites. Some features of meat eating resemble those elsewhere; predation is opportunistic, adult males monopolize most prey, a targeted killing bite is lacking and begging or active sharing is absent. Carcass owners employ evasive tactics, as meat is often competed over, but satiated owners may tolerate others taking meat. Other features are unusual; this is only the second study site with predation records for bushbuck and the only one for red-flanked duiker. The atypical prey and rarity of eating mammals probably reflects the difficulty of acquiring prey animals when vegetation cover is dense. Our data support the general prediction of the socioecological model that environments shape behavioural patterns, while acknowledging their intraspecific or intrageneric plasticity.

Objective: At some sites across Africa, chimpanzees consume army ants, often aided by stick-tools, although consumption frequencies vary greatly. Other populations do not eat these insects at all, despite apparent abundance. The relative importance of myrmecophagy 2 for chimpanzee diet therefore remains unclear. Major functional hypotheses consider army ants either as a preferred food or a fallback fare when preferred foods are scarce. We test these hypotheses for chimpanzees at Gashaka / Nigeria, where chimpanzees consume army ants much more frequently than elsewhere.Methods: Long-term records on seasonality of climate and availability of fruit as the chimpanzees' preferred staple food are compared to rates of recovered army ant dipping wands and army ant remains in faeces.Results: Despite strict seasonality in terms of rainfall and fruit abundance, myrmecophagy does not negatively correlate with fruit availability. Instead, ant eating is sustained year round at high levels, with 44% of faeces containing remains. Conclusions:Results contradict the fallback hypothesis and support the hypothesis of ants as preferred food. Nevertheless, ant-meals can normally provide only negligible amounts of nutrients. At Gashaka, however, nutritional yield may be significant, given that an ant dipping session provides 13 mg of dry weight to a chimpanzee. The species exclusively eaten here, Dorylus rubellus, might be particularly aggressive, thus resulting in greater harvesting success than elsewhere. Army ants may thus serve as a diet supplement or complement in terms of macro or micronutrients. We also speculate that dietary choices likely contain social dimensions that may strengthen group identity.

Many animals, including humans and chimpanzees (Pan troglodytes), eat insects, although frequencies vary greatly between populations. Insects are traditionally either seen as desired nourishment or a fallback fare compensating a shortage of preferred foods. We test these explanations against long-term data on chimpanzees at Gashaka, Nigeria. Here, chimpanzees harvest army ants much more frequently than elsewhere, while termite eating is completely absent. We report a pattern of strict seasonality in terms of rainfall and pronounced peaks in the abundance of fruit, the chimpanzees’ preferred staple food. Even so, evidence based on recovered ant-dipping wands and chimpanzee faecal samples indicates that myrmecophagy does not decrease when fruit becomes more abundant. Instead, ant-eating is virtually constant year round and chimpanzees eat them every other day or so. This contradicts the fallback hypothesis and supports the hypothesis of ants as preferred food. Army ants may thus serve as a supplement or complement in terms of macro - or micronutrients to the chimpanzees. Nevertheless, it remains puzzling why termites are not eaten at Gashaka, despite apparent availability and technological skills to extract insects. We therefore propose that dietary choices are also likely to contain a social element. The non-consumption of a perfectly edible food-item may reflect a "taboo" that comes at some cost. Similarly, army ant gathering is associated with painful bites, and self-experiments suggest that the highly chitinous insects do not taste well, compared to smaller arboreal ants and termites. We speculate that, in this way, mental concepts of identity versus otherness may develop that strengthen group cohesion. We do not have sufficient data for Nigeria, but speculations about social identity based on community-dependent behavioural uniformity are open to empirical testing. The principal method would be to document natural instances of “acculturation”, when female chimpanzees transfer from their natal into a neighbouring community.