![]() ![]() Surprisingly, we identified individuals of different age and sex moving from one group to another within just a few days, as well as other individuals found alone on some occasions and then integrated within groups on others. 40 km² to try to identify the great majority of the gorillas then present in the population. Also, the monitoring took place in a small study area of ca. The field monitoring took place in a very reduced time period, from May to August 2013, to obtain a snapshot of the composition of the population at that time. The genetic analyses of fecal samples collected in night nests of social groups and lone individuals allowed the identification of more than 120 gorillas, the study of the relatedness between them, and the determination of the gorillas present in each social group. However, the analysis of the population structure revealed that this high tolerance was a widespread phenomenon. One could think that these non-aggressive interactions were exclusive for these habituated gorilla groups. ![]() In some encounters the three gorilla groups were found together, adding up to more than 50 individuals. The interactions were frequently driven by young gorillas, but all age classes participated and silverback males showed remarkable tolerance towards these interactions. During the encounters, individuals from the different groups traveled, fed and even played peacefully together. The almost daily observations over 5 years (2013-2017) of three focal gorilla groups habituated to the presence of humans and with overlapping home ranges, allowed us to directly observe encounters between the groups in the forest. Consequently, the interactions between gorilla social units at these sites may not be representative of social behaviour within the forest. Moreover, not all western gorilla groups have access to such unique landscape features. In this sense, bais could represent abundant but geographically restricted resources, possibly located outside gorilla ranges and that, as such, do not need to be defended. Even though the frequent intergroup interactions were overtly peaceful at these sites, doubts remained about the real nature of western lowland gorilla ecology and behaviour in the surrounding dense forests where groups spent up to 99 % of their time (Magliocca & Gautier-Hion 2002). Nonetheless, the scarce accessibility and visibility inside the forests had insofar limited most of the studies on western lowland gorillas to bais, open clearings that work as rendezvous for multiple family groups foraging on plants rich in mineral salts. While in mountain gorillas the rare intergroup interactions frequently resulted in agonistic encounters/displays and even infanticide, aggressive interactions were exceptional among western lowland gorillas. Since the dawn of great ape studies, it was clear that the western lowland gorillas inhabiting the remote rainforests of the Congo River basin and the mountain gorillas ( Gorilla beringei beringei) from the volcanic slopes of the Rift Valley displayed remarkable differences in social behaviour. The research has revealed a dynamic social structure with frequent exchanges of individuals between groups favoured by a high degree of tolerance and peaceful coexistence among their members. This multidisciplinary study was based on five years of monitoring three gorilla groups habituated to human observers, and 4 months of intensive non-invasive genetic sampling of the entire population of an area of about 44 km² in the Ngaga Forest (Republic of the Congo). A recent study unveils some of the enigmas associated with the social behaviour of the western lowland gorilla ( Gorilla gorilla gorilla) from the impenetrable African equatorial forests it was the result of an international cooperation bringing together the efforts of scientists at Spanish and French research institutions assisted by the SPAC Foundation gGmbH (Germany). ![]()
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