Cooperative Problem-solving among non-human primates provides important insights into the evolution of social behavior and interaction. Although such behaviors have been documented in several great ape species, spontaneous, role-specialized cooperation between adult gorillas remains rarely reported. Here, we describe and analyze a recurring dyadic interaction between two captive adult female western lowland gorillas (Gorilla gorilla gorilla), Amelia (dominant) and Lisha (subordinate), who are half-sisters. The analysis is based on a primary event recorded via security cameras in 2024 and supplemented by opportunistic observations from 2021 to 2025. In the primary event, the two individuals combined an environmental feature with complementary body postures to overcome a spatial barrier: Lisha positioned herself quadrupedally atop a rock platform, enabling Amelia to climb onto her back and access a high-hanging Yellow Poinciana (Peltophorum dubium) branch (approximately 4.5 m above ground). Critically, both individuals shared the proximate goal of accessing and dislodging the branch, a goal that remained consistent across all documented events. This role differentiation was consistent across all documented observations. The 2024 event was followed by non-contested co-feeding and a branch-dragging display by Lisha, whereas the 2025 observation ended with exclusive consumption by Amelia, demonstrating variation in outcomes independent of the shared proximate goal. Although the interaction displays features consistent with elements of the social tool use (STU) framework, particularly voluntary participation and self-directed positioning, the shared proximate goal across all events and Lisha’s proactive initiation establish this as cooperative behavior rather than STU, regardless of whether communicative signals could be verified. Across observations, Lisha’s participation appeared voluntary, and no physical coercion by Amelia was observed. The precise mechanisms of communication remain unclear due to the absence of audio recordings. However, this does not undermine the classification as cooperation, which is fundamentally defined by shared proximate goals and functional interdependence, not by the mechanics of communicative exchange. This report contributes to the study of gorilla social behavior, highlighting the capacity for flexible, context-dependent cooperation in adult gorillas, providing important observations that may serve as a reference for future research on cooperative problem-solving among gorillas in captivity.
Protected areas are central to primate conservation worldwide, yet the contribution of adjacent non-protected forests remains poorly understood. We conducted the first systematic assessment of primate communities across the Tarap Hill Reserve Forest, Northeast Bangladesh, to compare primate communities between its formally protected and non-protected forest parts. We surveyed 147.32 km of diurnal and 100.34 km of nocturnal transects, recording 48 clusters of five diurnal primate species and 20 individual Bengal slow lorises. Western hoolock gibbon found only in protected forests, Northern pig-tailed macaque only in non-protected forests, whereas the remaining species were recorded in both. Relative density estimates varied among species, but forest protection status did not significantly influence overall primate encounter rates or species-specific cluster sizes. These findings highlight species-specific patterns associated with habitat protection status and may indicate the complementary conservation value of both protected and adjacent non-protected forests. Integrated management of both should therefore be important for sustaining primate populations and other wildlife in such fragmented landscapes.
Urbanization and habitat fragmentation expose arboreal wildlife to electrical infrastructure in Porto Velho, Rondônia state, Brazil. This study describes four fatal electrocution events involving Mico rondoni and examines the circumstances associated with the accidents. During seven months of monitoring in the Floresta neighborhood, all four deaths involved adults from the same group and occurred at a single recurrent site. The animals showed burns on the hands and feet, and one sustained trauma after falling. The concentration of events at one power-line location identifies a local electrocution hotspot but does not establish the frequency or population-level importance of this threat across the species’ range. The cases support site-specific mitigation, including technical assessment and insulation of hazardous electrical components, combined with monitored canopy crossings. Broader surveillance is required before the relevance of electrocution to M. rondoni conservation can be determined.
How behavioral variation is partitioned among intrinsic attributes, extrinsic conditions, and idiosyncratic individual signature has consequences for the targets of selection and the mechanisms by which behavior evolves. Once the structured sources of behavioral variation have been accounted for, any variation that remains and is consistently attached to particular individuals constitutes an individual signature. Contemporary frameworks recognize three axes along which such a signature can manifest: differences among individuals in mean expression (the classical personality axis, e.g., some individuals consistently more active than others); in plasticity (the reaction-norm slope, i.e., individuals differing in how strongly they adjust behavior to environmental change); and in predictability (residual intra-individual variability, i.e., individuals differing in how variable their behavior is from one occasion to the next). Whether an individual signature exists on any axis in energy-minimizing species, whose adaptive strategy may favor flexibility over consistency, has not been formally tested. We used 6486 focal observations on 17 mantled howler monkeys (Alouatta palliata) collected over 10 years to test for individual signature on all three axes after accounting for sex, reproductive state, age, group, year, food availability, temperature, and time of day. No axis showed a detectable signature: repeatability estimates were near zero (R = 0.008–0.034) with confidence intervals encompassing zero; random-regression models revealed no individual × environment interactions in responses to food availability; and residual intra-individual variability showed no among-individual signal once boundary-induced mean–variance coupling in proportional data was removed by logit transformation. Variance attributable to month and year exceeded that of individual identity by factors of four and 1.4, respectively. These convergent null results suggest that behavioral variation in this population is decomposable into structured ecological and demographic sources. Behavioral flexibility, not individual consistency, is the population-level strategy.
