Terrain ruggedness and human activities influence the distribution of Grauer’s gorillas ( Gorilla beringei graueri ) and eastern chimpanzees ( Pan troglodytes schweinfurthii ) in the Tayna Nature Reserve, Democratic Republic of Congo

Abstract The Albertine Rift Hotspot in east-central Africa is one of the most biodiverse regions in the world. It hosts a number of conservation-priority species, including Critically Endangered Grauer’s gorillas and Endangered eastern chimpanzees. Yet, prolonged insecurity in the region has made wildlife monitoring and conservation challenging. This is particularly true of the northeastern limits of the range of Grauer’s gorillas, where wide stretches of unprotected forest could harbor behaviorally and genetically unique peripheral populations of great apes and other species. Here, we developed a rapid wildlife survey method to map population distributions and monitor the impact of various human activities in the Tayna Nature Reserve in eastern Democratic Republic of Congo. Despite a lack of surveys since the early 2000s, we find that Grauer’s gorillas and eastern chimpanzees, as well as a number of smaller-bodied species, have persisted in Tayna. Observations of gorilla and chimpanzee signs were highly heterogeneous. They were less dense near human settlements and artisanal mines and peaked in areas with rugged terrain. The association with rugged terrain may be a result of historical anthropogenic pressure, behavioral avoidance of human activities, and/or ecological preference. Maintaining connectivity between patches of suitable great ape habitat will be critical for long-term great ape conservation in the Albertine Rift region. Our findings also demonstrate the utility of priority species monitoring driven by local communities for conservation initiatives. Competing Interest Statement The authors have declared no competing interest. Footnotes Reorganization, in particular the Introduction and Methods, for clarity and additional justification for our methodological choices, hypotheses, and predictions, with appropriate references; Minor addition to Results: calculated metrics to compare the efficiency of fast-transects to traditional distance transects; Expanded our Discussion regarding the relevance to conservation and involvement of local communities; Minor edits for clarity of the text; Fixed issue with figure quality in PDF