The Influence of Transect Use by Local People and Reuse of Transects for Repeated Surveys on Nesting in Western Lowland Gorillas (Gorilla gorilla gorilla) and Central Chimpanzees (Pan troglodytes troglodytes) in Southeast Cameroon
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Monitoring populations of endangered species over time is necessary to guide and evaluate conservation efforts. This is particularly important for nonprotected areas that ensure connectivity between protected populations but are prone to uncontrolled hunting pressure. We investigated whether use of transects by local people and transect reuse for repeated surveys influence great ape nesting and bias results. We conducted simultaneous marked nest count surveys over 12 mo on established and newly opened transects in a nonprotected area subject to traditional heavy use by local people and recorded forest composition and signs of human activity. Chimpanzee and gorilla density estimates and encounter rates per kilometer were lower on established transects than on new ones. A generalized linear model indicated that hunting activity, distance to a regularly used forest trail, and transect type (old or new) predicted chimpanzee nest abundance, and distance to the trail and transect type predicted gorilla nest abundance, with no effect of habitat type (percentage suitable habitat) for either species. We, therefore, suggest that the difference in great ape nesting is a result of high levels of hunting by local people on established transects and forest trails. Our results support the use of repeated line transect surveys for monitoring great ape populations in many circumstances, although we advocate taking precautions in nonprotected areas, to avoid the bias imposed by use of established transects for hunting.
KeywordsCentral chimpanzee Established transects Marked nest count surveys Nesting Transect reuse Western lowland gorilla
We thank the Flemish Government for core funding of PGS through the Centre for Research and Conservation of the Royal Zoological Society of Antwerp and the Ministry of Forests and Wildlife and the Ministry of Research and Innovation for permission to conduct the research. We thank Charles Yem Bamo, Fabrice Ottou Mbida, Germain Mbock, and John Carlos Nguinlong for their help during surveys, and all logistic staff of PGS and local workers in the community of Malen V for their individual invaluable contributions to this work. We also specifically acknowledge Charles-Albert Petre and Patrick Guislain and the editors and two anonymous reviewers for constructive advice.
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