Population Status, Threats, and Conservation of Preuss’s Red Colobus (Piliocolobus preussi) and Other Diurnal Primates in the Ndokbou-Makombe Forests, Cameroon

Abstract Primate populations worldwide are experiencing rapid declines due to habitat loss, degradation, and overexploitation. These pressures are particularly severe across sub-Saharan Africa and the Gulf of Guinea biodiversity hotspot, which supports several threatened and endemic species. The Ebo-Makombe-Ndokbou forests in southwestern Cameroon contain critical habitat for several of these species, including the Critically Endangered Preuss’s red colobus ( Piliocolobus preussi ), found only in southeastern Nigeria and western Cameroon. Hunting and habitat loss and degradation from logging and agriculture are the main threats to primates in this region. In 2018 and 2019, we conducted 571.51 km of reconnaissance surveys and recorded 12,347 h of audio data from passive acoustic sensors to assess primate relative abundance and detect acoustic evidence of gun hunting and logging activities in Makombe and Ndokbou forests. Overall primate sighting frequency was low compared with West African forests containing similar primate communities, with Cercopithecus species the most widespread and frequently encountered. We recorded no verified encounters with Preuss’s red colobus, but we detected a putative vocalization near the remote Mt. Sinai region of Ndokbou forest. Acoustic sensors recorded gunshot activity throughout the study area, with intensity highest near villages and logging roads. These patterns suggest that logging infrastructure may facilitate hunting access, contributing to reduced primate abundance and a community skewed toward smaller-bodied, more ecologically flexible species. The detection of a possible Preuss’s red colobus call indicates that a small, remnant population may persist in Ndokbou. However, the absence of visual confirmations despite extensive survey effort suggests the species is nearing local extirpation. We recommend additional surveys in the Mt. Sinai area to assess the presence of Preuss’s red colobus in Ndokbou forest. The potential extirpation of Preuss’s red colobus foreshadows the decline of the forest’s other threatened primate species. Protecting the Ebo-Makombe-Ndokbou forests is integral to primate conservation efforts in the Gulf of Guinea.