Here we present 192 new records of 22 species and subspecies of primates, collected in 56 different localities during 10 field expeditions across the arc of deforestation between 2015 and 2018. Based on such new records, we extend the ranges of Alouatta puruensis, Ateles chamek, and Saimiri collinsi; identify potential hybridization zones in Alouatta and Ateles species; redefine the range of Plecturocebus moloch; and clarify the ranges of P. baptista and P. hoffmannsi.

The Djaffa Mountains guereza (Colobus guereza gallarum) is an endemic Ethiopian taxon. Information about its distribution and population size is missing. We collected data on population density and size in four forests in the Ahmar Mountains in a line-transect survey and estimated 109.6 individuals per square kilometer within the study area. This comparatively high density is thus not the main conservation concern, but the fragmentation of the guereza habitat and population is.

Reports of male dominance in greater bamboo lemurs were not supported by data. We studied agonistic behavior in one captive group and could confirm this assertion, which sets this species apart from all other group-living lemurs.

In the context of the ManyPrimates initiative, our long-tailed macaques (Macaca fascicularis) rarely exchanged a given food item for a larger food reward at a later time. We tested whether possession of a high-value food item affected their performance and found that macaques displayed improved abilities when the value of the exchange item is reduced. This suggests that the possession of a high-value item contributed to the low performance of the monkeys in the original exchange protocol.