Primate population dynamics in Ngogo, Kibale National Park, Uganda, over nearly five decades

Many anthropogenic-driven changes, such as hunting, have clear and immediate negative impacts on wild primate populations, but others, like climate change, may take generations to become evident. Thus, informed conservation plans will require decades of population monitoring. Here, we expand the duration of monitoring of the diurnal primates at Ngogo in Kibale National Park, Uganda, from 32.9 to 47 years. Over the 3531 censuses that covered 15,340 km, we encountered 2767 primate groups. Correlation analyses using blocks of 25 census walks indicate that encounters with groups of black and white colobus, blue monkeys, and baboons neither increased nor decreased significantly over time, while encounters with groups of redtail monkeys and chimpanzees marginally increased. Encounters with mangabeys and L'Hoesti monkeys increased significantly, while red colobus encounters dramatically decreased. Detailed studies of specific groups at Ngogo document changes in abundances that were not always well represented in the censuses because these groups expanded into areas away from the transect, such as nearby regenerating forest. For example, the chimpanzee population increased steadily over the last 2 + decades but this increase is not revealed by our census data because the chimpanzees expanded, mainly to the west of the transect. This highlights that extrapolating population trends to large areas based on censuses at single locations should be done with extreme caution, as forests change over time and space, and primates adapt to these changes in several ways.