A Reassessment of the Population Size, Demography, and Status of Tanzania’s Endemic Kipunji Rungwecebus kipunji 13 Years on: Demonstrating Conservation Success

Fifty+ years of primate research illustrates complex drivers of abundance and increasing primate numbers

Many primate populations are threatened by human actions and a central tool used for their protection is establishing protected areas. However, even if populations in such areas are protected from hunting and deforestation, they still may be threatened by factors such as climate change and its cascading impacts on habitat quality and disease dynamics. Here we provide a long-term and geographically wide-spread population assessment of the five common diurnal primates of Kibale National Park, Uganda. Over 7 year-long or longer census efforts that spanned 52 years, our team walked 1466 km, and recorded 480 monkey groups. Populations were generally relatively stable with a few exceptions, for which no apparent causative factors could be identified. This stability is unexpected as many ecological changes documented over the last 34+ years (e.g., decreasing food abundance and quality) were predicted to have negative impacts. Populations of some species declined at some sites but increased at others. This highlights the need for large, protected areas so that declines in particular areas are countered by gains in others. Kibale has large areas of regenerating forest and this most recent survey revealed that after 20+ years, forest regeneration in many of these areas appears sufficient to sustain sizeable primate populations, except for blue monkeys that have not colonized these areas. Indeed, the average primate abundance in the regenerating forest was only 8.1% lower than in neighboring old-growth forest. Thus, park-wide primate abundance has likely increased, despite many pressures on the park having risen; however, some areas in the park remain to be assessed. Our study suggests that the restoration, patrolling, and community outreach efforts of the Uganda Wildlife Authority and their partners have contributed significantly to protecting the park and its animals.

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.

The Critically Endangered Hainan Gibbon (Nomascus hainanus) Population Increases but not at the Maximum Possible Rate

With the ongoing global biodiversity crisis in the Anthropocene, it is critical to understand how to save endangered species to “bend the curve” of biodiversity decline. The Hainan gibbon (Nomascus hainanus) is a Critically Endangered species that is endemic to Hainan Island. We performed two synchronized total count surveys in Hainan Tropic Rain Forest National Park in November and December of 2020 and 2021 by locating gibbon groups from their morning calls and conducting detailed counts in all potential habitat fragments. We compared our findings with existing data to model the population trend, and analyzed the potential and realized reproductive potentials. We found 5 groups with a total of 33 gibbons in 2020 and 35 in 2021, including 4 and 6 solitary individuals respectively. This is an increase of 169% since 2003, when there were 13 individuals with 2 groups and 2 solitary individuals. Logistic and linear curves fitted the 2003-2021 population census data equally well. Although the population is growing, it has not realized its full reproductive potential (when all adult females give births at 24-month intervals), suggesting that external factors like available habitat, as well as nutritional, physiological, and behavioral factors may be limiting the population. The gibbon’s recovery demonstrates that establishing a nature reserve with regular patrols, banning logging, curbing poaching, and environmental education have been effective. Because the Hainan gibbon population is still extremely small, carefully planned conservation actions, including an ambitious forest restoration program, will be needed to ensure the species’ continued survival.