Thirty years of arboreal wildlife trends in an African rainforest under evolving threats and researchers' presence

Long-term wildlife monitoring is necessary to inform adaptive management and assess conservation measures. The long-term presence of researchers may also indirectly induce positive effects for wildlife conservation by deterring harmful activities, such as hunting and resource extraction. However, long-term research is challenging and thus rare. Here, we assess long-term trends of wildlife near a research station that was established, abandoned, and reestablished. We conducted monthly surveys of arboreal wildlife from 1995 to 1999 and 2017 to 2024 in a protected Cameroonian rainforest where illegal hunting is common. Coinciding with the initial establishment of the research station, the relative abundance of 10 out of 12 arboreal species (hornbills, primates, and parrots) increased from 1995 to 1999. However, the station closed in 1999, and by 2017, the relative abundance of many species had decreased compared to levels in 1999. Finally, no species increased in relative abundance after the station reopened in 2017; instead, many declined between 2017 and 2024. Although we lack control sites, these results suggest that researchers' presence can sometimes have a protective effect, but also that this effect can be variable and limited depending on circumstances. The declining trends from 1999 to 2024 align with the evolving state of hunting in Central Africa, which is shifting toward increased commercial hunting and the use of guns that are more effective than snares for harvesting arboreal species. We recommend providing sustained support for research stations, collaborating with local communities to reduce bushmeat hunting, and enhancing enforcement against the international trade of hornbill casques and pet parrots.