Monitoring major biodiversity stronghold in war zones: Model predicts Lake Chad remains Africa’s most important wetland for waterbirds

Lake Chad is both one of the largest transboundary wetlands in Africa and a major biodiversity hotspot. As such, Lake Chad would require sound and long-term biodiversity monitoring, but it is also a war zone. Using several mitigation measures, we succeeded in surveying a major part of it in 2022 to estimate the abundance of wildlife. This study marked the first comprehensive population estimates for some species. Compared to previous total count approaches, we introduced an aerial distance sampling methodology to improve survey safety, repeatability, estimate uncertainty, and reduce detection bias. Due to strong security concerns, a portion of the lake was inaccessible. To overcome this limitation and estimate temporal trends, density surface modeling was applied to estimate species abundance over the entire lake. Locations of conflict events emerged as sites of higher densities for several species, suggesting a "refuge effect," a rare positive outcome of conflict zones on wildlife. Indeed, we also noted the persistence of endangered large mammal populations, possibly due to reduced anthropogenic pressure from displaced communities. Results indicated that Lake Chad hosts approximately 2.48 million waterbirds, to our knowledge the most important known wetland bird concentration in Africa. Updated population estimates revealed that some species may have experienced positive trends. However, a few species, including transcontinental ones, showed signs of reduced abundance. The study urges actions to protect this ecosystem of major importance for global biodiversity, recommending the establishment of a protected area and World Heritage status for Lake Chad.