Density estimates of African lions in Queen Elizabeth National Park

African lions are declining across much of their range, yet robust measures of population densities remain rare. The Queen Elizabeth Conservation Area (QECA; 2400 km2) in East Africa’s Albertine Rift has potential to support a significant lion population. However, QECA lions are threatened, and information on the status of lions in the region is lacking. Here, we use a spatially explicit search encounter approach to estimate key population parameters of lions in the QECA. We then compare home range sizes estimated from our models to those from a radio-collaring study implemented a decade earlier. We recorded 8243.5 km of search effort over 93 days, detecting 30 individual lions (16 female and 14 male) on 165 occasions at a rate of 2 lion detections/100 km2. Lion density in the QECA was 2.70 adult lions/100 km2(SD=0.47), while mean abundance was 71 individuals (SD=11.05). Worryingly, the movement parameter for male lions was 3.27 km and 2.22 km for females, suggesting >400%, and >100% increases in home range size, respectively, compared to a decade earlier. Sex ratio of lions in the QECA was lower (1 male: 0.75 females), when compared to a previously published review (mean=1:2.33). The large movements and skewed sex ratios we report on in this paper are likely a result of human driven prey depletion. Our results suggest lions in the QECA are in a precarious state and the lion densities are significantly lower than what they could be. As lions are under pressure throughout much of Africa, our study presents the utility of a census technique that could be used elsewhere as an early warning of lion declines.非洲狮在其绝大多数分布区内种群数量持续下降，但可靠的种群密度测算方法仍较为稀缺。东非阿尔伯特裂谷带内的伊丽莎白女王保护区（Queen Elizabeth Conservation Area, QECA，面积2400 km²）具备承载规模可观狮群种群的潜力。然而该区域内的狮子仍面临生存威胁，且当前关于本地区狮群现状的相关信息仍存在显著缺口。本研究采用空间显式搜索偶遇法（spatially explicit search encounter approach），对QECA内狮子的关键种群参数进行估算。随后将本研究模型所得的家域面积（home range size）估算结果，与十年前一项无线电项圈追踪研究（radio-collaring study）的成果进行对比。本次研究在93天内累计完成8243.5 km的搜索行程，累计165次观测到30头狮子个体（其中雌性16头、雄性14头），观测率为2头狮子/100 km²。QECA内的狮子种群密度为2.70头成狮/100 km²，标准差（standard deviation, SD）=0.47；平均种群丰度为71头个体，标准差（SD）=11.05。令人担忧的是，雄性狮子的移动参数为3.27 km，雌性为2.22 km，相较十年前的研究结果，二者的家域面积分别增加了400%以上和100%以上。QECA内的狮子种群性比为1雄性:0.75雌性，低于此前已发表综述报道的平均水平（均值为1:2.33）。本研究观测到的大范围移动与失衡性比，大概率是人类活动驱动的猎物枯竭所引发的结果。研究结果表明，QECA内的狮子种群正处于岌岌可危的状态，其种群密度远低于理论潜在承载水平。鉴于非洲多数区域的狮子均面临生存压力，本研究验证了一种普查技术的实用性，该技术可在其他区域用于预警狮子种群的下降趋势。