A high-resolution aerial camera survey of Uganda's Queen Elizabeth Protected Area improves detection of wildlife and delivers a surprisingly high estimate of the elephant population

Abstract

The Queen Elizabeth Protected Area (QEPA) hosts some 60% of Ugandas elephants and large populations of buffalo, hippopotamus and Uganda kob. However, the area is subjected to continued poaching, livestock incursions, animal disease and invasive plant species. Population estimates derived from aerial observers have shown great variability, and therefore trends are hard to discern. The Uganda Wildlife Authority (UWA) reguires precise wildlife population estimates to guide conservation actions. The aim of this study is to provide accurate and precise baseline estimates for wildlife populations of QEPA using aerial imagery and high sampling intensity, and to improve survey methods for determining future trends. High-resolution cameras, orientated at 45{degrees}, captured images along sample strips to left and right of the aircraft. Transects at 1 km separation gave a high sampling intensity of 28% to improve precision. We captured 43000 images for visual enumeration of 13 wildlife species. Population estimates ([Y]), standard errors (SE) and relative margins of error (RME =95% c.l/[Y]) were determined using Jolly II, Marriott and bootstrapping methods. With improved detection using imagery the QEPA elephant population is estimated at 4 711 {+/-} 1106 (95% c. I), which is 62% higher than the previous observer-based estimate of 2900 in 2014, and the highest since counts began in the 1960s. The survey achieved an RME for elephants of 23%, making this one of the most precise counts for any similar-sized elephant area in Africa. The buffalo, Uganda kob and hippopotamus populations have stabilized at safe levels but remain well below the high point of the mid-1990s; the high density of bone patches indicate high mortality, attributable to disease and to the continued invasion of the unpalatable grass species Imperata cylindrica, which now covers 50% of the grassland area. Our methods indicate that methods and sample parameters prescribed by international elephant counting standards can be revised and improved using aerial cameras, especially for smaller survey areas. Short Summary TextUgandas Queen Elizabeth Protected Area (QEPA) continues its recovery since the decimation of wildlife by militias in the 1970s, but it is challenging to track wildlife trends due to the variability in population estimates. To improve accuracy and precision, we conducted the first aerial count of QEPA using high-resolution imaging. This approach has indicated that the elephant population is at its highest levels since surveys began in the 1960s. Meanwhile, buffalo, topi and Uganda kob are stagnating below previous 1990s levels. We suggest the use of camera systems in future surveys to improve the accuracy and precision of counts, in order to guide effective management.