BY M. CHASE, S. SCHLOSSBERG, R. SUTCLIFFE, & E. SEONYATSENG
During the 2018 dry season, a fixed-wing aerial survey of elephants and wildlife was flown over the core conservation areas of northern Botswana as well as surrounding pastoral lands. This aerial survey was commissioned by the Department of Wildlife and National Parks (DWNP) and Elephants Without Borders (EWB).
A small fixed-wing plane was used to survey an area of 103,662 km2 . Surveyed areas included Moremi Game Reserve (GR), Chobe National Park (NP), Makgadikgadi and Nxai Pan NPs and surrounding Wildlife Management Areas (WMAs) and pastoral areas in Ngamiland, Chobe and Central districts. The 2018 survey expanded upon EWB’s 2014 and 2010 dry-season aerial surveys of northern Botswana through the addition of new strata south of the Okavango Delta near Maun, west of Makgadikgadi NP, and southeast of Ngwasha/Sepako near the Zimbabwe border.
The primary objective of this survey was to provide precise and accurate estimates of wildlife populations in the survey area, using repeatable, standardized methods. Secondary objectives included mapping the spatial distribution of elephants and other wildlife; determining the distribution of elephant carcasses, baobab trees, large birds, and livestock; and measuring trends in wildlife populations.
This report provides the results of this survey, including information on the spatial distribution, abundance, and recent trends of elephant and other wildlife populations. Maps and tables illustrating the distribution, numbers, density and trends of wildlife species in northern Botswana are provided.
The survey area was divided into 69 strata that largely conformed to the boundaries of WMAs and protected areas. For 62 strata, we used the sample count methodology, in which a subset of the stratum was surveyed via parallel transects spaced regularly 2-10 km apart. Sampling intensity in these strata ranged from 4 to 20%. In two strata, we conducted total counts in which the entire stratum was surveyed at high intensity so that the numbers of animals observed are assumed to be complete counts of the animals present. The remaining five strata utilized recce surveys in which non-systematic sampling was used to count animals in likely habitats. Recce surveys provide minimum population estimates.On all strata, high-resolution, wide-angle digital cameras were used to facilitate accurate estimation of herd sizes.
When we restricted the 2018 data to only areas surveyed in on the 2014 aerial survey of northern Botswana, we found that estimated numbers of elephants had increased slightly and non-significantly since 2014, from 122,634 ± SE of 5,101 in 2014 to 122,831 ± 4,769 on this survey (Z = 0.03, P = 0.98). By stratum, changes in elephant population sizes between 2014 and 2018 were highly variable, with substantial movements of elephants likely occurring between strata.
The estimated number of elephant carcasses of all age categories was 11,044 for the entire survey area and gives an estimated carcass ratio of 8.0% for the entire survey. For sample counts (used on 62 of 69 strata), the carcass ratio was 8.1%. Carcass ratios greater than 8% on sample counts indicate a population that is potentially declining. The carcass ratio on strata surveyed via total and recce counts was 2.9%.
Estimated numbers of elephant carcasses and carcass ratios both increased significantly between 2014 and 2018. For all carcasses, estimated numbers of carcasses increased by 21%, and ratios increased from 6.8% to 8.1% between 2014 and 2018. For fresh/recent carcasses, numbers increased by 593%, and fresh/recent carcass ratios increased from 0.1% to 0.7%. These results indicate that mortality rates of elephants have likely increased recently in northern Botswana.
During the aerial survey, we identified four regions where large numbers of fresh/recent elephant carcasses were observed, many of which showed clear signs of being poached, i.e. skulls were chopped to remove tusks, or carcasses were covered with brush. We used a helicopter to conduct ground verification of the cause of death of 33 fresh/recent carcasses observed during the survey that were suspected of being poached. All 33 of the carcasses were confirmed to have been poached based on suspicious human activity, axe marks and damage to the skull, and other signs. Additionally, we conducted ground-based status checks for 79 carcasses of category 3 (“old”) in NG 15, NG 18/19, and Chobe NP and found that 80% were poached. These results suggest that there is a significant elephantpoaching problem in northern Botswana that has likely been going on for over a year. The four poaching “hotspots” in northern Botswana are: NG 11/12/13, NG 15/18/19 & the Savuti section of Chobe NP, the vicinity of Maun, and NG 42.
Besides elephants, we observed substantial numbers of other wildlife species including: lechwe (population estimate = 88,584, the highest population estimate ever recorded for this species in northern Botswana), impala (77,694), zebra (60,170), and buffalo (28,534). Compared to 2014, populations increased significantly for hippopotamus, lechwe, reedbuck, sitatunga, fish eagle, and wattled crane. Populations of sable and saddle-billed stork decreased significantly since 2014.
We observed a total of 569 baobab trees during the survey, of which 14% were classified as small-sized trees. Dead trees (i.e. 100% damage, n = 20) accounted for 3.5% of the total number seen within the survey area. Estimated damage to trees increased significantly with both tree size class and elephant density in a stratum, though the effect of elephants on baobabs was weak.