Aerial Survey of Elephants and other Large Herbivores in Gonarezhou National Park (Zimbabwe), Zinave National Park (Mozambique) and surrounds: 2009
K.M. Dunham, E. van der Westhuizen, H.F. van der Westhuizen & E. Gandiwa
February 2010
Summary
Elephants and other large herbivores, wild and domestic, in Gonarezhou National Park in south-eastern Zimbabwe, Zinave National Park in southern Mozambique and surrounding lands were surveyed from the air during September 2009. The survey area lies within the Great Limpopo Transfrontier Conservation Area. A fixed-wing aircraft was used to conduct a sample survey, flying transects over the area.
The area surveyed totalled 16343 km2. It included 7112 km2 in Zimbabwe, including Gonarezhou NP, Malapati Safari Area and adjacent communal lands. In Mozambique, the survey area totalled 9231 km2 and included Zinave NP, part of Coutada 4 to the north of this park, the area north and south of the Save River between Gonarezhou NP and Zinave NP, and the zone along the Zimbabwe-Mozambique international border (which lies alongside Gonarezhou NP). The survey area was divided into 22 strata. Sampling intensity varied between strata and ranged from 6.3 to 21.1 %. The overall sampling intensity was 15.2 %.
Within the Zimbabwean survey area, the principal objective of the survey was to provide relatively precise and accurate estimates of the number of elephants and other large herbivores in the survey area as a whole, using a technique that could be executed within a reasonable time and at a reasonable cost. Secondary objectives included determination of the spatial distributions of elephants and other large herbivores; and estimation of the number and spatial distribution of elephant carcasses. The methods used were suitable for meeting the survey objectives, repeatable and technically robust. These methods were used for the first time to survey the wildlife populations of Zinave NP. Thus, this survey provides a baseline for monitoring future trends in the numbers and spatial distribution of wildlife and domestic livestock in Zinave NP and its surrounds.
Some large herbivores are not easily seen from the air and their numbers were undoubtedly underestimated. Nonetheless, population estimates are given for these species, because the estimates provide useful indices of abundance (with measures of precision) that can be used to determine spatial distribution, as well as temporal trends in population number. No corrections have been applied to any of the estimates to compensate for any undercounting or missed animals.
The estimated population numbers of the principal large herbivores in the survey area were: elephant 9281 (upper and lower 95% confidence limits ± 20.6 %); impala 6770 (± 34.2 %); buffalo 2742 (± 75.8 %); kudu 2832 (± 25.1 %); zebra 1500 (± 29.5 %); wildebeest 364 (± 81.8 %); giraffe 330 (± 59.5 %); eland 341 (± 112.2 %); nyala 546 (± 39.0 %); cattle 32240 (± 19.7 %); sheep and goats 24484 (± 19.8 %); and donkey 1393 (± 37.5 %).
For most wild species, the majority of the population was in Gonarezhou NP. The estimated population numbers of the principal large herbivores in Gonarezhou NP were: elephant 9123 (upper and lower 95% confidence limits ± 20.8 %); impala 6005 (± 37.4 %); buffalo 2274 (± 88.2 %); kudu 2285 (± 29.7 %); zebra 1385 (± 30.3 %); wildebeest 364 (± 81.8 %); giraffe 251 (± 61.6 %); eland 317 (± 120.2 %); nyala 370 (±50.8 %); waterbuck 360 (± 85.5 % ); cattle 2991 (± 51.3 %); and sheep and goats 452 (± 78.4 %). In the north of the park, the estimated number of huts built by people illegally resident there was 603 (± 55.3 %).
The 2009 estimate of the number of elephants in Gonarezhou NP was the highest estimate of the number of elephants in this park since sample surveys began there during 1975.
Zinave NP contained relatively few large herbivores, compared with Gonarezhou NP. The estimated population numbers of the principal medium and small herbivores in Zinave NP were: common duiker 899 (upper and lower 95% confidence limits ± 24.1 %); impala 150 (± 122.5 %); kudu 235 (± 63.5 %); oribi 254 (± 57.3 %); nyala 143 (± 64.3 %); cattle 620 (± 58.1 %); and sheep and goats 2039 (± 46.3 %). During a special river count along the section of the Save River that forms the northern boundary of Zinave NP, 88 hippopotamus and 38 crocodile were observed. People resident in Zinave NP have built an estimated 5033 huts (± 29.3 %).
The estimated total number of elephant carcasses (152) in the entire survey area represented 1.4 % of the total number of live and dead elephants. The all-carcass ‘ratio’ (i.e. the ‘ratio’ for elephant carcasses of all age categories) was also 1.4 % in the Zimbabwean portion of the survey area. In just one stratum was the all-carcass ‘ratio’ high: it was 18.9 % in the North Border stratum, on the Mozambican side of the Zimbabwe-Mozambique international border. No fresh (age category 1) or recent (age category 2) carcasses of elephants were seen in the search strips and so the 1+2 carcass ‘ratio’ was 0 % in the entire survey area and in both the Zimbabwean and Mozambican portions of it.
The area along the Save River between Gonarezhou NP and Zinave NP was occupied by relatively high densities of people and domestic livestock. Fields and commercial logging were common there. Hence, there appears to be no potential for this area to serve as a corridor for the movement of large animals between Gonarezhou NP and Zinave NP. The area of Sengwe communal land northwards of the Zimbabwe/Mozambique international border was also occupied by relatively high densities of people and domestic livestock and there appears to be no potential for this area to serve as a corridor for the movement of large animals between Gonarezhou NP and Kruger NP. However, within this area, a minefield that occupies a strip of land approximately 3 km wide, runs parallel to the international border and is unsettled by people, could perhaps serve as a wildlife corridor after the landmines have been cleared.
This survey was the seventh aerial survey of the wildlife populations of Gonarezhou NP since the severe drought of 1991/92. A trend analysis of the results of these surveys revealed that the estimated numbers of all elephants, elephants in cow herds, buffalo, eland, kudu, waterbuck and zebra have all increased significantly since that drought. The numbers of elephant bulls, giraffe and impala did not show statistically significant trends.
A trend analysis of survey results from before the drought was less successful, because some species were not included in all pre-drought surveys, while for other species the time series of population estimates was probably too short to determine a trend reliably. For elephant, the time series was longer and with more population estimates: overall, the number of elephants in the park did not increase during the decade before the drought, presumably as a consequence of elephant culling. Only zebra number increased significantly in the years before the drought. It then declined during the drought by approximately 50%.
