Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats

Application of distance sampling to estimate population densities of large herbivores in Kruger National Park

J. M. Kruger A , B. K. Reilly B C and I. J. Whyte A
+ Author Affiliations
- Author Affiliations

A South African National Parks, Private Bag X402, Skukuza 1350, Republic of South Africa.

B Department of Nature Conservation, Tshwane University of Technology, Private Bag X680, Pretoria 0002, Republic of South Africa.

C Corresponding author. Email: reillybk@tut.ac.za

Wildlife Research 35(4) 371-376 https://doi.org/10.1071/WR07084
Submitted: 4 July 2007  Accepted: 5 June 2008   Published: 27 June 2008


Aerial surveys have been used in the Kruger National Park, South Africa, to count large ungulates since the late 1970s. After 1998, aerial line-transect sampling using fixed-wing aircraft and Distance analyses replaced the ‘total’ counting method. This paper investigates these methods and three sampling intensities for estimating the densities of nine large ungulate species in Kruger National Park. Estimates suitable for the detection of population trends and making management decisions were decided by examination of coefficients of variation (set <20%, a priori). Despite the likely violation of some key assumptions of Distance sampling methods, analyses gave population estimates with adequate coefficients of variation for monitoring trends in impala, giraffe, zebra, kudu, white rhinoceros, and elephant bull populations. Significant improvements in precision were obtained at higher sampling intensities for kudu, giraffe, bull elephants and white rhinoceros, but these species already had sufficiently precise population estimates for the detection of trends at the lowest sampling intensity (15%). The estimates for warthog, wildebeest and waterbuck populations were, however, insufficiently precise for assessing population trends. Increasing sampling intensity to 22% and higher did not significantly increase the precision of the Distance estimates for these species. Shortcomings in interpretation of the data caused by violations of critical assumptions of analyses are identified and discussed.


We thank all the observers who have contributed to aerial surveys of mammals at KNP since 1998. The suggestions of Glenn Edwards, Peter Fleming and an anonymous referee improved the manuscript.


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