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

Abstract

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.

A comparison of multiple indicator kriging and area-to-point Poisson kriging for mapping patterns of herbivore species abundance in Kruger National Park, South Africa

“…A frame fitted to the aircraft (or calibrated strips drawn on the side windows of the aircraft) enabled animals to be located within distance classes (up to 50, 100, 200 and 400 m) from the plane on either side (see Figure 2 in Kruger et al 2008). This means that observations were made along East–West running transects that were 800 m wide, but also included a 36 m invisible zone under the aircraft.…”

“…It involved almost 4 months of near-constant flying with four observers on board. In 1998, the park-wide census approach was replaced by a sampling strategy whereby the number of animals is recorded along 800 m wide East–West transects, spaced at intervals of 2.5–5.6 km (Kruger et al 2008). However, such strip transects leave ‘gaps’ in the data spatially.…”

“…2006). Currently, Kruger Park scientists use the ‘DISTANCE’ software developed by Thomas et al (2004) for this analysis (Kruger et al 2008). …”

From numbers to ecosystems and biodiversity: A mechanistic approach to monitoring

“…These commonalities illustrate that the approach to use large mammal censuses as a primary basis of decision making in SANParks (e.g. Kruger et al 2008) requires additional information to assess fully whether management objectives have been reached within an adaptive management framework . However, such approaches may be comparable across parks.…”

Management Effectiveness and Potential for Tourism of Peri-Urban Lusaka National Park, Zambia: A Preliminary Assessment

“…Estimating wildlife abundance is an important integral part of wildlife research programmes and prerequisite for effective wildlife management (Jachmann, 2001). However, determination of wildlife abundance can be complex (Reilly, 2002;Kruger, Reilly, & Whyte, 2008). Limiting elements for accurate wildlife determination in the savannah environment include vegetation cover, characteristics of animal species, skills of surveyors and equipment employed.…”