Abstract
Estimating wildlife abundance is central to conservation. We compared two widely practiced standards for counting animals - aerial strip surveys and ground line transects - with interpreted counts of animal tracks. At equal sampling intensity in semiarid savanna with good visibility all three methods produced similar population estimates and precision for six large herbivores. This comparison adds empirical support for the use of track count data to estimate population density rather than being restricted to ambiguous indices of relative abundance. Although expected to capture more species than aerial surveys, we found line transects limiting because encounter rates by direct sightings were relatively low; a minimum threshold 40 observations was achieved for only 1/3 of antelope species in 648.4 km of transect. By contrast, animal track counts returned exceedingly high encounter rates that allowed estimation of abundance for the entire large predator-prey community and mapping density-distributions more completely. Unlike aerial surveys conducted by Botswana's wildlife authority, the track survey provided opportunity to involve local people in the research process. The track survey cost 40% less than the aerial survey, and could be reduced a further 3-fold if trackers collected data autonomously without motor vehicles. Counting animals by their tracks is ultimately constrained to regions with appropriate substrates. However, in suitable environments like the Kalahari, we suggest that a citizen science driven by expert local trackers could ultimately replace conventional wildlife counts, generating knock-on benefits to conservation beyond improved data.
Highlights
Efficient methods of estimating wildlife numbers in-situ are of fundamental importance to modern conservation, yet a limited number of approaches dominate the toolkit available to practitioners
We surveyed Kgalagadi District 2 (KD2), a Wildlife Management Area (WMA) occupying 6425 km2 in southwestern Botswana bound by Kgalagadi Transfrontier Park (KTP) to the south, KD1 and KD12 WMAs to the west and east respectively, and KD3 communal grazing lands to the north (Fig. 1)
Besides continuing standard surveys in the Kalahari for the purpose of consistency in long-term monitoring, we found little evidence that direct sightings are superior to tracks in terms of achievable precision, species comprehensiveness, distribution mapping, and costs
Summary
Efficient methods of estimating wildlife numbers in-situ are of fundamental importance to modern conservation, yet a limited number of approaches dominate the toolkit available to practitioners. Wildlife managers in developing countries are influenced by prevailing literature on field methods despite local conditions favoring alternative approaches. This paper poses the question: Can Kalahari trackers collect equivalent information as the aerial survey and ground line transects (distance sampling) routinely conducted by Botswana's wildlife authority, and can they do it as efficiently? We sought an answer by comparing simultaneous counts made by air, ground line transects and tracks, their achievable precision, and evaluate efficiency in terms of encounter rates and survey costs. The question and answer are important, in developing countries especially, where both conservation and poverty alleviation are fundamental policy agendas (Agrawal and Redford, 2006), local involvement in conservation has become imperative (Hulme and Murphree, 2001), and simple cost-effective means of biodiversity monitoring are sorely needed (Danielsen et al, 2005).
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