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Using simulations of past and present elephant (Loxodonta africana) population numbers in the Okavango Delta Panhandle, Botswana to improve future population estimates

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Abstract

An ability to reliably estimate population numbers, trends and densities of wildlife has a prominent role in conservation and management of wetlands. We use aerial surveys and simulation techniques to explore the results of past and present elephant population surveys in the Okavango Delta Panhandle, Botswana, and use these to propose a technique of simulation to improve counts in the future. Population numbers and density estimates from past survey results show large fluctuations, which are unlikely to come from reproduction. Reasons for such variations could be attributed to imprecision in survey techniques or may be because only part of the elephant range is being surveyed. Simulated surveys of hypothetical elephant populations were used to explore the effect of different survey techniques, spatial distributions of animals and spatial scale on the precision of aerial survey population estimates and trends. Our study reveals the usefulness of using simulations to test the reliability of survey data and plan more efficient surveys. We also find that while there may be some uncertainty in individual population estimates, there is more certainty in the recorded trends. These findings reinforce the need to address elephant management in the Okavango and surrounding wetland systems and call for the urgent consideration of management strategies such as fence realignments to affect the objectives of the Kavango Zambezi Transfrontier Conservation Area (KAZA TFCA) initiative, which will help relieve elephant population pressure.

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Acknowledgments

We thank the Botswana Ministry of Environment, Wildlife and Tourism, and the Namibian Ministry of Environment for granting permission for these surveys to take place and we are grateful to the Botswana Defence Force for granting permission for allowing the surveys to cross the international border between Botswana and Namibia. We are sincerely thankful to the Wildlife Conservation Society, Wilderness Wildlife Trust and Elephants Without Borders who provided funding for the survey. Thank you to the surveying team, including K. Landen for her observer skills and photo-correction analysis, and to the pilots namely A. Parnass and M. Holding for providing both their planes and piloting services to the project.

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Correspondence to Anna Songhurst.

Appendices

Appendix 1

See Table 3.

Table 3 Herd number, type and mean herd size by observer on strip transects

Appendix 2

See Table 4.

Table 4 Estimates of elephant numbers in the eastern Okavango Panhandle by block/strata, 1996–2010

Appendix 3

See Fig. 5.

Fig. 5
figure 5

Plot showing root mean square errors at different sampling intensities, different shades represent varying degrees of spatial clustering in elephant distribution (radius of herd)

Appendix 4

See Table 5.

Table 5 Population estimates within the potential elephant range of the Okavango Panhandle population, including the Okavango Delta, the West Caprivi and South East Angola

Appendix 5

See Fig. 6.

Fig. 6
figure 6

Population estimates from the Okavango Delta, Okavango Panhandle, West Caprivi and South East Angola, (see Appendix 4 for data used)

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Songhurst, A., Chase, M. & Coulson, T. Using simulations of past and present elephant (Loxodonta africana) population numbers in the Okavango Delta Panhandle, Botswana to improve future population estimates. Wetlands Ecol Manage 23, 583–602 (2015). https://doi.org/10.1007/s11273-015-9440-4

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