Wetlands Ecology and Management

, Volume 23, Issue 4, pp 583–602 | Cite as

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

Original Paper

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.

Keywords

Elephant Wetlands Human–wildlife conflict Okavango Delta Population estimates Simulation 

References

  1. Abadi F, Gimenez O, Ullrich B, Arlettaz R, Schaub M (2010) Estimation of immigration rate using integrated population models. J Appl Ecol 47:393–400CrossRefGoogle Scholar
  2. Anon (2012) Strategic environmental assessment for the Okavango delta ramsar site (ODRS). Department of Environmental Affairs and SAREP, GaboroneGoogle Scholar
  3. Baddeley A, Turner R (2010) Spatstat ‘Package’: spatial point pattern analysis, model fitting, simulation, tests. CRANGoogle Scholar
  4. Barnes RFW, Barnes KL, Alders M, Blom A (1991) Man determines distribution of elephants in the rainforest of north-eastern Gabon. Afr J Ecol 29:54–63CrossRefGoogle Scholar
  5. Baumgartener MF (1997) The distribution of risso’s dolphin (Grampus griseus) with respect to the physiography of the northern Gulf of Mexico. Mar Mamm Sci 13:614–638CrossRefGoogle Scholar
  6. Blanc JJ, Barnes RFW, Craig GC, Dublin HT, Thouless CR, Douglas-Hamilton I, Hart JA (2007) African elephant status report 2007. Occasional paper series of the International Union for Conservation of Nature Species Survival Commission. African Elephant Specialist Group IUCN, GlandGoogle Scholar
  7. Booth VR, Dunham KM (2014) Elephant poaching in Niassa Reserve, Mozambique: population impact revealed by combined survey trends for live elephants and carcasses. Oryx. doi:10.1017/S0030605314000568 Google Scholar
  8. Buckland ST, Anderson DR, Burnham KP, Laake JL (1993) Distance sampling: estimating abundance of biological populations. Chapman & Hall, LondonCrossRefGoogle Scholar
  9. Calef GW (1988) Maximum rate of increase in the African Elephant. Afr J Ecol 26:323–327CrossRefGoogle Scholar
  10. Cassidy L, Fynn R, Bongani S (2013) Effects of restriction of wild herbivore movement on woody and herbaceous vegetation in the Okavango Delta Botswana. Afr J Ecol 51(4):513–527CrossRefGoogle Scholar
  11. Caughley G (1974) Bias in aerial surveys. J Wildl Manag 38:921–933CrossRefGoogle Scholar
  12. Caughley G, Grigg GC (1981) Surveys of the distribution and density of kangaroos in the Pastoral Zone of South Australia, and their bearing on the feasibility of aerial surveys in large and remote areas. Aust Wildl Res 8:1–11CrossRefGoogle Scholar
  13. Chamaille-Jammes S, Valeix M, Fritz H (2007) Managing heterogeneity in elephant distribution: interactions between elephant population density and surface-water availability. J Appl Ecol 44:625–633CrossRefGoogle Scholar
  14. Chase MJ (2007) Home ranges, transboundary movements and harvest of elephants in northern Botswana and factors affecting elephant distribution and abundance in the Lower Kwando River Basin. PhD, University of MassachusettsGoogle Scholar
  15. Chase M (2011) Dry season fixed-wing aerial survey of elephants and wildlife in Northern Botswana, September–November 2010. Elephants Without Borders, KasaneGoogle Scholar
  16. Chase MJ, Griffin CR (2003) Ecology, population structure and movements of elephant populations in northern Botswana. Conservation International, KasaneGoogle Scholar
  17. Chase MJ, Griffin CR (2006) Elephant distribution and abundance in the Lower Kwando River Basin and West Caprivi. Final report. US Wildlife and Fisheries, KasaneGoogle Scholar
  18. Chase MJ, Griffin CR (2009) Elephants caught in the middle: impacts of war, fences and people on elephant distribution and abundance in the Caprivi Strip, Namibia. Afr J Ecol 47:223–233CrossRefGoogle Scholar
  19. Craig GC (1998) Aerial survey of northern Namibia. Ministry of Environment and Tourism, WindhoekGoogle Scholar
  20. Crawley M (2007) The R book. Wiley, ChichesterCrossRefGoogle Scholar
  21. Douglas-Hamilton I, Burrill A (1991) Using elephant carcass ratios to determine population trends. Afr Wildl Res Manag 1:98–105Google Scholar
  22. Dudley JP, Craig GC, Gibson D, Haynes G, Klimowicz J (2001) Drought mortality of bush elephants in Hwange National Park, Zimbabwe. Afr J Ecol 39:187–194CrossRefGoogle Scholar
  23. DWNP (1996) Aerial census of wildlife and some domestic animals in Botswana. Dry season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  24. DWNP (1999) Aerial census of wildlife and some domestic animals in Botswana. Dry and wet season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  25. DWNP (2001) Aerial census of wildlife and some domestic animals in Botswana. Dry season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  26. DWNP (2002) Aerial census of wildlife and some domestic animals in Botswana. Dry season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  27. DWNP (2003) Aerial census of wildlife and some domestic animals in Botswana. Dry season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  28. DWNP (2004) Aerial census of wildlife and some domestic animals in Botswana. Dry season report. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  29. DWNP (2005) Aerial census of wildlife and some domestic animals in Botswana. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  30. DWNP (2006) Aerial census of wildlife and some domestic animals in Botswana. Department of Wildlife and National Parks, Government of Botswana, GaboroneGoogle Scholar
  31. Elphick CS (2008) How you count counts: the importance of methods research in applied ecology. J Appl Ecol 45:1313–1320CrossRefGoogle Scholar
  32. Eltringham SK (1982) Elephants. Blandford Books Ltd., PooleGoogle Scholar
  33. Eltringham SK (1991) The illustrated encyclopaedia of elephants: from their origins and evolution to their ceremonial and working relationship with man. Salamander, LondonGoogle Scholar
  34. Ferreira SM, van Aarde RJ (2009) Aerial survey intensity as a determinant of estimates of African elephant population sizes and trends. South Afr J Wildl Res 39:181–191CrossRefGoogle Scholar
  35. Foley CAH, Faust LJ (2010) Rapid population growth in an elephant Loxodonta africana population recovering from poaching in Tarangire National Park, Tanzania. Oryx 44:205–212CrossRefGoogle Scholar
  36. Gumbricht T, Wolski P, Frost P, McCarthy TS (2004) Forecasting the spatial extent of the annual flood in the Okavango delta, Botswana. J Hydrol 290:178–191CrossRefGoogle Scholar
  37. Hargrove JW, Borland CH (1994) Pooled population parameter estimates from Mark-recapture data. Biometrics 50:1129–1141CrossRefPubMedGoogle Scholar
  38. Hoare RE (1999) Determinants of human–elephant conflict in a land-use mosaic. J Appl Ecol 36:689–700CrossRefGoogle Scholar
  39. Hone J (2008) On bias, precision and accuracy in wildlife aerial surveys. Wildl Res 35:253–257CrossRefGoogle Scholar
  40. Jachman H (2002) Comparison of aerial counts with ground counts for large African herbivores. J Appl Ecol 39:841–852CrossRefGoogle Scholar
  41. Jackson TP, Mosojane S, Ferreira SM, Aarde RJV (2008) Solutions for elephant Loxodonta africana crop raiding in northern Botswana: moving away from symptomatic approaches. Oryx 42:83–91CrossRefGoogle Scholar
  42. Jolly GM (1965) Explicit estimates from capture–recapture data with both death and immigration—stochastic model. Biometrika 52:225–247CrossRefPubMedGoogle Scholar
  43. Jolly JM (1969) Sampling methods for aerial censuses of wildlife populations. East Afr Agric For J 34:46–49Google Scholar
  44. Khaemba WM, Stein A, Rasch D, de Leeuw J, Georgiadis N (2001) Empirically simulated study to compare and validate sampling methods used in aerial surveys of wildlife populations. Afr J Ecol 39:374–382CrossRefGoogle Scholar
  45. Laake J, Dawson MJ, Hone J (2008) Visibility bias in aerial survey: mark-recapture, line-transect or both? Wildl Res 35:299–309CrossRefGoogle Scholar
  46. Marsh H, Sinclair DF (1989) Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. J Wildl Manag 53:1017–1024CrossRefGoogle Scholar
  47. Marsh H, Harris ANM, Lawler IR (1997) The sustainability of the indigenous Dugong fishery in Torres Strait, Australia/Papua New Guinea. Conserv Biol 11:1375–1386CrossRefGoogle Scholar
  48. Marsh H, Lawler IR, Kwan D, Delean S, Pollock K, Alldredge M (2004) Aerial surveys and the potential biological removal technique indicate that the Torres Strait dugong fishery is unsustainable. Anim Conserv 7:435–443CrossRefGoogle Scholar
  49. Matérn B (1986) Spatial variation. Springer, New YorkCrossRefGoogle Scholar
  50. McIntosh TE, Rosatte RC, Hamr J, Murray DL (2009) Development of a sightability model for low-density elk populations in Ontario, Canada. J Wildl Manag 73:580–585CrossRefGoogle Scholar
  51. Mendelsohn J, El Obeid S (2004) Okavango River: the flow of a lifeline. Struik, Cape TownGoogle Scholar
  52. Merz G (1986) Movement patterns and group size of the African forest elephant (Loxodonta africana cyclotis) in the Tai National Park, Ivory Coast. Afr J Ecol 24:133–136CrossRefGoogle Scholar
  53. MET (2008) Aerial survey of north east Namibia. Ministry of Environment and Tourism (MET), Namibian Government, WindhoekGoogle Scholar
  54. MET, M.o.E.a.T. (2004) Aerial survey of north east Namibia, 11 August–19 September 2005. Ministry of Environment and Tourism, WindhoekGoogle Scholar
  55. Milner-Gulland EJ, Rowcliffe JM (2007) Conservation and sustainable use: a handbook of techniques. Oxford University Press, OxfordCrossRefGoogle Scholar
  56. Mosepele K, Moyle PB, Merron GS, Purkey DR, Mosepele B (2009) Fish, floods, and ecosystem engineers: aquatic conservation in the Okavango Delta, Botswana. Bioscience 59:53–64CrossRefGoogle Scholar
  57. Moss C (1988) Elephant memories. Morrow, New YorkGoogle Scholar
  58. Moss C (1996) Getting to know a population. In: Kangwana KF (ed) Studying elephants. African Wildlife Foundation, Nairobi, pp 58–74Google Scholar
  59. Moss C (2001) The demography of an African elephant (Loxodonta africana) population in Amboseli, Kenya. J Zool London 255:145–156CrossRefGoogle Scholar
  60. Moss CJ, Poole JH (1983) Relationships and social structure in African elephants. In: Hinde RA (ed) Primate social relationships. Blackwell Scientific, Oxford, pp 315–325Google Scholar
  61. Norton-Griffiths M (1978) Counting animals. African Wildlife Leadership Foundation, NairobiGoogle Scholar
  62. Owen-Smith N (1988) Megaherbivores. The influence of very large body size on ecology. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  63. Pearse AT, Reinecke KJ, Dinsmore SJ, Kaminski RM (2009) Using simulation to improve wildlife surveys: wintering mallards in Mississippi, USA. Wildl Res 36:279–288CrossRefGoogle Scholar
  64. Pollock KH, Marsh HD, Lawler IR, Alldredge MW (2006) Estimating animal abundance in heterogeneous environments: an application to aerial surveys for dugongs. J Wildl Manag 70:255–262CrossRefGoogle Scholar
  65. Pulliam HR (1988) Sources, sinks and population regulation. Am Nat 132:652–661CrossRefGoogle Scholar
  66. R Development Core Team (2010) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar
  67. Redfern JV, Viljoen PC, Kruger JM, Getz WM (2002) Biases in estimating population size from an aerial census: a case study in the Kruger National Park, South Africa. South Afr J Sci 98:455–460Google Scholar
  68. Rivest LP, Potvin F, Crepeau H, Daigle G (1995) Statistical methods for aerial surveys using double-count technique to correct for visibility bias. Biometrics 51:461–470CrossRefGoogle Scholar
  69. Rodwell TC, Tagg J, Grobler M (1994) Wildlife resources in the Caprivi, Namibia: the results of an aerial census in 1994 in comparison with past surveys. Ministry of Environment and Tourism, WindhoekGoogle Scholar
  70. Rutina LP, Moe SR (2014) Elephant (Loxodonta africana) disturbance to Riparian Woodland: effects on tree-species richness, diversity and functional redundancy. Ecosystems 17:1384–1396CrossRefGoogle Scholar
  71. Samuel MD, Pollock KH (1981) Correction of visibility bias in aerial surveys where animals occur in groups. J Wildl Manag 45:993–997CrossRefGoogle Scholar
  72. Songhurst A (2012) Competition between people and elephants in the Okavango Delta Panhandle, Botswana. Ph.D., Imperial CollegeGoogle Scholar
  73. Songhurst A, McCulloch G, Coulson T (in press) Finding pathways to human–wildlife coexistence—a risky business. OryxGoogle Scholar
  74. Southwell C, Low M (2009) Black and white or shades of grey? Detectability of Adelie penguins during shipboard surveys in the Antartic pack-ice. J Appl Ecol 46:136–143CrossRefGoogle Scholar
  75. Stein A, Georgiadis N (2006) Spatial marked point patterns for herd dispersion in a Savanna wildlife herbivore community in Kenya. In: Baddeley A, Gregori P, Mateu J, Stoica R, Stoyan D (eds) Case studies in spatial point process modelling. Springer, Berlin, pp 261–273CrossRefGoogle Scholar
  76. Tawana Land Board (2005) Land use plan for Ngamiland. Tawana Land Board, MaunGoogle Scholar
  77. Thomas CD, Kunin WE (1999) The spatial structure of populations. J Anim Ecol 68:647–657CrossRefGoogle Scholar
  78. Trimble MJ, Ferreira S, van Aarde RJ (2009) Drivers of megaherbivore demographic fluctuations: inference from elephants. J Zool 279(1):18–26CrossRefGoogle Scholar
  79. van Aarde RJ, Jackson TP (2007) Megaparks for metapopulations: addressing the causes of locally high elephant numbers in southern Africa. Biol Conserv 134:289–297CrossRefGoogle Scholar
  80. Verlinden A, Gavor IKN (1998) Satellite tracking of elephants in northern Botswana. Afr J Ecol 36:105–116Google Scholar
  81. Walker BH, Emslie RH, Owen-Smith RN, Scholes RJ (1987) To cull or not to cull: lessons from a southern African drought. J Appl Ecol 24:381–401CrossRefGoogle Scholar
  82. White LJT (1994) Biomass of rain forest mammals in the Lope Reserve, Gabon. J Anim Ecol 63:499–512CrossRefGoogle Scholar
  83. Whitehouse AM, Hall-Martin AJ (2000) Elephants in Addo Elephant National Park, South Africa: reconstruction of the population’s history. Oryx 34:46–55CrossRefGoogle Scholar
  84. Wittemyer G (2001) The elephant population of Samburu and Buffalo Springs National Reserves, Kenya. Afr J Ecol 39:357–365CrossRefGoogle Scholar
  85. Wright IE, Reynolds JE, Ackermann BB, Ward LI, Weigle BL, Szelistowski WA (2002) Trends in manatee (Trichechus manatus latirostris) counts and habitat use in Tampa Bay 1987–1994: implications for conservation. Mar Mamm Sci 18:259–274CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  1. 1.Ecoexist ProjectMaunBotswana
  2. 2.Elephants Without BordersKasaneBotswana
  3. 3.Department of ZoologyUniversity of OxfordOxfordUK

Personalised recommendations