Detection probabilities of ungulates in the eastern Swaziland lowveld

Authors: B.A. Collier, R. A. McCleery, K. W. Calhoun, K. G. Roques, A. Monadjem

The management of large ungulates in southern Africa necessitates reliable monitoring programmes to direct management action. Monitoring programmes for large ungulates typically rely on spotlight survey methods, but do not address variation in detection rates between surveys or observers. In 2009, we used a multiple observer survey technique to estimate detection probabilities for large ungulates in lowveld savanna habitats in Swaziland. Spotlight detection probabilities for all ungulates ranged between 0.22 and 0.57. Species-specific spotlight detection rates for the two most detected species, impala (Aepyceros melampus) and blue wildebeest (Connochaetes taurinus), were 0.48 and 0.61, respectively. At our open savanna study site, detection rates were higher and abundance estimates were fairly consistent. In our more enclosed savanna habitat, both detection rates and resulting abundance estimates were variable. Our results suggest that when monitoring large ungulate populations, managers should conservatively assume they are missing approximately 50% of the population available for surveying.We recommend that managers consider methods which incorporatemultiple observers into survey practices and consider using multiple data sources to assist with population management decisions.

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