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Stellenbosch University (2000)

The statistics of helicopter total counts of large ungulates in sourish mixed bushveld, northwest arid bushveld and mopane veld, Republic of South Africa

Reilly, Brian Kevin

Titre : The statistics of helicopter total counts of large ungulates in sourish mixed bushveld, northwest arid bushveld and mopane veld, Republic of South Africa

Auteur : Reilly, Brian Kevin

Université de soutenance : Stellenbosch University

Grade : Doctor of Philosophy (PhD) 2000

Résumé
The use of helicopters has become almost universally accepted as the method of choice in the enumeration of large ungulates in Southern Africa. In most cases decisions affecting management of these populations are made based on a single count result. In all these instances the within technique variance is ignored, often leading to decisions based on type I or type II statistical errors where the within technique variance is misconstrued as the population change. Many studies have investigated the issue of accuracy of counting methods and a few have quoted precision values for various methods. Very few have, however, investigated power and those extant have approached the problem from a prospective point of view and predicted power values. This study has made use of replicated counts from 12 sites of the original 23 in four vegetation types of the then Transvaal Province. The study sites vary in terms of size and all counts were undertaken with an experienced, trained team in which only four observers were used. A comprehensive post hoc analysis of the results of the field surveys shows precision and power to vary widely according to species and vegetation type and concludes that gamecounting results are largely site specific. A decline in observations during the course of four hours of survey is demonstrated and although the exact cause cannot be determined, correction factors have been constructed for two vegetation types. Observers are shown to differ from one another in observation profile during the course of surveys. This study demonstrates, describes and quantifies the existence of several phenomena suspected to exist by experienced game counters, biologists and wildlife managers and makes proposals in terms of improving the data returned from expensive aerial surveys.

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Page publiée le 7 mars 2016, mise à jour le 27 juin 2017