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

[摘要] ENGLISH ABSTRACT:The use of helicopters has become almost universally accepted as the method ofchoice in the enumeration of large ungulates in Southern Africa. In most casesdecisions affecting management of these populations are made based on asingle count result. In all these instances the within technique variance isignored, often leading to decisions based on type I or type II statistical errorswhere the within technique variance is misconstrued as the population change.Many studies have investigated the issue of accuracy of counting methods and afew have quoted precision values for various methods. Very few have, however,investigated power and those extant have approached the problem from aprospective point of view and predicted power values. This study has made useof replicated counts from 12 sites of the original 23 in four vegetation types of thethen Transvaal Province. The study sites vary in terms of size and all countswere undertaken with an experienced, trained team in which only four observerswere used. A comprehensive post hoc analysis of the results of the field surveysshows precision and power to vary widely according to species and vegetationtype and concludes that gamecounting results are largely site specific. A declinein observations during the course of four hours of survey is demonstrated andalthough the exact cause cannot be determined, correction factors have beenconstructed for two vegetation types. Observers are shown to differ from oneanother in observation profile during the course of surveys. This studydemonstrates, describes and quantifies the existence of several phenomenasuspected to exist by experienced game counters, biologists and wildlifemanagers and makes proposals in terms of improving the data returned fromexpensive aerial surveys.

[发布机构] Stellenbosch University