Statistical analysis of bird atlas data from Swaziland

Master Thesis


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University of Cape Town

The question of what determines the observed geographical distributions of animal species is one of great interest to natural scientists. In general terms, these distributions are known to be related to a number of environmental factors, but the nature of the relationships and the relative importance of the different factors remain poorly understood. This investigation sets out to obtain more insight into these questions by using statistical methods to explore the relationships between the observed geographical distributions of bird species in Swaziland and a number of environmental variables. In 1985 I set out to compile a bird atlas of Swaziland. Data were accumulated between 1985 and 1991 and the bird atlas submitted to a publisher in May 1993. The text of the bird atlas is included here as Appendix 2 because it provides the essential background to this dissertation. The introductory section of the atlas includes a description of the data gathering process. The analysis included in the bird atlas was aimed at a popular readership and was not intended to form part of an academic dissertation Chapter 1 describes the use of logistic regression to investigate the relationships between the bird distribution patterns and a set of environmental variables and to predict the distributions. Chapter 2 describes the results of applying the methods described in Chapter 1 for all of the bird species for which data were available. Because this paper was aimed at a different readership, some repetition of material contained in Chapter 1 was unavoidable. In Chapter 3, biplot techniques were used to obtain a graphical representation of the bird atlas data.