Table of contents ACKNOWLEDGEMENTS ......................................................................................................................................... 9 ABSTRACT ............................................................................................................................................................10 ABBREVIATIONS ...................................................................................................................................................12 1 INTRODUCTION ...........................................................................................................................................13 1.1 INTRODUCTION ........................................................................................................................................13 1.1.1 Desertification .................................................................................................................................13 1.1.2 Birds in arid and semi-arid ecosystems .............................................................................................14 1.1.3 Biodiversity ......................................................................................................................................16 1.1.4 Birds as biological indicators ............................................................................................................18 1.1.5 Habitat selection ..............................................................................................................................18 1.1.6 Community ecology ..........................................................................................................................20 1.2 MOTIVATION ...........................................................................................................................................20 1.3 OBJECTIVES AND HYPOTHESIS .......................................................................................................................20 1.3.1 Research question ............................................................................................................................20 1.3.2 Hypothesis .......................................................................................................................................20 1.3.3 Objectives: .......................................................................................................................................21 1.4 RESEARCH FRAMEWORK .............................................................................................................................21 2 LITERATURE REVIEW ....................................................................................................................................22 2.1 FACTORS AFFECTING AVIAN DIVERSITY AND COMMUNITIES IN ARID ECOSYSTEMS .......................................................22 2.1.1 Water ..............................................................................................................................................22 2.1.2 Temperature ....................................................................................................................................23 2.1.3 Food ................................................................................................................................................24 2.1.4 Breeding requirements .....................................................................................................................25 2.1.5 Migration and movements ...............................................................................................................26 2.1.6 Habitat ............................................................................................................................................26 2.1.7 Rivers ...............................................................................................................................................28 2.2 MANAGEMENT ........................................................................................................................................28 3 METHODS ....................................................................................................................................................30 3.1 THE BIOTA PROJECT .................................................................................................................................30 3.2 RESEARCH AREA .......................................................................................................................................32 3.2.1 Rooiklip ............................................................................................................................................34 3.2.2 Weissenfels ......................................................................................................................................35 3.2.3 Claratal ............................................................................................................................................36 3.2.4 Neudamm ........................................................................................................................................37 3.2.5 Okasewa ..........................................................................................................................................37 3.3 SAMPLING DESIGN ....................................................................................................................................38 3.3.1 Bird surveys .....................................................................................................................................38 3.3.2 Vegetation survey ............................................................................................................................45 3.4 ENVIRONMENTAL FACTORS ..........................................................................................................................46 3.4.1 Rainfall ............................................................................................................................................46 3.4.2 Habitat types ...................................................................................................................................46 3.5 DATA ANALYSIS ........................................................................................................................................47 3.5.1 Microsoft Excel.................................................................................................................................48 3.5.2 Graphpad Prism 4 ............................................................................................................................49 3.5.3 PC-ORD 6.0 ......................................................................................................................................49 4 RESULTS .......................................................................................................................................................52 4.1 VEGETATION HEIGHT..................................................................................................................................52 4.2 OBSERVER BIAS ........................................................................................................................................52 4.3 SPECIES-ACCUMULATION CURVES ..................................................................................................................53 4.4 IDENTIFYING GROUPS .................................................................................................................................53 4.4.1 Cluster analysis of transects .............................................................................................................54 4.4.2 Cluster analysis of sample units ........................................................................................................55 4.4.3 MRPP ...............................................................................................................................................55 4.5 BIRD SPECIES RICHNESS, ABUNDANCE AND DIVERSITY: ALL OBSERVED BIRD SPECIES INCLUDED. ......................................56 4.5.1 Species richness across the aridity gradient: all observed bird species ...............................................67 4.5.2 Species richness by habitat types: all observed bird species ...............................................................67 4.5.3 Abundance across the aridity gradient: all observed bird species.......................................................68 4.5.4 Diversity: all observed bird species across the aridity gradient and habitat type ................................69 4.5.5 Non-contributive bird species ...........................................................................................................69 4.6 ANALYSES AFTER REMOVING NON-CONTRIBUTIVE BIRD SPECIES .............................................................................71 4.6.1 Species richness ...............................................................................................................................71 4.6.2 Abundance .......................................................................................................................................78 4.6.3 Diversity ...........................................................................................................................................79 4.6.4 Avian biomass ..................................................................................................................................81