Community Ecology of Mangrove Birds
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Community Ecology of Mangrove Birds Mohd-Azlan J. BSc. (Hons) Forestry, MSc. Research Institute of Environment and Livelihood Faculty of Engineering, Health, Science and the Environment Thesis submitted for the degree of Doctor of Philosophy September 2010 I declare that this work, now submitted as a thesis for the degree of Doctor of Philosophy of the Charles Darwin University, is the result of my own investigations, and all references to ideas and work of other researchers have been specifically acknowledged. I certify that the work embodied in this thesis has not been accepted in substance for any degree, and is not currently submitted in candidature for any other degree MOHD AZLAN JAYASILAN ABDUL GULAM AZAD SEPTEMBER 2010 ii ACKNOWLEDGEMENTS I would like to acknowledge the help I have received from many people during the last four years. This research was made possible by the support of the Ministry of Higher Education, Malaysia and University Malaysia Sarawak. The fieldwork was supported by Australian Research Council Mosquito grant. Before all others, my supervisor Professor Michael Lawes deserves my utmost gratitude for his patience and support throughout my candidature. I am indebted to him for his expert advice on experimental design, database skills, and statistical analysis as it was integral to this research. I am grateful to Dr. Richard Noske for all the training, guidance and comments on earlier drafts. I am deeply appreciative. You are responsible for developing my interest in birds! I am thankful to Professor Stephen Garnett’s guidance and support in redirecting the original project; otherwise I would be still counting bats in the mangroves. I appreciate advice from Professor Corey Bradshaw during the early stages of this project. I also thank Dr. Donald Franklin for his advice and help. Drafts of this thesis were read in part by Professor Stephen Garnett and Dr. Jim Sanderson. I am indebted to them for their comments. It is an honour for me to work with these people. Some of the plant specimens were identified by the Northern Territory Herbarium. I am grateful to Darwin City Council, the Northern Territory Department of Planning and Infrastructure, the Royal Australian Air force, Parks and Wildlife Commission Northern Territory and Power and Water for access to the mangroves. It was difficult to find volunteers to work in the humid, muddy and crocodile infested mangroves. However, a handful of people helped me occasionally. I am grateful to Arianti Atong, Hanan, Ilman, Julie Riehl, Beau Austin and Ria Fitriana. Many friends and colleagues have helped and provided encouragement during this journey - thank you Therese Fitzgerald, Indra Asmara, Beau Austin, Clive McMahon, Julian Gorman, Rachel Carey, Lisa Petheram, Muhammad Nawaz and Arturo Izurieta. The encouragement from my parents, Mr. & Mrs. Azad was an important part of achievements. My inspiration, my 3 fantastic children Hanan (7), Ilman (5) and Karisma (2 - who is younger than the thesis), and my wife, Arianti Atong, my iii saviour each and every day, I am heartily thankful for their patience, good advice and unconditional love. Their sacrifice, support, encouragement and understanding during my frequent mental absence throughout this project made this thesis possible. My years in Darwin have been memorable and I will always be grateful to the people of this marvellous country for my time here. I hope that in some small way they find this work useful. I dedicate this thesis to Richard Noske whose passionate enthusiasm for mangrove birds was inspirational. Alhamdulillah. iv TABLE OF CONTENTS Acknowledgments………………………………………………………………iii Table of Contents……………………………………………………………….v List of Figures……………………………………………………….…………..viii List of Tables……………………………………………………………………xii Abstract………………………………………………………………………….xv CHAPTER 1: General introduction 1.1 Introduction…………………………………………………………. 1 1.2 Biogeography, evolution and distribution of mangroves …………... 1 1.3 Mangrove ecosystem………………………………………………... 2 1.4 Biodiversity in mangroves……………………….…………………. 3 1.5 Patterns in avian community ecology………………………………. 5 1.6 Avifauna of mangroves……………………………………………... 6 1.7 Threats to mangroves ecosystem…………………………………… 9 1.8 Aims and objectives………………………………………………… 12 CHAPTER 2: General Methodology 2.1 Study region………………………………………………………… 15 2.2 Climate……………………………………………………………… 16 2.3 Tidal variation………………………………………………………. 17 2.4 Vegetation…………………………………………………………... 18 2.5 Other vertebrate communities in Darwin mangroves………………. 19 2.6 Study sites………………………………………………………….. 20 2.6.1 Leanyer………………………………….………………… 21 2.6.2 Ludmilla…………………………………………………... 22 2.6.3 Rapid Creek……………………………………………….. 24 2.6.4 East Point…………………………………….…………… 24 2.6.5 Casuarina Coastal Reserve……………….……………….. 24 2.6.6 Charles Darwin National Park……….…………………… 24 2.6.7 East Arm-Berrimah……………………………………….. 24 2.6.8 East Arm-Tivendale road…………………………………. 24 2.6.9 East Arm Hamaura Road…………………………………. 25 2.6.10 Buffalo Creek……………………………………………. 25 2.6.11 Mindil……………………………………………………. 25 2.6.12 Bay View………………………………………………… 25 2.6.13 Nightcliff………………………………………………… 25 2.7 Data collection……………………………………………………… 25 2.7.1 Bird census techniques……………………………………. 26 2.7.2 Insect sampling technique………………………………… 29 2.7.3 Flowering phenology…………………………………….. 29 2.7.4 Vegetation diversity and habitat heterogeneity…………… 30 2.7.5 Diversity indices and the use of species richness...………. 31 CHAPTER 3: Bird community structure and density in mangroves of northern Australia: area-dependent or not? 3.1 Introduction…………………………………………………………. 33 3.2 Methods……………………………………………………………... 35 v 3.2.1 Bird census methods and density estimation…………….. 35 3.2.2 Species accumulation and rarefaction…………………….. 37 3.2.3 Species diversity………………………………………..... 38 3.2.4 Area and isolation measurements………………………… 38 3.2.5 Species-area analysis……………………………………… 39 3.2.6 Minimum critical patch size………………………………. 40 3.2.7 Density compensation…………………………………….. 40 3.2.8 Ecological functional groups…………………………….. 41 3.2.9 Effects of seasonality on mangrove birds………………… 42 3.3 Results………………………………………………………………. 42 3.3.1 Bird species richness and diversity……………………….. 43 3.3.2 Species-area curves……………………………………….. 44 3.3.3 Minimum critical patch size………………………………. 49 3.3.4 Population density………………………………………… 51 3.3.5 Density compensation…………………………………….. 51 3.3.6 Function-area relationship………………………………… 56 3.3.7 Effects of seasonality on mangrove bird diversity………... 62 3.4 Discussion…………………………………………………………... 62 3.4.1 Species diversity and density……………………………... 62 3.4.2 Effects of seasonality on the mangrove bird community…. 64 3.4.3 Species-area relationships………………………………… 65 3.4.4 Density compensation and density-area relationships……. 68 CHAPTER 4: Null model analysis of nestedness and species co- occurrence of bird assemblages in mangrove forests 4.1 Introduction…………………………………………………………. 70 4.2 Methods……………………………………………………………... 73 4.2.1 Study sites and bird census……………………………..... 73 4.2.2 Nested subset analysis…………………………………….. 74 4.2.3 Potential causes of nestedness…………………………….. 75 4.2.4 Co-occurrence patterns…………………………………… 76 4.2.5 Testing the effect of area and bird biomass on species occupancy…………………………………………………. 77 4.3 Results…….………………………………………………………… 78 4.3.1 Nested subset analysis…………………………………….. 78 4.3.2 Potential mechanisms of nestedness: selective extinction or colonisation...................................................................... 81 4.3.3 Co-occurrence metrics……………………………………. 82 4.3.4 Species occurrence and bird body mass and patch area ….. 84 4.4 Discussion…………………………………………………………... 86 CHAPTER 5: The role of habitat heterogeneity in structuring mangrove bird assemblages 5.1 Introduction…………………………………………………………. 92 5.2 Methods……………………………………………………………... 95 5.2.1 Study sites, vegetation and bird sampling methods………. 95 5.2.2 Habitat heterogeneity measurements…………………….. 95 5.2.3 Diversity indices………………………………….………. 97 5.3 Data analysis…………………………………………...…………… 97 5.3.1 Indicator species analysis (IndVal)……………………….. 97 vi 5.3.2 Principle Component Analysis……………………………. 98 5.3.3 Generalised linear models………………………………… 99 5.4 Results………………………………………………………………. 100 5.4.1 Bird distribution in mangrove zones……………………… 100 5.4.2 Indicator species analysis…………………………………. 102 5.4.3 Habitat heterogeneity……………………………………... 104 5.4.4 Habitat heterogeneity and bird species composition……… 106 5.4.5 Habitat heterogeneity predictors of bird species richness and density……...………………………………………… 108 5.5 Discussion………………………………………...…………….…... 112 CHAPTER 6: Resource partitioning and foraging ecology of mangrove bird communities 6.1 Introduction…………………………………………………………………. 117 6.2 Methods……………………………………………………………………... 119 6.2.1 Foraging observations…………………………………….. 119 6.2.2 Flowering phenology and insect availability…………...… 120 6.2.3 Ordination………………………………………….…..…. 121 6.2.4 Bipartite “network” Analysis……………………………... 122 6.3 Results………………………………………………………………………. 126 6.3.1 Foraging ecology…………………………………………. 126 6.3.2 Ordination ……………………………………………….. 131 6.3.3 Structure of interaction network…………………………. 134 6.3.4 Effect of climate seasonality on food resources…………... 137 6.4 Discussion…………………………………………………………………... 140 CHAPTER 7: The community ecology of mangrove birds: A synthesis 7.1 The influence of patch size on species richness…………………………….. 147 7.2 The influence of habitat heterogeneity on mangrove birds…………………. 150 7.3 Matrix effects and species composition in the mangroves………………….. 151 7.4 Bird community dynamics in the