Foraging ecology and habitat use of wading birds and shorebirds in the mangrove ecosystem of the Caéte Bay, Northeast Pará, Brazil Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) Angefertigt am Zentrum für Marine Tropenökologie des Fachbereiches 2 der Universität Bremen Bremen und am Institut für Vogelforschung „Vogelwarte Helgoland“ Wilhelmshaven vorgelegt von Kerstin Kober Bremen 2004 Tag des öffentlichen Kolloquiums: 27.07.2004 Gutacher der Dissertation: Prof. Dr. Ulrich Saint-Paul Prof. Dr. Franz Bairlein Diese Dissertation wurde mit Hilfe einer Promotionsförderung der Konrad-Adenauer Stiftung (Begabtenförderung) und eines “DAAD Doktorandenstipendiums im Rahmen des gemeinsamen Hochschulsonderprogramms III von Bund und Ländern” des DAAD erstellt. Contents Contents CONTENTS ABBREVIATION LIST SUMMARY RESUMO ZUSAMMENFASSUNG 1 GENERAL INTRODUCTION ............................................................................................1 2 MATERIALS AND METHODS..........................................................................................6 2.1 STUDY AREA AND SAMPLING SITES ...............................................................................6 2.2 STUDY DESIGN ..........................................................................................................10 2.2.1 Environmental conditions and the benthic community .................................................. 11 2.2.2 Avian community ........................................................................................................... 15 2.2.3 Exclosures ..................................................................................................................... 21 2.3 STATISTICAL ANALYSIS ..............................................................................................24 2.3.1 Data preparation............................................................................................................ 24 2.3.2 Univariate statistical methods........................................................................................ 25 2.3.3 Multivariate statistical methods/Ordination.................................................................... 25 3 THE TROPICAL TIDAL FLATS – ENVIRONMENTAL CONDITIONS AND THE BENTHIC COMMUNITY .................................................................................................29 3.1 INTRODUCTION ..........................................................................................................29 3.2 RESULTS ...................................................................................................................30 3.2.1 Sediment........................................................................................................................30 3.2.2 Salinity ........................................................................................................................... 31 3.2.3 Time of emergence........................................................................................................ 32 3.2.4 The macrobenthic community – availability of prey organisms for the birds................. 32 3.3 DISCUSSION ..............................................................................................................48 4 MIGRANT MEETS RESIDENT – DISTRIBUTION AND STRUCTURE OF THE AVIAN COMMUNITY ..................................................................................................................54 4.1 INTRODUCTION ..........................................................................................................54 4.2 RESULTS ...................................................................................................................55 4.2.1 Taxonomic composition................................................................................................. 55 4.2.2 Abundances................................................................................................................... 58 4.2.3 Spatial distribution ......................................................................................................... 59 4.2.4 Guilds............................................................................................................................. 64 4.3 DISCUSSION ..............................................................................................................67 Contents 5 FORAGING AT TROPICAL TIDAL FLATS – BIRDS IN RELATION TO THE BENTHIC COMMUNITY ..................................................................................................................72 5.1 INTRODUCTION ..........................................................................................................72 5.2 RESULTS ...................................................................................................................74 5.2.1 Harvestable prey fraction............................................................................................... 74 5.2.2 Diet ................................................................................................................................ 77 5.2.3 Distribution of birds in relation to macrobenthos ........................................................... 83 5.3 DISCUSSION ..............................................................................................................89 6 AVIAN CONSUMPTION AND FORAGING BEHAVIOUR..............................................96 6.1 INTRODUCTION ..........................................................................................................96 6.2 RESULTS ...................................................................................................................97 6.2.1 Time budgets................................................................................................................. 97 6.2.2 Calculated consumption .............................................................................................. 101 6.2.3 Exclosures ................................................................................................................... 106 6.2.4 Behaviour..................................................................................................................... 109 6.3 DISCUSSION ............................................................................................................114 7 REFERENCES..............................................................................................................126 8 ACKNOWLEDGEMENTS.............................................................................................139 9 LIST OF FIGURES........................................................................................................140 10 LIST OF TABLES .........................................................................................................143 11 APPENDICES ...............................................................................................................147 11.1 APPENDIX I: METHODS .........................................................................................147 11.2 APPENDIX II: ENVIRONMENTAL CONDITIONS AND THE BENTHIC COMMUNITY............152 11.3 APPENDIX III: DISTRIBUTION AND STRUCTURE OF THE AVIAN COMMUNITY...............164 11.4 APPENDIX IV: THE BIRDS IN RELATION TO THE BENTHIC COMMUNITY ......................169 11.5 APPENDIX V: AVIAN CONSUMPTION AND FORAGING BEHAVIOUR .............................177 Abbreveation list Abbreveation list In some instances, for example in some figures, the use of the full names and expressions was not possible or practical. In these cases short forms were used, which are listed below: Bird names Study areas Collared Plover copl Furo Grande FG Great Egret greg Furo do Chato FC Grey Plover grpl Ilha de Canelas C Greater Yellowlegs grye Little Blue Heron lbhe Experimental treatments Marbled Godwit mago Exclosures Ex Red Knot knot Control C Ruddy Turnstone turn Procedural Control PC Sanderling sand Short-billed Dowitcher sbdo Scarlet Ibis scib Others Spotted Sandpiper sdsa Gross food intake GFI Snowy Egret sneg Ash free dry weight AFDW Semipalmated Plover sppl Semipalmated Sandpiper spsa Tricolored Heron tche Whimbrel whim Willet will Yellow-crowned Nightheron ycnh Summary Summary Only little is known of wintering and resting shorebirds in tropical environments. The objective of this thesis was to describe the environment and the food availability the birds encounter in the tropics, the bird community in this habitat, the relationship between birds and environment/prey and the effects of bird consumption at tropical tidal flats. The study was conducted at the Bragantinian peninsula in the Northeast of Brazil, an area previously characterized as of major importance for migratory shorebirds. The study area was a poor and very variable foraging habitat, comprising an overall low content of organic material, many physical disturbances and high fluctuations of sediment conditions and salinity. Presumably as a result, the diversity, abundance and biomass of the benthos was very low compared to other tropical areas. The benthos also showed a strong spatial and temporal variability, especially on the lower taxonomic level. “Worms” were the numerically dominating group, which were accessible for all birds but provided only low biomass values. Bivalves and crustaceans included also large and biomass rich individuals, but they were less abundant and harvestable for only few large bird species. Thus, for many birds a large part