Temporal and spatial use of resources by black swans (Cygnus atratus) on the Vasse-Wonnerup wetlands This thesis is presented for the degree of Bachelor of Science Honours, College of Science, Health, Engineering and Education; Environmental and Conservation Sciences, Murdoch University. By Zoë Kissane (BSc, BEd) 2019 Declaration I declare that this thesis is my own account of my research and contains as its main content, work which has not previously been submitted for a degree at any tertiary education institution. Zoë Kissane ii Abstract Black swans are large herbivorous waterbirds with a dietary preference for submerged aquatic plants. They are endemic to Australia and are known to be opportunistic in their use of habitat. The largest regular breeding colony of black swans in the south west of Western Australia occurs in the Ramsar listed Vasse-Wonnerup wetlands. Although home to large numbers of waterbirds, it is a highly eutrophic and modified system and little is known about the effect of water management decisions on waterbird ecology. Therefore, the aim of this study was to determine the main drivers of temporal and spatial black swan abundance over an annual cycle, and the seasonal composition of black swan diet. Seasonal swan counts were conducted (5 counts per season; in all seasons) across ten sites, where abundance, activity and use of habitat were recorded. To determine seasonal composition of swan diet, faecal samples were collected in all seasons and analysed using microscopy and molecular genetics (DNA). Results showed there was a significant difference between both regional (F4,80 = 11.02, p< 0.001) and seasonal swan abundance (F3,80 = 80.11, p< 0.001), with mean swan abundance highest in winter (n=2073) and spring (n=1960) (summer n=245; autumn n=360). The proportion of plant material in swan faecal matter varied seasonally, with macrophytes found in greater proportions to other plants in spring ( = 67.75, p < 2 4 0.001). In contrast, Lamprothamnium macropogon and samphire plants were found in higher proportions than all other plants in autumn ( = 101.32, p < 0.001) and winter 2 4 ( = 28.06, p < 0.001). Lamprothamnium macropogon and salt marsh plants such as 2 4 samphires are important components of black swan diet, particularly in the absence of submerged aquatic plants. These results have important implications for wetland management, because they show the importance of fringing salt marsh vegetation for iii swan populations. As salt marsh habitat is a threatened ecological community, these results emphasize the importance of protecting this vegetation, not just at this site but the Swan Coastal Plain and Australia more broadly. iv Acknowledgments Firstly, I would like to acknowledge and pay my respects to the Wardandi people, who are the Traditional Owners of the land on which my research took place. This project would not have been possible without the help and assistance from many people. My sincere gratitude and thanks to my supervisors Dr Jane Chambers and Dr Jill Shephard for all of their support and guidance over this past year. Thank you for making sure I had all my swans in a row, for sharing your expert knowledge with me and providing help, guidance and support all the way to the finish line. Thanks to Dr Stephen Beatty, Dr Robyn Paice and Dr Nicola Armstrong for their assistance and guidance with statistical analysis, and to Dr Belinda Robson for her assistance identifying the invertebrates found during microscopy on swan faecal samples. Thanks also to the folks from the Department of Water and Environmental Regulation, in particular Dr Kath Lynch and her team in Busselton, who let me tag along (or rather kayak along) during water sampling out on the wetlands on many occasions. Thanks also to Dr Linda Kalnejais from DWER who assisted with water data retrieval and interpretation. The DNA component of this project was conducted by the folks at the Australian Genome Research Facility, and I would like to acknowledge and thank Dr David Chandler and his team for their efforts with this. For help and assistance during the early planning stages of this project I’d like to extend a special thanks to Larissa Izakovic, who braved the snake infested wetlands with me numerous times in search of the perfect swan spotting sites. Thanks also to the folks at the Department of Biodiversity, Conservations and Attractions who also assisted in the planning stages by sharing their expert site and swan knowledge with me. In particular, thanks to Dr Jim Lane and Alan Clarke from the DBCA Busselton office, and Kim Williams and Chris Taylor from the DBCA Bunbury office. I spent a lot of time counting swans and collecting swan poo, and could not have done either without the help and assistance from many fieldwork volunteers. A very special v thanks to my mother, Kathleen Power, my number one field assistant who came out with me rain, hail or shine in search of swans and their poo. There is no way I would have completed my fieldwork without her ongoing support and I’m so very grateful for all the time that was volunteered and the warm cups of tea we shared together out on the wetland. Thanks also to Larissa, Anna, Barry and the Conservation and Land Management students from Bunbury TAFE who also volunteered their time in the field, as well as Ailsa and John Hohnen for allowing me access to their property for my swan counts. Last but certainly not least I would like to extend a very special thanks to my partner, family and friends, who supported me throughout this challenging experience. The messages of support, home cooked meals and tolerance of every second conversation I had being about swans was so very much appreciated. vi Table of contents 1. Introduction ...................................................................................................... 1 1.1 The black swan (Cygnus atratus) ............................................................................. 2 1.1.1 Distribution and habitat ........................................................................................... 2 1.1.2 Breeding and food requirements ............................................................................ 4 1.1.3 Diet and food preferences ....................................................................................... 5 1.1.4 Influence of water level changes on distribution .................................................... 7 1.2 Impacts of swans on wetland plants ....................................................................... 8 1.2.1 Grazing patterns of swans ....................................................................................... 9 1.2.2 Impacts of swan grazing on wetland vegetation ................................................... 10 1.3 Current study ....................................................................................................... 12 1.3.1 The Vasse-Wonnerup wetlands ............................................................................ 12 1.3.2 Threats to waterbirds on the Vasse-Wonnerup wetlands..................................... 13 1.3.3 Study aims and hypotheses ................................................................................... 15 2. Methods ......................................................................................................... 17 2.1 Study site ............................................................................................................. 17 2.2 Black swan abundance, distribution and use of habitat ......................................... 18 2.3 Water and plant sampling ..................................................................................... 21 2.4 Black swan diet analysis ....................................................................................... 24 2.4.1 DNA analysis and primer design ............................................................................ 24 2.4.2 Microscopy ............................................................................................................. 26 2.5 Data analysis ........................................................................................................ 32 3. Results ............................................................................................................ 36 3.1 The effect of season and water availability (depth) on black swan presence, abundance and distribution on the Vasse-Wonnerup wetlands. ..................................... 36 3.1.1 Swan abundance and distribution across seasons and regions ............................ 36 3.1.2 Comparison with historical swan counts ............................................................... 40 3.1.3 Factors influencing abundance and distribution: season and water depth .......... 42 3.2 Seasonal composition of black swan diet and the relationship between seasonal changes in plant species availability to black swan abundance and distribution across the Vasse-Wonnerup wetlands. ........................................................................................... 44 3.2.1 Seasonal availability of aquatic plants ................................................................... 44 3.2.2 Seasonal composition of black swan diet .............................................................. 47 vii 3.2.3 Seasonal comparison of swan diet and plant community composition ................ 54 3.3 Associations between black swan activity and use of habitat. ................................ 58 4. Discussion ......................................................................................................