Identifying threats and conservation priorities across an international migration pathway

Abstract

Animal migrations are among the most extraordinary natural phenomena. Alarmingly, reports of widespread declines of migratory species are emerging from regions around the world, and the drivers of such declines are rarely well understood. This is principally a result of the vast geographic range that migratory animals inhabit, which may cover millions of square kilometres over multiple political jurisdictions, leading to difficulty in identifying the factors causing declines. This thesis addresses the problem of identifying threatening processes and understanding the effects of global change on migratory species, using migratory shorebirds in the East Asian-Australasian Flyway as a model system. In this thesis I present new methods, gather original data and conduct novel quantitative analyses that improve our understanding of the conservation of migratory species in a rapidly changing world.In Chapter 1, I develop the conceptual basis of this thesis by providing a practical and theoretical overview of issues relating to the conservation of migratory species. I examine the current state of knowledge and highlight the gaps and limitations of current research that hinder conservation efforts, concluding that knowledge of the threats affecting migratory systems across the full range of the migration is often limited. For migratory shorebirds in the East AsianAustralasian Flyway, where approximately 60 species regularly move from the Russian and American Arctic to non-breeding grounds in Asia, the Pacific, Australia and New Zealand, I show that decision making is severely hampered by a paucity of information on even the most basic threatening processes in the flyway. Indeed, I demonstrate that there is a clear and urgent need to discover the primary threatening processes operating in the flyway, and to improve our understanding of the impact of threats on populations of migratory shorebirds.Shorebirds require coastal habitat to achieve migration, yet coastlines around the world are under immense pressure from disturbance and development. However, there are no quantitative estimates of intertidal habitat loss at large spatial scales, owing to the difficulty of mapping dynamic coastal environments. In Chapter 2, I develop a new remote sensing method for mapping change of coastal wetlands over very large areas. Implementing this method across 14,000 kilometres of the Chinese, North Korean and South Korean coastlines, I report the first quantitative assessment of the status of migratory shorebird habitat at their staging sites (Chapters 3, 4 and 5). I show that coastal habitats in the Yellow Sea are declining at a rate that rivals many of the worlds’ major at-risk ecosystems, such as tropical forest, seagrass and mangrove ecosystems. In Chapter 5, I show that the current network of protected areas is limited in its effectiveness at reducing coastal habitat loss, through a combination of threats that could be ameliorated by local management and regional processes that drive degradation, and provide guidance on effective management of coastal areas.Knowledge of how threats such as declining habitat, climate change and human exploitation impact migratory shorebird populations is essential to allow targeted implementation of conservation actions across more than 26 countries that comprise the East Asian-Australasian Flyway. Building on Chapters 2-5, in Chapter 6 I investigate the effects climate variability and habitat loss of on two similar populations of a long-distance migratory shorebird (bar-tailed godwit Limosa lapponica). I demonstrate widespread and sustained declines of two subspecies of the bartailed godwit and relate those to the habitat losses I discovered earlier in my thesis. Finally, I synthesise the thesis by placing my results in the context of the broader scientific literature, acknowledging the limitations of my research, and suggesting future research directions given the significant new contribution I have provided in this thesis (Chapter 7). My work has transformed our knowledge of the threats impacting migratory shorebirds, and provides a framework for identifying and understanding the impact of threatening processes on any migratory species. More broadly, it has significantly contributed to the conservation of one of the world’s least understood coastal ecosystems and will lead to improved management of Australia’s migratory shorebird species.