Wetlands support biodiversity and provide critical ecosystem services but have been severely impacted by human activity. Shorebirds are a diverse group of waterbirds that usually forage in shallow water, making them highly dependent on wetlands. Coastal shorebirds are increasingly threatened in the East Asian-Australasian Flyway where coastlines are heavily developed and wetlands have been extensively modified and degraded. In this human-dominated landscape, shorebirds sometimes aggregate in artificial wetlands associated with human production activities including agriculture, aquaculture and salt production. However, it is unknown whether artificial habitat use is widespread by shorebirds across the flyway, if such habitats could help to offset negative population trends, or how artificial habitats should be managed alongside natural habitats to achieve conservation outcomes. This thesis investigates the use of artificial and natural habitats by shorebirds in heavily developed coastal regions of the East Asian-Australasian Flyway, and suggests conservation and management actions in this setting.
Chapter 2 presents the first large-scale review of coastal artificial habitat use by shorebirds in the East Asian-Australasian Flyway. Analysing data from multiple monitoring programs and the literature, it shows that 83 shorebird species have occurred on more than 170 artificial sites of eight different land uses throughout the flyway, including 36 species in internationally important numbers. However, occurrence and foraging on artificial habitats is uneven among species, and different land uses support varying abundances and species diversity. Saltworks host a larger and more diverse shorebird assemblage than other artificial habitats, but are threatened by conversion to land uses of lesser habitat value.
Chapter 3 presents a detailed case study of artificial habitat use in a critical stopover area comprising ~150 km of coastline in Jiangsu province, China. It shows that most shorebirds are completely limited to artificial habitats during high tide because natural intertidal wetlands are covered by seawater and no natural habitat remains in the supratidal zone. Further, most shorebirds were observed using artificial habitats almost exclusively for roosting (rather than foraging), and selected larger ponds with less water and vegetation cover and fewer built structures nearby, characteristics that can be cultivated through management. These results suggest that jointly managing artificial supratidal and natural intertidal habitats would benefit shorebirds in this region, and this approach is likely applicable to sites throughout heavily developed regions of the flyway.
Chapter 4 uses long-term monitoring data from five highly developed coastal regions of Australia to show that a high proportion of all shorebirds (more than one-third in four regions and more than two-thirds in two regions) use artificial habitats at high tide. It indicates that a relatively low proportion of migratory and coastal habitat specialist shorebirds use artificial habitats, suggesting they may be less flexible in their habitat use and thus less able to use non-tidal habitats than non-migratory and generalist/inland specialist species. Most species-region combinations did not show a significant temporal trend in the proportion of birds that use artificial habitats, suggesting relatively consistent use of artificial habitats over time. These results indicate that a framework for high tide habitat management that includes artificial habitats alongside preservation of remaining natural habitats could make a significant contribution to shorebird conservation in Australia.
Smooth cordgrass Spartina alterniflora is a known threat to shorebirds along the heavily developed coast of mainland China. It spreads along intertidal flats and makes them effectively unavailable to shorebirds for foraging, and can reduce the quality of supratidal roost sites. The intersection of S. alterniflora invasion and loss of intertidal flats from other processes including land reclamation presents a double threat, with both pressures narrowing the extent of habitat available for foraging and roosting. However, the spatial overlap between S. alterniflora and shorebird distribution in mainland China is unknown. Chapter 5 therefore maps the extent of S. alterniflora coverage of coastal sites used by internationally important numbers of shorebirds, estimates recent change in the spatial extent of intertidal flats at the same set of sites, and investigates where these two threats to important shorebird habitat intersect. It shows that S. alterniflora occurs on > 50% of important shorebird sites, 79% of which also experienced a decrease in intertidal extent between 2000 and 2015. These results suggest an urgent need for targeted S. alterniflora control, and can help to guide investment.
This thesis demonstrates that shorebirds in heavily developed coastal areas of the East Asian-Australasian Flyway use natural intertidal wetlands and artificial supratidal habitats as an inter-connected landscape. Significant threats remain to both types of habitat, requiring additional conservation and management action. Urgent needs include formally incorporating artificial habitats into conservation frameworks (Chapter 2; Chapter 4); securing or creating large roost sites with unvegetated areas of shallow water in the supratidal zone of human-dominated coastal areas (Chapter 3); and, controlling S. alterniflora at important shorebird sites in China, especially those that have already experienced intertidal flat loss (Chapter 5).