Waterbird assemblages of Australia’s largest east-coast wetland complex: environmental determinants of spatial and temporal distribution

Context The extensive Burdekin–Townsville seasonal freshwater wetlands in the Queensland tropics (adjacent to an intertidal Ramsar site) support important waterbird assemblages within and downstream of the Burdekin–Haughton irrigation area. Little evidence is available of the environmental drivers of these assemblages, possibly including the extensive development of irrigated agriculture. Aims We described the composition and dynamics of freshwater waterbird assemblages to identify their environmental determinants and underpin conservation management. Methods We used up to four decades’ worth of records of waterbird assemblages, and collected biophysical data from 57 sites and water quality data for 32 sites. We predicted that these measured variables would determine assemblage composition, thereby elucidating the environmental drivers of the assemblages. Key results In total, 100 waterbird and shorebird species were recorded. Individual samples were strongly nested. Species richness increased with area but density decreased. Richness had a humped relationship with water depth. Linear modelling identified mostly weak relationships between species, assemblages and environmental variables (e.g. nutrients). Abundances mostly increased during the dry season but irrigation tailwater reduced seasonal variation in some wetlands. No apparent change in common species’ assemblages was evident over four decades. Conclusions The wetlands provide extensive, diverse habitats for rich waterbird assemblages, despite impacts of agricultural development. Impacts on waterbirds appear to be buffered by the extent and complexity of the wetland mosaic that includes modified wetlands. Implications Holistic, active management is required to ensure the long-term conservation of habitats for waterbirds and other biota in the Burdekin–Townsville seasonal freshwater wetlands. Inclusion of these freshwater wetlands in the Ramsar site would be beneficial.