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Waterbirds in the Lake Eyre Basin (1983-2012): an asessment of wetland condition at different spatial scales


Executive Summary

This report analyses long-term annual aerial survey data collected for waterbird communities across approximately 10% of wetlands across the eastern part of the Lake Eyre Basin, collected between 1983 and 2012, a period of 30 years. Waterbird data were used as an assessment of the condition of the wetlands in the Lake Eyre Basin, supplied by the rivers and creeks of the Lake Eyre Basin. These analyses formed part of the Lake Eyre Basin Rivers Assessment. This report included an analysis of waterbird communities surveyed along four out of 10 survey bands crossing eastern Australia. Aerial surveys provided estimates of counts of all waterbird species, breeding occurrences and estimates of the fullness of wetlands each year of all waterbodies (>1ha), rivers and creeks, floodplains, dams and lakes within survey band(30km wide). We estimated total numbers, nests, and broods for each wetland of more than 50 species (some could not be identified to species). We analysed total numbers, species richness, abundances of functional groups, number of breeding records (nests and broods) and number of breeding species at two scales: Lake Eyre Basin area surveyed and individual wetlands. We also generated long-term trend estimates for the 10 most common species at a basin scale and 12 most common species at the wetland scale.

Waterbird data were a useful indicator showing spatial and temporal differences but these reflected natural boom and bust cycles. At the Lake Eyre Basin scale, the data clearly showed that the Lake Eyre Basin wetlands supported some of the larger concentrations of waterbirds on the continent, averaging about 116,000 waterbirds but reaching as high as half a million waterbirds. The number of species varied between 23 and 47 species. Of all the functional groups, ducks tended to dominate abundance with about 70% of the waterbirds. Unlike some other regions of Australia (e.g. Murray-Darling Basin), there was little evidence for any long term decline for any of the waterbird variables investigated. There were no trends in abundance, species richness, breeding abundance, breeding species richness or abundances of any of the six functional groups (ducks, herbivores, large wading birds, piscivores, shorebirds). This is a good indication that the condition of the wetland systems which are supplied by Lake Eyre Basin rivers remain in largely natural condition, unaltered over the 30 years for which data were available. These data provide a strong quantitative basis for the Lake Eyre Basin Rivers Assessment within the context of high natural variability, experienced in such arid zone regions where flooding and dry periods are spatially and temporally unpredictable. We also identified some key variables that were consistently important in explaining waterbird abundance at the Lake Eyre Basin. These included positive relationships with lagged rainfall, flow data for Cooper Creek, wetland area in the Lake Eyre Basin (lagged by a year), wetland area in the Murray-Darling Basin in the year of the survey and the Southern Oscillation Index.

At the scale of the individual wetland, we examined the changes in all response variables examined at the large scale of the Lake Eyre Basin for 11 of the major wetlands. We showed there were similarities in the waterbird communities within this group of wetlands, with waterbird communities of freshwater wetlands clustering reasonably close but apart from waterbird communities on saline wetlands. There was also little evidence for any temporal trajectory in the way that the entire waterbird community changed over time. There were positive effects between flooding, flow and rainfall in the Lake Eyre Basin and waterbird abundances at the individual wetland scale.

The long-term data provided a quantitative basis to identify potential thresholds of potential concern for waterbird response variables identified at the Lake Eyre Basin scale. We derived some potential thresholds for the lower 10% and 25% confidence limits for response variables. Further, exceedance of these thresholds can be measured against frequency or concurrent exceedance to derive thresholds of potential concern. Such thresholds of potential concern can also be derived for individual wetlands and each of the relevant response variables. These provide a useful guide for examining exceedances of thresholds of variability. Ultimately, actual thresholds of potential concern need to be derived with managers and policy makers. Thresholds of potential concern could also be derived based on declines in other wetland systems or rivers for each of the waterbird response variables; this could include a comparison of abundances for the first and last threshold for example. Also analyses should include likely driving variables, including time since last flooding, flow and wetland area, many of which were related to waterbird responses.

There were clear differences in abundance, species richness and the composition of functional groups and species among the 11 wetlands. Of most significance, Lake Galilee, Lake Hope, Lower Cooper Lakes and Lakes Torquinie and Mumbleberry stood out in terms of abundance and species richness. These wetlands also tended to have the highest frequencies of breeding species and numbers of broods and nests recorded. There were clear relationships between waterbird communities which usually related to the local area flooded and often the amount of wetland in the Lake Eyre Basin surveyed, lagged by a year. This probably provided sufficient time for a build-up in waterbird populations after reproduction and successful recruitment.

Overall, there was no evidence for any metric of waterbird communities in the Lake Eyre Basin showing any declining trend. There was reasonably high variability and spatial differences between wetlands but no evidence of any trends in waterbird responses apart from clear relationships with natural factors such area of wetland, area of Lake Eyre Basin wetlands, rainfall and flow. This analysis of waterbird communities over a period of 30 years across a large proportion of the Lake Eyre Basin provides strong evidence of the excellent condition of the Lake Eyre Basin wetlands and their rivers.