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Revision of the East Asian-Australasian Flyway Population Estimates for 37 listed Migratory Shorebird Species

Hansen BD, Fuller RA, Watkins D, Rogers DI, Clemens RS, Newman M, Woehler EJ & Weller DR (2016) Revision of the East Asian-Australasian Flyway Population Estimates for 37 listed Migratory Shorebird Species. Report for the Department of the Environment. BirdLife Australia, Melbourne.

This report provides an update of population estimates for the 37 species of migratory shorebirds in the East Asian – Australasian Flyway (EAAF) that regularly visit Australia. Population estimates for shorebirds in the EAAF are important in application of Australia’s Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). The EPBC Act is triggered when proposed actions, such as developments or land use changes, are likely to have a significant impact on important habitat for migratory shorebirds, defined by criteria outlined in the Convention on Wetlands of International Importance (Ramsar Convention) and the Wildlife Conservation Plan for Migratory Shorebirds (2015). In these conservation instruments, shorebird habitat is considered internationally important if it regularly supports 1% of the EAAF population of a migratory shorebird species, and nationally important, under the Wildlife Conservation Plan for Migratory Shorebirds, if it regularly supports 0.1% of an EAAF population of any migratory shorebird species (with the exception of Latham’s Snipe, for which the threshold is 0.05%).

An update of the EAAF estimates was considered important for several reasons. First, recent studies have demonstrated ongoing declines many species of migratory shorebird in Australia, so their populations may now be lower than they were at the time of the last assessment of shorebird populations in the EAAF. Secondly, there are now more shorebird count data on which to base population estimates. With the establishment of the Shorebirds 2020 program in 2007, there has been an increase in volunteer participation and site coverage in Australian shorebird counts; similarly, site coverage by shorebird counters is increasing in many other EAAF countries. Thirdly, accurate population estimates are needed to assess whether land development proposals should be referred for assessment under the EPBC Act. Finally, previous estimates of EAAF populations have not attempted to quantify the number of shorebirds in regions where no surveys have been done. The availability of more powerful analysis tools has enabled the interrogation of existing data in order to estimate numbers of non-counted shorebirds in remote and rarely visited regions.

Analytical approaches used in this project varied between species, according to data availability. Broadly, we collated shorebird counts carried out in the shorebird non-breeding season (November-March) from Australia (Shorebirds 2020 program), New Zealand (Ornithological Society of New Zealand) and 16 countries in Asia (Asian Waterbird Census). Generally, we calculated average numbers over the past five years on a site-by-site basis. We estimated the extent of unsurveyed coastal shorebird habitat using a global bathymetry map and a spatially-explicit global model of tidal amplitude to identify regions where tidal flats that could support shorebirds may occur. An extrapolation process was then used to estimate the number of shorebirds expected in these unsurveyed areas. Extensive consultation with shorebird counters and other experts with detailed local knowledge helped refine regional estimates and extrapolations.

For 18 (mainly coastal) species with the most reliable and extensive count data, we found a strong relationship between the population estimates, and breeding range and density.
The resultant model was used to estimate flyway populations for the remaining 19 shorebird species considered in this study, many of which are significantly undercounted on their non-breeding grounds because they occur in sites or habitats where few surveys are done.

Our work in compiling these population estimates has revealed a number of important knowledge gaps, which should be addressed in order to inform future revisions:

● inadequate shorebird monitoring across northern and inland Australia;
● the need for further exploration for shorebird sites in Indonesia and Papua New Guinea;
● a lack of intertidal habitat mapping around the flyway;
● a lack of mapping of shorebird count areas outside Australia.

We emphasize that any differences between these estimates and previous estimates cannot be used to draw conclusions about population change. The reader must instead refer to specialist studies aimed at detecting trends. Many of our estimates are higher than previous figures, principally as a result of improved knowledge about shorebird populations including increased count coverage, the estimation of shorebird numbers in unsurveyed areas and the use of an estimate based on breeding range size for non-coastal species. Nevertheless, ongoing population declines swamped these effects in some species, with current flyway population estimates now lower than previous assessments.

Download the report from the Australian Government website