Determinants of preferred intertidal feeding habitat for Eastern Curlew: A study at two spatial scales
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Broadscale habitat use by Eastern Curlews (Numenius madagascariensis) in their non-breeding range in eastern Australia was assessed using low tide surveys on feeding grounds, where 60 skilled volunteers made repeated counts of the birds on intertidal flats, across 41% (9500 ha) of the intertidal habitat within Moreton Bay, Australia. We analysed 32 defined sections of intertidal flat, of roughly equal area (mostly 200-400 ha), which varied greatly in their curlew density (2-47 birds per 100 ha) and also in substrate and other environmental features. Sites with the least resistant substrates had densities three times those with the most resistant substrates. Of 10 environmental characteristics measured for each site, substrate resistance was the best predictor of curlew density (r2 = 0.45). Characteristics that were poor predictors included distance to the nearest roost, level of human disturbance and distance to urban settlement. For a finer-scale assessment, microhabitat use and feeding behaviour were recorded during low tide within 12 intertidal flats, which varied in size (23-97 ha), substrate, topography and other features. Across all flats, curlews strongly preferred to feed relatively close (0-50 m) to the low-water line. They fed on a variety of substrates (including sand, sandy-mud, mud and seagrass) in broadly similar proportions to their occurrence in the habitat. There was a statistically significant preference for sand, although its magnitude was not strong. These results indicate that curlews select habitat most strongly at a between-flat rather than within-flat scale.