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Shorebirds are declining all around the world, mostly due to deterioration of the estuarine habitats used in winter and migration. Estuaries cover small areas, so it is essential to guarantee that shorebirds can access all the tidal flats where they usually feed at low-tide. Studying use of space by dunlins (Calidris alpina) in the Tagus estuary (Portugal), we noted that lack of suitably located high-tide roosts can limit the access of shorebirds to feeding habitats. Density of dunlins on foraging areas declined significantly with distance to the nearest roost, and fewer than 20% individuals foraged more than 5km from two roosts where they were dye-marked. So to permit full access to feeding areas it is important to maintain a network of suitably located high-tide roosts. We developed a GIS modelling methodology to evaluate the adequacy of existing roost networks, and to estimate the consequences of losing or creating new …