Valuing coastal habitats: predicting high-tide roosts of non-breeding migratory shorebirds from landscape composition

Conservation of critical habitats for shorebirds (Charadriiformes : Charadrii), usually requires spatially explicit identification of each habitat. Most non-breeding shorebirds depend on two critical habitats: foraging (intertidal flats) and roosting (safe and open supratidal sites). We used published information on use of high-tide roosts by shorebirds to develop models of roost selection (probability of occurrence) and usage (mean abundance) for 12 species of shorebirds spending the non-breeding season in Moreton Bay, in subtropical eastern Australia. Selection of roosts was most strongly affected by the proximity to a large foraging area, field of view and to a lesser extent by composition of the surrounding landscape. Abundance of the most common species, such as Bar-tailed Godwit (Limosa lapponica), Eastern Curlew (Numenius madagascariensis) and Whimbrel (N. phaeopus), depended on distance to the nearest large foraging area or the size of the roost per se. Our results suggest that the shorebird species occurring in a subtropical Australian estuary use two generalised types of roosts: exposed ocean-front roosts typified by supratidal spits and sandbars and patches of claypan saltmarsh in the upper reaches of the tidal range surrounded by mangroves. The amount of these habitats available in Moreton Bay was examined by visiting unmonitored sites with a predicted high probability of occupancy by two key species, Eastern Curlew and Bar-tailed Godwit. Few of the unmonitored sites currently supported many shorebirds. These data suggest that despite the high demand on coastal land for urban development in Moreton Bay, suitable roosting habitat is still available near their foraging areas.