Résumé
Tidal habitats sustain fragile ecosystems, undergoing pressures from coastal artificialization and rising sea levels. Saltpans are a substitution habitat for birds that breed, winter or stop-over along coastlands where most pristine tidal habitats have been removed. Balancing the economical, patrimonial and biodiversity values of former saltpans is thus needed to mitigate the threats posed by global changes on waterbirds. In this study, we scrutinized the influence of management practices on waterbirds on two isolated saltpans located on the French Mediterranean shore, several tens of kilometres apart from other suitable habitats. We analysed three years of bird counts for nine protected species that breed, forage and roost on these saltpans. We used a multispecies hierarchical model to relate variations in bird counts to water levels, oxygenation and salinity, the three parameters targeted by the saltpans management plan to promote bird settlement. We showed that the hypersaline conditions that dominate in these saltpans are suboptimum to most species, suggesting that waterbird concentrations are dictated by the lack of alternatives in the surrounding landscape rather than by habitat suitability. Intraspecific variations in species' responses to these variables should orient towards the creation of a habitat mosaic within the saltpans. Eventually, between-site differences in bird responses to water conditions pointed the effects of disturbance, predation and other landscape-level features. Our results reveal that high waterbird numbers on isolated saltpans may be a misleading measure of their ecological suitability, and that management on these sites needs to incorporate conflicts and complementarity in species' habitat use.