Coastal wetlands are decreasing globally, so that many migratory shorebirds depending on them during their non-breeding season also face population declines. Yet, spatiotemporal variation in habitat use remains under-investigated, despite its importance for a holistic conservation approach. To help fill this gap, this study assessed the variation in Common redshank (Tringa totanus) habitat use in two Portuguese wetlands, the Tagus estuary and the Ria Formosa, across tidal and diel cycles, ecologically meaningful periods within the non-breeding season, and shellfish exploitation intensities. GPS tracking data from 19 individuals, spanning six non-breeding seasons, was analysed with habitat maps, shellfish exploitation maps and statistical tests in QGIS and R. The resulting habitat-use proportions, home ranges and electivity indices showed negligible to extensive variation across factors and avoidance of high shellfisher densities in the Tagus estuary and the cultivation plots in the Ria Formosa. These findings demonstrate that redshanks rely on a mosaic of natural and anthropogenic habitats and that current shellfish exploitation practices constitute functional habitat loss. This therefore raises doubts about the effectiveness of existing conservation frameworks and suggest efforts to be directed to maintain diverse supratidal refuges and restrict shellfish exploitation, considering species- and site-specific studies.
Key words: Tringa totanus, Habitat selection, Wintering, Seasonal variation, Intertidal flats, Shellfish harvesting, Bivalve aquaculture, GPS telemetry
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