Patterns of association and habitat use by migrating shorebirds on intertidal mudflats and saltworks on the Tavira Estuary, Ria Formosa, southern Portugal

Abstract

Patterns of association and habitat use were studied on intertidal mudflats and adjacent saltworks during spring and autumn migration in 1999 on the Tavira estuary, Ria Formosa, southern Portugal. Twenty of the thirty species studied, mainly Charadriiformes, winter in and/or migrate through Tavira. The species distribution patterns were highly influenced by habitat – mostly because of the vast diversity of habitats available such as intertidal mud, mud/sand flats and saltworks – and to a lesser degree by tide and month. Migrant species, all gregarious, were the most characteristic of the saltworks during low tide. Non-tidal habitats were used as alternative foraging sites at high tide in summer, but these were also the main foraging sites used during migration periods, significantly supporting several migrant shorebird populations. Overall, this study reinforces the idea that even small estuaries, like that at Tavira, play a crucial role for considerable numbers of shorebirds during migration.