SHORT-TERM EFFECTS OF INTERTIDAL MACROALGAL BLOOMS ON THE MACROHABITAT SELECTION AND FEEDING-BEHAVIOR OF WADING BIRDS IN THE MONDEGO ESTUARY (WEST PORTUGAL)

The possible effects of intertidal macroalgal blooms on the feeding di stribution and behaviour of the waders in the Mondego Estuary (West Po rtugal) are discussed in the present paper. The presence of algae over the sediments did not deter the waders absolutely from feeding in a p lace, but most species did show some tendency to avoid highly eutrophi c areas. However, there were no clear signs that the species redistrib uted themselves within the Estuary as the amount of algae changed, nor did the alternative feeding habitats (the salt pans) seem to be used more when algae were particularly abundant on the mud flats. In one sp ecies, bird numbers, rather than the amount of algae present, explaine d the numbers of birds using the salt pans when the two factors were c onsidered together in a multiple regression analysis. There were no st riking differences between algae-free and algae-weeded areas in some a spects of the foraging of two representative species, the scolopacid D unlin Calidris alpina and the charadriid Grey Plover Pluvialis squatar ola. The results suggest either: (1) that the presence of algae did no t strongly influence the distribution of the feeding waders, at least in the conditions prevailing during the study; or (2) that most waders were able to adapt to feeding on weeded areas; perhaps through subtle and undetected alterations in their feeding behaviour. (C) 1996 Acade mic Press Limited