The effect of southwestern Atlantic burrowing crabs on habitat use and foraging activity of migratory shorebirds

Southwestern Atlantic estuaries (Southern Brazil to Northern Patagonia, Arg entina) are characterized by the presence of an intertidal burrowing crab C hasmagnathus granulata. This crab species is an important bioturbator which lives in large assemblages and excavates semi-permanent burrows that affec t sediment characteristics. Our observations showed that distribution of th e crabs in the Mar Chiquita coastal lagoon, Argentina (37 degrees 45'S, 57 degrees 26'W) affected habitat use and feeding success of migratory shorebi rds. During the migratory season the two-banded plover (Charadrius falkland icus) foraged more frequently inside crab beds, and yellowlegs (Tringa flav ipes and T. melanoleuca) fed more frequently outside crab beds. Focal obser vations on the feeding behavior of the white-rumped sandpiper (Calidris fus cicollis) and the two-banded plover inside and outside crab beds showed tha t the plover was a visual searcher and captured more prey inside crab beds, and the white-rumped sandpiper was a tactile feeder. Although consumption rates (prey min(-1)) did not differ between sites, their efficiency (prey p robe(-1)) inside crab beds was less. These differences were probably relate d to changes in sediment characteristics and prey behavior, which vary with crab activity. Burrowing crabs alter the suitability of intertidal habitat s used by shorebirds in southwestern Atlantic estuaries, We believe that th e same profess could be occurring with other burrowing crustaceans such as thalassinidean shrimps in other estuaries of the world and could have impor tant implications for management of flats for shorebirds.