At Antofagasta, northern Chile, two oystercatcher species coexist: the white oystercatcher, Haematopus palliatus pitanay and the black oystercatcher H. ater. Both species forage on an intertidal system where the middle fringe is dominated by the tunicate Pyura praeputialis (= Pyura stolonifera bradleyi; Kott 1997). According to the literature, differences in the morphology of their bills (length and width) segregate the foraging roles of white and black oystercatchers when the birds coexist in the same habitat. H. palliatus pitanay is best adapted for capturing soft bodied preys, while black oystercatcher H. ater attack "hard" preys (i.e. preys with calcareous shells). We consider here that the tunicate P. praeputialis as a soft bodied prey because the tunic, composed of tunicine, is soft and pliable. We compare ecological aspects between the two oystercatchers species in Antofagasta, such as: (a) abundance of oystercatchers and other coastal birds preying on P. praeputialis, (b) the spatial distribution of the oystercatchers in the Pyura bed during foraging periods, (c) Pyura size preferences of oystercatchers, (d) handling time, (e) consumption rate and (f) preference of other invertebrates prey items distinct from Pyura. The results show that H. palliatus pitanay attacks more frequently Pyura than H. ater, and that H. ater attacks more frequently "hard" preys such as: limpets, snails, mussels and sea urchins.