. Bulletin of the British Ornithologists' Club. pass at a small group of night herons. In 1972 we found a South American Tern Sterna hirundinacea that had been eaten by a falcon. Several large nests on steep cliffs along the south shore were presumably made by Black-chested Buzzard-Eagles Geranoaetus melanoleucus, but we did not observe this species in the immediate area. Shorebirds: American Oystercatchers Haematopm palliatus are abundant residents of Golfo San Jose. Along the sandy beaches of the south and east coasts the population averages eight to ten pairs per mile. Cliffs along the nort
. Bulletin of the British Ornithologists' Club. pass at a small group of night herons. In 1972 we found a South American Tern Sterna hirundinacea that had been eaten by a falcon. Several large nests on steep cliffs along the south shore were presumably made by Black-chested Buzzard-Eagles Geranoaetus melanoleucus, but we did not observe this species in the immediate area. Shorebirds: American Oystercatchers Haematopm palliatus are abundant residents of Golfo San Jose. Along the sandy beaches of the south and east coasts the population averages eight to ten pairs per mile. Cliffs along the north shore limit oystercatcher habitat there, but even so the birds remain extremely common. We estimated the population at 600 individuals. The species seems to maintain territories all the year, so that in most areas pairs are spaced out regularly along the beach. However, in some areas, such as Isla de los Pajaros, flocks of 20 or more occurred and fed together without interaction on the exposed Figure 3. A pair of American Oystercatchers Haematopus palliatus left, and a hybrid with a Blackish Oystercatcher H. ater, Golfo San Jose. In several locations (, Punta Conos, Isla de los Pajaros) dark mudstones outcrop along the bay, and many are covered with extensive mussel beds. These areas provide habitats for the small resident population of Blackish Oystercatchers H. ater. This species occasionally hybridizes with H. palliatus in this area (Fig. 3, and Jehl in prep.). Wintering Magellanic Oystercatchers H. leucopodus occupied the mudflats of the southwestern corner in each year. These birds tended to remain together in large flocks and did not usually associate with or interact with the American Oystercatchers that utilized the same feeding areas. Small flocks of Falkland Plovers Charadrius falklandicus occurred on almost every mudflat. Most flocks consisted of 10 to 15 birds, though some were as large as 200. The huge increase in 1972 is almost certainly a result
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