Diving patterns in the Antarctic Shag

CASAUX RICARDO

WATERBIRDS (DE LEON SPRINGS, FLA.)

Año: 2004 vol. 27 p. 382 - 387

1524-4695

Send proofs to                             Diving patterns in the Antarctic Shag       RICARDO CASAUX       Instituto Antártico Argentino, Cerrito 1248, 1010 Buenos Aires, Argentina Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Rivadavia 1917, (1033) Buenos Aires, Argentina          Internet: pipocasaux@infovia.com.ar     Present address: Laboratorio de Ecología Acuática, Universidad Nacional de la Patagonia, Sarmiento 849, 9200 Esquel, Chubut, Argentina              Abstract.The diving patterns of the Antarctic Shag (Phalacrocorax bransfieldensis) were studied by direct observation on individuals foraging at Harmony Cove, Nelson Island, South Shetland Islands, during the 1995/96 and 1996/97 breeding seasons. The individuals observed foraged in shallow waters mainly solitarily and presumably dived aerobically. The shags displayed relatively short diving bouts composed of few dives. During the 1995/96 breeding season, the duration of the dives decreased with the increase in the number of dives per bout and increased with the diving depth. These relationships were not statistically significant in 1996/97. In both seasons, the duration of the dives was positively related with both the surface resting time preceding and succeeding the dive which may indicate that these birds display anticipatory or reactive dives probably according to the foraging conditions. Shags at the surface were seen swallowing fish larger than 15 cm; smaller fish as well as invertebrates may have been ingested underwater. The mean diving efficiencies of the bouts fall within the range reported for phalacrocoraciids, but values of diving efficiency below unity were observed.