Abstract

QUINTANA, Flavio; MORELLI, Federico  and  BENEDETTI, Yanina. Efficient dive in shallow waters: diving behavior and feeding pattern of the Rock Shag, Phalacrocorax magellanicus, at two Patagonian colonies. Ecol. austral [online]. 2002, vol.12, n.1, pp.19-28. ISSN 1667-782X.

By means of radio-telemetry techniques, we study the diving behavior and feeding performance of adult Rock shags (Phalacrocorax magellanicus) from Punta Loma and Isla Vernacci, two colonies of the Patagonian coast, Argentina. In both colonies, Rock shags dived continuously (without diving bouts) during foraging trips (mean dive duration: 47-50 s, mean subsequent surface interval: 14-18 s) and showed high dive efficiencies (3.2-3.8, dive time/recovery time). Tracked birds from the two colonies spent 31- 35% of daylight hours at sea, diving (including dive and recovery times) for 92% of the foraging trip. They undertook many (2.6-3.7 trips/day) and prolonged (1.7-2.6 h) trips per day, and made a high number of dives per foraging trip (78-138). These results suggest a high foraging effort (diving time per foraging trip) for Rock shags from the two studied colonies, necessary to reach the daily food requirements. This high foraging effort could be associated with low prey abundance, the existence of a patchy and/or low quality food resource (in energetic terms), or both.

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