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Marine Ecology Progress Series

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MEPS 183:263-273 (1999)  -  doi:10.3354/meps183263

Three-dimensional space utilization by a marine predator

David Grémillet1,*, Rory Paul Wilson1, Sandra Storch1, Yann Gary2

1Institut für Meereskunde Kiel, Abteilung Meereszoologie, Düsternbrooker Weg 20, D-24105 Kiel, Germany
2Groupe Ornithologique Normand, Université de Caen, F-14032 Caen Cedex, France
*Present address: Institute of Terrestrial Ecology, Banchory Research Station, Hill of Brathens, Glassel, Banchory, Kincardineshire AB31 4BY, Scotland, UK E-mail:

ABSTRACT: Diving seabirds should evolve a variety of foraging characteristics which enable them to minimize energy expenditure and to maximize net energy gain while searching for prey underwater. In order to assess the related ecological adaptations in a marine predator, we studied the at-sea distribution and the diving behaviour of 23 cormorants Phalacrocorax carbo (Linnaeus) breeding at the Chausey Islands (France) using VHF-telemetry and data loggers recording hydrostatic pressure. Birds foraged within an area of approximately 1131 km2 situated north-east of the breeding colony. This zone represents only 25% of the maximal potentially available area that the birds may utilize considering their maximum foraging range of 35 km. Individual birds remained within restricted individual foraging areas (on average 18 and 10% of the total utilized area in 1994 and 1995, respectively) throughout the study period. Moreover, the cormorants studied conducted an average of 42 dives per foraging trip, lasting for an average of 40 s (maximum 152 s), and reached an average maximum dive depth of 6.1 m (maximum 32 m) with median descent and ascent angles calculated to be 18.7° and 20.3°, respectively. Overall, 64% of all dives were U-shaped dives and 36% V-shaped dives. We use these results to demonstrate how both specialization and opportunism may support the remarkably high foraging efficiency of this marine predator.

KEY WORDS: Phalacrocorax carbo · Diving behaviour · Foraging strategy · Specialization vs opportunism · Wildlife telemetry

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