Diet and foraging effort of Adélie penguins in relation to pack-ice conditions in the southern Ross Sea |
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Authors: | David G Ainley Peter R Wilson Kerry J Barton Grant Ballard Nadav Nur Brian Karl |
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Institution: | (1) H.T. Harvey & Associates, P.O. Box 1180, Alviso, CA 95002, USA e-mail: harveyecology@worldnet.att.net, Fax: 408 263 382, US;(2) Landcare Research New Zealand Ltd., Private Bag 6, Nelson, New Zealand, NZ;(3) Point Reyes Bird observatory, 4990 Shoreline Highway, Stinson Beach, CA 94970, USA, US |
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Abstract: | We investigated the diet and aspects of foraging effort among Adélie penguins (Pygoscelis adeliae) breeding at three colonies on Ross Island, in the southwestern Ross Sea – Capes Royds, Bird and Crozier – during the chick-provisioning
period of three austral summers, 1994–1995, 1995–1996 and 1996–1997. During the study period, pack-ice cover differed in waters
offshore of these colonies, by colony, seasons and year. Diet differed among colonies only slightly. The fish Pleuragramma antarcticum was the most important prey, especially during years or periods within years when little pack ice was present. With respect
to krill, which composed the remainder of diet, juvenile Euphausia crystallorophias were consumed predominantly in a year of heavy pack-ice cover; more adult krill were consumed in 2 years when pack ice was
sparse. Foraging trip duration differed by colony, season and year and was related directly to distance from the colony to
the nearest pack ice. The amount of food brought to chicks increased as trip duration increased, to a point (2 days), but
then decreased as duration increased further (up to 4 days). On the basis of data on mass of parents and of meal sizes to
chicks, it appeared that on the longest trips more of the food gathered by parents was used for self maintenance; on the longest
trips, parents lost body mass. Successful foraging during chick rearing, the period when adult foraging is most intense, appears
to depend on the proximity of pack ice to nesting colonies for this penguin species.
Received: 1 October 1997 / Accepted: 25 April 1998 |
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