Antarctic Science



Leopard seal predation rates at penguin colonies of different size


DAVID G. AINLEY a1c1, GRANT BALLARD a2, BRIAN J. KARL a3 and KATIE M. DUGGER a4
a1 H.T. Harvey and Associates, 3150 Almaden Expressway, Suite 145, San Jose, CA 95118, USA
a2 PRBO Conservation Science, 4990 Shoreline Highway, Stinson Beach, CA 94970, USA
a3 Landcare Research New Zealand, Private Bag 6, Nelson, New Zealand
a4 Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331-3803, USA

Article author query
ainley dg   [PubMed][Google Scholar] 
ballard g   [PubMed][Google Scholar] 
karl bj   [PubMed][Google Scholar] 
dugger km   [PubMed][Google Scholar] 

Abstract

In a study designed to elucidate the factors that might differentially affect the well being and biology of Adélie penguins (Pygoscelis adeliae) that breed in colonies of different size, we investigated the predation rates on penguins by leopard seals (Hydrurga leptonyx) over a period of six years. The study colonies varied in size across the full range for this penguin species, contrasting with previous studies in which data were gathered only at very large colonies, and only in single years. The number of seals present varied directly with the amount of penguin traffic in the areas near the beach, where most predation takes place. Seals were present persistently only when penguin traffic exceeded about 250 penguins per hour. Predation rates also varied with penguin traffic in a curvilinear fashion, leveling off where traffic exceeded about 1200 penguins per hour. With respect to predation, it appears to be advantageous for Adélie penguins to nest in very small or very large colonies. At large colonies, the number of penguins moving to and from the colony ‘swamp’ the seals' predatory efforts, thus reducing the chances that an individual penguin will be taken. Small colonies are of little interest to the seals.

(Received December 16 2004)
(Accepted March 21 2005)


Key Words: Adélie penguin; colony size; Hydrurga leptonyx; predator swamping; Pygoscelis adeliae.

Correspondence:
c1 dainley@penguinscience.com


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