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First published online June 16, 2004
Journal of Experimental Biology 207, 2649-2662 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01067

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Antennae on transmitters on penguins: balancing energy budgets on the high wire

Rory P. Wilson^1,*, Jan M. Kreye¹, Klaus Lucke² and Heather Urquhart³

¹ Institut für Meereskunde, Düsternbrooker Weg 20, D-24105 Kiel, Germany
² Forschungs- und Technologiezentrum Westküste, Hafentörn, D-25761 Büsum, Germany
³ New England Aquarium, Central Wharf, Boston, MA 02110, USA

^* Author for correspondence (e-mail: rwilson{at}ifm-geomar.de)

Accepted 30 April 2004

The effect of externally mounted antennae on the energetics of penguins was studied by mounting various antennae on a transducer fixed to a model Magellanic penguin Spheniscus magellanicus to determine drag, run at speeds of up to 2 m s^–1 in a swim canal. For rigid antennae set perpendicular to the water flow, measured drag increased with increasing swim speed. Increasing antenna length (for lengths between 100 and 200 mm) or diameter (for diameters between 1 and 4 mm) resulted in accelerating increased drag as a function of both antenna length and diameter. Where antennae were positioned at acute angles to the water flow, drag was markedly reduced, as was drag at higher speeds in flexible antennae. These results were incorporated in a model on the foraging energetics of free-living Magellanic penguins using data (on swim speeds, intervals between prey encounters, amount ingested per patch and dive durations) derived from previously published work and from a field study conducted on birds from a colony at Punta Norte, Argentina, using data loggers. The field work indicated that free-living birds have a foraging efficiency (net energy gain/net energy loss) of about 2.5. The model predicted that birds equipped with the largest rigid external antennae tested (200 mm x 3 mm diameter), set perpendicular to water flow, increased energy expenditure at normal swim speeds of 1.77 m s^–1 by 79% and at prey capture speeds of 2.25 m s^–1 by 147%, and ultimately led to a foraging efficiency that was about 5 times less than that of unequipped birds. Highly flexible antennae were shown to reduce this effect considerably. Deleterious antenna-induced effects are predicted to be particularly critical in penguins that have to travel fast to capture prey. Possible measures taken by the birds to increase foraging efficiency could include reduced travelling speed and selection of smaller prey types. Suggestions are made as to how antenna-induced drag might be minimized for future studies on marine diving animals.

Key words: penguin, Spheniscus magellanicus, external antennae, drag, energy expenditure, foraging efficiency

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