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First published online February 15, 2006
Journal of Experimental Biology 209, 845-859 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02064

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The effects of depth, temperature and food ingestion on the foraging energetics of a diving endotherm, the double-crested cormorant (Phalacrocorax auritus)

Manfred R. Enstipp^1,*, David Grémillet¹ and David R. Jones²

¹ Centre d'Ecologie et Physiologie Energétiques, CNRS, 23 Rue Becquerel, F-67087 Strasbourg Cedex 2, France
² Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4

^* Author for correspondence (e-mail: manfred.enstipp{at}c-strasbourg.fr)

Accepted 22 December 2005

Avian divers are confronted with a number of physiological challenges when foraging in cold water, especially at depth. Besides the obvious constraint imposed by the necessity to return to the surface for gas exchange, cold water temperatures and a reduction in body insulation due to the increase in pressure with dive depth will elevate the energetic costs of foraging in these endotherm divers. The complex effect that depth has on the diving energetics of aquatic birds has largely been ignored. To date, no study has assessed the impact of depth on diving energetics over a significant depth range, naturally encountered by the diver. We used open-circuit respirometry to study the energetic requirements of a foot-propelled pursuit diver, the double-crested cormorant (Phalacrocorax auritus albociliatus), when diving in a shallow (1 m) and deep (10 m) dive tank and when resting in air and water. We also investigated the modifying effects of air or water temperature and feeding status on the costs associated with diving and resting. Of all factors investigated, dive depth exercised the strongest influence on diving metabolic rate. Diving to 10 m depth increased metabolic rate on average by 22% when compared with shallow diving. Declining temperatures in air and water significantly elevated metabolic rate of cormorants resting in air and water as well as during diving. Feeding before resting in water or diving increased metabolic rate by 5–8% for at least 2 h. Cormorants maintained an elevated stomach temperature (>42°C) when resting in water and during diving, even at cold temperatures. The elevated dive costs during deep diving, when compared with shallow diving, are most likely a consequence of the increased thermoregulatory costs associated with a greater heat loss to the water at depth. Nevertheless, our study shows that dive costs in double-crested cormorants are similar to those of other foot-propelled avian divers.

Key words: diving energetics, depth, double-crested cormorant, temperature, HIF, heat loss

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COST OF DEEP DIVING FOR CORMORANTS

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JEB 2006 209: 0. [Full Text]  

This article has been cited by other articles:

				M. R. Enstipp, D. Gremillet, and D. R. Jones Heat increment of feeding in double-crested cormorants (Phalacrocorax auritus) and its potential for thermal substitution J. Exp. Biol., January 1, 2008; 211(1): 49 - 57. [Abstract] [Full Text] [PDF]

				K. Phillips COST OF DEEP DIVING FOR CORMORANTS J. Exp. Biol., March 1, 2006; 209(5): iii - iii. [Full Text] [PDF]