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First published online December 14, 2007
Journal of Experimental Biology 211, 49-57 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.012229

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Heat increment of feeding in double-crested cormorants (Phalacrocorax auritus) and its potential for thermal substitution

Manfred R. Enstipp^1,*, David Grémillet^1,2 and David R. Jones³

¹ Institut Pluridisciplinaire Hubert Curien (IPHC), Département Ecologie, Physiologie et Ethologie (DEPE), UMR 7178 CNRS-ULP, 23 Rue Becquerel, F-67087 Strasbourg Cedex 2, France
² NRF Centre of Excellence at the Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
³ Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T 1Z4, Canada

View larger version (16K): [in this window] [in a new window]   Fig. 1. Examples of changes in rates of oxygen consumption (O2) associated with the voluntary ingestion of a single herring. (A) The bird was resting within its thermoneutral zone (TNZ) and fed a 100 g herring at time zero. (B,C) Birds were resting at sub-thermoneutral conditions (below 9°C) and fed a 100 g (B) or 60 g herring (C), respectively at time zero. The initial peak in O2 is related to movements during the feeding event and was excluded (using linear interpolation, see broken line) when calculating HIF (indicated by the shaded area). The horizontal broken line denotes resting O2, established from the stable period preceding feeding.

View larger version (9K): [in this window] [in a new window]   Fig. 2. Changes in oxygen consumption rate (means ± s.e.m., in multiples of resting value) of double-crested cormorants after voluntary ingestion of a single herring (mass 60 or 100 g) when resting in air at temperatures within or below their thermoneutral zone (TNZ) (lower critical temperature 9°C). Sample sizes for the various conditions are indicated in Table 1.

View larger version (8K): [in this window] [in a new window]   Fig. 3. Respiratory exchange ratio (RER=CO2/O2) of double-crested cormorants before (time zero) and after ingestion of a 100 g herring (means ± s.e.m., N=5 birds, n=14 trials), when resting at air temperatures within their thermoneutral zone. The solid and broken lines indicate the theoretically expected RER values when birds metabolise exclusively lipid or protein, respectively.

View larger version (7K): [in this window] [in a new window]   Fig. 4. Mean stomach temperature (± s.e.m.) of double-crested cormorants during HIF trials at air temperatures within their thermoneutral zone (N=5 birds, n=12 trials). The temperature drop at 0 min is caused by the ingestion of a 100 g herring. Note that temperature reaches pre-ingestion levels within 40 min of eating the fish, after which temperature remains stable throughout the remainder of the trial.

View larger version (7K): [in this window] [in a new window]   Fig. 5. Time required by resting cormorants to warm ingested fish of varying mass to body temperature. Temperature of fish ingested was 5°C, while mean stomach temperature of birds before ingestion was 41.1±0.4°C (N=5 birds, n=49 trials). The insert shows a temperature trace recorded by a MiniTemp-xl-logger inside a 100 g herring. The fish was kept inside a refrigerator and fed to a cormorant (within 2 min of removal from the refrigerator) at time zero, as indicated by the arrow.