The relative importance of physiological and behavioraladaptation in diving endotherms: a case study with great cormorants

Great Cormorant (Phalacrocorax carbo) Science Article 10

abstract

Extensive morphological and physiological adjustments are assumed to underpin the adaptations of diving birds tohigh thermoregulatory costs. However, the role of behavioral adaptations has received little consideration. We have assessedthe relative importance of physiological and behavioral adjustments in aquatic endotherms by studying the case of the poorlyinsulated great cormorant (Phalacrocorax carbo) in two contrasting thermal environments: Normandy (water temperature12 deg C) and Greenland (water temperature 5 deg C). Major differences were found in the feeding behavior of birds breeding in thetwo regions. Greenland birds showed a 70% reduction in time spent swimming relative to those in Normandy. Reduction inGreenland was achieved first by reducing time spent on the surface between dives and secondly by returning to land in betweenintensive bouts of diving. Total daily energy intake of cormorants was similar in both areas but prey capture rates in Greenlandwere 150% higher than those in Normandy. Our study shows that in a cold foraging environment, poorly insulated greatcormorants significantly increase their foraging efficiency. To do this they rely on ecological adaptive patterns (minimizationof time spent swimming in cold water and increased prey capture rates) far more than physiological adaptations (minimizinginstantaneous costs). This finding supports predictions by Gremillet and Wilson (1999) that great cormorants can cope witha wide range of abiotic parameters despite their morphological handicaps, provided they can adjust their distribution to exploitdense prey patches.

D. Gremillet, S. Wanless, D. M. Boertmann, R.P. Wilson, Acta Zoologica Sinica 52(Supplement): 528-534, 2006

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