Double-crested Cormorant (Phalacrocorax auritus) Science Article 3
Diving endotherms inhabiting polar regions face potentially high thermoregulatory costs. Unless properly insulated, these animals will lose vast amounts of heat when diving in cold water, which has to be balanced by heat production. Heat generated as a by-product of digestion (heat increment of feeding, HIF) or from exercising muscles might be important in maintaining thermal balance under such conditions, as it would reduce the need for shivering thermogenesis.
Manfred R. Enstipp et al., The Journal of Experimental Biology 211, 49-57