Thermoregulation in feeding baleen whales: Morphological and physiological evidence

Gray whales (Eschrichtius robutus) expose their immense oral cavities repeatedly to frigid waters when feeding. Morphological structures for heat conservation in the tongues of gray whales are described here in detail. Numerous individual countercurrent heat exchangers converge at the base of the tongue to form a bilateral pair of vascular bundles called the lingual rete. Temperature measurements taken from a live captive gray whale calf indicated that more heat could be lost through the blubber layer over the body than through the tongue, despite the fact that the tongue is far more vascularized and has much less insulation. Hence, these heat exchangers substantially reduce heat loss when these whales feed in cold waters. The evolution of these structures was a physiological prerequisite for baleen whale breeding.