Great Hornbill Casque Functions as a Thermoregulatory Radiator

Hornbills (Bucerotidae) are defined by their casques, structures that are extensions of the beak. The purpose of these structures, which take diverse forms, has been subject to speculation. In this study, it is asserted that a primary function of the casque is thermoregulation, its large vascularised surface area functioning as a structure to facilitate heat exchange. Infrared thermography on a Great Hornbill (Buceros bicornis) revealed that the bird’s casque exhibited significant percentage of heat loss in relation to the body's resting heat production along a temperature gradient of 19.2 to 34.2°C. The results indicate that the casque is capable of dissipating a disproportionate amount of heat in relation to the rest of its body and even comparable to major thermal windows in other animals.