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Heat Exchange from the Toucan Bill Reveals a Controllable Vascular Thermal Radiator

Science  24 Jul 2009:
Vol. 325, Issue 5939, pp. 468-470
DOI: 10.1126/science.1175553

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Toucan Heat Exchanger

Toucans are instantly recognizable by their large bills, which in the toco toucan (Ramphastos toco) accounts for about one-third of the total body length. The toucan's bill has been interpreted as a sexual ornament and as an adaptation for handling fruit. Tattersall et al. (p. 468) explore an alternative explanation in which the bill serves primarily as a thermoregulator. Infrared thermography techniques, which allow detailed observations with minimal disturbance to the birds, show that the birds alter blood flow to the bill according to ambient conditions, effectively using it as a radiator to “dump heat.”

Abstract

The toco toucan (Ramphastos toco), the largest member of the toucan family, possesses the largest beak relative to body size of all birds. This exaggerated feature has received various interpretations, from serving as a sexual ornament to being a refined adaptation for feeding. However, it is also a significant surface area for heat exchange. Here we show the remarkable capacity of the toco toucan to regulate heat distribution by modifying blood flow, using the bill as a transient thermal radiator. Our results indicate that the toucan's bill is, relative to its size, one of the largest thermal windows in the animal kingdom, rivaling elephants’ ears in its ability to radiate body heat.

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