Actual experiment with the Toucan's beak

The geometry of the bill (broad rather than slender) is exactly what one would expect to maximize the interior surface area and increase the evaporation potential.

The Toucan's beak appears quite heavy, but is actually light.  It is hollow, made of the protein keratin with thin rods of bone to support it – similar in consistency to a hard sponge.

A Toucan's bill is about 30 or 40 per cent of its total body surface area, so it's like you throwing out a sail and dumping all your body heat into it.  During an actual experiment, captive Toucans were used with an infrared camera trained on their beaks.  What was found is that as the birds got hotter, their bills glowed brighter on the camera images.  As they cooled, they began shutting down blood flow to blood vessels that run thick near the beak's surface.  The Toucan's ability to control heat-bearing blood flow to the beak, like adjusting a thermostat in your house, was one of the study's key findings.  So sensitive is the bird's internal thermostat that the beak lit up the research cameras to different degrees as the Toucans progressed through their stages of sleep at night.

Plate-billed Mountain Toucan pair

Plate-billed Mountain Toucan pair

Swainson's Toucan

Final thoughts on the beak

Although Toucans do use their beaks at one time or another for one or more of the purposes previously mentioned, none of those ideas fully explain how the big beak got there in the first place.  Unlike the other theories, the cooling function theory follows the classic form of an evolutionary driving force.  It was there in some measure at the beginning, since all birds do gape to cool off.  Any small increase in beak size would be rewarded with a definite small increase in heat tolerance.  The magnitude of the advantage to the otherwise well insulated Toucan makes it believable that it would be worth the inconvenience to evolve the bill.

The adult Toucan bill is capable of emitting only five percent of the bird’s total body heat when it needs to conserve warmth, but up to 100 percent when it needs to cool off.  Coordinated valves can pinch off or open blood vessels leading into the beak. This makes the Toucan bill one of the most efficient temperature regulation systems in the animal world.  Who would have guessed that the Toucan's enormous, multi-hued proboscis was really a prosaic radiator?

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Copyright © 2011, Susie Christian