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Sunday, June 12, 2011

The truth behind hummingbird tongues

University of Connecticut researchers Alejandro Rico-Guevara and Margaret Rubega used transparent artificial flowers and high-speed cameras to watch hummingbirds take their nectar meals. The resulting videos surprised even the scientists.

Conventional wisdom has it that hummingbirds use capillary action to such up their liquid diet. In other words, it was thought that the sugary liquids were drawn up by the surface tension of the liquid within the confines of the tiny hummingbird tongue tubes. One flaw in this theory is that hummingbirds routinely eat liquids with double the sugar levels that can be quickly brought up by capillary action alone.

By using their high tech cameras, the researchers found that the hummingbirds were actually using their tongues to enclose the fluids. Each hummingbird tongue contains two forks that can each curl inward to form two tiny tubes. As the tongue enters the nectar solution, the forks spread open. Over the next 15 milliseconds, those forks close into tubes, entrapping the enclosed liquid and bringing it into the bird's mouth. Hummingbirds can perform this act up to 20 times each second. The mechanism of opening and curling into tubes is so energy efficient that even the tongues of dead birds will open and shut when drawn in and out of sugar solutions.

Close-up views of a hummingbird's tongue. A tongue's two forks uncurl in nectar (top), but curl back up to trap the sugary fluid when leaving it (bottom).
Alejandro Rico Guevara/PNAS.