Alejandro Rico-Guevara
Margaret A. Rubega1
Department of Ecology and Evolutionary Biology
University of Connecticut

Tai-Hsi Fan
Department of Mechanical Engineering
University of Connecticut

The tongue tip of a hummingbird drinking nectar out of a “transparent flower.”

Hummingbirds are superheroes of the natural world. Drinking nectar fuels their spectacular aeronautical feats, and they are extremely efficient at it. What surprised us is how they do it. Hummingbirds gather nectar by cycling their tongues in and out of the fluid. By filming the feeding motion of wild hummingbirds at “transparent flowers” at high-speed (up to 2400 frames/second), we observed that when the forked tongue enters the fluid, the tongue tips separate, and two tiny tubes at the tongue tip open up. These structures, which are edged with fine, flat flaps, spread out over a wide area to trap the nectar. When the tongue is withdrawn, the flaps roll back over the tongue tips as they pass out through the air-nectar interface, reforming two tubes with nectar inside, which then stick to each other.

This image is a snapshot of the tongue tip of a Baron’s hermit (Phaethornis baroni) drinking nectar out of a Heliconia flower with a “window” made of glass cover slips. The tongue is withdrawn from left to right and passes through the liquid-air interface at a speed of around 37 cm/s. The licking rate is about 10 Hz. At medium Reynolds numbers, the meniscus and ripples formed at the interface reveal a subtle interplay of inertial, viscous, and surface tension effects that assist the refurling of the tongue tips, which in turn traps the nectar on the tongue.

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This image can be freely reproduced with the accompanying credit: "Alejandro Rico-Guevara (University of Connecticut).."