How Exactly Do Hummingbirds Eat and Drink?

For 180 years, physicists and biologists used the “capillary theory” to explain how hummingbirds feed and drink. To simplify this 1830s theory, consider hummingbird biology.  

The capillary theory says hummingbirds have forked tongues. Lamellae cover its fork-shaped tongue. The tongue separates when it enters the flower, extending the lamellae. The “fork” points reunite when the bird pulls its tongue back. Lamellae roll inward to catch nectar in the tongue.  

Scientists believed tongue-stretching extracted nectar. The liquid was assumed to climb tube walls due to molecular surface tension. Tension holds the liquid together and pulls the fluid column to the bird's throat. This operates like a straw.  

A 19th-century expert believed that simple physics would cause nectar to ascend in the tongue's tubes, providing hummingbirds their energy-boosting sugar-heavy elixir.  

Problems with the theory. The hummingbird cannot use its throat grooves as microscopic straws since they don't reach its throat.   

Second, testing the hypothesis was so complex that it was never done. Indeed, the capillary idea was controversial yet accepted for nearly 180 years.  

At the University of Connecticut in the early 21st century. Biologists used computer programs to illustrate their hypotheses about nature. Based on the capillary principle, they expected that hummingbirds prefer liquid nectar.  

Alejandro Rico-Guevara, a UConn graduate student, challenged the investigators' premise because many birds favored richer nectars. Rico-Guevara and his Ph.D. tutor, Associate Professor Margaret Rubega, sought to understand more than what was written and accepted.  

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