“I was in this very odd position,” says Rubega. “I was only a graduate student and all these really well-known people had done all this math. How could they be wrong?”
Even while she turned her attention to other birds, the hummingbird dilemma continued to gnaw at her. And decades later, as a professor at the University of Connecticut, she hired a student named Alejandro Rico-Guevara who would help her solve the mystery.
Born in Colombia, Rico-Guevara remembers spotting a hermit hummingbird on a fateful field trip in the Amazon. In the jungle, most animals are heard rather than seen, but the hermit flew right up and hovered in front of his face. “It was just there for a split second but it was clear that it had a completely different personality than other birds in the forest.” He fell in love, and started studying the birds. And when he read the capillary-action papers, he felt the same pang of disbelief that Rubega did. “We decided to go after it,” says Rubega. “Is it capillary action? And if not, what’s going on? We just wanted to know.”
Rico-Guevara handcrafted artificial flowers with flat glass sides, so he could film the birds’ flickering tongues with high-speed cameras. It took months to build the fake blooms, to perfect the lighting, and to train the birds to visit these strange objects. But eventually, he got what he wanted: perfectly focused footage of a hummingbird tongue, dipping into nectar. At 1,200 frames per second, “you can’t see what’s happening until you check frame by frame,” he says. But at that moment, “I knew that on my movie card was the answer. It was this amazing feeling. I had something that could potentially change what we knew, between my fingers.”
Here’s what they saw when they checked the footage.
As the bird sticks its tongue out, it uses its beak to compress the two tubes at the tip, squeezing them flat. They momentarily stay compressed because the residual nectar inside them glues them in place. But when the tongue hits nectar, the liquid around it overwhelms whatever’s already inside. The tubes spring back to their original shape and nectar rushes into them.
The two tubes also separate from each other, giving the tongue a forked, snakelike appearance. And they unfurl, exposing a row of flaps along their long edges. It’s as if the entire tongue blooms open, like the very flowers from which it drinks.
When the bird retracts its tongue, all of these changes reverse. The tubes roll back up as their flaps curl inward, trapping nectar in the process. And because the flaps at the very tip are shorter than those further back, they curl into a shape that’s similar to an ice-cream cone; this seals the nectar in. The tongue is what Rubega calls a nectar trap. It opens up as it immerses, and closes on its way out, physically grabbing a mouthful in the process.