Fellows in the News

When Margaret Rubega first read about how hummingbirds drink, she thought to herself: That can’t possibly be right.

Hummingbirds drink nectar using tongues that are so long that, when retracted, they coil up inside the birds’ heads, around their skulls and eyes. At its tip, the tongue divides in two and its outer edges curve inward, creating two tubes running side by side. The tubes don’t close up, so the birds can’t suck on them as if they were straws. Instead, scientists believed that the tubes are narrow enough to passively draw liquid into themselves. That process is called capillary action. It’s why water soaks into a paper towel, why tears emerge from your eyes, and ink runs into the nibs of fountain pens.

This explanation, first proposed in 1833, was treated as fact for more than a century. But it made no sense to Rubega when she heard about it as a graduate student in the 1980s. Capillary action is a slow process, she realized, but a drinking hummingbird can flick its tongue into a flower up to 18 times a second. Capillary action also is aided by gravity, so birds should find it easier to drink from downward-pointing flowers—and they don’t. And capillary action is even slower for thicker liquids, so hummingbirds should avoid supersweet nectar that’s too syrupy—and they don’t.

“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?”

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