Last year, high-speed footage of hummingbirds drinking overthrew the centuries-old notion that the birds feed using capillary action. Instead, it turns out the birds trap the nectar by curling their tongue around it. Now, new research in the Proceedings of the Royal Society B has shown that there might have been some truth in those old notions after all.
Hummingbirds possess a unique tongue shape — a pair of flexible semi-circular grooves. What the researchers found is that hummingbirds' tongues use a combination of both methods to carry liquid. It's both "elastocapillary deformation of the hummingbird's tongue and capillary suction along its length", causing them to dub the appendage a "self-assembling capillary syphon."
The tongue's flexibility allows the bird to rapidly drop its tongue into fluids, curl so that the opening angle is an optimal 150° (which, apparently, it is), and then raise the trapped liquid into its mouth and release it. The capillary action raises the liquid up the tongue's length, and is especially useful for gathering nectar from shallower flowers.
It's a remarkably complex and specific appendage — and the researchers believe it may even have co-evolved with flower shapes. Since the hummingbird is such an important cross pollinator, flowers may have evolved to fit a hummingbird's tongue, as much as the other way around.
Image: © Wonjung Kim, François Peaudecerf, Maude W. Baldwin, and John W. M. Bush