Hummingbird tongues are tiny pumps that suck up nectar—not merely passive strawlike structures as long thought, new research suggests. In a few studies of lab-reared hummers, scientists noted that the birds sometimes used capillary action—the tendency of a liquid to be pulled into a narrow space, even upward against gravity—to draw nectar into the long hollow tips of their cylindrical tongues. But a 5-year study of hummingbirds in the wild, including 18 species from seven of the nine major groups, found that the birds almost never relied on capillary action to collect nectar. Instead, researchers noticed the tongue’s pumping action when they watched detailed, slow-motion videos of feeding hummers (such as the video above of Amazilia amazilia, the Amazilia hummingbird). When a bird first extends its tongue, the normally tubular tip is flattened shut. But when the tongue reaches its sweet reward, the tissues spring back to their normal cylindrical shape, creating a suction that fills a tongue-tip reservoir in just a few milliseconds. Finally, the bird retracts its tongue and squeezes the nectar from the reservoir, again flattening the tongue in advance of its next slurp, the researchers report online today in the Proceedings of the Royal Society B. While feeding, hummingbirds flick their tongues in and out about 14 times per second, on average, the researchers note. They’d flick just one-third as often, they estimate, if they relied on capillary action rather than active pumping.
(Video credit: Alejandro Rico-Guevara)