Tiny, jewel-colored sunbirds dart between flowers in Africa and Asia, probing deep into blooms with their long, curved bills. For more than a century, scientists assumed these birds simply drew up nectar the same way many other nectar-feeders do, i.e., by dipping their tongues and letting surface tension pull the liquid along. A new study shows they do something far more remarkable: they actively suck the nectar through their tongues like living straws.
The discovery, published in Current Biology, comes from high-speed videos of live sunbirds, detailed micro-CT scans of their tongues and bills, and fluid-dynamics models that tested exactly how nectar moves. Lead author David Cuban and his colleagues studied seven species spanning a range of body and bill sizes. In every case, the birds kept their bills slightly open, inserted only the tip of the tongue into the nectar, and held it there while the sweet liquid flowed steadily toward the mouth.
“Using tube-like tongues, sunbirds are able to move nectar from flowers to their mouths by generating a pressure differential along the length of the tongue, a remarkable feat for animals without lips or cheeks,” the researchers report in the study.
The tongue itself is built like a series of tiny tubes: the tip splits into two hollow cylinders, the middle section forms a single sealed channel, and the base presses against the roof of the mouth to create a tight seal. By lifting the tongue base upward and then pulling it downward, the bird enlarges the space inside the sealed cavity, lowering the pressure and drawing nectar up the entire length.
Simple capillary action, the passive rise of liquid in a narrow tube, could not explain the speed or the pattern the team observed. Nor could models that added inertia. Only a model that included an actively generated pressure difference matched the video data. In some clips, nectar even began moving mouthward before the tongue tip touched the reservoir again, and air bubbles could be seen traveling inside the tongue — clear signs that suction, not surface tension alone, was at work.
The finding highlights a striking case of evolutionary divergence. Many nectar-feeding birds have converged on similar long bills and tongues to reach the same sugary reward. Yet the actual drinking mechanics differ. Sunbirds rely on this intralingual suction instead of the fluid-trapping or tongue-wringing methods used by hummingbirds and most honeyeaters.
“This behavior, intralingual suction, provides a new example of the distinct feeding mechanisms employed by various nectar-feeding birds despite their convergence upon the same dietary niche,” the authors note. “This discovery raises new questions for both vertebrate and invertebrate groups that feed on liquid food.”
Citations
David Cuban et al. Divergent nectar-feeding mechanisms evidenced by intralingual suction in sunbirds. Current Biology. Published online March 27, 2026. DOI: 10.1016/j.cub.2026.02.067
