The beaks of hummingbirds, which are elongated and slender, somewhat resemble drinking straws. The quickness with which these birds extract nectar from flowers and feeders may create the illusion that their beaks function like straws. However, recent studies indicate that this analogy is not very accurate.
A recent online publication in the Proceedings of the Royal Society Interface, led by Alejandro Rico-Guevara, an assistant professor of biology at the University of Washington, has uncovered the unexpected flexibility of the hummingbird’s beak. The findings reveal that while drinking, hummingbirds swiftly manipulate different parts of their beaks at once, performing a complex and synchronized movement with their tongues to quickly draw up nectar.
Although these rapid actions might be hard for the human eye to detect, they are crucial for the survival of hummingbirds.
“Most hummingbirds obtain nectar while hovering in the air,” explained Rico-Guevara, who also serves as curator of ornithology at the UW’s Burke Museum of Natural History and Culture. “Hovering requires a lot of energy; moving straight at a moderate speed is less taxing. Therefore, hummingbirds strive to conserve energy while feeding quickly from difficult spots, necessitating special adaptations for speed and effectiveness.”
Previous studies had established that hummingbirds quickly extend their tongues to drink nectar, but the specific role of their beaks in this feeding process was not well understood. The research team gathered high-speed videos of various hummingbird species feeding from transparent feeders in Colombia, Ecuador, and the U.S. By examining this footage and merging it with data from micro-CT scans of hummingbird specimens at the Yale Peabody Museum, they uncovered the complex beak movements involved in feeding:
- The hummingbird extends its tongue by slightly opening the tip of its beak.
- Once the tongue collects nectar, the tip of the beak closes.
- To draw the nectar up through the beak, the midsection remains tightly closed while the base is opened slightly.
- Finally, the tip reopens to extend the tongue again, a sequence that many hummingbird species can repeat 10-15 times per second.
Hummingbirds possess uniquely structured tongues that sometimes resemble intricate origami designs, perfect for capturing nectar. This recent research emphasizes the essential role of the beak in drinking, revealing its surprising level of flexibility despite its seemingly rigid form.
“We already knew that hummingbird beaks have some degree of flexibility, such as bending at the lower bill while catching prey,” noted Rico-Guevara. “Now, we understand that the beak plays an active and crucial part in pulling up nectar that the tongue retrieves.”
Moreover, the functionality of the beak sets hummingbirds apart, as they utilize two distinct methods for collecting and transporting liquid: the lapping mechanism (known as Couette flow) commonly used by dogs and cats, and Poiseuille flow, a suction-based method seen in mosquitoes feeding or humans using a straw. Most animals employ either one method or the other, but hummingbirds are an unusual case of leveraging both approaches.
“It’s logical that they would need both techniques to access nectar deep within flowers and to feed rapidly and effectively,” added Rico-Guevara.
Future studies may focus on identifying the muscles that facilitate these movements and examining how the beak’s flexibility is influenced by its other functions, like capturing insects.
“As flowers have evolved various shapes and sizes, hummingbird beaks have adapted in response,” said Rico-Guevara. “With each question we resolve about hummingbird adaptations, new ones emerge. There’s still so much to discover.”
The study includes contributions from co-authors Diego Sustaita, an associate professor at California State University, San Marcos; Kristiina Hurme, an assistant teaching professor of biology at UW; independent researcher Jenny Hanna; Sunghwan Jung, an associate professor at Cornell University; and Daniel Field, a professor at the University of Cambridge. The research received funding from the Walt Halperin Endowed Professorship in the UW Department of Biology, the Washington Research Foundation, and U.K. Research and Innovation.
