Hummingbird Beak Is a Nectar Wringer

New high-speed movies of hummingbirds show how
nectar in the retracting tongue is drawn into the mouth

Frame from the animation of the hummingbird tongue as a nectar trap (Illustra Media). Individual flaps unfurl within the liquid, then close tightly as the tongue is retracted, storing loads of nectar into cylinders for offloading within the beak.

Yesterday’s post replayed Illustra Media’s animation of the hummingbird tongue, which acts as a nectar trap or pump. That was an amazing discovery by Alejandro Rico-Guevara and Margaret Rubega back in 2019. But it’s only half the story. How does the bird retrieve the nectar load once the tongue retracts into the beak? Since the retraction often opposes gravity, there must be more going on than capillary action. Suction, like drinking through a straw, won’t work since the beak is unable to form a vacuum. Since the beak is opaque, what happens has been a black box—till now.

Rico-Guevara and Rubega have been refining their techniques, and now have a new model of nectar retrieval inside the beak of hummingbirds. It is described in a new open-access paper containing movie clips filmed at high speed.

Nectar feeding beyond the tongue: hummingbirds drink using phase-shifted bill opening, flexible tongue flaps and wringing at the tips (Rico-Guevara, Hurme, Rubega and Cuban, Journal of Experimental Biology, April 2023). The authors discuss five potential models for nectar retrieval, then explain what they found with high-speed cameras filming the birds from different orientations. Transparent feeders allowed them to watch the tongue’s action back in 2019. This time, they were able to peer into the black box of the beak with special lighting that made the internal apparatus translucent. Filming 24 individuals of 9 genera and species in Colombia, Ecuador and the USA with beaks of different lengths and curvatures, they revealed the workings of nectar retrieval. They believe it works by “hydraulic displacement” as incoming loads of nectar push previous loads farther back into the mouth.

The consistency of tongue and bill movements across species supports the idea that the mechanics of intraoral nectar flow are similar across species. The intraoral transport of a single nectar load is at least a two-step process; the first load stays inside the bill until the tongue base pushes it backwards, as a second load comes in (Fig. 5F), and so forth. A minimum of two licks is required to move a single nectar load from the flower to the throat (Fig. 5; Movie 3). This could explain why hummingbirds extend their tongues beyond their bill tips after foraging bouts (A.R-G., personal observation): they could be emptying the tongue grooves by extruding them completely and at the same time clear the inside of their bills by raking any remnants of nectar with their tongue wings. In order to maximize nectar uptake efficiency, offloading as much nectar as possible from the tongue is paramount for maintaining the maximum loading capacity across consecutive licks. After squeezing the tongue to unload the nectar inside the bill, the liquid must be transported towards the throat to be swallowed; if this process is not rapid and complete, the rate at which the bird can add additional nectar to the intraoral space is limited, and thus so is its overall intake rate. Hydraulic displacement could potentially move consecutively ‘stacked’ loads backwards, but we believe that when the tongue rakes a load mouthwards, the filling of an empty intraoral cavity would be faster than it would be if that load would need to push other ‘stacked’ loads on the way. We predict that for shorter protrusion distances, and/or longer bills, more than two licks would be required to transport a single load intraorally….

Credit: Illustra Media

Since the paper is open-access and the movie clips are embedded, readers can watch what happens. In the concluding discussion, the authors explain why the entire process of nectar feeding is required to calculate feeding efficiency.

The discoveries from the work detailed in this paper reveal a crucial component of nectar feeding in hummingbirds that, although as relevant as nectar collection by the tongue (summarized in Rico-Guevara et al., 2019a), had previously been unstudied. A full grasp of every stage of the drinking process is the necessary first step to enable predictive modelling in terms of drinking efficiency of a given bill under determined floral access and nectar properties. This approach could link the vast hummingbird morphological variation to differential performance on the wide variety of bird bill–flower corolla pairings (Rico-Guevara et al., 2021). With this first experimental exploration of intraoral transport of nectar, the foundation is set for comparative biomechanical studies to evaluate the diverse nectar feeding hypotheses (Cuban et al., 2022) and associated adaptations of unrelated clades of nectarivorous taxa (e.g. honeyeaters, sunbirds and many others; Hewes et al., 2022), to better elucidate the extent of convergent and alternative solutions to this unique feeding challenge.

It should be noted that the authors assume evolution and do not offer a creationary view of the mechanism, but their affirmation of evolution appears somewhat indirect:

As the consensus is that the evolutionary trajectory and remarkable biology of hummingbirds arises from feeding on flowers (Rico-Guevara et al., 2021; Leimberger et al., 2022), research on how they drink the floral nectar is pivotal to understanding their evolution.

In the paper, mention of evolution is limited to beak length between hummingbirds, not the origin of the hummingbirds or birds from ancestors. There are no phylogenetic trees shown, or mentions of mutation or natural selection other than one passing reference to “selective forces” affecting beak length, a microevolutionary issue.

Hummingbird eggs with dime for comparison (DFC). Into those tiny eggs is packed all the code to make a magnificent flyer and nectar feeder.

Creationists accept variation within created kinds, so the paper is not arguing for Darwinian macroevolution.

We appreciate this cutting-edge research on hummingbirds by Rico-Guevara and team. They point out that the top and bottom of the bill are tightly matched with the tongue for the function of transporting the nectar load gathered by the nectar trap in the tongue. They also note that retrieval is very rapid: 20 milliseconds, or 2/100ths of a second—similar to the blink of an eye. This all happens as the wings are beating at 500 times a second, allowing the bird to hover in position.

As Paul Nelson says in the film Flight: The Genius of Birds, hummingbirds are like jewels with their brilliant colors. People are rightly fascinated with them and wish to attract the miniature birds with feeders. Nelson says we respond to hummingbirds at a higher level than mere rationality—not irrational, but as if admiring the work of an artist.