Hummingbird tongues are elastic micropumps

Abstract

Pumping is a vital natural process, imitated by humans for thousands of years. We demonstrate that a hitherto undocumented mechanism of fluid transport pumps nectar onto the hummingbird tongue. Using high-speed cameras, we filmed the tongue -fluid interaction in 18 hummingbird species, from seven of the nine main hummingbird clades. During the offloading of the nectar inside the bill, hummingbirds compress their tongues upon extrusion; the compressed tongue remains flattened until it contacts the nectar. After contact with the nectar surface, the tongue reshapes filling entirely with nectar; we did not observe the formation of menisci required for the operation of capillarity during this process. We show that the tongue works as an elastic micropump; fluid at the tip is driven into the tongue's grooves by forces resulting from re-expansion of a collapsed section. This work falsifies the long-standing idea that capillarity is an important force filling hummingbird tongue grooves during nectar feeding. The expansive filling mechanism we report in this paper recruits elastic recovery properties of the groove walls to load nectar into the tongue an order of magnitude faster than capillarity could. Such fast filling allows hummingbirds to extract nectar at higher rates than predicted by capillarity-based foraging models, in agreement with their fast licking rates.

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“…Since the tongue transformations are purported as passive, in theory they could be replicated under laboratory conditions thus validating or rejecting previously proposed biomechanical hypotheses (e.g. Rico-Guevara et al 2015). The aims of this paper are 1) to provide a description of the coupling of the components of the feeding apparatus in hummingbirds -namely the bill-tongue three-dimensional fit, 2) to describe the tissue architecture and surfaces of the tongue tip, 3) to characterize and contextualize the gross and detailed morphology of the hummingbird feeding apparatus both in a comparative (among birds) and ecologically relevant (biomechanics) framework, and 4) to perform experiments to reveal the extent to which the feeding structures can passively transform to contribute in the nectar collection process (i.e.…”

“…Hence, hummingbird tongues are easily squeezed to unload the nectar inside the bill (Rico-Guevara and Rubega 2011), yielding to storage of elastic potential energy in the flattened tips, which is then released when the tongue is reinserted in the nectar (Rico-Guevara 2014), thereby improving liquid uptake efficiency. The proper functioning of hummingbird tongue grooves as dynamic structures depends on the balance between pliability and elasticity; in particular, the latter has to be strong enough to help the pumping process to extract nectar but weak enough to keep the grooves flattened until they contact the nectar surface (Rico-Guevara et al 2015). Several scaling models and applications have been developed on the basis of recent discoveries of biological phenomena and underlying physical explanations (see Vogel 2011), which opens the way for deeper studies of the influence of the surface characteristics (e.g.…”

Intrasexually selected weapons

“…In nectar‐feeding birds, ISWs come as modifications of the bill tips to stab and pluck feathers (e.g. Rico‐Guevara & Araya‐Salas, ; Rico‐Guevara & Rubega, ; A. Rico‐Guevara, personal observations), however, bill tip shape is finely tuned to interact with the tongue in order to optimize nectar extraction efficiency (Rico‐Guevara & Rubega, ; Rico‐Guevara, Fan & Rubega, ; Rico‐Guevara, ). Hence, even ISWs that are not exaggerated structures (such as in spiders and salmon) can have an impact on the naturally selected function of the modified trait.…”

Bring your own camera to the trap: An inexpensive, versatile, and portable triggering system tested on wild hummingbirds

“…These small, superb fliers visit flowers quickly without perching–difficult subjects for camera traps to detect and record. We have studied hummingbirds drinking nectar from artificial feeders (Rico‐Guevara & Rubega, ) and have developed predictions from biomechanical principles (Rico‐Guevara, Fan, & Rubega, ) that necessitate testing in the wild. Hummingbirds may visit a flower at intervals from 10 minutes to a few hours (Araujo & Sazima, ; Rodrigues & Rodrigues, ), so camera trapping becomes imperative to collect data without researcher‐intensive monitoring.…”