Hummingbird tongues are elastic micropumps.
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.
Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269, USA Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá DC, Colombia a.rico@uconn.edu.
Alejandro
A
Rico-Guevara
Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA.
Tai-Hsi
TH
Fan
Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269, USA.
Margaret A
MA
Rubega
D000818:Animals; D001696:Biomechanical Phenomena; D001717:Birds / Q000033:anatomy & histology / Q000502:physiology*; D005247:Feeding Behavior; D057048:Plant Nectar; D014059:Tongue / Q000033:anatomy & histology / Q000502:physiology*; D014741:Video Recording
D057048:Plant Nectar
capillarity; feeding mechanism; fluid dynamics; hummingbird foraging