Fig. 4.

Conceptual hypothesis for lamellar movements during the licking (tongue) cycle. (Left column) Frames from the high-speed videos showing a lateral view of the bill tip and the tongue of a living Indigo-capped Hummingbird (Amazilia cyanifrons). Green arrows identify the cross-sections denoted in the middle column. (Center column) Cross-sections of the tongue tip showing the shape of the lamellae on each frame in the Left column. (Right columns) Conceptual depiction of the hypothesized relative contributions of the most important contributors to lamellar movements on each shape of the lamellae. Red stands for elastic potential energy (U_e), blue for surface energy (γA), and black for Laplace pressure (p). (A) The cycle begins when the tongue is protruded through a narrow space left when the bill tips are separating from each other. (B) Tongue penetrating the nectar located in the artificial feeder on the Left. (C) Maximum protrusion distance of the tongue in this licking cycle. (D) Tongue leaving the fluid while being retracted inside the bill. (E) Tongue almost fully retracted inside the bill; when the bill closes the cycle starts again. Scale bars, 1 mm.