Movie 2.

Dorsal view of a hummingbird drinking nectar. High-speed video (500 fps) of a Rufous-tailed hummingbird (Amazilia tzacatl), the nectar reservoir is located on the left. Note how the tongue tip splits inside the nectar, bending downwards and sideways; this is one of the reasons for using orthogonal angles in order to accurately track the displacement of the tongue. Achieving this backlit visualization through the keratin allowed us to track the nectar menisci inside the bill.