Meeting Abstract

129.2  Monday, Jan. 7  Tongue loading and intraoral transport of nectar in hummingbirds RICO-GUEVARA, A.*; RUBEGA, M.A.; Univ. of Connecticut; Univ. of Connecticut a.rico@uconn.edu

Hummingbirds have remarkably high metabolic rates, amazing speed and aerodynamic control, and they are classic examples of coevolution with flowering plants. All of these facts are related to a single reality: they have evolved to efficiently find and rapidly consume small, scattered nectar pools. We describe here the biomechanics of every step of fluid capture and transport, including the processes by which the nectar is loaded onto and fills the tongue, offloaded inside the bill and transported to the throat. We filmed (high-speed videos up to 1000 fps) 20 species of hummingbirds in localities throughout the Americas. We coupled high-speed cameras to a dissecting microscope to film how the whole tongues of four recently deceased specimens filled with nectar at the tongue-nectar interface. Instead of the capillary filling long thought to be responsible for loading the tongue, we found a surprising mechanism of elastic expansion of the tongue that accounts for its complete filling with nectar. To further understand the feeding process, we used MicroXCT scans to create three-dimensional reconstructions of bills and tongues at a scale that allows measurement of internal volumes and hence calculation of nectar flow rates. Lastly, to elucidate fluid transport inside the bill, we used illumination techniques that allowed us to film nectar flow through the whole beak of live hummingbirds. We were able to visualize nectar flow through the keratin, to track nectar menisci, and to follow bubble formation. We found that hummingbirds exploit hydrostatic pressure to move fluid inside the bill and we describe an unexpected role of the tongue base in nectar transport. These combined data help us understand how their ability to efficiently extract all of the nectar from flowers affects hummingbird ecology and evolution.