The hummingbird tongue fills with nectar even when only the tip is immersed. That energy subsequently facilitates the pumping of more nectar. When the hummingbird squeezes nectar off its tongue during protrusion, it is collapsing the grooves and loading elastic energy into the groove walls. The tongue structure is collapsed during the time it crosses the space between the bill tip and the nectar pool, but once the tip contacts the nectar surface, the supply of fluid allows the collapsed groove to gradually recover to a relaxed cylindrical shape as the nectar fills it. Rather than wicking, he says, the nectar is drawn into the tongue by the elastic expansion of the grooves after they are squeezed flat by the beak. “The best and most recent 2014 explanation via Rico-Guevara who explains that a hummingbird’s tongue, which can be stuck out about the same length as its beak, is tipped with two long skinny tubes, or grooves. Journal of Ornithology, 79: 425-491.Īlejandro Rico-Guevara dis-proves that theory. Beitrage zur morphologie und entwicklungsgeschichte der zunge der Trochilidae, Meliphagidae und Picidae. The Naturalists Library: A General History of Hummingbirds of the Trochilidae, Kessinger Publishing, 276pp It would be a simple, passive way for nectar to travel up the tongue. The capillary action theory made sense since a hummingbird's tongue has two tube-like grooves. Surface tension holds the liquid together and drags the whole fluid column upwards. Adhesion of the liquid molecules to the inner tube walls makes the liquid climb the sides. The physics of capillary action is based on two significant forces. The idea was that their tongues would fill with nectar in the same way a small glass tube fills passively with water. Historically (or for over 184 years), scientists and biologists (Jardine & Martin 1833) believed that hummingbirds stretched their tongues to extract nectar from flowers or feeders through capillary action. We propose a conceptual mechanical explanation for this unique fluid-trapping capacity, with far-reaching practical applications (e.g., biomimetics).Hummingbirds have long, thin bills and tongues with channels, bristles, and papillae. Our findings have ramifications for the study of feeding mechanics in other nectarivorous birds, and for the understanding of the evolution of nectarivory in general. Our results rule out previous conclusions from capillarity-based models of nectar feeding and highlight the necessity of developing a new biophysical model for nectar intake in hummingbirds. We also show that the tongue-fluid interactions are identical in both living and dead birds, demonstrating that this mechanism is a function of the tongue structure itself, and therefore highly efficient because no energy expenditure by the bird is required to drive the opening and closing of the trap. Instead, we show that the tongue tip is a dynamic liquid-trapping device that changes configuration and shape dramatically as it moves in and out of fluids. We demonstrate that the hummingbird tongue does not function like a pair of tiny, static tubes drawing up floral nectar via capillary action. Existing biophysical models predict optimal hummingbird foraging on the basis of equations that assume that fluid rises through the tongue in the same way as through capillary tubes. Hummingbird tongues pick up a liquid, calorie-dense food that cannot be grasped, a physical challenge that has long inspired the study of nectar-transport mechanics.
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