4/25/2023 0 Comments Hummingbird tongueSo how does the rest of the tongue fill with nectar? Remember, they can drain a flower's nectar with around 15 licks in under a second! We predicted that capillarity was too slow to account for the fast licking rates observed in free-living hummingbirds. It would be a simple, passive way for nectar to travel up the tongue.īut from watching hummingbirds in my ( Rico-Guevara's) native Colombia, we felt that capillarity just wasn't fast enough to keep up with how hummingbirds feed. 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 tube walls makes the liquid climb the sides. The physics of capillary action relies on two forces. The idea was that their tongues would fill with nectar in the same way a small glass tube fills passively with water. For over 180 years, scientists believed that to drink nectar, hummingbirds relied on capillary action. They're perfectly adapted for reaching deep into a flower. Hummingbirds' skinny tongues are about the same length as their bills. And what we found was quite different from the conventional wisdom since the 1800s. In our new study, we were able to slow them down on video to see how they really drink nectar. Each flower doesn't offer a lot, so to make a living off tiny amounts of nectar spread throughout the forest, hummingbirds are tiny, fast and feisty.įeeding on nectar is hummingbirds' defining characteristic, but until now scientists didn't know the exact mechanics of how they do it. Rico-Guevara says, "Our research shows how hummingbirds really drink and provides the first mathematical tools to accurately model their energy intake, which in turn informs our understanding of their foraging decisions and ecology.What makes them so intriguing to us is the result of this simple dietary choice: they drink nectar. This offered an opportunity to directly compare the two mechanism and measurements clearly demonstrated that the capillary filling rate was significantly slower than expansive filling. Thanks to this unusual incident, high speed video captured one of the two grooves being filled by expansive filling, as usual, while the other was being filled by capillarity. This occurred when, during initial tongue protrusion, one of the groove tips adhered to the feeder wall before the tip reached the surface of the nectar pool and the groove tip bent as the tongue continued to move forward. In the hundreds of licks studied, the researchers observed capillarity only once, acting on a single tongue groove. The researchers measured 96 foraging bouts of 32 focal birds belonging to 18 species from seven out the nine main hummingbird clads. Observations and measurements were taken from seven countries throughout the Americas where free-living, never handled hummingbirds were feeding at modified transparent feeders simulating nectar volumes and concentrations of hummingbird pollenated flowers. The expansive filling mechanism uses the elastic recovery properties of the groove walls to load nectar on the tongue in an order of magnitude that allows the hummingbirds to extract nectar at higher rates than are predicted by capillarity-based foraging models. The compressed tongue remains flattened until it contacts the nectar surface, after which the tongue reshapes, filling entirely with nectar. What is actually taking place, the researcher report, is that during the offloading of the nectar inside the bill, hummingbirds compress their tongues upon extrusion. Their data shows that fifty years of research describing how hummingbirds and floral nectar have coevolved will have to be reconsidered.
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