My favorite research articles are those that turn over long-held convictions about what plants and animals actually do in the world. An example, from my own lab, was the work by my graduate student, Stephanie Gardner, on leaf-nosed snakes (genus Phyllorynchus), which are common but reclusive snakes in the southwestern U.S. deserts. Every field guide parlayed a highly unusual natural history in which the snakes attack the locally abundant banded gecko (Coleonyx variegatus) and eat only their tails, which the geckos proceed to regenerate. What an amazing system in which a predator is not actually a predator, because it is harvesting a renewable resource! Great story, but altogether wrong. The snakes eat lizard and snake eggs, never geckos or their tails. Oops.
Today’s blog entry reverses an even broader established non-fact in animal biology. Ornithologists and zoological anatomists have “known” for almost two centuries how hummingbirds draw the vital nectar from the flowers they select. The system was purported to operate on the physical principle of capillarity. The short version of capillarity is that fluids will draw themselves up into long, narrow tubules. Put a slim drinking straw into your soda and look through the side. You’ll see that the soda level inside the straw is slightly above the level of your soda. Bingo—capillarity. Make the straw really thin (like the bill of a hummingbird), and the fluid will be drawn way above its level in the container.
Problem #1: This process really does not work well in thick, sticky, syrupy fluids like high-quality nectar. Everyone seems to have ignored that uncomfortable fact for a few hundred years. Problem #2: Hummingbirds don’t do this at all, as our colleagues Rico-Guevera and Rubega from University of Connecticut, have found. Instead, they use their long tongue (which would simply get in the way of a capillarity system), as a nectar-grabbing device in the form of a split tongue-tip (yes, a bit like a snake) and use repeated, very fast tongue pulses to piston-feed the nectar along the beak and into the mouth. See the links below, and be sure to watch the videos in each link.
Sure, this is a quite complicated system, and the authors get credit for teasing apart the functionality of it. But, in my mind, the brilliance of the authors here was simply having the inherent curiosity to challenge an “established fact” that did not quite live up to their standards of logic. And then they did the most basic and valuable of all scientific endeavors—they simply looked, observed, and measured nature. Great, great stuff here!
Here is a nice overview article, from The Atlantic:
Here is the original publication (BE SURE TO WATCH THE VIDEOS POSTED IN THE SUPPLEMENTAL MATERIALS!):
Rico-Guevera, A. and M. A. Rubega. 2017. The hummingbird tongue is a fluid trap, not a capillary tube. Proceedings of the National Academy of Sciences (USA) 108: 9356–9360
Joe Mendelson, PhD
Director of Research