Flamingos are most commonly known for their bright pink plumage, and perhaps their preference for standing on one leg. They’re a type of wading bird in the family Phoenicopteridae and currently there six valid, living species, including four species throughout the Americas and two in Afro-Eurasia. The common name of flamingo comes from the Portuguese and/or Spanish flameno, meaning flame-colored. A similar backstory exists for the genus name Phoenicopterus, from the Greek phoinikopteros or crimson/red-feathered. As such, based on their etymological history, the idea that they are most known for the coloration of their plumage should not be a surprise.
Among ornithologists, however, flamingos are known for their ability to thrive in food-poor environments like salt flats, alkaline lakes, and hot springs because they are adept at filtering out tiny shrimp, worms, and other creatures. And, new research presented at the Society for Integrative and Comparative Biology (SICB) conference considers how they may be able to achieve this.
The research, led by Víctor Ortega-Jiménez from the University of Maine, suggests that the secret is in the mastery of fluid mechanics. In other words, the flamingos are using physics of the water to get particles to their mouths.
Flamingos are known for their specialized filter-feeding system, which works due to their anatomy comprised of their unique beak shape and tongue structure. Previous work has found that flamingos are able to pump water in and out of their mouths using tongues as a piston pump (a type of pump where a high-pressure seal reciprocates with the piston, usually used to move liquids) which traps particulate matter in the lamellar structure of their beak. These lamellar structures are comprised of complex rows of hair-like structures within the flamingo beak, thereby trapping food particles. These anatomical features, combined with vertical and lateral (side-to-side) head movements allow the birds to filter out microparticles from the muddy water.
But, how this adaptation worked exactly had been unclear. In other words, how does the role of flow perturbations generate by the head movements aid in the retention and filtration of food particles?
Using flamingos at Zoo Atlanta, the kinematics of head movement as well as a 2D DPIV (Particle Image Velocimetry, used as a method for flow visualization) were used to analyze wading and feeding behaviors. Then, a 3D printed model of a flamingo head was used for further testing.
Results suggest that the birds stomp their feet and dance in a small circle, which kicks up any muck below the surface, and then effectively stir the water into a swirling vortex which helps to pull the food into a place where they can reach it. They put their beaks just below the surface and quickly open and close their mouths (a behavior called “chattering”) while darting their tongue in and out to create a suction. Flamingos then abruptly lift their head, causing a sort-of tornado, enabling them to suck food upwards toward their mouth. They then walk forward and skim the water’s surface while their bill faces backwards, creating a mechanism for the food to be concentrated right at the tip of their beak.
These behaviors are relatively sophisticated and extraordinary. While they may look a bit odd to a casual observer, they are, in turn, generating a really useful water flow. More research into these behaviors may provide insight into how they evolved, and continue to help us understand these brightly colored birds.
Sources: Science, Integrated Taxonomic Information System (ITIS), SCIB, Philosophical Transactions of the Royal Society B, University of Maine
