Flamingos, often pictured standing still with their heads submerged in water, make for a pretty picture. But peep underwater, and you'll find the tall, elegant pink birds bobbing their heads, chattering their beaks, and creating mini tornados to efficiently guide microscopic prey into their mouths, according to a new study.
"Think of spiders, which produce webs to trap insects. Flamingos are using vortices to trap animals, like brine shrimp," lead author Victor Ortega Jiménez, from the University of California, Berkeley, said in a statement.
Jiménez and his colleagues discovered the birds' deft use of physics while observing three Chilean flamingos (Phoenicopterus chilensis) at Nashville Zoo in the U.S. They trained the birds to feed from a water-filled aquarium, and used high-speed cameras and other equipment to film and analyze the flamingos' feeding behavior underwater.
The researchers also used 3D-printed models of the flamingos' feet, head and L-shaped bills to confirm their observations through experiments and simulations in the laboratory.
The team found that flamingos aren't passive feeders waiting for prey to come to them. Rather, the birds work hard: they stomp their floppy webbed feet to churn up the bottom sediments, and move their angled, chattering beaks in ways that create tiny vortices that trap tiny plankton and invertebrates, propelling them into their mouths.
Experiments with the 3D replicas helped break it down.
Moving like dancers, flamingos slightly stomp their feet in shallow water while positioning their heads upside down in front of their feet. During each downward stomp of the cycle, the webbed feet spread out. Moving upward, they fold slightly. Simulations showed this movement creates vortices that travel to where the beak is.
Furthermore, the way a flamingo jerks its head straight upward from the water creates a vortex along the vertical axis. Its beak chattering, in which it opens and shuts its lower beak at a rate of about 12 times per second, generates more vortices, while the L-shaped beak itself triggers vortices near the water's surface while skimming. All these motions concentrate and move the sediments and prey efficiently, the researchers found.
Alejandro Rico-Guevara, an evolutionary biologist at the University of Washington, who wasn't involved in the study, told The New York Times that while several hypotheses have been put forward about how flamingo beaks work, "until recently we didn't have the tools to study it." He added this study reveals "a uniquely evolved way to capture tiny and evasive prey."
The study's authors write that understanding how flamingos use fluid dynamics to improve collection of sediments and prey could help design systems to better capture other tiny particles, like microplastics, from water.
Banner image of a Chilean flamingo feeding in shallow water. Image courtesy of Victor Ortega Jiménez/UC Berkeley.