At first glance, flamingos standing quietly on thin legs in shallow alkaline lakes with their heads submerged in the water may seem serene and passive inhabitants of water bodies. However, this apparent immobility hides active and complex hunting mechanisms. Under the surface of the water there is real movement - a biomechanical performance involving the legs, necks and unique beaks of these
birds.
Recent research conducted at the Nashville Zoo with scientists from the University of California at Berkeley, Georgia Institute of Technology, Kennesaw State University and other organizations reveals a little-known aspect of Chilean flamingos (Phoenicopterus chilensis).
Using three-dimensional printed models of these birds' legs and beaks, the researchers studied in detail how flamingos create water vortices to efficiently concentrate and capture food.
Associate Professor of Integrative Biology at UCLA Victor Ortega Jimenez, one of the lead authors of the study, emphasizes that flamingos are not at all the passive filterers they are often thought to be.
According to him, these birds have an active predatory lifestyle. They do not just filter small particles, but deliberately hunt mobile organisms such as shrimp. To cope with the task of concentrating their prey, flamingos resort to the help of physical phenomena - creating mini-tornadoes and whirlpools.
The birds use their webbed feet to stir or "whip" bottom sediments, lifting them into the water column. These movements create large swirls, which the flamingo then directs upward by moving its head like a piston. The beak, with its distinctive L-shape and flattened front end, helps to create fine whirlpools that direct food particles directly into the mouth, from where it is filtered.
The flamingo's beak is unique in that its front end is flattened at an angle, so that when the bird's head is upside down in the water, the flat part is parallel to the bottom. This allows the flamingo to use another technique that researchers have documented as another way to extract food, called skimming.
Flamingos extend their necks forward as they move through the water and make rhythmic movements with their beaks. These actions create von Karman's vortexes - orderly flows resembling oscillating sheets that effectively capture prey and guide it to the mouth opening.
These discoveries are seriously changing the perception of flamingos' abilities. Instead of slow and lazy filter feeders, they are now highly efficient hunters who skillfully use hydrodynamics to survive. Creating eddies, channeling sediment, and trapping prey in specially designed streams are all elements of a complex strategy honed by
evolution.
Photo: phys.org
In addition to zoological discoveries, the work of Ortega Jimenez and his colleagues may find practical applications in engineering and ecology. The knowledge gained could form the basis of technologies designed to extract microplastics and other small pollutants from water. The principles could also be used to create self-cleaning filters and biorobots that can move in viscous media like flamingos without losing stability or efficiency.
Vibrating
Victor Ortega Jimenez, originally from the Mexican city of Puebla, became interested in the unique behavior of flamingos quite by accident. A visit to the Atlanta Zoo with his wife and daughter shortly before the start of the
COVID-19 pandemic became the starting point of his scientific fascination. During a walk, he began videotaping flamingos feeding in an aviary, but the footage showed only faint ripples on the surface of the water - no obvious signs of what was happening underwater. It was this visual paradox that sparked his research interest.
"We see only the surface - smooth, calm. But what's going on underneath it? We don't know that, and that was the whole scientific question," the scientist recalls.
At the time, Ortega Jimenez was working as a postdoctoral fellow at Kennesaw State University (Georgia) and was in search of a new research topic. Flamingo feeding behavior seemed to him an underappreciated and promising area of study.
As he himself notes, his approach to science is close to the tradition of Darwinist naturalism: he seeks to understand how animals - from microscopic nematodes and flies to birds and other large fauna - interact with their environment, be it air, water, or even electromagnetic fields.
After leaving Kennesaw, Ortega Jimenez continued his scientific endeavors in the Saad Bhamla lab at the Georgia Institute of Technology. There, he joined forces with engineers and gained access to Chilean flamingos kept at the Nashville Zoo. The team set up a series of high-precision observations, using laser illumination to visualize tiny gas bubbles rising in the water. This allowed them to see clearly for the first time the swirls that form around flamingos' heads and beaks as they feed.
Jimenez then moved to the University of Maine at Orono, where he became an assistant professor. Here he significantly improved modeling methods: new, more accurate 3D models of the beak and legs of flamingos were printed, with the help of which it was possible to reproduce the fine details of the movement of water and sediment. The scientist paid special attention to the behavior of the beak during the so-called "vibration" - a frequent and rhythmic flapping, which is used by birds to grab food.
The next step was a move to the University of California at Berkeley in 2024, where Ortega Jimenez continued his research with an even higher level of technological detail. He assembled an experimental setup in which a real flamingo beak was attached to an actuator that mimicked the characteristic beak movements.
Inside the structure was a small pump that mimicked the work of the tongue, creating a suction effect - similar to the way flamingos capture prey. The results of the experiment were striking.
Vibrations of the flamingo's beak radically increase the efficiency of hunting: the number of shrimp captured by vibrating was seven times higher than in the case of the usual passive flow of water through the beak.
"This mechanism is a real boon," says the scientist. "Vibration is not just a side effect, it is a key element that multiplies the feeding efficiency of flamingos many times over. We have shown that they are not just filtering water, but actively using physics to capture live prey."
Photo: phys.org
This work was the culmination of many years of interdisciplinary collaboration, combining zoology, biomechanics, fluid physics and engineering. A new scientific work, to be published in 2024, summarizes the results of this complex research and opens up prospects not only for a better understanding of bird behavior, but also for the creation of innovative technologies based on natural principles.
Perfect paws
"Feeding the flamingo starts from the bottom - from the feet," Jimenez emphasizes. If you carefully observe the bird standing in very shallow water, you may notice it making strange movements on the spot or doing circular "dances." These seemingly chaotic gestures have a strictly functional purpose - they trigger the complex hydrodynamic process necessary for effective hunting.
The peculiarity of the flamingo's legs is that they are not only long and thin, but also have webbing - as in many waterfowl or wading birds, but unlike geese or ducks, the flamingo's webbing is hanging, that is, not stretched rigidly between the toes.
This allows them to easily pull away from the bottom surface when lifting their feet, without creating a "sucking in" effect - one of the reasons why humans find it difficult to move on muddy bottoms. When moving through the water, flamingos do not stomp but glide, minimizing drag.
To investigate the influence of foot shape and mobility on water movement, Ortega Jimenez developed models of flamingo feet of two types - rigid and flexible. Experimental results showed that flexible designs were significantly better at guiding sediment, forming stable eddies before each step. The rigid models, on the other hand, mostly created turbulent flows that were less predictable and less effective in the context of moving food particles.
In parallel, the researchers focused on the beak, a unique L-shaped structure that allows flamingos to feed while holding their heads upside down. Using three-dimensional models and slow-motion photography, the team found that rapidly pulling the head vertically upward in the water creates a spiral vortex twisted around a vertical axis.
This vortex creates a low-pressure zone into which food particles are drawn. Measurements have shown that the speed of the flamingo's head can reach 40 cm/s, and the mini-tornadoes that form are strong enough to catch even fast organisms such as copepods (microscopic crustaceans).
An important mechanism - vibrating - consists of high-frequency movements of the flamingo's beak, in which the upper part remains stationary while the lower part moves at a frequency of 12 vibrations per second.
This creates micro-vortices that envelope the beak, helping to draw food inside. Studies have confirmed that during vibration, the amount of food captured increases many times over.
Computer simulations conducted by Professor Tien Yee of Kennesaw State University (KSU-Marietta) have confirmed experimental observations. Using computational fluid dynamics techniques, Yee created a three-dimensional simulation of the currents occurring around the paws and beak. These calculations were then tested under laboratory conditions in an artificial pond with live shrimp and floating eggs.
In simulating a behavior called skimming, where a flamingo moves forward by extending its neck and flapping its beak, the model showed the formation of symmetrical vortices on either side of the beak. These vortices capture and return food particles back to the mouth opening, increasing feeding efficiency.
"This is the real trickery that hydrodynamics itself dictates," Jimenez says. "The bird literally controls the currents to bring the food back to the capture zone."
But the research doesn't end there. In upcoming projects, Jimenez's team plans to study how the flamingo's tongue functions as a pump and to examine how the ridged edges on its beak filter food, especially in extreme conditions of salty and alkaline water. These details are key to understanding how flamingos manage to feed in extremely hostile environments.
Photo: travelask.ru
"Flamingos are not just pretty pink birds," the scientist emphasizes. "They are a super-specialized filtering machine, involving not only beak and head, but also legs, neck and complex behavioral algorithms. All of this serves one purpose - capturing the smallest and most agile prey."
In addition to Yee and Ortega Jimenez, postdoc Pankaj Rohilla, graduate student Benjamin Seleb, Professor Saad Bhamla of the Georgia Institute of Technology, and Jake Belair, representing the Nashville Zoo, were involved in the creation and implementation of this comprehensive study.
The study was an example of interdisciplinary work where biology, engineering and fluid physics converged to unravel one of nature's most elegant feeding strategies.