If you've really seen how flamingos are eaten, you know how charmingly singular it is. They bob the heads of the opposites in the water, and make a kind of waddle cha cha, through small crustaceans, insects, microscopic algae, and other small aquatic bites, across shallow water.
Victor Ortega Zimenez, an integrated biologist at the University of California, Berkeley, remembers being fascinated by the behavior for the first time in 2019 while traveling with his wife and children to the Atlanta Zoo. Ever since, he had been wondering exactly what was happening beneath the surface.
“The birds looked beautiful, but for me the big question was, “What is the hydrodynamic mechanism involved in filter feeding in flamingos?”,” he said.
Back at home, he was surprised that there was no explanation in the scientific literature, so he decided to produce one himself. After years of meticulous research, he and his colleagues arrived at the astonishing finds explained on Monday in the minutes of the National Academy of Sciences. They found flamingos are active predators who use the way water flows to clean their prey and pour it directly into their mouths.
“We're challenging the idea that flamingos are just passive filter feeders,” said Dr. Ortega Zimenez. “As a spider produces a net, flamingos produce a vortex.”
Dr. Ortega Zimenez's collaborators included three highly supportive flamingos from the Nashville Zoo: Matty, Marty and Cayenne. Zookeepers trained birds and fed them into clear containers, allowing researchers to record what was going on using high-speed cameras and fluid dynamic methods. Scientists produced oxygen bubbles and added food particles to measure and visualize the flow of water given to birds. After initial observations with living birds, the team constructed a 3D model of a flamingo head, which they used to explore the bird's biomechanics more accurately.
Flamingos discovered that they frequently and quickly retracted their heads when they fed. Each of these movements produces tornado-like vortexes and upwelling of particles from the bottom towards the surface of the water. Further observations and experiments with mechanical beaks revealed that flamingos are rapidly pounding their beak while lifting their heads, but still underwater, but they are responsible for flowing directly towards the bird's mouth and helping them capture prey. Their bent L-shaped beaks were also important for generating vortices and recirculating them. They fed the surface and enjoyed the rewards of their designed flows.
Another “surprising discovery” was what birds do with their feet, as Dr. Ortega Zimenez said, and researchers explored using mechanical flamingo feet and computational modeling. The dance-like movement beneath the surface added to the vortex, pushing additional particles towards the bird's waiting mouth, feeding upside down in the water. Taken together, these findings suggest that flamingos are “a superfeed machine with highly specialized superfeed machines using the whole body for feeding.”
Cornell University biophysicist Sunghwan Jung praised the “notably demonstrate the way biological morphology and motion control and play a functional role in surrounding fluids.”
Alejandro Rico Gevala, an evolutionary biologist at Washington University Seattle University, is also not involved in the work, but the new paper agreed to rest the notion that flamingos are passive in a way that filters feeds. “There were a lot of hypotheses surrounding how their strange bills would work,” he said.
In addition to solving that mystery and revealing “a uniquely evolved way to capture small evasive prey,” he continued. This study suggests another evolutionary reason for bird webbed feet beyond simply being a good paddle.
Now that Dr. Ortega Zimenez's curiosity about the liquid dynamics fired by the flamingo, he plans to turn his attention to what is happening in the bird's beak while feeding. To sum up, such discoveries could ultimately lead to bioinspired technologies that capture toxic algae and microplastics, he said.
“What is the centre of filter feeding in flamingos?” he said. “As scientists, we want to understand both the shape and function of these fascinating and mystical birds.
