New research led by the University of California, Berkeley and the Georgia Institute of Technology reveals that flamingos, far from being passive filter-feeders, are active predators that use flow-induced traps to capture agile invertebrates.
Flamingos feed by dragging their flattened beaks forward along the bottom of shallow lakes. To increase the efficiency of feeding, they stomp dance to churn the bottom, create an upwelling vortex with their heads and clap their beaks constantly to draw food, like brine shrimp, into their mouths. Image credit: Aztli Ortega.
“Flamingos are actually predators, they are actively looking for animals that are moving in the water, and the problem they face is how to concentrate these animals, to pull them together and feed,” said Dr. Victor Ortega Jiménez, a researcher at the University of California, Berkeley.
“Think of spiders, which produce webs to trap insects. Flamingos are using vortices to trap animals, like brine shrimp.”
For the study, Dr. Ortega Jiménez and his colleagues trained Chilean flamingos (Phoenicopterus chilensis) at the Nashville Zoo to feed from a water-filled aquarium over several weeks.
Utilizing high-speed cameras and particle image velocimetry, they filmed and analyzed their feeding behavior, using fine food particles and oxygen bubbles for flow visualization.
They found that the birds use their floppy webbed feet to churn up the bottom sediment and propel it forward in whorls that the birds then draw to the surface by jerking their heads upward like plungers, creating mini tornados.
All the while, the birds’ heads remain upside down within the watery vortex, their angled beaks chattering to create smaller vortices that direct the sediment and food into their mouths, where it’s strained out.
The beak of a flamingo is unique in being flattened on the angled front end, so that when the bird’s head is upside down in the water, the flat portion is parallel to the bottom. This allows the flamingo to employ another technique called skimming.
This involves using its long, S-shaped neck to push its head forward while rapidly clapping its beak, creating sheet-like vortices — von Kármán vortices — that trap prey.
“This suite of active feeding behaviors belies the flamingo’s reputation as a passive filter feeder,” Dr. Ortega Jiménez said.
“It seems like they are filtering just passive particles, but no, these animals are actually taking animals that are moving.”
The authors also employed computational fluid dynamics to simulate on a computer the 3D flow around the beak and the feet.
They confirmed that the vortices do indeed concentrate particles, similar to experiments using a 3D-printed head in a flume with both actively swimming brine shrimp and passively floating brine shrimp eggs.
“We observed when we put a 3D printed model in a flume to mimic what we call skimming, they are producing symmetrical vortices on the sides of the beak that recirculate the particles in the water so they actually get into the beak. It’s this trick of fluid dynamics,” Dr. Ortega Jiménez said.
The team’s findings appear in the Proceedings of the National Academy of Sciences.
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Victor M. Ortega-Jimenez et al. 2025. Flamingos use their L-shaped beak and morphing feet to induce vortical traps for prey capture. PNAS 122 (21): e2503495122; doi: 10.1073/pnas.2503495122
