Imma Perfetto
Cosmos science journalist
Flamingos are known for posing serenely on one leg in extreme wetlands, placidly bobbing their heads into the shallow water to feed. But a new study has revealed there’s more going on beneath the surface than meets the eye.
It seems flamingos create controlled underwater chaos to actively trap their prey, according to the research in the journal Proceedings of the National Academy of Sciences
They use a repertoire of behaviours, including stomping feet, jerking heads, and chattering beaks, to create swirling “underwater tornadoes” that concentrate and funnel prey into their mouths.
“Flamingos are actually predators, they are actively looking for animals that are moving in the water,” says lead author of the paper Victor Ortega Jiménez, an assistant professor of integrative biology at the University of California Berkeley in the US.
“The problem they face is how to concentrate these animals, to pull them together and feed. Flamingos are using vortices to trap animals, like brine shrimp.
“It’s not just the head, but the neck, their legs, their feet and all the behaviours they use to effectively capture these tiny and agile organisms.”
Credit: Victor Ortega Jiménez, UC Berkeley
Ortega Jiménez and his collaborators trained Chilean flamingos at the Nashville Zoo to feed from a shallow aquarium.
They used high speed cameras and laser light to view the gas bubbles created in the water to visualise the animals’ feeding behaviour. They then confirmed their observations using fluid dynamics computer simulations and experiments using 3D printed models of flamingo beaks and feet.
They found that flamingos stomp their floppy webbed feet to churn up the sediment beneath them, propelling it forward in whorls.
The birds then draw these vortexes towards the water’s surface by jerking their heads upward at speeds of about 40cm/s, creating mini tornadoes that concentrate particles of food.
Credit: Victor Ortega Jiménez, UC Berkeley
These small vortices are strong enough to trap even agile invertebrates, such as brine shrimp and microscopic crustaceans called copepods.
The flamingos’ heads remain upside down within this watery vortex, with their unique beaks angled so that the flat front end stays parallel to the bottom. They then “chatter”, clapping the lower beak open and shut about 12 times every second, to create smaller vortices that direct sediment and food into their mouths.
Experiments with 3D replicas of flamingo beaks revealed that chattering increases the number of brine shrimp captured by the beak seven-fold.
They found that flamingos also use a technique called “skimming”, which involves pushing the head forward while chattering to create sheet-like vortices – called von Kármán vortices.
Credit: Victor Ortega Jiménez, UC Berkeley
“We observed when we put a 3D printed model in a flume to mimic what we call skimming, [it produces] symmetrical vortices on the sides of the beak that recirculate the particles in the water, so they actually get into the beak,” Ortega Jiménez says.
“It’s this trick of fluid dynamics.”
The team believes that their findings could be used to design better systems for concentrating and sucking up particles, such as microplastics, from water.
Next, Ortega Jiménez aims to determine the role of the flamingo’s piston-like tongue and how the comb-like edges of the beak filter prey out of the water.
