Rare shorebirds called phalaropes practice an unusual water dance to help them consume their prey: They spin in tight, quick circles on the water by kicking one foot harder than the other, creating upward jets that pump tiny, out-of-reach insects and crustaceans toward the surface. The birds then dip their bills into the upwelling and feed at high speed. Now, a research team finds that these dizzying birds choose neighbors that spin in the same direction. The cliquishness of right-footed and left-footed birds helps keep the peace within a flock as phalaropes scarf down food, the team suggests.
The research answers a question “anyone who’s ever watched phalaropes spinning like demented wind-up toys has wondered about,” says Margaret Rubega, curator of ornithology at the University of Connecticut, Storrs, who was not involved in the work.
The study grew out of a canceled field season during the coronavirus pandemic. “We could still watch videos,” says Jorge Gutiérrez, a bird ecologist at the University of Extremadura and lead author on a report of the results published last month in Behavioral Ecology. “And thanks to those videos, we could study this curious behavior.”
Gutiérrez and co-author Andrea Soriano-Redondo noted the spin direction of each bird in 909 videos of feeding phalaropes on YouTube, Vimeo, and other free online sources. Taken in North and South America, Europe, and Asia, the videos captured birds belonging to one of three species—Wilson’s phalaropes (Phalaropus tricolor), red-necked phalaropes (P. lobatus), and red phalaropes (P. fulicarius).
The footage supported what Gutiérrez and other researchers had long suspected: For phalaropes, spinning is “lateralized,” meaning each bird tends to favor spinning to the right or left. Only three of the 73 birds filmed more than once were ambidextrous, turning in both directions.
Flocks contained a mix of right-footed and left-footed birds. But within those flocks, individuals preferred to spin near birds whose spin direction matched their own: The nearest neighbor of a bird that turned right was twice as likely to also turn right as left, the researchers documented.
There’s a benefit to this coordination, Gutiérrez says. As phalaropes spin, they also slowly float sideways, which allows them to constantly move to fresh feeding spots. But birds spinning in opposite directions creep toward each other and risk colliding and fighting over food. The researchers found that neighbors with synchronized spinning threatened one another one-third as often as those that were out of sync. Rubega, who has studied how phalaropes feed, likens opposite-turning phalaropes to right-handed and left-handed people seated next to each other at the dinner table. “You’re going to bump elbows a lot,” she says. “You’re going to interfere with one another while you’re reaching for the same salt shaker.”
Gutiérrez and Soriano-Redondo suggest phalaropes follow a simple rule of thumb: “Choose neighbors who spin in the same direction as me.” That rule could be adaptive, they say, as it helps the birds eat without interruption. And in fact, feeding phalaropes can peck up to 180 times per minute, faster than any other bird.