Peregrine falcons, the fastest known animal on Earth, barrel through the air in pursuit of prey at speeds over 370 kilometers per hour (230 miles per hour) during a specialized attack strategy referred to as “stooping”. Surveying from up to 915 meters (3,000 feet) above their targets, peregrines begin a stoop by pulling their wings back into an aerodynamic "T" shape and plummeting toward their intended target with such astonishing precision that they can end their descent by snatching their prey with their oversized talons or knocking them unconscious.
Given the incredible coordination of visual tracking and body movement required to pull off a stoop, scientists have long wondered why peregrines bother to dive – especially since they can already fly at speeds much faster than their prey species.
Now, a study by Dutch and English researchers suggests that diving at high speeds increases the bird’s likelihood of catch success by boosting their ability to perform tight maneuvers.
As reported in PLOS Computational Biology, the team built a complex, 3D model of peregrine hunting using measurements taken from real-world observations of the birds’ physical properties, flight dynamics, and reaction times. Then, they assessed the outcomes of simulated hunts against a starling prey wherein the model bird stooped or flew normally at various speeds.
According to their data, straight-flying prey are most easily caught when the falcon collides with the prey at lower speeds of 125-160 km/h (78-100 m/h). On the other hand, if a peregrine is pursuing a starling that moves erratically – more reflective of prey trying to escape – stoops from high above that enable the falcon to reach speeds over 360 km/h (220 m/h) were most successful. This occurs because peregrines accelerating at such rates are able to execute amazingly controlled turns far exceeding the maneuvering capabilities of a starling traveling at a lower speed, even though a starling would be able to out-maneuver a peregrine if both were moving similarly fast.
Peregrine falcons hunting starlings. Video credit Nick Dunlop
As interesting as these findings may sound, peregrine expert Glenn Stewart of the Predatory Bird Research Group believes that the authors’ explanation of stoop success fails to take into account a major factor – eyesight.
“We don’t fully understand what and how peregrines see,” Stewart told IFLScience. “A peregrine eye has two foveas – we have just one – enabling them to quickly judge speed and distance simultaneously.”
He continues that the birds’ unique eye anatomy allows them to focus on prey while keeping their head aerodynamically tucked, a trick non-raptor birds can’t perform.
Furthermore, this type of study can’t quantify the impact of acquired skill. Stewart adds: “And of course, practice-practice-practice helps them survive.”
“Young peregrines fly well but are clumsy their first day or so in the air. They chase one another, other raptors, and are known to practice in-air captures by snatching dragonflies and knocking the tops of flowers. Within just a few days they transform themselves from bumbling landings to true masters of the sky – yes in literally three days!"