Peregrine falcons may well be the fastest hunters in the animal kingdom. Famously, they attack smaller birds, like starlings, by using a technique called a stoop. This involves flying upwards to a high altitude then dive-bombing back down at breathtaking speeds that regularly reach more than 200 mph (320 km/h). The fastest stoop ever recorded stands at 242 mph (nearly 390 km/h).
Such speeds would garner respect on the Autobahn and the Formula 1 circuit, alike. For the peregrine, it’s a matter of survival. High-speed stoops enable them kill their prey with massive mid-air impacts. It’s arguably effective, but why peregrines rely on a manoeuver that comes with such tremendous physical and cognitive demands is unclear, to say nothing of the risks associated with plummeting earthward into a flock of starlings at nearly one third the speed of sound.
Perhaps it’s just to conserve energy, some suggested. Or perhaps high speeds help the birds catch prey. But beyond the death-blow of the impact, it wasn’t clear how traveling that fast could be an advantage.
A starling caught unawares is likely to have been traveling in a relatively straight path, meaning the peregrine would have little to do but aim and let gravity do the rest. Even when starlings turn, they tend to do so quite smoothly. However, when a threat is detected, their maneuvering becomes erratic.
Logically, it would seem that a high-speed attack would be useless in this situation, making it harder for the peregrine to follow the starling’s sharp turns, but new research published in PLOS Computational Biology reveals that the aerodynamics actually work in the peregrine’s favor.
Researchers at the University of Groningen in the Netherlands and at Oxford University used 3D computer simulations to analyze the hunting behaviors of peregrine falcons and the evasive maneuvers of starlings. It turns out that starlings are quite good at outmaneuvering peregrine falcons if the peregrines are flying relatively slowly. Indeed, a starling can always escape a peregrine flying at the same speed.
However, this advantage begins to disappear as the peregrine increases its speed by stooping. To catch that starling traveling in a straight path, the peregrine only needs to stoop at around 90 mph (~150 km/h). But if the starling detects a threat and begins to fly erratically, this isn’t good enough. The simulations revealed that peregrines are most effective at catching erratically flying starlings when they achieve stooping speeds just shy of 225 mph (360 km/h). This was consistent with observations in the real world.
The simulations revealed that such high speeds provide peregrine falcons with superior turning force, as well as higher control and agility in rolls. As a result, they have much greater maneuverability at these speeds and are more lethal.
The researchers point out that gravity should not get all the credit — peregrine falcons would not be able to achieve this without fine-tuned physical control and extraordinarily precise vision.
