The peregrine's hunting dive, or stoop, is the fastest recorded movement of any animal. Measured stoops have exceeded 300 kilometres per hour, with a frequently cited maximum of about 389 kilometres per hour from a skydiving trial with a trained bird. Level flapping flight is far slower, on the order of 60 to 100 kilometres per hour.
Each nostril contains a small bony tubercle. The standard explanation is that it acts as a baffle, slowing and disrupting the air entering the nares so the bird can still breathe under high ram pressure. The comparison with engine inlet cones is often made.
That explanation is plausible and repeated in most references, but it rests on anatomy and analogy rather than on physiological measurement in a diving bird. Peregrines also have a nictitating membrane that clears and protects the eye during the stoop, which is better documented.