The feedback system used to guide the flight of Harris’ hawks when chasing prey and prevents them being thrown off the pursuit by erratic manoeuvres is based on a mixed mathematical guidance law. The findings are published in Nature Communications this week.

Previous research has shown that falcons intercept prey using the same guidance law as homing missiles. However, this so-called proportional navigation does not describe a feasible path through the cluttered habitats that other species of birds, such as hawks, frequent when targeting highly manoeuvrable prey.

Graham Taylor and Caroline Brighton used high-speed cameras to capture the flight trajectories of five captive-bred Harris’ hawks during 50 flights against an erratically manoeuvring artificial target. The authors then modelled the flights to determine the mathematical guidance law that most closely fits the hawks’ attack trajectories. They found that Harris’ hawks use a mixed guidance law in which turning during pursuit is determined by feedback on the rate at which the line-of-sight changes, and the angle between the hawk’s direction of attack and its line-of-sight to the target (the deviation angle). The authors argue that this mixed law improves the speed of response and reduces the risk of overshoot in a pursuit.