Hunting hawks hold clues to catching rogue drones
Studying raptor attack modes has implications for mechanical aerial defence. Nick Carne reports.
To help design good drones that can intercept bad drones, scientists have taken a close look at the way hawks attack their prey.
In particular, they wanted to see if there is some kind of pattern involved in how these large birds set and adapt their flight paths.
Previous research has shown that falcons – which have a similar modus operandi – track their prey using proportional navigation, the same guidance law as used for homing missiles.
This works well for aerial targets but can be thrown off by the zigzagging manoeuvres of terrestrial prey such as hares or jackrabbits. As such, suggest Caroline Brighton and Graham Taylor form the University of Oxford, UK, it will not necessarily lead to a feasible path through the cluttered habitats hawks frequent.
So how do hawks operate?
To find out, Brighton and Taylor used high-speed cameras to capture the flight trajectories of five captive-bred Harris' Hawks (Parabuteo unicinctus) during 50 flights against an erratically-moving artificial target – a dummy bunny towed around a series of pulleys.
Using video reconstruction techniques to measure the 3D trajectory of the hawk and its target, they then ran a computer simulation to see how closely the attack behaviour was modelled by different kinds of guidance law.
Their finding, published in the journal Nature Communications, is that hawks use a mixed guidance law, in which their turn rate is determined by feeding back information on the angle between the direction to their target and their current flight direction, together with information on the rate at which the direction to their target is changing.
The researchers argue that this reduces the risk of overshooting in the close pursuits to which hawks are adapted, but would produce an inefficient flight path if used in the long-range interception behaviours of falcons.
And this, they say, has potential applications to the design of drones for pursuing and capturing rogue drones in cluttered environments, a reality brought home by the drone attack at London’s Gatwick Airport in 2018.
“Hawks are masters of close pursuit through clutter, so we think they have a thing or two to teach us about how to design a new kind of drone that can safely chase down another,” says Taylor.