Wildlife experts in US west have found small aircraft are ideal for protecting humans and livestock from predators

The first time that Terry Vandenbos watched a bear run from a drone, on a spring day two years ago, he was chasing the animal himself. After he saw the grizzly cross a road near his property, the Montana rancher hopped on his all-terrain vehicle, planning to scare it away from his cattle if needed.

But the bear began sprinting away when he was still far from it, looking over its shoulder as it ran, and Vandenbos looked up too; overhead, a small drone was following the bear, its four propellers emitting a high-pitched whine as it sent the animal towards a nearby lake.