The United States government is now patrolling almost half the border with Mexico with drones alone. The drones are patrolling areas where there are no agents, camera towers, ground sensors or fences.

And Border Patrol officials plan to expand the strategy to the Canadian border.

It’s a significant departure from what has been the decades-old approach emphasizing boots on the ground, and fencing.

Since 2000, the number of Border Patrol agents along the 1,954 mile border has more than doubled, topping 18,000, while fencing was multiplying by nine times to 700 miles.

The Border Patrol’s Predator B drones sweep remote mountains, canyons and rivers with a high-resolution video camera, then return in about three days for a second look. 

The information about the patrols comes from two officials with direct knowledge of the effort, who commented anonymously, since the details of the program have not been made public.