The predators here are wild animals, they can arrive, depart at any time during the night-time, not to mention move through without being noticed. While you wait you can be creative with the landscape or shoot some of the smaller mammals like the Red Fox which frequents the area, or some of the bird species around.
The low light levels allow a sufficiently slow shutter speed to be attained, it is then simple to create this effect, all you need is time to perfect the slow vertical panning motion, and before you know it, the bears are back!
