Set your camera for video, if it has that feature, and you will soon see what triggers it. Branches or grass blowing in the wind farther out than what you might think is normal will trigger. Also flying moths and other insects at night can cause the camera to trigger.
I have Spy Point IRB trail cameras that will detect larger movement out to 150 yards in the day time if the conditions are right: ex. ( moving vehicles, machinery etc.) Passing the camera on a quad riding away from the camera, once the camera detected me it will keep videoing me as long as I am in the line of sight and the video hasn't timed out. I have travelled well over 300 yards going away several different times in day light. Coming back I may have to be 50 to 100 feet, but the size of the quad is much smaller than machinery or vehicles moving across the line of sight as compared to coming toward the camera.
fastetti: nice picture. Thanks for sharing.