they could be testing something too.... I remember a few year ago there was a bunch small engine airplanes circling (like for a long time) the metro area in minnesota. I believe they were testing some fancy new gadget. http://www.startribune.com/nighttime-flight-circles-low-over-twin-cities-for-hours/305398901/  The planes use “persistent wide-area surveillance” to photograph large areas for hours at a time, Stanley said. The captured images allow authorities to go back in time, if necessary, to trace pedestrians and vehicles who come to their attention. Other devices known as “dirtboxes,” “Stingrays” or “IMSI catchers” can capture cellphone data. Stanley said it’s still unclear what technologies have been used in the surveillance flights.