Proabably made by humans. But if so, still surprising that such elaborate patterns can be accomplished without detection of the perpetrators during the act.
Actually they have been detected and filmed in the act.
oh its easy to skirt detection, when you are the owner of the land, lol. He is probably making a bundle this week from all those air heads. Elaborate patterns in circular form are easy to make. Take a rope spiked to the radii point, then merely walk in a circle. And a few other techniques to make the interior cuts - all well known to those of us who have participated in such pranks before.