I lead mountain bike rides on private reserve land for the Nature Conservancy. We had this one group of over enthusiastic guys who would not stay behind the ride leaders. On a particularly steep hill, then got ahead of me and the other leaders. As I topped the hill, I heard a sharp and very loud "Ki-aaaaaacwwwkkkk" and saw the guys come racing across the trail 100 miles an hour - just behind was the momma redtail whose nest they had stumbled upon. She wasn't more than 3 feet above the ground and swooping fast on the guys who had to dive into the dirt. Appears since the got ahead of us, the guys decided to take a nature break... at the wrong spot. Now they understand why we tell them not to go off trail!!! It was worth every minute!