Suddenly their gazing was interrupted as every head snapped up and swiveled to the same direction. To human eyes, there was no indication why, but after a few minutes a male showed up in the distance, trailing a few females. You can see him and his attendant females (as a dot) directly under a tree between two hills. I don't know how the females knew about the male; it could have been sound or smell, but surely it wasn't sight.