Formation

During my walk today I was, as I often do, listening to a pod in my earphones when there was a sudden, disturbing sound, like a pack of motorcycles. But the season for them are over so I took off my earphones and heard that the noice was coming from above, I got my iPhone camera out and just managed to get a picture before they disappeared behind the trees. Some flying club, or maybe the air force is apparently practicing formation flying using small propeller airplanes. One of them seemed a bit off formation, I guess that's why they need to practice. 
During the second week of December, the air force usually do "Christmas tree flying", a tradition that started sometime around 2015. As the name suggests, they fly in a formation looking like a huge Christmas tree. The formation usually have 8-16 JAS-jets and make a huge noice. They fly very slowly and close together and the sight is quite spectacular.
Maybe this was a group practicing, looking more like cranes than a tree.