There are 21 Stone Eagles in the game, three in each mission (except mission 1 and 9). As always, some of the eagles are very well hidden, and others are placed in easy spots. You have to destroy the eagles with your weapons; you can do this from up close or from a hundred meters away; it's up to you.
In the spoilers of each mission, you will find the map of the mission and the marked eagles, so they should be easy to find. If you have any problems or need help, the video is also available. I tried to reach as many eagles as possible from one position in the video.
Mission 2 (Dead Drop)
Mission 3 (Sonderzüge Sabotage)
Mission 4 (Collision Course)
Mission 5 (Devil's Cauldron)
Mission 6 (Assault on Fort Rouge)
Mission 7 (Lock, Stock and Barrels)
Mission 8 (End of the Line)
Video:
If you need help with other collectibles, I have a complete guide for each mission and a single video for all collectibles.
Mission 1 + 2 - Behind Enemy Lines + Dead DropMission 3 - Sonderzüge SabotageMission 4 - Collision CourseMission 5 - Devil's CauldronMission 6 - Assault on Fort RougeMission 7 - Lock, Stock and BarrelsMission 8 - End of the LineAll in OneLights, Camera, Achtung - Target Führer DLC