The game is 99.99% finished. Every site is 100% completed: documents, relics etc. The only thing not done, is the side mission to shoot the carrier bird.
I ran past the gate where it is located, when the mission started. It probably flew away. Now, even when using survival instincts, where green concentric circles should appear, no green highlighted bird can be found. I've walked around the main building, with the truck in front, and I've gone up the mountain, to the radio on top that you should destroy. However, wherever I look there's no bird.
To enlarge my search area, I have been into the copper mill and up the hill towards the prison. Has anyone got any clue as to where the missing bird could be?