Feathers are a widely used crafting material in Far Cry Primal for a lot of things. You can get them from birds but most of the time these birds are difficult to hunt because they are constantly moving and are, for the most part, too far away to be shot! Most birds lose feathers when you kill them - only a few will provide you with rare feathers. This guide, produced thanks to Gosunoob, gives you an easy method to get feathers and hunt birds.
Where to find feathers: on the hunt
The first method is to find a place where the birds are numerous. There are flocks of birds that fly around the northern area of the map where they are quite easy to kill. You can find this location towards the northwest outpost, south of the Little River. If the birds spot you, they will try to run away, but they are no match for you! There is also a pack of dholes in the area which prey on birds. If you come across dead birds, then it is easy to tear off their feathers. Don't forget to bring winter clothes before you go, or you could freeze to death!
Where to find feathers: eagles
If you really want to go eagle hunting, there is a smart way to do it. Use Hunter's Vision to find an eagle, then follow it. At one point, it will go to the ground to feed. During the few seconds it will be placed, this is your only chance! Prepare well because if it takes off again, it's too late. So as soon as you see him diving, sneak up as close as you can and shoot an arrow. It's a lot easier than trying to shoot him down while he's in the sky.
There is also a possibility to have feathers in your stash as a daily reward. But the quantity is often minimal, so you better not count on it and go hunting for piafs instead!