Craban-slayer (Advanced)  

There is a way better spot then the above link. The quest in Eregion "the Roosting Tree" Has a location where at least 20 - 25 birds Spawn. They are approximately on the Shoulder of the wall above the Peno Eregion Name on the Map. The Are can be defined with a crevice and small stack of Boulders. Occasionally worms, foraging tuskers will replace the birds in areas. Simply kill them and more Birds will spawn, I assume its a random mob spawn locations. But the 20 birds are always there around the Boulders within 100m of either side and above them.

I just did 360 Crebain in under 1 hour 30 minutes with no accelerator here. 39.4 by 8.5 Location (roughly)