When you kill a bird you get 1 or 2 feathers. Kill enough birds to get at least 5 feathers. Save game just in case cosmos don't work or malfunctions. Use cosmos to scan 5 feathers. Craft that color feather arrow once. Use cosmos to scan 4 feathers. Keep going down one by one using cosmos each time until you get 1 code on cosmos then change it to 999 feathers and craft again. Now you have 998 feathers.
These are some locations I found the birds on
White Bird 21 E 1 N
Red Bird 46 E 25 W favorite spot for this bird because it has high hill 25 E 0 N 42 E 22 N
Yellow Bird 52 E 43 N 28 E 30 N good spot high hill
Blue Bird 38 E 27 N good spot has high hill also has green birds at this spot 24 E 6 N also has white birds
Green Birds 38 E 27 N good spot high hill also has blue birds 2 E 14 N 27 E 3 N