Arcane Feathers is a side quest in Dragon Age II Mark of the Assassin DLC available if you bring Anders as one of your companions.
An unusual bird feather has been found. See if there are more.
Acquisition
This quest appears in Hunting Grounds - West in the middle of the map. There will be a Mabari barking up at a tree.
Walkthrough
There are a total of three feathers you need to find.
1. Hunting Grounds - West - In the middle of the map where a Mabari is barking up a tree.
2. Chateau Haine - On the left chest in the Gate puzzle room.
3. Dungeons - Right once you enter through the Crack in the Wall
Result
Once the third feather has been found a treasure cache will be marked on the map. Its location is found in the Mountainside Path after you first encounter the Tal-Vashoth Leader.
Rewards
Bugs
the Arcane Feather at the Gate puzzle room might not be obtainable (can't select it). If it's not sparkling to show you can pick it up then you have Hawke stand on the tile in front of the left chest, and Tallis standing on the other tile in front of the right chest, this should unlock the exit AND the chest so you can pick up the feather.