Very simple one here guys.
The thing with this achievement is you have to get a stack of 65 buffs and you can only get a maximum of 67 and the stack expires after 8 seconds; therefore very unforgiving.
You have to get all the birds very quickly. Obviously.
Except ... if you're in a raid you get the stacking buff but you don't get the quest credits so you can just keep on going until you manage to stack those buffs up to 65.