Part of the answer may be in where you are located. Here in Toledo, Ohio cockatiels, this time of year, routinely get yeast infections in their sinuses. In birds, this is part of the sinus system and it surrounds the eye internally. Often when they have a sinus infection, they can loose feathers in that area or over the nares. Many of our older cockatiels are on an omega fatty acid supplement that includes other components for heart disease. At the dose we provide for them, they have not had that problem. We do not go above 0.1 mls once a day with that supplement. We try to get our cockatiel patients on Lafeber NutriBerries as it is balanced as a pellet including the omega fatty acids. It is best to start by crumbling them and put on newspaper on top of the grate in the cage, mixed with some of their seed. Cockatiels are granivores so NutriBerries are a great option for them.
Hope this helps,
Susan Orosz PhD, DVM, Dipl ABVP (Avian), Dipl ECZM (Avian)
Bird and Exotic Pet Wellness Center, Toledo, Ohio