Since it's holding onto the feathers, if you determine that it isn't a food source like some of the others noted I'd guess nits of lice. From what I understand the nits are usually found around the head unfortunately. Another food source that can cause that is yogurt and/or milk. They take a bite/drink, then shake their heads to clean off the beak. It will go all over them, the walls, ground, floor, etc. But it usually will come right off. If it does turn out to be parasites, the information in this article may be of use. I think the bugs themselves like to hang out around the vent. If it is nits, they can be up there.