Did you know that Chickens and other birds  has natural oil  for grooming? It was called Uropygial gland.

I love this part on chickens,I love to eat it.  I call it Chicken Ass/Butt though it was not really the ass since it was located on the back part many call it that way, it was an Oil grands located dorsally at the base of the tail, the birds using it for their grooming and beauty making their feathers shiny. When preparing it for cooking , it should be remove since it taste bitter when ate and cooked.