pileum
noun
pi·le·um ˈpī-lē-əm 
plural pilea ˈpī-lē-ə
: the top of the head of a bird from the bill to the nape
Word History
Etymology
borrowed from Latin pilleus, pīleus, pilleum, pīleum "felt cap" — more at pileus
First Known Use
1874, in the meaning defined above