apterium

(from the article `feather`) Unlike the hair of most mammals, feathers do not cover the entire skin surface of birds but are arranged in symmetrical tracts (pterylae) with areas ... ...act as insulation. The major contour feathers of the wing (remiges) and tail (rectrices) and their coverts function in flight. Contour feathers ... In...
Found on http://www.britannica.com/eb/a-z/a/91

Apterium

unfeathered area between feather tracts
Found on http://www.pugetsound.edu/academics/academic-resources/slater-museum/biodiv
No exact match found