pterylosis
/ˌtɛrɪˈləʊsɪs/Ornithology
noun
The arrangement or disposition of the feathers of a bird, especially where this occurs in distinct tracts (pterylae); an instance of this.
Origin
Mid 19th century; earliest use found in Thomas Huxley (1825–1895), biologist and science educationist. From pteryla or its etymon post-classical Latin pteryla + -osis, after German Federnstellung, lit. ‘position of the feathers’.