A covert feather on a bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 is one of a set of feather

Feather

Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...

s, called coverts, which as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.

Wing-coverts

The upperwing-coverts fall into two groups: those on the inner wing, which overlay the secondary flight feathers, known as the secondary-coverts, and those on the outerwing, which overlay the primary flight feathers, the primary-coverts. Within each group, the feathers form a number of rows. The feathers of the outermost, largest, row are termed greater (primary-/secondary-) coverts; those in the next row are the median (primary-/secondary-) coverts, and any remaining rows are termed lesser (primary-/secondary-) coverts. The underwing has corresponding sets of coverts (the names upperwing-coverts and underwing-coverts are used to distinguish the corresponding sets). In addition the front edge of the wing is covered with a group of feathers called the marginal coverts. Within each group of wing-coverts, the rows of feathers overlap each other like roof tiles (the greater coverts are overlain by the median coverts, which in turn are overlain by the outermost row of lesser coverts, and so on).

Tail-coverts

The uppertail and undertail coverts cover the base of the tail feathers above and below. Sometimes these coverts are more specialised. The "tail" of a peacock is actually very elongated uppertail coverts.