A covert feather on a bird is one of a set of feathers, called coverts, which as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.[1]
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).
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.
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