Pennae

Pennae is the plural of penna, Latin for feather. In scientific usage, pennae refer to the feathers of birds or other feathered animals and collectively to their plumage.

Feathers are keratinous structures grown from follicles in the skin. Each feather comprises a calamus (the hollow stalk embedded in the skin), a rachis (the central shaft), and a vane formed by interlocking barbs and barbules. Feathers are categorized as pennaceous (with a firm vane) or plumulaceous (soft at the base). Major types include contour feathers, down, semiplumes, filoplumes, and bristles.

Flight and tail feathers are the remiges and rectrices, respectively. These pennaceous feathers are shaped for aerodynamics, and birds replace them through molting, a cycle that varies by species and season.

Feathers serve flight, insulation, waterproofing, camouflage, and signaling. Color comes from pigments such as melanins, carotenoids, and porphyrins, or from microscopic structures that produce iridescence. Feather diversity reflects ecological needs and behavior, from streamlining to courtship displays.

Historically, pennae were used as writing quills; the term helped give rise to the English word pen. In anatomical or paleontological contexts, pennae may be used to describe feather arrangements or features in fossil birds.