The paired forelimb of birds, especially modified for flight. In penguins (family Spheniscidae) the wings have become secondarily modified for swimming and similarly in other non-flying species of the 'ratite' orders or running birds they have become secondarily reduced. These non-flying birds are freed from restrictions on the ratio of body weight to wing and tail area (to maintain flight capabilities).
Some generalizations can be made about the wing shape. First of all, a bird's wing is convex on the top surface and concave below, with a thicker leading edge (bones), to provide good upward lift. Birds spending most time in flight usually evolved long, narrow wings (which tend to be pointed in seabirds but broader in landbirds) with the primaries often separated towards the end (e.g. albatrosses), while slow or short-time fliers, and those hunting in enclosed areas like woodlands, have relatively short and more rounded wings (e.g. Sparrowhawk). Except for flight (or swimming) as main function, the wings are used for balancing (particularly when perching), as weapons during courtship and breeding, and in displays of many species in which they are widely spread and may be vibrated. The feathers of the wing (see picture) are divided into flight feathers or remiges and wingcoverts or tectrices (also listed). The flight feathers grow from the skin and point backwards, each feather partially overlapping the next. They are divided into the primaries, attached to the manus (hand) part of the wingbones, and the secondaries (or cubitals) attached to the ulna ('underarm' bone). Birds typically have 11 primaries, of which the outermost is often rudimentary or absent, although a number of birds have 9 or 12 and the Ostrich has as many as 16, and the cassowaries as few as 2 or 3. The wingcoverts cover the rest of the wing and part of the primaries (see 'wingcoverts'). See also 'flight'.

Alternative forms for wing : primaries, primary, secondaries, secondary, tertial, tertials, wings.