 Secondaries are connected to the ulna. In some species, the ligaments that bind these remiges to the bone connect to small, rounded projections, known as quill knobs, on the ulna; in other species, no such knobs exist. Secondary feathers remain close together in flight (they cannot be individually separated like the primaries can) and help to provide lift by creating the airfoil shape of the bird's wing. Secondaries tend to be shorter and broader than primaries, with blunter ends (see illustration). They vary in number from 6 in hummingbirds to as many as 40 in some species of albatross. In general, larger and longer-winged species have a larger number of secondaries. Birds in more than 40 non-passerine families seem to be missing the fifth secondary feather on each wing, a state known as diastataxis. In these birds, the fifth set of secondary covert feathers does not cover any remex, possibly due to a twisting of the feather papillae during embryonic development. Loons, grebes, pelicans, hawks and eagles, cranes, sandpipers, gulls, parrots, and owls are among the families missing this feather.
