The hovering of hummingbirds is facilitated by their skeletal structure and musculature. The majority of birds have six pairs of ribs, whereas hummingbirds have eight, distributed along a deep keel, and an elongated sternum, allowing the placement and attachment of powerful flight muscles. The arms are much shorter, with the result that 70% of the wing skeleton is composed of hand bones. The upper articulation moves freely at the shoulder joint, allowing optimal movements in all directions, including 180° axial rotations. The hummingbird's muscle composition is unique and structured in such a way that it takes a longer time for it to tire. Its two flying muscles account for more than 30% of its muscular mass, whereas they account for about 20% in migratory birds.
Credit: The world of the hummingbird, Robert Burton, Firefly Book, 2001