The upper jaws of birds, unlike those in many tetrapods, move relative to the skull and are often flexible along their length, whereas the lower jaw (mandible) is usually a rigid structure formed by the fusion of several bones, flexing only where it meets the skull. Here we describe a previously unnoticed mandibular bending movement in hummingbirds, in which the distal half of the mandible is actively flexed downwards and the gape widens to catch flying insects. The hummingbird is thought to have developed a long narrow bill as it specialized in feeding on floral nectar, but the bird's need to supplement its diet with insects must have contributed to the surprising flexibility of its jaw.
This tiny bird has a neat trick to trap flies in mid-air with its long nectar-seeking beak.
Video sequence of hummingbird flying with open jaws