Meeting Abstract
60.7 Tuesday, Jan. 6 Anatomy of the hummingbird flight motor WELCH, KC*; KEENEY, BK; ALTSHULER, DL; Univ. of California, Riverside; Univ. of California, Riverside; Univ. of California, Riverside kenwelch@ucr.edu
Both small size and the ability to hover distinguish hummingbirds from other avian groups. Some of the unique features of the hummingbird musculoskeletal system have been described as important adaptations to their mode of flight. However, we still know comparatively little about how the hummingbird flight motor, particularly the ultrastructure and neuroanatomy of motor elements in the wing, differs from that of other birds. Here we describe the gross anatomy, fiber composition, and the spinal motor pools of the pectoralis and several muscles of the proximal wing of the Anna’s hummingbirds (Calypte anna). These data are compared to data from zebra finches (Taeniopygia guttata), also obtained in our laboratory, as well to published data from other bird species. All flight muscles examined in both the Anna’s hummingbird and zebra finch were found to be uniformly composed of fast oxidative glycolytic (FOG; type IIa) fibers. Although the homogeneity of fiber type composition (FOG) of the pectoralis muscle of small, volant bird species has long been appreciated, the homogeneous fiber type composition of all other examined muscles in the wing of the zebra finch and Anna’s hummingbird stands in stark contrast to studies on even slightly larger birds, such as the English sparrow. The distribution and quantity of motoneurons innervating the pectoralis, and a control muscle, the extensor metacarpi radialis, within zebra finches and Anna’s hummingbirds are highly similar. These findings indicate that specialization for flight in the smallest bird species corresponds with distinct differences in the design of the flight machinery, compared to larger species. However, these results also reveal relative similarity between these two small species with respect to the functional design of the flight machinery, despite striking differences in the modes of flight employed by hummingbirds and finches.
