MCFARLAND, J.**; MEYERS, R.A.; Weber State University; Weber State University: Anatomy and Histochemistry of Hindlimb Flight Posture in Shorebirds
During flight, birds support their hindlimbs in one of two possible positions. A flexed limb posture (seen in perching birds and parrots, among others) involves flexion of the hip, knee, and ankle joints, and results in a tucking of the legs beneath the body. An extended limb posture (seen in shorebirds, raptors, and others) occurs when the hip and knee joints are flexed, but the ankle joint is extended so that the legs trail caudally. During flight, muscles must hold the legs in these positions for lengthy periods of time, and should therefore, contain populations of slow muscle fibers to facilitate these postures. We used both gross dissection and histological techniques to examine select hindlimb muscles in American Avocets (Recurvirostra americana) and other species to determine the anatomical specializations associated with this extended hindlimb posture. We expected to find postural muscles composed entirely of slow fibers, but rather, we found that all muscles examined contained both fast and slow fibers. Percentages of slow fibers from two birds ranged from about 10 to 80 % for 12 limb muscles examined. In contrast to the forelimb, which contains uniformly slow muscles presumed to function only in postural support of the folded wing, we did not find muscles purely dedicated to the postural support of the hindlimb during flight. We believe this is due to the multiple functions of the hindlimb in birds. While muscles of the wing are utilized primarily to produce flight or fold the wings when not in flight, the muscles of the leg must function not only during flight, but also in standing, walking, running, or swimming. Therefore, the muscles of the hindlimb are designed to produce versatile actions, both postural and dynamic in nature. Preliminary data shows a similar pattern in the hindlimb muscles of other species. Supported by NSF-REU grant #DBI-0353505, NIH grant #DC004390, and WSU.
