DAVIS, H.*; DIAL, K. P.; Univ. of Montana, Missoula; Univ. of Montana, Missoula: Bipeds Ascending: Avian Locomotor Performance During Incline Running.
Recent work suggests that some bipedal ground birds use their forelimbs in novel ways to increase escape performance up steep inclines (Dial 2003). To better understand how bipedal birds in general negotiate sloped terrestrial environments, we surveyed (using high-speed video, 125-250 fps) both juvenile and adult representatives from several basal avian groups (Ratites, Tinamiformes, Galliformes) as they ascended the maximum possible incline for each species. A comparison of limb kinematics (e.g., hindlimb joint angles; forelimb angles of attack, wing planforms and stroke angles) among five species during incline running revealed a continuum of locomotor patterns. Emus (having extremely reduced wings) were capable of negotiating a maximum of 45º, while ostriches and rheas (possessing substantial wings) were capable of ascending inclines of up to 65º. Ratites, while exhibiting secondarily reduced shoulder skeletal morphologies (converging on the primitive condition), appeared to recruit their forelimbs for stability. Chilean tinamous possess an intermediate pectoral skeletal morphology and also exhibited a transitional locomotor pattern between ratites and galliforms. At shallower inclines, tinamous used their wings for balance but when negotiating steeper slopes (>75º) their flapping wing motions resembled those of chukars. Chukar partridge started recruiting their wings on 60º slopes to enhance hindlimb traction enabling them to ascend inclines of up to 100º; they also possess a derived pectoral skeletal morphology common to most volant species. The capacity to jointly recruit powerful hindlimbs with flapping forelimbs enables galliforms to negotiate most complex terrestrial habitats and may represent the evolutionary trajectory leading to the evolution of avialan flight.