Head-bobbing is the fore-aft movement of the head exhibited by some birds during terrestrial locomotion. It is primarily considered to be a response to enhance vision. This has led some researchers to hypothesize that head-bobbing should be found in birds that are visual foragers and may be correlated with the morphology of the retina. In contrast, other researchers suggest that head-bobbing is mechanically linked to the locomotor system and that its visual functions are secondarily adapted.;This dissertation explored the mechanics of terrestrial locomotion and head-bobbing of birds in both the lab and field. In the lab, the kinetics and kinematics of terrestrial locomotion in the Elegant Crested Tinamous ( Eudromia elegans) were analyzed using high-speed videography and ground reaction forces. In the field, the kinematics of the terrestrial locomotion of charadriiform birds were analyzed using high-speed videography.;These biodynamic studies found that birds have two distinct locomotor transitions. The first transition occurs as they move from vaulting mechanics to bouncing mechanics, and the second transition occurs when they incorporate an aerial phase during running. Thus, many birds use grounded running during intermediate speeds. Also, this study found in general that head and neck movements are coordinated with limb movements during terrestrial locomotion in charadriiform birds, but were not coordinated in the Elegant-crested Tinamou. Thus, the coordination is neither perfect nor obligatory.;Additionally, the evolutionary histories of retinal morphology, head-bobbing and foraging type in birds were investigated through a comprehensive review of avian literature. The data were compiled and mapped onto a composite avian phylogeny. Then, the correlation of characters was analyzed using pairwise comparisons.;This study found that a nasal unifoveate retina with a band-shaped area centralis, non-head-bobbing and visual foraging appear to be the ancestral character states for birds. Additionally, there were no significant correlations between head movement, retinal pattern or foraging mode. Although some general trends were observed, most were within clades and, thus, a result of the independent evolutionary history of head movement, retinal pattern or foraging mode.