Bipedal locomotion in birds: the importance of functional parameters in terrestrial adaptation in Anatidae

The kinematic characteristics of a bird's walk vary according to whether th e species is cursorial or not. To increase their speed, running birds incre ase the frequency of their movements, whereas non-running birds preferentia lly increase the amplitude. Previous studies have shown that these differen ces are accompanied by differences in posture; however, the observations we re carried out on different species. Do these differences correspond to mor phological differences linked to the history of the particular species, or do they reflect more effective solutions from a mechanical point of view? T wo breeds of the duck Anas platyrhynchos platyrhynchos, the mallard and the Indian runner, which have different locomotor behaviours, are compared. Th e mallard is a dabbling duck with the typical horizontal duck posture, whil e the Indian runner is a terrestrial duck that carries its trunk very erect . The kinematic characteristics of the walks of both breeds were studied. T he observed differences in posture between the mallard and the Indian runne r have repercussions in the kinematic features of locomotion. The strategie s used to increase speed differ in the two breeds: the mallard increases th e amplitude of its movements, like other non-running birds, while the India n runner increases the frequency of its movements, as cursorial birds do. T hus, behavioural adaptation to terrestrial locomotion is associated with fu nctional adaptation (upright posture) that permits a more effective mechani cal solution without requiring obvious morphological modifications.