Head orientation and trajectory of locomotion during jumping and walking in domestic chicks.

The relationships between the head orientation of domestic chicks and their trajectory of locomotion were examined in three tasks: jumping over gaps of different depths and widths; walking on surfaces of different slopes; and walking on a level transparent surface above a slope. Head orientation was measured as the angle between the horizontal and a line joining the centre of the eye to the beak tip. At the initiation of a jump, head angle increased with increasing depth of the gap but was not affected by gap width. During walking, head angle increased with increasing downwards slope of the walking surface and decreased with increasing upwards slope. The same effect of a downwards slope was observed when chicks walked on a level transparent surface above a slope, indicating that the effect does not depend on kinaesthetic information. The findings are discussed together with measurements of pigeon head orientation during landing flight. Explanations in terms of specialised retinal areas, binocular visual fields and lower visual field myopia are considered and rejected. It is proposed that the results instead reflect a general role of head orientation as a component in the visual control of locomotion in birds.