Head-bobbing and head orientation during landing flights of pigeons

1.	The head-bobbing rhythm previously reported in pigeons Columba livia during approximately level landing flights also occurs in upwards landing flights. This finding strengthens the evidence that head-bobbing in flight is linked specifically to approach to a landing target, and that the behaviour has a visual function.
2.	In both level and upwards flights, head-bobbing arises from an oscillating flexion and extension of the neck. Rhythms in translation and rotation of the body do not make a detectable contribution to head-bobbing.
3.	Head-bobbing occurs at the same frequency as the wingbeat cycle and in a fixed phase relationship to it.
4.	The orientation of the head relative to the horizontal is correlated with the trajectory of upwards approach to a perch. In contrast to downwards landing flights, this relationship cannot have the function of keeping the perch in focus during landing. It is proposed instead that it enables the head to be bobbed along the axis which maximizes amplification of optic flow.