Neck flexion related activity of flight control muscles in the flow-stimulated pigeon

Summary

Pigeons blown upon from in front were subjected to trapezoidal or stepped laterad neck flexions. The left-right response pattern of wing and tail muscles was regularly correlated with the direction of static neck flexion (Fig. 2). There was no difference whether the head or the body was deflected. In stepped neck flexions, the correlation between muscle activity and stimulus going in the on-direction was often greater than in the off-direction (Fig. 3, M. abd. ind.). Different muscles of the same pigeon frequently showed quite different stimulus-response relationships (Fig. 3 A and B). The muscle responses to steps of neck flexion were tonic (Fig. 2, M. abd. ind.), phasic-tonic (Fig. 2, 1. M. lat. caud.) or only phasic (Fig. 4C), and their time characteristics varied greatly. If not only the pigeon's breast but also its head was blown upon, the left-right activity of muscles depended on the flow direction relative to the head and on the direction of the head's yawing moment (Fig. 5). The left-right activity pattern of muscles was the same in forced and in spontaneous (active) head deflections (Fig. 6A); correlation between head-to-body angle and finger muscle activity was maximal at zero time displacement (±25 ms) between the two pigeon's outputs (Fig. 6B and C). We assume that there exist neck reflexes on wing and tail muscles which are ‘switched on’ when the pigeon is blown upon, and that these reflexes might act as a servo-mechanism which, as proposed by Groebbels (1929), causes the body to follow its beak during flight.