© 2001 by The Society for Integrative and Comparative Biology
Control of the Cranio-Cervical System During Feeding in Birds1
1 Department of Evolutionary Morphology, Institute of Evolutionary and Ecological Sciences, Leiden University, Kaiserstraat 63, 2311 GP Leiden, The Netherlands
The avian neck is a complex, kinematically redundant system, which plays a role during inter alia food prehension and manipulation. Kinematical analysis shows that chickens (Gallus domesticus) move their vertebrae according to a geometric principle that maximizes angular rotation efficiency. The movement pattern shows simultaneous rotations in some joints, while not in the others. Anseriformes show a pattern of successive, rather than simultaneous rotations in the rostral part of the neck. A kinematical model indicates that the geometric principle produces an anseriform-like pattern only if a constraint on the movement of the caudal vertebrae is introduced. The strength of this constraint, required for a realistic simulation, is related to the amount of stretch in the long dorsal neck muscles (M. biventer and M. longus colli dorsalis), which have a different configuration in Anseriformes compared to the chicken. To investigate whether the difference in movement pattern is a result of differences in anatomy only, or also of differences in neuromotor patterns, the EMG-patterns of the neck muscles of the mallard and chicken during drinking and pecking were studied. Considerable overlap in the activity of antagonists is found in mallards, but not in chickens. Muscles in the rostral part of the neck are activated successively in mallards, but simultaneously in chickens. We conclude that the difference in movement patterning between chickens and Anseriformes, results from both a difference in the control system of the neck, and a difference in the anatomy. The anseriform pattern is found in water as well as on land, which suggests that neck movement in both environments is controlled by the same neuromotor patterns. The modifications in motor control system and anatomy of the Anseriformes may have evolved as an adaptation to aquatic feeding, since the anseriform pattern is energetically more beneficial in an aquatic environment than on land.