Control of the Cranio-Cervical System During Feeding in Birds

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 thatmaximizes angular rotation efficiency. The movement patternshows simultaneous rotations in some joints, while not in theothers. Anseriformes show a pattern of successive, rather thansimultaneous rotations in the rostral part of the neck. A kinematicalmodel indicates that the geometric principle produces an anseriform-likepattern only if a constraint on the movement of the caudal vertebraeis introduced. The strength of this constraint, required fora realistic simulation, is related to the amount of stretchin the long dorsal neck muscles (M. biventer and M. longus collidorsalis), which have a different configuration in Anseriformescompared to the chicken. To investigate whether the differencein movement pattern is a result of differences in anatomy only,or also of differences in neuromotor patterns, the EMG-patternsof the neck muscles of the mallard and chicken during drinkingand pecking were studied. Considerable overlap in the activityof antagonists is found in mallards, but not in chickens. Musclesin the rostral part of the neck are activated successively inmallards, but simultaneously in chickens. We conclude that thedifference in movement patterning between chickens and Anseriformes,results from both a difference in the control system of theneck, and a difference in the anatomy. The anseriform patternis found in water as well as on land, which suggests that neckmovement in both environments is controlled by the same neuromotorpatterns. The modifications in motor control system and anatomyof the Anseriformes may have evolved as an adaptation to aquaticfeeding, since the anseriform pattern is energetically morebeneficial in an aquatic environment than on land.