Pecking in the chicken (Gallus gallus domesticus): Motion analysis and stereotypy

Stereotypy of pecking in chickens as a result of similar sensory input, was analysed by employing the Coefficients of Variation and Concordance. Movements of head, beak and tongue, filmed with a high speed camera, and the beak's gape recorded with a Magnetic Resistive Sensor were analysed. While assessing the food before the peck, the posture of the head and the lower bill's elevation are stereotyped. When approaching the food the beak opens and starts to close again for the grasp before touching the food. The head's posture at maximum gape and the upper bill's maximum elevation suggest stereotypy, which is supported by concordance values. It is concluded that the preprogrammed movement stereotypy is superimposed upon mechanical limitations imposed by the jaw apparatus. The predominantly astereotyped withdrawal of the head is sometimes used for repositioning of the seed, but usually for initiating transport of the food. Based on concordance, gapes and lower bill movements during transport cycles constitute Fixed (i.c. stereotyped) Action Patterns. Here, instead of mechanical constraints, the exteroceptive stimuli by the pea are a readily available cause for stereotypy.