A fixed four-stroke scratching sequence in domestic chickens: a neuro-ethological analysis

Domestic chickens (Gallus gallus domesticus) exhibit a stereotyped four-stroke scratching sequence during ground foraging: a single scratch on the initiating side, followed by two consecutive scratches on the opposite side, and then a final single scratch on the initiating side. This four-scratch bout is consistently followed by a backward step and visual inspection of the exposed area. The sequence is neither a simple spinal reflex nor a cognitively deliberate action. This paper proposes a four-tier neuro-behavioral model to explain the phenomenon. Spinal central pattern generators provide the rhythmic alternating scaffold. Brainstem fixed action patterns encode the asymmetric 1-2-1 temporal template and a built-in stop-after-four counter. Cerebellar-basal ganglia circuits modulate force, amplitude, and initiation or termination based on sensory feedback. The avian brain lacks the neocortical architecture required for abstract counting. The four-stroke structure is interpreted as an evolutionarily optimized minimal information-gathering unit. This descriptive ethological note documents a previously unreported temporal pattern in avian foraging behavior and provides a testable neural framework for future quantitative investigation.