Preflight development of bilateral wing coordination in the chick (Gallus domesticus): effects of induced bilateral wing asymmetry.

The performance of bilaterally synchronous wing-flapping by chick hatchlings suggests but does not prove the existence of a bilateral coordinating mechanism. The present research tests for bilateral coordination by using the technique of induced asymmetry. The onset of bilateral wing coordination was defined as the age when induced bilateral asymmetry produced by right wing amputation, immobilization, or weighting influenced the drop-evoked flapping rate of the left wing. Unilateral right wing immobilization or weighting immediately before testing reduced the flapping rate of the contralateral left wing of 3-5 day chicks, the youngest examined. Weighted and unweighted wings flapped synchronously. Therefore, a mechanism which acts across the body midline to synchronize wing-flapping by slowing the rate of the more rapidly flapping wing to match that of its slower contralateral partner was present by 3-5 days. This is several days before the onset of flight. The flapping rate of the left wing of chicks that had their right wing amputated on Day 1 was similar in rate to that of intact chicks when tested at 7 and 13 days. "Wing-flapping" on the amputated side of some unilateral amputees was made visible by a prosthesis attached to the stump of the amputated wing. Bilaterally coordinated flapping in the unilateral amputees indicated that the sensory and trophic periphery of a given wing and flight-related adaptive significance are not necessary for the postnatal production of bilaterally synchronized wing-flapping. However, the slowed flapping produced by unilateral wing weighting or immobilization indicates that wing-flapping rate is modulated by sensory feedback, even at preflight stages.