The development of adult responses from responses given during imprinting by the domestic chick

Abstract

The responses of a naive day-old chick to a three-dimensional motionless object of about its own size include: ( a) Approach, ( b) investigatory pecks at points on its surface, ( c) pecks which are often rapidly repeated, are aimed at the object in general, and are often delivered immediately after an approach from a distance, ( d) pressing part of the body against the object, ( e) climbing on top of the object. Pecks are most common during the first two days of life and decrease during tests on subsequent days. Testosterone causes both single and repeated pecks to increase in number again. The change becomes both marked and significant after about ten days at the dosage use. Bodily contacts and mounting show similar changes. In experiments with an object which moved more variably, pecks and attempts to mount developed into aggressive behaviour, and mounting into copulation. The wing lowering and scratching of the waltz, which also appears, and the cloacal lowering of copulation are not obviously related to responses present in naive chicks, and are best regarded as new patterns. However, the direct relation between the other components of aggressive and sexual behaviour, and responses shown by the naive day-old chick suggests that the attachment of the latter to an imprinting object may be the first step leading to the later evocation of the adult response systems by such objects. A similar situation may exist in the guinea pig. Visually naive animals mount a moving block, and such behaviour is probably increased in frequency by testosterone.