Observations on the incidence of following of visual and auditory stimuli in naive mallard ducklings (Anas platyrhynchos).

Abstract

Abstract The responses of naive mallard ducklings to simple moving models and to simple calls (rapidly repeated "kom") were studied at different posthatch ages, ranging from 3 to 240 hours. i. The proportion of ducklings following moving models, not accompanied by calls, gradually decreased from 58 % at io-20 hours to 17 % at 240 hours. 2. The proportion of ducklings responding to moving models by avoidance rose steeply with increasing age, beginning with 46% at I0-20 hours and reaching ioo% at 240 hours, or probably earlier, between 80 and 240 hours. 3. The proportion of ducklings ready to follow auditory stimuli showed a steep initial rise, culminating in a maximum of 85% reached at 40-5o hours, and followed by a final decrease, although not so marked as in the case of visual stimuli. At 240 hours, the proportion of followers was still as high as 50 %. 4. Ducklings which had not initially followed moving objects could be induced to do so by presenting the model in combination with auditory stimuli. After this procedure, they followed the model even when no auditory stimuli were presented. 5. Some ducklings reacted to moving models by aggressive behaviour (threat posture and attack), or by pumping head movements similar to the pre-copulatory display of the adult mallard. 6. The discrepancy between the long persistence of the following tendency in naive ducklings and the existence of an early critical period found by HESS is discussed. It is suggested that the departure of mallard ducklings from the nest often takes place at an age well past the critical period. Under these circumstances the long persistence of a high level of responsiveness to stimuli releasing the following reaction must have a high adaptive value, particularly in connection with the dangerous journey of the brood from the nest to the nearerst water. The curve for the following of auditory stimuli probably reflects the true state of the following tendency more closely than the curve for the following of visual stimuli, which is depressed by escape tendencies in older ducklings. Ignorance of the long persistence of the responsiveness to unconditioned stimuli eliciting the following response may have been a source of error in some current work on imprinting.