Distress calling induced by reductions in group size in ducklings reared with conspecifics or imprinting stimuli

Abstract

Peking ducklings were reared for 1–2 weeks with either 9 or 12 companions, which were either conspecifics or imprinting stimuli (blocks of foam rubber). They were then tested for their tendency to distress call as the number of companions was reduced systematically. Consistent with prior research, ducklings reared with conspecifics modulated their distress calling as a function of both the number of companions with which they were reared and the number of companions with which they were tested. In contrast, ducklings reared with moving imprinting stimuli gave few if any distress calls, regardless of the number of stimuli with which they were reared or tested, as long as at least one imprinting stimulus was present. The difference in responding did not reflect just a lack of attachment to the imprinting stimuli, since when all stimuli were removed these ducklings gave as many distress calls as the ducklings that had all their conspecifics removed. Finally, ducklings reared with stationary imprinting stimuli displayed an erratic pattern of distress calling when the number of test stimuli was manipulated. These latter ducklings appeared to be less strongly imprinted than the ducklings reared with either conspecifics or moving imprinting stimuli. Implications for understanding duckling perception of brood size and thenature of sibling vs. filial imprinting are examined.