Filial Imprinting in an Altricial Bird: the Blackbird (Turdus Merula)

Abstract

In altricial birds there are studies about sexual imprinting but there is no experimental evidence about filial imprinting. The work reported here was carried out to inquire into this question in the blackbird (Turdus merula). In experiment 1, 40 nestlings were taken from their nests at 6-7 days of age and bred in visual isolation. The chicks were fed by hand in darkness. At different ages (10, 11, 12 and 13 days post-hatching) they were fed by a stuffed blackbird during 10 feeding sessions. Tests giving a choice between the familar model and a novel one were performed 24 and 36 hours after training, and the begging behaviour as well as fear responses were recorded. Only 11 day old trained chicks showed a significant preference towards the familiar model, which seems to support the existence of an optimal period for filial bond construction in this species. In experiment 2 the possibility of a predisposition to the species characteristics was controlled. At the age of 11 days, 16 chicks were fed either with a plush bird (Group P) or with a cardboard box (Group B). 24 hours after training one testing session was carried out, using a stuffed blackbird as unfamiliar model. Control subjects were tested to determine whether any naive preference existed. Both Group P and Group B showed a significant preference towards the familiar model, whereas control subjects exhibited no preference for either model. These results suggest the existence of only one kind of filial imprinting with similar characteristics in altricial birds and in precocial ones.