Redwing (Turdus iliacus) Science Article 1
A significant proportion of Redwings Turdus iliacus reject non-mimetic model Cuckoo Cuculus canorus eggs experimentally introduced into their nests. However, very few cases of Cuckoo parasitism have been recorded for this species. In the present study we tested the hypothesis that egg rejection by Redwings has evolved as a defence against conspecific brood parasitism. There are strong indications that conspecific parasitism occurs among Redwings and a case of parasitism of a Redwing nest by the closely related Fieldfare Turdus pilaris is described. The Redwings’ reactions against a foreign conspecific egg introduced into their nests were observed, and also those exhibited against a Fieldfare egg which resembles Redwing eggs. The rejection rate for foreign eggs was about 20%, which was statistically significantly higher than the value for another experimental group for which no egg manipulations were made but where the nest owners were exposed to a stuffed Fieldfare dummy. The rat e of Redwing aggression against a female conspecific dummy placed at the nest was higher than that recorded, in experiments in the same area, against a Cuckoo dummy placed at the nest. This reaction and the observed egg rejection behaviour support the hypothesis that Redwings have evolved a defence against conspecific brood parasitism
Grendstad L.C., Moksnes A. & Roskaft E., ARDEA 87 (1): 101-111.