Cross-fostering of pied flycatchers (Ficedula hypoleuca) to heterospecific hosts in the wild:: A study of sexual imprinting

Learning from parents during early development may crucially influence future mate choice decisions of birds. Such sexual imprinting is thought to be important to many fields of evolutionary ecology, including sexual selection, hybridization, speciation, and interspecific brood parasitism. Most results have been obtained from controlled experiments on captive birds. Hence, there is a need to study sexual imprinting and the development of species recognition under more natural circumstances. I have cross-fostered a migratory bird, the pied flycatcher Ficedula hypoleuca, to nests of two resident species, the larger great tit Parus major, and the smaller blue tit P. caeruleus, by adding a single egg to the clutch, or by swapping whole clutches. No cross-fostered bird recruited to the local breeding population from the mixed brood treatment but sample size was small. However, for the whole brood treatment, cross-fostering had no apparent effect, compared to controls, on local recruitment, natal dispersal, mating success, breeding success, or sexual display responses to intruders. Hence, there were no signs that the cross-fostered birds were sexually imprinted on the host. The results are discussed in relation to sexual imprinting, natal dispersal, interspecific brood parasitism, and conservation of endangered birds.