In the late 1960s a series of developments in linguistics, developmental psycholinguistics and animal communication led to a convergent model of vocal development in human and nonhuman species. As presented by Lenneberg (1967) and Marler (1970), the development of language and of bird song required exposure to species-specific codes during a sensitive period of development, after which subsequent learning was extremely limited. The amount of input required could be quite small, and this input could be effective regardless of social interactions. Both birds and humans needed intact hearing and an extensive time for practice (babbling for human infants, subsong and plastic song for birds) to acquire adult competence in vocal production. Subsequent to this practice crystallization occurred, and further changes in vocal structure were rare.

This paradigm has led to extremely productive research over the past 25 years, not only in the study of vocal development but also in the understanding of the neurological controls of vocal production. However, as researchers interested in the ontogeny of primate and avian vocal communication, we have become increasingly aware of the need to consider some modifications to this paradigm. Some forms of social stimulation can extend sensitive periods for song learning in birds, and songs and calls in some species can be modified throughout life, often in response to changes in social stimuli. Parrots, dolphins and great apes with exceptional training acquired codes with some similarities to human language. Yet at the same time there was little evidence of vocal plasticity in nonhuman primates, suggesting a gap in continuity of developmental processes in the evolution from birds to humans.

INTRODUCTION

Vocal learning is a very widespread characteristic of songbirds, and a large variety of these learning processes has been described over the last decades. Learning can lead to different types of variation and results in song sharing that can be geographically localized and is then considered as “dialects.” The distribution of these variations can be limited to a few birds and/or cover large areas. Experimental studies have given precise information about the mechanisms involved, in particular in terms of “timing.” However, naturalistic validations may be necessary for us to fully understand the functional significance of vocal learning (see discussion of the sensitive periods, in the literature). There is a need for integrative studies and it is important to consider communication in its own context, which is that of social interaction (for language as a social act, see Goodwin 1990). A social organization needs an adapted communicative system, and comparative studies can give us hints about the evolutionary bases of vocal learning. Comparison can be made between species or phylogenetic groups but also between populations of a same species.

Likely candidates to help us to understand these processes are highly social animals that can adapt to different social environments. Starlings clearly correspond to this definition and here I examine through experimental and naturalistic studies the possible relation between song acquisition, song sharing and social organization.

The European starling (Sturnus vulgaris) occupies the largest geographic range of all the species of Sturnus (Feare 1984). It is present in Asia and in Europe from Scandinavia to Spain and Italy, and even in North Africa. It has also been introduced successfully in North America, New Zealand, and South Africa.