Tutor model syntax influences the syntactical and phonological structure of crystallized songs of white-crowned sparrows

Songbirds undergo a sensitive period in which exposure to adult song is necessary for normal vocal development. During this period, a template is formed and later used as a model for comparison via auditory feedback. In montane white-crowned sparrows, Zonotrichia leucophrys oriantha, whose song typically consists of four to five distinct segments (phrases), exposure to syntactically overlapping phrase pairs during the sensitive period provides the minimum sufficient information for song assembly; exposure to isolated phrases is insufficient. This suggests that a template representing phrase-pair information is sufficient for guiding normal song production. However, birds may also store and use the additional information they receive when tutored with full song. In the present study, we tutored white-crowned sparrows with a range of phrase sequence information. We found that sparrows tutored with varying levels of syntax information differed in the syntactical (phrase sequence) and phonological (phrase structure) characteristics of their final songs. Sparrows tutored with isolated phrases produced songs that were syntactically and, surprisingly, phonologically deficient. The crystallized songs of birds tutored with full song generally consisted of five phrase types, whereas those of birds tutored with phrase pairs generally had four phrase types. In addition, birds tutored with phrase pairs combined phrases from different tutors in their final songs, while birds tutored with full song did not. These results suggest that the additional syntactical information present in full song is stored and later used. Also, the ability to accurately reproduce phrase structure is linked to the availability of syntax information during the sensitive period.