The development of within-song type variation in song sparrows

We investigated the development of within-song type variation in song sparrows, Melospiza melodia, with two experiments designed to determine how exposure to within-type variation influences the song-learning process and whether within-type variation itself is a learned trait. In the first experiment, we compared learning between two groups of males, one group tutored exclusively with song models presented with no variation, and the other group tutored exclusively with song models presented with a range of within-type variation that is normally produced by birds in the field. The two groups in this experiment did not differ significantly in any measure of how well they learned, suggesting that exposure to within-type variation has no measurable influence on the learning process overall. Nor did the groups differ in the expression of within-song type variation in their own adult songs, demonstrating that within-type variation is not a learned feature of song sparrow song. In the second experiment, we tutored a single group of birds with both invariant and variable models, allowing us to ask how within-type variability affects learning preferences. Young birds preferentially copied song type models presented with variation significantly more than invariant models. Taken together, these experiments provide insight into the evolution of within-song type variation in song sparrows, although the functional significance of this level of variation and learning preferences based on variation remain enigmatic. (C) 1999 The Association for the Study of Animal Behaviour.