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Abstract
Cultural transmission can increase the flexibility of behavior, such as bird song.
Nevertheless, this flexibility often appears to be constrained, sometimes by preferences
for learning certain traits over others, a phenomenon known as "biased" learning or
transmission. The sequential colonization of the Atlantic Islands by the chaffinch
(Fringilla coelebs) provides a unique model system in which to investigate how the
variability of a cultural trait has evolved. We used novel computational methods to
analyze chaffinch song from twelve island and continental populations and to infer
patterns of evolution in song structure. We found that variability of the subunits
within songs ("syllables") differed moderately between populations but was not predicted
by whether the population was continental or not. In contrast, we found that the sequencing
of syllables within songs ("syntax") was less structured in island than continental
populations and in fact decreased significantly after each colonization. Syntactical
structure was very clear in the mainland European populations but was almost entirely
absent in the most recently colonized island, Gran Canaria. Our results suggest that
colonization leads to the progressive loss of a species-specific feature of song,
syntactical structure.