But previous work
showed that in Serinus spp. body size is not even related to song
frequency (Cardoso & Mota 2007), which is the trait most
dependent on size (Bradbury & Vehrencamp 1998). Also, the effect
of vegetation density on song is typically small by comparison to
the range of between-species differences (Boncoraglio & Saino
2007), and therefore our negative result is not unexpected:
a small effect relative to the range of song variation in the group
should be difficult to detect. This reinforces the interpretation that
sexual selection, rather than other aspects of natural selection or
size constraints, was the main driver of song diversification in this
group and the main cause of song homoplasy.