On the evolution of vocal development in island chaffinch populations

PhD ThesisThe oscine songbirds learn songs with a remarkably high diversity of vocal learning strategies, and it remains uncertain how such variety has evolved. In most instances, individuals of a species learn songs similar in structure, but in isolated populations different patterns can emerge. Comparing island and continental populations therefore provide a platform to examine evolution in song learning, and typically this has been achieved through examining how their songs differ. In this thesis, I looked to utilise three alternative perspectives to this when comparing continental and Atlantic Island populations of the chaffinch family Fringilla. Firstly, I performed the first computational comparison of the sensorimotor phase of development in free-living individuals. Secondly, I assessed the presence of female singing in the Atlantic Islands, describing the acoustic structure of songs and assessing their behavioural function. Thirdly, I compared whether populations differ in how discriminate against precisely and less-precisely learned songs through speaker playback experiments. In utilising different perspectives, I aimed to produce a more complete understanding of how song learning can differ between continental and island populations and use this to isolate the underlying factors causing song learning to evolve. Two major differences in song learning were uncovered in the Atlantic Islands Fringilla; female singing and the slowing of sensorimotor development. Slower development could be linked to a weakening of sexual selection, for which indirect evidence was obtained with islands chaffinches not discriminating against precisely learnt songs unlike continental birds. This finding also led to the development of a new potential factor behind the evolution of song; the degree to which individuals utilise memories of songs they produce to guide sensorimotor feedback. Female singing likely assists in defending territories instead, which are maintained year-round in the islands potentially due to reduced seasonality