The development of female song in a southern songbird, the New Zealand bellbird (Anthornis melanura). (#272)
Oscine song development is comprised of different motor phases; sub-song, plastic song and crystallisation of full adult song. Studies on these phases have shown variability in development over time between species but not between sexes. Here we compare the motor phases for both sexes and describe how female song develops in the New Zealand Bellbird (Anthornis melanura), a species where both sexes sing a diversity of complex song types. Sub-song was sung by females as young as 6 weeks old and 4 weeks old in males. Plastic song was detected at 15 weeks old in females and 13 weeks old in males. Both sexes sung a full repertoire of crystallised songs prior to their first breeding season. Spectral analysis and consistency correlations were used to analyse the female syllables throughout the song motor phases at different age groups. Peak frequency and entropy of individual syllables stabilised and became more consistent over time. The delivery of individual syllables also varied with more complex syllables taking longer to stabilise than others. Hence, female NZ bellbirds develop complex song types in an equivalent manner to males, and comparable to the development in other male oscines. The research on song function and ontogeny in female NZ bellbirds has significant implications for current knowledge of the evolution of song and its functions. This research also provides a foundation for understanding the costs and benefits of female song repertoires and has implications for the development of local song dialects. Complex repertoires sung by females may be advantageous in territorial defence but likely incur costs in terms of song learning processes. This research progresses our understanding of song learning in females and enables a direct comparison of the learning process between sexes within the same species.