Data from: Song discrimination by nestling collared flycatchers during early development

Pre-zygotic isolation is often maintained by species-specific signals and preferences. However, in species where signals are learnt, as in songbirds, learning errors can lead to costly hybridization. Song discrimination expressed during early developmental stages may ensure selective learning later in life but can be difficult to demonstrate before behavioural responses are obvious. Here we use a novel method, measuring changes in metabolic rate, to detect song perception and discrimination in collared flycatcher embryos and nestlings. We found that nestlings as early as seven-days-old respond to song with increased metabolic rate, and, by nine-days-old, have increased metabolic rate when listening to conspecific as compared to heterospecific song. This early discrimination between songs likely leads to fewer heterospecific matings, and thus higher fitness of collared flycatchers living in sympatry with closely related species.