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 7 days old respond to song with increased metabolic
rate, and, by 9 days old, have increased metabolic rate when listening to
conspecific when compared with heterospecific song. This early
discrimination between songs probably leads to fewer heterospecific
matings, and thus higher fitness of collared flycatchers living in
sympatry with closely related species.