Animals face many perceptual challenges early in life, including in some cases the need to recognize members of their own species. Early species discrimination abilities are especially well documented for songbirds, with nestlings and even embryos responding preferentially to conspecific vocalizations. It remains unknown, however, whether and how such preferences may be altered by early acoustic experience. In the first field study to intentionally manipulate the sound environment of wild nestlings, we here exposed nestling swamp sparrows, Melospiza georgiana, in the field to playback of song from their own subspecies or from another subspecies that breeds in a different habitat and differs in morphology and song traits. Following an average of 4 days of exposure, we temporarily removed nestlings from their nests and tested them, individually, with unfamiliar consubspecific, heterosubspecific and heterospecific probe songs. We found that nestlings previously exposed to consubspecific songs did not show song type discrimination. By contrast, nestlings previously exposed to heterosubspecific songs chirped more often in response to consubspecific songs as compared to heterosubspecific songs. These results suggest that nestling song discrimination is influenced by auditory experience within their first week of life, that exposure to diverse sets of songs might enhance song discrimination abilities and that perceptual conspecific biases in songbirds are precise to the subspecies level. More broadly, our study implies that events immediately following hatching have the potential to guide later song learning, stimulus categorization and premating isolation among diverging populations. & COPY; 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
