Early song discrimination by nestling sparrows in the wild

Songs play an important role in premating isolation in birds. However, when songs are learned, experience with both conspecific and heterospecific songs in early life could lead to the development of both mixed songs and mixed preferences. One way that such learning errors can be prevented is if birds can discriminate between songs of different species prior to learning and preferentially memorize conspecific songs. Prior captive studies have shown that white-crowned sparrows, Zonotrichia leucophrys, are able to discriminate songs early in the process of song memorization, after about 10 days since hatching. I studied early song discrimination in wild golden-crowned sparrows, Zonotrichia atricapilla, the sister species of white-crowned sparrow. The two species occur syntopically in the study population, and therefore sparrows were expected to selectively learn conspecific songs. Playbacks of songs elicited vocal responses from nestlings as young as 6 days old, and nestlings responded more to conspecific songs than to songs of the sympatric white-crowned sparrow subspecies. These results suggest that conspecific song templates exist at the onset of song memorization, and this could allow golden-crowned sparrows to learn the songs of their own species correctly despite syntopy with their sister species. I suggest that studying species recognition prior to learning could provide fresh insights into the evolution of reproductive isolation and song divergence.