Species-Specific Auditory Forebrain Responses to Non-Learned Vocalizations in Juvenile Blackbirds

Abstract

Species recognition mediates the association of individuals with conspecifics. Learned cues often facilitate species recognition via early social experience with parents and siblings. Yet, in some songbirds, the production of species-typical vocalizations develops in the absence of early social experiences. Here, we investigate the auditory-evoked neural responses of juvenile red-winged blackbirds (Agelaius phoeniceus), a nonparasitic (parental) species within the Icterid family and contrast these results with a closely related Icterid parasitic species that lacks parental care, the brown-headed cowbird (Molothrus ater). We demonstrate that immediate early gene (IEG) activity in the caudomedial mesopallium (CMM) is selectively evoked in response to conspecific non-learned vocalizations in comparison to 2 types of heterospecific non-learned vocalizations, independent of the acoustic similarity patterns between the playback stimuli. This pattern, however, was not detected in the caudomedial nidopallium (NCM). Because the red-winged blackbird is a parental species, the conspecific non-learned vocalization is presumably a familiar sound to the juvenile red-winged blackbird, whereas the heterospecific non-learned vocalizations are novel. We contrast results reported here with our recent demonstration of selective IEG induction in response to non-learned conspecific vocalizations in juvenile parasitic brown-headed cowbirds, in which conspecific non-learned vocalizations are presumably novel. In this case, selective IEG induction from conspecific non-learned vocalization occurred within NCM but not within CMM. By comparing closely related species with stark differences in the early exposure to conspecifics, we demonstrate that CMM and NCM respond to familiar vs. novel non-learned vocalizations in a manner that parallel previously reported regional responses to learned vocalizations such as conspecific songs.