Different vocal signals, but not prior experience, influence heterospecific from conspecific discrimination

Efficient communication between animals requires specificity to ensure that animals distinguish relevant signals from background noise. Research on discrimination between the acoustic signals of heterospecific versus conspecific animals, especially in birds, has focused on the songs produced by breeding males, in spite of the fact that animals produce other types of acoustic signals such as calls and duets. We used acoustic playback experiments to evaluate whether tropical white-eared ground-sparrows, Melozone leucotis, use calls, male solo songs and duets to discriminate conspecific from heterospecific competitors. We also evaluated whether prior experience influences competitors' discrimination by comparing responses among populations of white-eared ground-sparrows that are allopatric and sympatric with a congeneric competitor species (Prevost's ground-sparrows, Melozone biarcuatum). White-eared ground-sparrows displayed more intense responses to conspecific vocalizations than they did to congeneric vocalizations. The duets produced in response to conspecific playback exhibited higher bandwidth and maximum frequency, lower minimum frequency and longer duration than duets produced in response to heterospecific playback. These results suggest that white-eared ground-sparrows use information encoded in vocalizations to discriminate competitors from noncompetitor species. The observed responses were not influenced by previous experience; white-eared ground-sparrows displayed similar responses whether they lived in sympatry or allopatry with the congener simulated through playback. Our results expand our understanding of how animals use different types of vocalizations to discriminate conspecific from heterospecific signals.

► We played conspecific and heterospecific calls, solos and duets to ground-sparrows.
► Playback of calls and solos incited little aggression in white-eared ground-sparrows.
► Conspecific and congeneric duets incited the most aggressive responses.
► Acoustic features of duets sung after playback reveal conspecific discrimination.
► Even populations living in allopatry showed conspecific discrimination.