Vocal Advertising and Sex Recognition in Eared Grebes

As a preliminary display of the Discovery Ceremony, male and female Eared Grebes (Podiceps nigricollis) advertise in bouts of 1-12 calls. Although superficially similar, female Advertising calls were significantly higher in frequency than male calls for all three frequency measures taken. Playback experiments demonstrated that courting males readily distinguished advertising calls of unpaired females from those of unpaired males. When the playback speed of the male calls was increased by 10%, courting males responded to them as though they were female calls, demonstrating that call frequency or duration cues play an important role in sex recognition. Since courting grebes already know the species and sex of their display partner upon hearing its initial, spontaneous advertising, the many elaborate and vigorous pair-formation displays of the Discovery Ceremony of grebes may be functioning in mate choice decisions at more subtle levels.