Relationships among male size, reproductive success, female choice and male advertising calls in Little Penguins (Eudyptula minor)

The role of male acoustic features in the process of mate choice was investigated in Little Penguins (Eudyptula minor). Male call features and the calling behaviour may reveal important information on male attributes that could affect female choice. Larger males showed more aggressive behaviour to simulated nest intruders than smaller males. Chicks of larger males also grew at a faster rate than those of smaller ones, possibly because of differences in the quality of food delivered to chicks or paternal genetic effects on chick growth. However, there were no differences in fledging age, mass or success between larger and smaller males. Larger males also appeared to occupy or select better nest site; they occupied low and middle elevation nesting sites in comparison to smaller males, probably because the sites reduce energetic costs of walking on land. Larger males also mated earlier in the breeding season than smaller ones, suggesting that females may prefer larger males. Thus, male body size may play an important role in the attraction of potential mates in Little Penguins. Acoustic signals can influence female responses to males particularly in nocturnal seabirds. Larger males were found to produce lower-pitched call elements in their exhalation phrases than smaller males. In playback experiments with two loudspeakers, females did not distinguish low from high-pitched calls, although they responded vocally only to low-pitched calls. In another experiment, using current mate and stranger calls, females were more likely to approach their partners’ call and responded vocally only to their current partners, regardless of the stranger’s call pitch and, therefore, apparent size. Females may recognise their partners’ call and maintain mate fidelity even when larger, potentially more successful, strangers are presented. In addition to the effect of call pitch, calling patterns of males could influence female choice. By conducting experiments with a dual-speaker design in which calls from one speaker consistently overlapped those from the other speaker, I found that females approached overlapping advertising calls more than overlapped calls or a silent control speaker. The ‘masking effects’ of call overlap may obscure information that females require for mate choice. Alternatively, females may simply be able to locate overlapping calls more easily. It is possible that call overlap is associated with dominance or other quality indicators of the callers; thus, females may approach overlappers more often because they represent higher quality mates. My results indicate that acoustic signals can reflect the qualities of the males and that female Little Penguins may prefer larger males to enhance their reproductive potential