Female koalas prefer bellows in which lower formants indicate larger males
Benjamin D. Charlton a,*, William A. H. Ellis b, Jacqui Brumm c, Karen Nilsson c, W. Tecumseh Fitch a
a Department of Cognitive Biology, University of Vienna, Vienna, Austria
b Koala Research Centre of Central Queensland, Central Queensland University, Rockhampton, Queensland, Australia
c Lone Pine Koala Sanctuary, Brisbane, Queensland, Australia
Despite an extensive literature on the role of acoustic cues in mate choice little is known about the specific vocal traits that female mammals prefer. We used resynthesis techniques and playback experiments to examine the behavioural responses of oestrous female koalas, Phascolarctos cinereus, to male bellows in which a specific acoustic cue to body size, the formants, were modified to simulate callers of different body size. Oestrous females looked longer towards, and spent more time in close proximity to, loudspeakers broadcasting bellows simulating larger male koalas. These findings suggest that female koalas use formants (key components of human speech) to select larger males as mating partners, and represent the first evidence of a marsupial mating preference based on a vocal signal. More generally, these results indicate that intersexual selection pressures to lower formants and exaggerate size are present in a marsupial species, raising interesting questions about the evolutionary origins of formant perception.