Voice Breaking in Males Results in Sexual Dimorphism of Green Woodhoopoe Calls

Abstract

Summary Ontogenetic changes and sexual differences in the acoustic structure of green woodhoopoe (Phoeniculus purpureus) ‘kek’ calls were investigated in a wild population. At fledging, the calls of males and females were indistinguishable in terms of fundamental frequency, frequency modulation, peak frequency and call duration. After 3-5 months, however, the male voice ‘broke’ (i.e. underwent a significant decrease in fundamental frequency), while there was no change in female call structure. Consequently, the fundamental frequency of adult male calls was 48% lower than that of adult females, and there was no overlap in the call frequencies of the sexes in adulthood. The change in male voice occurred within a 23 week period and no intermediate call frequencies were recorded. The timing of the voice break did not correspond with a change in overall body size, suggesting that growth of the syrinx was not the proximate cause. However, it did coincide with the stage in development when male bill length grew to exceed that of all females and when males began to lose their distinctive brown throat patch, providing some indirect evidence that hormonal control may be important.