Variation in singing behaviour reveals possible functions of song in male golden whistlers

Abstract

Male song has been shown to have two major functions, repelling rivals and attracting mates. Yet much debate still exists as to what extent male singing strategies have been influenced by selection pressures imposed by each sex. I use a combination of song recordings and playbacks to investigate how male competition and female choice may have shaped song structure and behaviour in migratory golden whistlers (Pachycephala pectoralis). Song output was low during territory establishment but increased dramatically when breeding commenced. Singing during the female fertile period may be an effective paternity guard against potential cuckolders. During this period, males decreased their song output when more neighbouring females were fertile, possibly reflecting an inability to concurrently guard a mate and pursue extra-pair fertilisations. However, high singing rates were maintained after the fertile period, suggesting that males may also sing to attract extra-pair copulations. Song repertoire size increased with male age and may signal male quality. Repertoires included two broad song-types: simple 'whistle' songs and more complex 'melodic' songs. Whistle songs were often sung by breeding males and may be more effective at broadcasting information at long-distances. In contrast, melodic songs were commonly sung in close-range male encounters and may contain more information about signaller quality. During vocal contests, males exhibited a range of countersinging behaviours, including song-type switching, song-type and frequency-matching, and song overlapping, which may reflect a hierarchical mode of signalling aggression. Each sex may have imposed different selection pressures on the vocal output of male golden whistlers.