ORIGINAL ARTICLE Solos, duets and choruses: vocal behaviour of the Rufous-naped Wren (Campylorhynchus rufinucha), a cooperatively breeding neotropical songbird David W. Bradley Æ Daniel J. Mennill Received: 4 September 2008 / Revised: 21 December 2008 / Accepted: 9 February 2009 Ó Dt. Ornithologen-Gesellschaft e.V. 2009 Abstract Vocal communication in duetting and chorusing birds is a growing area of study in avian ecology, yet much remains unknown about temporal and population-level variation in these complex vocal signals. In this study, we describe the acoustic structure and temporal variation in solos, duets, and choruses in the Rufous-naped Wren (Campylorhynchus rufinucha), a cooperatively breeding neotropical passerine. We collected focal recordings of 19 groups to assess both diel and seasonal variation in vocal output, as well as population-wide sharing of vocal signals. We found that birds produce a complex array of vocalisa- tions, including tonal, frequency-modulated syllables grouped into phrases, as well as stereotyped, atonal sounds. Songs are produced as solos or combined into duets and choruses. Solo and duet songs show a dawn chorus effect. Solo song rate, but not duet or chorus rate, varied across breeding stages. The majority of phrases are shared amongst groups, significantly more amongst groups in nearby terri- tories. We suggest that chorus songs may be an important indicator of group identity and may play a role in main- taining group territories, but do not play a role in relation to the breeding cycle. The degree of population-wide phrase- sharing suggests either short-distance dispersal or delayed song learning. This paper is the first fine-scale description of vocal behaviour in this species and enhances our under- standing of group-singing in a complex social environment. Keywords Rufous-naped Wren Á Campylorhynchus rufinucha Á Duet Á Chorus Á Cooperative breeding Introduction Avian vocal duets are coordinated acoustic signals pro- duced by two individuals, usually a mated pair in a long- term pair bond (Farabaugh 1982). Several non-mutually exclusive hypotheses have been proposed for the function of duetting, the most widely supported of which concern joint resource defence, mate defence, paternity defence and as a signal of partner commitment (Hall 2004). These hypothesised functions represent varying levels of coop- eration and conflict between the sexes and help explain the adaptive value of coordinated singing from the perspective of both the male and the female. Although avian duetting has received modest attention, we know less about the adaptive value of avian chorusing. This complex, coordi- nated behaviour occurs when more than two birds combine their vocalisations into an acoustic display (e.g. Seddon 2002; Baker 2004; Hale 2006). Choruses are necessarily more complex than duets because more individuals are involved, each with differing degrees of motivation for conflict or cooperation. It has been suggested that choruses may function similarly to duets, either cooperatively in joint resource defence (Reyer and Schmidl 1988; Brown and Farabaugh 1991; Wingfield and Lewis 1993; Seddon 2002; Baker 2004; Hale 2006) and in maintaining social bonds within the group (Brown et al. 1988), or in conflict Communicated by J. Fjeldsa ˚. D. W. Bradley Á D. J. Mennill Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B3P4, Canada Present Address: D. W. Bradley (&) Department of Biological Sciences, University of Waikato, Gate 1 Knighton Road, Private Bag 3105, Hamilton 3240, New Zealand e-mail: db63@waikato.ac.nz 123 J Ornithol DOI 10.1007/s10336-009-0393-3