Duetting behavior in a Neotropical ovenbird: sexual and seasonal variation and adaptive signaling functions

Abstract

Duetting is a collective behavior and might have multiple functions, including joint territory defense and mate guarding. An important step toward understanding the adaptive function of bird song is to determine if and how singing behavior varies seasonally. However, seasonal patterns for duetting species are different from the pattern described for species in which only the male sings, because song function may vary according to sex, singing role (initiator vs responder) and level of duet organization (individual vs pair). We investigated whether patterns of seasonal variation in duetting depends on these factors, which would suggest different interpretations of song function. We studied social pairs of a Neotropical bird species (rufous hornero Furnarius rufus) for seven consecutive months, recording vocal and territorial behaviors. Overall, partners coordinated 61% of their songs into duets and many song traits (song initiation rate, song output and duet rate) peaked in territorial contexts. Males engaged in territorial interactions with strangers more often, initiated more songs, and answered proportionately more of their partners’ songs than females. Male song initiation rate peaked during the pre‐ and post‐breeding stages, whereas females initiated more songs during the non‐breeding season. Both sexes answered partner songs faster and at higher rates during the pre‐breeding and female fertile stages. Partners duetted at a higher rate during the pre‐ and post‐breeding stages. Finally, song initiation rates and duet rate, but not song answering rates, correlated with frequency of territorial interactions with strangers. Although our findings indicate that song function may vary with sex, singing role and level of duet organization, our results suggest that in general duet functions to defend common territories and as a mutual mate guarding strategy in the rufous hornero.

Partners coordinate territorial defense against simulated intruders in a duetting ovenbird

“…Rufous hornero males initiated most songs, answered partner‐initiated songs more promptly and sang longer phrases in duets than did females in both aggressive and nonaggressive contexts (Diniz, Silva‐Jr, et al, ). This suggests that males have a primary role in territory defense (Brumm & Goymann, ).…”

“…Both parents contribute equally to parental care (Massoni, Reboreda, López, & Aldatz, ). Juveniles delay dispersal, staying in their parents' territories from four to nine months (Diniz, Silva‐Jr, et al, ; Fraga, ).…”

“…Sound spectrograms of female solo (a), male solo (b), and duet (c, female phrase in red, male phrase in blue) in the rufous hornero. Adapted from Diniz, Silva‐Jr, et al (), Diniz et al ()…”

“…Sexual conflict is presumably less intense in the nonbreeding season than in the breeding season, which makes this an adequate season to study the coordination between partners in territory defense (e.g., Hall & Peters, ). Moreover, territorial interactions (number and duration) do not vary between breeding and nonbreeding seasons for both sexes in the rufous hornero (Diniz, Silva‐Jr, et al, ). Studied adults were molecularly sexed ( n = 30) or had their sexes assigned based on their partner's sex ( n = 2).…”

“…We did not quantify song answering rate (Logue, ) since the birds emitted only 1.89 ± 1.10 songs/trial (mean ± SD , n = 122 songs, 61 trials). We classified as song initiator the bird that started a song before its partner (Hall & Peters, ), regardless of whether it was answered (i.e., duets or chorus) or not (i.e., solos) by its partner (Diniz, Silva‐Jr, et al, ). The song responder was the bird that sang after its partner had sung, thus creating a duet or chorus (Logue & Krupp, ).…”