Frequent duets, rare choruses, and extremely rare solos: year-round singing behavior in Chubb’s Cisticola

Abstract

Our current understanding of the function of coordinated acoustic displays usually comes from studies conducted over a short period of the breeding season. However, the function of particular types of vocalizations may vary according to sex and context, and such displays can extend beyond the time of reproduction. To fully understand this phenomenon, analyses of year-round singing behavior are required. In the current study, we focused on a small, year-round territorial Afrotropical songbird, Chubb’s Cisticola (Cisticola chubbi). We analyzed the structure of songs during the breeding season as well as year-round changes in the proportion of solos, duets, and choruses to investigate the potential function(s) of each type of vocalization. We found that: (1) females produced whistling notes, while males generated trilling ones; (2) up to five individuals formed coordinated choruses, and (3) individuals were always near to each other during cooperative singing. Over the course of a year, the majority of syllables recorded were duets (82%), with rarer choruses (16%) and extremely rare solos (2%). Outside of the breeding season, males produced the most solos, while females produced more at the beginning of the breeding season. The proportion of choruses was highest at the end of breeding season. Frequent year-round production of duets and choruses strongly supports territory defense as the main function of joint singing, while the highest proportion of choruses at the end of the breeding season suggests that offspring take part in the chorus. To better understand cooperative singing, it is essential to extend our looking beyond the breeding season.

Seasonally variable and sex‐specific motivation for cooperative resource defence in a duetting songbird—The Chubb's cisticola

“…Recordings were collected in 2013–2014 using directional microphones (Sennheiser ME67 with K6 power module) connected to digital recorders (Marantz PMD 620 or Olympus LS‐10; WAV files, 48 kHz/16‐bit sampling rate). In Chubb's cisticola solo songs are sung extremely rarely (Budka et al, 2023), thus obtaining recordings of this type of vocalisation was our limitation. Therefore, we used recordings of six solo males, six solo females and six duets to prepare experimental sound samples (five syllables from each individual/pair; removed background noise by using band‐pass filter = 0.5 kHz, normalised peak amplitude to 90%; Figure 1).…”

“…Only .7% of all recorded songs were solos, while most solo syllables were combined with duets and choruses within a song. Chubb's cisticola appears to be a species in which the share of solo syllables is one of the lowest in duetting birds (<2% of syllables sung unprovoked by playback (Budka et al, 2023), 4% in conflict interactions), which suggests a strong evolutionary pressure for cooperation (Keenan et al, 2020). Unfortunately, we were not able to find the unique signal used by birds for clustering.…”

“…Sometimes the birds dispersed in dense vegetation which obstructed visual cues produced as typical contact signals before a cooperative response. Therefore, we hypothesise that when birds are far away from each other they use calls to locate group members in space but in the close distance they may use visual signals (wing and tail movements; Budka et al, 2023) to coordinate a duet. Such behaviour gives evidence against the maintaining contact as a duet function hypothesis and supports other explanations, such as signalling quality, signalling commitment or joint resource defence (Hall, 2004).…”

“…The Chubb's cisticola inhabits open and semi‐open habitats in Afrotropical highlands. Birds live in pairs or groups of a few individuals and defend territories year‐round (Budka et al, 2023; Ryan, 2020). The biology and ecology of Chubb's cisticola are poorly known.…”

“…However, solo syllables can be found in songs containing duet and chorus syllables (ca 2% of syllables), suggesting that in some parts of a song the mate does not follow the song of their partner. The proportion of solo syllables in naturally vocalising birds is the highest at the beginning of the breeding season in the case of females, while males produce most solos at the end of the breeding season (Budka et al, 2023).…”