Structure and functions of Yellow-breasted Boubou (Laniarius atroflavus) solos and duets

Abstract

Background Birds have extremely well-developed acoustic communication and have become popular in bioacoustics research. The majority of studies on bird song have been conducted in the temperate zones where usually males of birds sing to attract females and defend territories. In over 360 bird species mostly inhabiting the tropics both males and females sing together in duets. Avian duets are usually formed when a male and female coordinate their songs. We focused on a species with relatively weakly coordinated duets, with male solo as the prevailing vocalisation type. Methods Instead of analysing a set of recordings spread over a long time, we analysed whole day microphone-array recordings of the Yellow-breasted Boubou (Laniarius atroflavus), a species endemic to West African montane rainforests. We described the structure of the solo and duet vocalisations and temporal characteristics of daily activity based on 5,934 vocal bouts of 18 focal pairs and their neighbours. Results Birds had small, sex specific repertoires. All males shared three types of loud whistles functioning as song type repertoires in both solos and duets. Females vocalised with five types of harsh, atonal notes with a more variable and usually lower amplitude. Three of them were produced both as solos and in duets, while two seem to function as alarm and excitement calls given almost exclusively as a solo. Solos were the most common vocalisation mode (75.4%), with males being more vocally active than females. Duets accounted for 24.6% of all vocalisations and in most cases were initiated by males (81%). The majority of duets were simple (85.1%) consisting of a single male and female song type, but altogether 38 unique duet combinations were described. Males usually initiated singing at dawn and for this used one particular song type more often than expected by chance. Male solo and duet activities peaked around dawn, while female solos were produced evenly throughout the day. Discussion Yellow-breasted Boubou is a duetting species in which males are much more vocal than females and duetting is not a dominating type of vocal activity. Duet structure, context and timing of daily production support the joint resource defence hypothesis and mate guarding/prevention hypotheses, however maintaining pair contact also seems to be important. This study provides for the first time the basic quantitative data describing calls, solos and duet songs in the Yellow-breasted Boubou.

Yellow‐breasted Boubous (Laniarius atroflavus) jointly defend territories with male‐led duets against stranger pairs, males and females

“…Males and females are sexually monochromatic and inhabit dense natural forest undergrowth as well as human changed habitats such as the edge of clearings or secondary scrubs (Borrow & Demey, 2014; Fry, 2020; Riegiert et al., 2004; Stuart, 1986). Birds vocalise both in solos and in duets and defend year‐round territories (Fry, 2020; Riegiert et al., 2004; Wheeldon et al., 2020). Their song repertoire is very small, and males produce three discrete types of short, tonal songs, with females producing three types of atonal harsh notes.…”

“…All categories of song phrases are produced as solos (~75% of vocal activity) and are also used in duets (~25% of vocalizations), with males being much more vocal than females. Males produce more solos than females and lead about 81% of duets (Wheeldon et al., 2020). When they sing in duets, the male and female can be at very different distances from each other.…”

“…In particular, notes were taken for location where simultaneous neighbouring pairs were heard, in order to identify the boundaries of territories. In 2014, we also used an 8‐channel microphone array which recorded birds in each territory a day before experiments as well as during and after experiments with each pair (details of natural singing extracted from array recordings are presented in Wheeldon et al., 2020). This approach has significantly helped to understand territorial behaviour of the studied species.…”

“…Usually, during or just after the experiment, neighbours would vocalise from their own territories. In addition to these observations, a visual inspection of spectrograms allowed for the comparison of songs between treatment which indicated that the same pairs were tested in the following attempts (see Wheeldon et al., 2020 for methods).…”

“…In this study, we focused on the Yellow‐breasted Boubou which is endemic to montane, rainy forests of Cameroon and Nigeria (W Africa). The acoustic communication of this species comprises of both male and female solos as well as duets (Fry, 2020; Riegiert et al., 2004; Wheeldon et al., 2020).…”