Data from: Booming far: the long-range vocal strategy of a lekking bird

The pressures of selection acting on transmission of information by acoustic signals are particularly high in long distance communication networks. Males of the North African houbara bustard (Chlamydotis undulata undulata) produce extremely low-frequency vocalisations called ‘booms’ as a component of their courtship displays. These displays are performed on sites separated by a distance of on average 550 m, constituting exploded leks. Here, we investigate the acoustic features of booms involved in species-specific identity. We first assessed the modifications of acoustic parameters during boom transmission at long-range within the natural habitat of the species, finding that the frequency content of booms was reliably transmitted up to 600 m. Additionally, by testing males’ behavioural responses to playbacks of modified signals, we found that the presence of the 1st harmonic and the frequency modulation are the key parameters for species identification, and also that a sequence of booms elicited stronger responses than a single boom. Thus, the coding-decoding process relies on redundant and propagation-resistant features, making the booms particularly well adapted for the long range transmission of information between males. During the booming phase of courtship, two sensory modalities - acoustic and visual - act in synergy. The acoustic component is dominant in the context of intra-sexual competition. While the visual component is not necessary to induce agonistic response, it acts as an amplifier and reduces the time of detection of the signaller. The utilisation of these adaptive strategies allows houbara males to maximize the active space of vocalizations emitted in exploded leks.在远距离声学通信网络中，自然选择压力对声学信号的信息传递过程施加了极强的选择压。北非波斑鸨（Chlamydotis undulata undulata）的雄性个体会发出被称为‘booms’的极低频鸣声，作为其求偶展示的组成部分。这类求偶展示会在平均间距达550米的场地间开展，由此形成了分散求偶场（exploded leks）。本研究旨在探究与物种特异性识别相关的booms鸣声声学特征：我们首先评估了该物种自然栖息地内，booms鸣声在远距离传输过程中的声学参数变化，结果发现其频谱成分可在600米范围内稳定传输。此外，通过测试雄性个体对经过修改的信号回放的行为反应，我们发现第一谐波（1st harmonic）的存在与频率调制（frequency modulation）是物种识别的关键声学参数；同时，连续多段booms鸣声比单段booms鸣声能引发更强的行为反应。由此可见，该鸣声的编码-解码过程依赖于冗余且抗传输衰减的声学特征，使得booms鸣声非常适配雄性个体间的远距离信息传递。在求偶的booms发声阶段，两种感官模态——听觉与视觉——协同发挥作用：在同性种内竞争场景中，听觉信号占据主导地位；尽管视觉信号并非引发争斗反应的必要条件，但它可作为信号放大器，缩短接收者对信号发出者的识别时长。通过运用这些适应性策略，波斑鸨雄性个体能够最大化其在分散求偶场中发出鸣声的有效传播空间。