1. Birdsong is used in reproductive context and, consequently, has been shaped by strong natural and sexual selection. The acoustic performance includes a multitude of acoustic and temporal characteristics that are thought to honestly reveal the quality of the singing individual.
2. One major song feature is frequency and its modulation. Sound frequency can be actively controlled, but the control mechanisms differ between different groups. Two described mechanisms are pressure-driven frequency changes in suboscines and control by syringeal muscles in oscines.
3. To test to what degree these different control mechanisms enhance or limit the exploitation of frequency space by individual species and families, we compared the use of frequency space by tyrannid suboscines and emberizid/passerellid oscines.
4. We find that despite the different control mechanisms, the songs of species in both groups can contain broad frequency ranges and rapid and sustained frequency modulation (FM). The maximal values for these parameters are slightly higher in oscines.
5. Furthermore, the mean frequency range of song syllables is substantially larger in oscines than suboscines. Species within each family group collectively exploit equally broadly the available frequency space.
6. The narrower individual frequency ranges of suboscines likely indicate morphological specialization for particular frequencies, whereas muscular control of frequency facilitated broader exploitation of frequency space by individual oscine species.

中文翻译：

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雀类不同频率控制机制及频率空间的开发

1. 鸟鸣用于生殖环境，因此受到强烈的自然选择和性选择的影响。声学表演包括许多声学和时间特征，这些特征被认为可以诚实地揭示歌唱者的素质。
2. 歌曲的一大特点是频率及其调制。可以主动控制声音频率，但不同组之间的控制机制不同。两种描述的机制是 suboscines 中的压力驱动频率变化和 oscines 中的注射器肌肉控制。
3. 为了测试这些不同的控制机制在多大程度上增强或限制了单个物种和家庭对频率空间的利用，我们比较了 tyranid suboscines 和 emberizid/passerellid oscines 对频率空间的使用。
4. 我们发现，尽管控制机制不同，但两组物种的歌曲都可以包含广泛的频率范围和快速且持续的频率调制 (FM)。这些参数的最大值在 oscines 中略高。
5. 此外，oscines 中歌曲音节的平均频率范围比 suboscines 大得多。每个科群内的物种共同利用同样广泛的可用频率空间。
6. suboscines 较窄的个体频率范围可能表明特定频率的形态专业化，而对频率的肌肉控制促进了个体 oscine 物种对频率空间的更广泛利用。