Animal songs differ from calls in function and structure, and have comparative and translational value, showing similarities to human music. Rhythm in music is often distributed in quantized classes of intervals known as rhythmic categories. These classes have been found in the songs of a few nonhuman species but never in their calls. Are rhythmic categories song-specific, as in human music, or can they transcend the song–call boundary? We analyze the vocal displays of one of the few mammals producing both songs and call sequences: Indri indri. We test whether rhythmic categories (a) are conserved across songs produced in different contexts, (b) exist in call sequences, and (c) differ between songs and call sequences. We show that rhythmic categories occur across vocal displays. Vocalization type and function modulate deployment of categories. We find isochrony (1:1 ratio, like the rhythm of a ticking clock) in all song types, but only advertisement songs show three rhythmic categories (1:1, 1:2, 2:1 ratios). Like songs, some call types are also isochronous. Isochrony is the backbone of most indri vocalizations, unlike human speech, where it is rare. In indri, isochrony underlies both songs and hierarchy-less call sequences and might be ancestral to both.

中文翻译：

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等时性是灵长类动物呼叫和唱歌的祖先条件


动物歌曲在功能和结构上与叫声不同，具有比较和翻译价值，与人类音乐表现出相似之处。音乐中的节奏通常分布在称为节奏类别的量化音程类别中。这些类别在一些非人类物种的歌曲中被发现，但从未在它们的叫声中被发现。节奏类别是特定于歌曲的，就像人类音乐一样，还是可以超越歌曲的界限？我们分析了少数既能发出歌曲又能发出叫声的哺乳动物之一：Indri indri。我们测试节奏类别 (a) 在不同上下文中生成的歌曲中是否保守，(b) 存在于呼叫序列中，以及 (c) 歌曲和呼叫序列之间是否存在差异。我们表明节奏类别出现在声音表现中。发声类型和功能调节类别的部署。我们在所有歌曲类型中都发现了等时性（1:1 比例，就像滴答作响的时钟的节奏），但只有广告歌曲显示出三种节奏类别（1:1、1:2、2:1 比例）。与歌曲一样，某些呼叫类型也是同步的。等时性是大多数 indri 发声的支柱，这与人类语言不同，在人类语言中这种情况很少见。在 indri 中，等时性是歌曲和无层次调用序列的基础，并且可能是两者的祖先。