Abstract
In mammals, complex songs are uncommon and few studies have examined song composition or the order of elements in songs, particularly with respect to regional and individual variation. In this study we examine how syllables and phrases are ordered and combined, ie “syntax”, of the song of Tadarida brasiliensis, the Brazilian free-tailed bat. Specifically, we test whether phrase and song composition differ among individuals and between two regions, we determine variability across renditions within individuals, and test whether phrases are randomly ordered and combined. We report three major findings. First, song phrases were highly stereotyped across two regions, so much so that some songs from the two colonies were almost indistinguishable. All males produced songs with the same four types of syllables and the same three types of phrases. Second, we found that although song construction was similar across regions, the number of syllables within phrases, and the number and order of phrases in songs varied greatly within and among individuals. Last, we determined that phrase order, although diverse, deviated from random models. We found broad scale phrase-order rules and certain higher order combinations that were highly preferred. We conclude that free-tailed bat songs are composed of highly stereotyped phrases hierarchically organized by a common set of syntactical rules. However, within global species-specific patterns, songs male free-tailed bats dynamically vary syllable number, phrase order, and phrase repetitions across song renditions.
Highlights
The use of vocal displays by animals to defend territories and attract females is widespread [1,2]
In this paper we examine composition and phrase order, ie ‘‘syntax’’ of male Brazilian free-tailed bat song (Tadarida brasiliensis)
Song Characteristics We examined 319 songs from 17 bats in Austin and 93 songs from 16 bats in College Station, for a total of 412 songs from 33 bats
Summary
The use of vocal displays by animals to defend territories and attract females is widespread [1,2]. Among vertebrates these vocalizations most often take the form of simple repetitions of one or a few syllables and are generally referred to as mating or advertisement ‘‘calls’’. Songs are often hierarchically organized where notes are combined into syllables, syllables into motifs and motifs into phrases with multiple layers of repetition or periodicities [7,8] While these features are common in birds, evidence of hierarchical syntax in mammals is scarce
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