Versatility and Stereotypy of Free-Tailed Bat Songs

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.

Syntactic structure and geographical dialects in the songs of male rock hyraxes

“…Similar studies of call syntax among mammals are very rare, and geographical dialects have been demonstrated mostly with acoustic rather than syntactic features. Campbell [49] and May-Collado & Wartzok [50] used inflection points in the spectral contour of dolphin whistles to compare geographically distinct populations, and Bohn [17] used a Markov model to quantify the syntax of bat syllables, which is probably the closest technique to ours. Some studies have analysed simple syntax in primate vocalizations by comparing the transition frequencies between notes [20,21].…”

“…Some bats show a syntactic vocal repertoire that is of a complexity similar to that of birds [17]. Cetaceans also exhibit complex vocal communication [2], including syntactic structure [18].…”

Isolation calls of the bat Saccopteryx bilineata encode multiple messages

“…Hyrax song encodes information about body weight, size, body condition, hormonal levels and social status in different song elements (Koren & Geffen, 2009). The above mentioned studies and others (e.g., Bohn et al, 2009;Jahelková et al, 2008;Müller & Manser, 2008;Templeton et al, 2005) demonstrate that the temporal segregation of information occurs in vocalizations under both natural selection and sexual selection pressures.…”

Los sistemas combinatorios animales no tienen dualidad: Hockett tenía razón

“…Al descubrimiento de este sistema se fueron añadiendo paulatinamente otros, como los de los tamarinos algodonosos (Cleveland y Snowdon, 1982), monos capuchino (Robinson, 1984), gibones (Mitani y Marler, 1989), murciélagos (Kanwal et al, 1994;Bohn et al, 2009), y, muy recientemente, damanes roqueros (Kershenbaum et al, 2012). El hallazgo sucesivo de esos sistemas fue muy sorprendente, dada su gran semejanza estructural con la organización del lenguaje.…”

“…Por todo ello, y teniendo en cuenta que no todas las combinaciones son posibles, algunos autores han aplicado al procedimiento jerárquico-combinatorio del canto de los pájaros el término de 'gramática' (Anderson, 2004;Snowdon, 1993). Esto mismo rige para el resto de sistemas, como por ejemplo el canto de los murciélagos: en su estudio de una población de murciélagos cola de ratón (Tadarida brasiliensis), Bohn et al (2009) señalan que "free-tailed bat songs are composed of highly stereotyped phrases hierarchically organized by a common set of syntactic rules" (Bohn et al, 2009: 1). De hecho, esos autores muestran que los murciélagos forman sus cantos mediante tres tipos de frases (píos, trinos y zumbidos), y la combinatoria del sistema se rige por tres reglas básicas: (1) el canto siempre empieza con píos, (2) un trino no sigue a un zumbido, y (3) el zumbido se emite en la parte final del canto.…”