Bats Follow Musical Rules When Writing Love Songs

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Making a mix of love songs for your special someone? Looking for something lively to slip in between Sonny and Cher's "I Got You Babe" and The Temptations' "My Girl"? I highly recommend a little number called "Chirp-Buzz-Buzz" by...a group of Brazilian free-tailed bats.

Turns out that bats are quite the romantic crooners, using "love song" vocalizations to attract females (and in some cases, to scare away intruding males). According to a new study*, their love songs are more complex than previously thought and have a number of musical rules. The researchers—from the Department of Biology at Texas A&M University, the Section of Neurobiology at the University of Texas at Austin and Bat World, a bat sanctuary and rehabilitation center in Mineral Wells, Texas—spent close to four years recording and analyzing the songs of two populations of Brazilian free-tailed bats (also known as Mexican free-tailed, scientific name Tadarida brasiliensis). The first group was a captive colony of about 60 bats in Austin, maintained by one of the study's authors. The second group was a wild colony of approximately 100,000 to 250,000 bats within Texas A&M's athletic complex in College Station.

After examining a total of 412 songs from 33 bats and comparing song variation within and across individuals and between the two different colonies, the researchers determined the male bats use several types of syllables with  individual sounds to create three easily recognizable phrases:

Chirps are complex phrases composed of "A" and "B" syllables**.
*
Trills are composed of short (mean = 3.4 ms) downward FM syllables that can be connected or are separated by short silent intervals.
*
Buzzes are composed of short (3 ms) downward FM syllables that are never connected.

These phrases, in turn, are used in different combinations to produce songs. The researchers found that particular phrase sequences kept coming up and identified several rules governing phrase order:

1) Songs begin almost exclusively with chirps.

2) Trills do not follow buzzes, but instead always follow chirps or another trill.

3) The majority of buzzes (90%) are followed by another buzz or occur at the end of the song (songs containing a buzz ended in a buzz 84 % of the time).

This may not seem like very impressive music theory, but complex songs and specific structural "language rules" are rare among mammals; previous mammalian research hasn't gone much further than determining that song elements are used in a non-random order. These bats' songs and the rules that govern them, though, may be "more analogous to those of some birds than to other mammals," say they researchers. Birds and their songs have long been the basis for understanding vocal production and the evolution of vocal complexity as well as the physiology of vocal production. With this new study, there's a foundation for future research into mammalian vocals, "a model not only to study communication similarities in other animals, but also human speech," says lead author Kirsten M. Bohn.

Here's a video featuring the vocal stylings of Sid the bat, with commentary by researcher Dr. George Pollak:

* Bohn KM, Schmidt-French B, Schwartz C, Smotherman M, Pollak GD. (2009). Versatility and Stereotypy of Free-Tailed Bat Songs. PLoS ONE 4(8):e6746. doi:10.1371/journal.pone.0006746

** "A" syllables are short (5 ms) downward frequency modulated (FM) sweep syllables. "B" syllables are longer (17ms) and more complex, often beginning with an upward FM followed by a longer downward FM and sometimes ending with another upward FM.

October 20, 2009 - 6:24am
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