March 9 2010

12:00 BSRB 154

Ecolunch: Kazutoshi Sasahara
UCLA Ecology and Evolutionary Biology

Structural design principles of a complex birdsong


Birdsong is an acoustic signal primarily used in male-male aggression and also in male-female attraction. Some songbirds, such as the Brown Thrasher and the Sage Thrasher, sing extremely-complex song consisting of an immense variety of syllable types. What structural design principles work on such complex birdsong? This is an important question for the evolution of animal communication systems, yet little is known. This is because previous studies more focused on repertoire size (the number of different syllable types) as a measure of song complexity rather than song structure (the organization of syllables).
One obvious fact is that diverse syllable types are arranged in a sequence; neither uniformly nor randomly, but in an interesting way.
Here we explore structural design principles underlying complex birdsong through two types of network analyses of California Thrasher song. We will find that the song network---transition relationships among different syllable types has a `small-world' architecture where groups of syllable types are sparsely connected, and also has a well-balanced constitution of deterministic and non-deterministic `transition motifs' (local transition types) than that of random networks which lack any structural design principles. Furthermore, we will show that the singing dynamics on the song network can be attributed mainly to a first-order Markov process. These findings suggest an ingenious song structure, which may be evolutionary-shaped and individually-tuned, for efficiently producing song complexity, a key factor in animal communication.















































































































































































































































































































































































































































































































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