bird song - loudness vs complexity

[turttle]

I was looking for interesting bird articles, and came across this one. It essentially says that birds trade off loudness of song with complexity - the louder, the less complex, and that the larger the bird, the louder the song (in general). Since loudness affects territory size, but complexity can convey information, there are interesting evolutionary trade-offs.

Loudness of birdsong is related to the body size, syntax and phonology of passerine species - CARDOSO - 2009 - Journal of Evolutionary Biology - Wiley Online Library

Loudness of birdsong is related to the body size, syntax and phonology of passerine species

1. G. C. CARDOSO

Abstract

Songs of passerines are generally complex, long-range acoustic signals, and are highly diverse across species. This diversity must nevertheless be shaped by the capabilities of the avian vocal physiology. For example, within species, loudness has been shown to trade-off with aspects of song complexity. Here, I ask if such trade-offs with loudness influenced the evolutionary diversification of song among passerines. Comparing perceived song loudness across > 140 European and North American species showed that loudness is positively related to body size and to singing with simple trilled syntax, and negatively related to aspects of syllable complexity. Syntax and syllable phonology together explained more variation than body size did, indicating that the acoustic design of songs is an important factor determining loudness. These results show for the first time that loudness covaries with, and possibly limits, song complexity across species, suggesting that a trade-off with loudness shaped the evolutionary diversification of passerine song.