Behavioral Ecology Advance Access published online on August 23, 2007
Behavioral Ecology, doi:10.1093/beheco/arm078
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Inferring performance in the songs of dark-eyed juncos (Junco hyemalis)
a Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA b Department of Biology, Indiana University, 1001 East 3rd Street, Bloomington, IN 47405, USA
Address correspondence to G.C. Cardoso. E-mail: cardoso{at}uchicago.edu.
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Abstract |
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Within bird species, songs differ in their attractiveness to females or effectiveness in male–male interactions. Some songs are more difficult to sing than others, and receivers may use a singer's performance of difficult songs as a means for evaluating the quality of the singer. The concept of song performance aims at quantifying how physiologically demanding are different songs. Using variation between song types of dark-eyed juncos, Junco hyemalis, we show that some song traits trade off with costly aspects of song output—short intervals between syllables or loud sound amplitude—suggesting that those traits are difficult to sing. First, after controlling for other traits, long syllables require longer intervals for recovery. This supports the idea that a measure of "respiratory performance" could be based on the relative lengths of syllables and intervals. Second, some syllable traits trade off strongly with sound amplitude, suggesting that these traits may be difficult to sing at high amplitudes. The ratio of frequency bandwidth and trill rate has been used to infer performance in other bird species, but we found no evidence that frequency bandwidth trades off with any aspect of song output in the junco. The negative association of bandwidth with trill rate may instead be a passive consequence of syllable length, with longer syllables randomly accumulating frequency modulation. We conclude that bird receivers may best evaluate how well a song is performed if they integrate multiple cues and discuss how researchers may similarly devise measures of song performance.
Key words: bird song, dark-eyed junco, Junco hyemalis, song performance.
Received 23 February 2007; revised 18 July 2007; accepted 20 July 2007.
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