Meeting Abstract

36.2  Monday, Jan. 5  Is song length an important signal of aggression in Blue Grosbeaks? LATTIN, Christine; Eastern Kentucky University christine.lattin@tufts.edu

Although investigators have examined how males in some bird species use different songs in their repertoire for different signaling purposes, less is known about how birds alter the characteristics of individual songs to convey different messages. To test the hypothesis that song length is an important signal of aggression for male Blue Grosbeaks (Passerina caerulea), I did playback experiments (n = 15) using short, medium-length and long songs. In addition, I recorded male Blue Grosbeaks (n = 18) from 1 May to 31 July 2007 in natural aggressive contexts ranging from spontaneous advertisement to short-range countersinging with conspecifics. Playback experiments ran from 7-29 July 2007. Playback order was randomly determined, and tests separated by several days. I noted the focal male’s location every 15 s, as well as the closest approach to the playback speaker, number of flights, number of calls (‘chip’ notes), and number of songs. Compared to their response to short and medium-length songs, male Blue Grosbeaks came closer to the speaker (p = 0.0026) and remained closer to the speaker (mean distance; p = 0.0072) during and after playback of long songs, and uttered more songs (p = 0.023) in post-playback. The mean number of syllables per Blue Grosbeak song increased in more aggressive natural contexts (p=0.0002), from a mean of 12.02+/-0.3 syllables/song during spontaneous advertisement to 17.21+/-0.3 syllables/song in short-range aggressive encounters. These results suggest that altering song length is one way male Blue Grosbeaks can signal different levels of aggressive intent to conspecific males.