Body size limits low-frequency songs.

<p>a) Low-frequency trill song types (Trills 1, 2 and 3) were sung at lower frequencies by large than small males (regression line: y = −0.58x+17.49). Points represent mean peak frequency for each male, including Trills 1, 2 and 3. b) The lower bound of the relationship between frequency and body size had a negative slope (y = −0.51x+15.60, regression line fitted through black points, with minimum frequency in each tarsus length bin, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056717#s2" target="_blank">Methods</a>). Each point represents a song. c) Tarsus length does not predict the mean frequency of all a male's trill song types (y = 0.17x+0.77). Points represent mean peak frequency for each male, including all trill types.