RESULTS
The phylogenetic signal of individual song traits varied from
moderateehigh (0.48 < l < 0.82 for four traits) to very low (l < 0.1
for eight traits, Table 1). PCA on the song measurements returned
four PCs with eigenvalues larger than random. These four PCs
explained 66% of the song variation across species (eigenvalues and
trait loadings for the individual PCs are given in Table 1). High PC1
scores indicate mostly long songs with complex syllables; high PC2
scores indicate songs with fast syllable rate; high PC3 scores indicate
acoustically dense songs (high proportion of sound) with few
trills; high PC4 scores indicate mostly long songs. PC scores for each
species are in the Supplementary Material and are illustrated
graphically in Fig. 1a. Scores of PCs 1 and 4 had high or moderate
phylogenetic signal (l ¼ 0.72 and 0.51, respectively), and scores of
PCs 2 and 3 had very low signal (both l ¼ 0.03).