Cisticola erythrops do not sing distinct song types, but instead combine syllables to form a wide variety of vocal productions. Across the entire geographical range, C. erythrops individuals constructed mixed syllable songs (a,c) which included multiple syllable types arranged in variable orders, and repeated syllable songs (b) which included one or more repeated syllable type(s). Individuals across the entire geographical range also sang both song types in duets or choruses with conspecifics (c). Mixed syllable songs lasted an average of 8.4 ± 6.4 s (but could be up to 319 s long) and were delivered at a rate of 3.62 ± 0.7 syllables s−1. Repeated syllable songs were significantly more brief (t46 = 4.25, p < 0.0001), lasting only for 2.4 ± 1.1 s, but were delivered at a nearly identical rate (t46 = 0.092, p = 0.927) of 3.6 ± 1.1 syllables s−1. Song duration and production rate did not differ geographically (duration: F1,46 = 4.00, p = 0.051, rate: F1,46 = 1.23, p = 0.273).
Three types of songs sung by Cisticola erythrops: (a) mixed syllable song; (b) repeated syllable song; (c) a chorus of mixed syllable songs.
We identified 48 syllable types produced by C. erythrops and found that individuals used up to 14 syllable types in a single singing bout. Because sampling efforts were not exhaustive, these numbers are surely underestimates of total repertoire size. Syllable repertoire sizes did not vary significantly by latitude (F1,46 = 2.82, p = 0.10). The most common syllable types, including a broadband ‘tick’ an upsweeping ‘weep’ syllable and others were produced by birds across the geographical range of the species. In fact, even uncommon syllables were sometimes produced in distant locations. For example, one syllable was recorded in only three sites, two of which were separated by 4753 km. Conversely, 23 per cent (n = 13) of bird pairs recorded in the same location shared no syllable types. Mantel tests indicated that syllable sharing correlated with geographical distance (r = −0.169, p = 0.02), but not with subspecies identity (r = 0.0583, p = 0.205).
The acoustic properties of ‘weep’ syllables varied within and between locations (). The first and second principal components generated by our analysis explained 52.5 and 21.0 per cent of the total variation in syllable shape. Regression analysis indicated that 25 per cent of the variance in PC-1 was explained by latitude (F1,20 = 6.65, p = 0.018). The three subspecies did not segregate in a plot of PC-1 versus PC-2; 95 per cent confidence ellipses overlapped heavily (electronic supplementary material).