The rich get richer: song complexity predicts song element sharing and song output in song sparrows Melospiza melodia

Animal signals are often complex, raising the possibility that different aspects of a signal may convey different types of information. Birdsong, for example, may simultaneously advertise the singer's condition during early life (through song complexity), location of song learning (through local song structure) and current condition (through song output). Each of these aspects of song is behaviourally salient: females generally prefer complex over simple song, local over nonlocal song, and high over low rates of song output. We examined the degree to which these three components of song convey complementary versus redundant information, in eastern song sparrows, Melospiza melodia melodia. One measure of song complexity, syllable repertoire size, was positively related to syllable sharing with other birds in the local population. This finding suggests that these aspects convey somewhat redundant information and that local-sounding song may in part advertise song-learning ability. A second measure of song complexity, song repertoire size, was positively related to song output, despite the widely differing developmental timescales over which song complexity and output are thought to vary. Condition during early development may have carryover effects on adult condition; alternatively, complex singers may have most to gain from advertising this attractive signal. Finally, despite our finding that both syllable sharing and song output were related to song complexity, syllable sharing and song output were not themselves significantly correlated. Overall, the three ostensibly independent aspects of song investigated here appear to overlap substantially in the information they convey.