Randomization analyses: Mimicry, geographic variation and cultural evolution of song in brood-parasitic straw-tailed whydahs, Vidua fischeri

Although bird song has been an important model for investigating questions of behavior development, cultural evolution and population differentiation, the quantitative methods of analysis have been problematic. Here we develo p and apply quantitative randomization methods to test hypotheses about the se processes in a natural population of birds. Songs of the African brood-p arasitic straw-tailed whydahs (Vidua fischeri) and songs of their host spec ies, the purple grenadier (Granatina ianthinogaster), were compared in audi ospectrograms for similarity to test the following hypotheses: Whydahs mimi c the songs of their host species, they have local song dialects, neighbori ng males match their song themes, local males match the songs of local host s, remote populations have different songs according to their geographic di stance, and songs undergo cultural evolution over time across generations. Randomization analyses were completed using (1) Mantel matrix statistics an d (2) tree-based measures employing Sankoff optimization of Manhattan matri ces and approximate randomizations. Our results provide evidence for song m imicry, local song dialects, matching song themes between neighboring males , song matching of local whydah mimics and grenadier song models, correspon dence of song differences and geographic distance, and cultural continuity with change in song traditions within a local population. These randomizati on methods may be useful in other studies of animal communication, and they are sufficiently general for use both with distance matrices derived eithe r from naturalistic impressions of song similarity as in our example or fro m acoustic measurements.