Consistency and individual variation in common song types of an urban bird: a multi-population comparison over a decade
Individual variation in singing behavior is influenced by cultural evolution, environmental constraints, and population dynamics. In closed-ended songbird species, aging may be associated to temporal song variations in individual birds due to vocal apparatus deterioration. However, song variations may also arise as a result of extrinsic factors that induce behavioral changes. In this study, we aimed to examine song-type consistency over 13 years in four populations of the White-eared Ground-sparrow (Melozone leucotis, Aves: Passerellidae) along an urban-rural gradient. We also compared within and between-individual variation to determine potential population-level responses. We used long-term data from singing males to quantify five fine structural characteristics (minimum frequency and maximum frequencies, bandwidth, peak frequency, and song duration) for two most common song types from each population. Song consistency differed between fine-structure characteristics, song types, and populations. Contrary to our expectations, we found that the Highly urbanized population had greater between-individual variance, associated with anthropogenic disturbances such as habitat structure and noise pollution, suggesting non-uniform individual responses. The Medium, Low urbanized, and Rural populations, on the other hand, had higher levels of within-individual variance, associated to individuals' age. Our study brings insight into how both intrinsic and extrinsic factors can influence song consistency and highlights how cultural evolution within a species can diverge across populations experiencing distinct environmental contexts.