Individual, population, and geographic differentiation in advertising song of the Blyth’s reed warbler, Acrocephalus dumetorum (Sylvidae)

Abstract

Processes of differentiation in the advertising song of the Blyth’s reed warbler have been studied both within local populations and over the species range. Individual vocal repertoires of males from the Moscow and Kostroma regions and the Southern Urals include 30 to 104 (on average, 55.3 ± 17.0) song types, with 45.9–84.4% (61.3 ± 10.5%) of song types being common to all males of a given population. The rate of accumulation of new common song types drops with an increase in the number of males included in comparison. The appearance of many song types in the repertoire cannot be attributed to imitation, at least within one geographic population. The repertoires of males from one geographic population are more similar to each other than to those from other populations. The degree of acoustic similarity of song repertoires between different populations is inversely related to the distance between them, but no such relationship has been revealed for the repertoires of individual males within the same population. Many song types are widespread almost throughout the species range. Songs of males from the southern part of the range differ in an accelerated performance rhythm, chaotic syntax, and unstable phonetic structure. Consideration is given to probable causes of song specificity in southern populations and to some parameters of individual song variation and other factors than can contribute to the formation of vocal repertoires in the Blyth’s reed warbler, such as nesting site fidelity, vocal mimicry, and song improvisation.