Syllable sharing and changes in syllable repertoire size and composition within and between years in the great reed warbler, Acrocephalus arundinaceus

Abstract

The syllable repertoire size of the great reed warbler (GRW) is known to underlay female preferences. However, its stability over a season—a key factor of this quality-related feature—has never been tested. Similarly, syllable repertoire composition, syllable sharing and its function in GRW have received little attention so far. GRW syllables fit into two categories: whistles and rattles. They differ in structure but nothing is known about their function. In the present study we analyze the above aspects of GRW vocalization. We found that syllable repertoire size and composition were stable within a season but significantly changed between years. Longitudinal analyses revealed that the changes in repertoire size were influenced more by the season than the age of individuals. The repertoire size correlated with harem size. Changes in repertoire size were significantly smaller than changes in composition, indicating varying seasonal usage of syllables present in the repertoires of individual birds. Syllable sharing was high and indifferent between neighbors and distant males. This pattern suggests that syllable sharing in GRW acts as a dialect. High levels of within- and between-season repertoire similarity among all recorded birds supported this view. Whistles were more shared and repeatable within and between seasons than rattles. We suppose that whistles may play an important role in determining a local dialect due to their lower changeability both between individuals and years. Within-season similarity of whistle repertoire to other males correlated with harem size, but similarity of rattle repertoire did not. This correlation may result from a female preference for philopatric males using the local dialect.