Variation in the song of the great reed warbler Acrocephalus arundinaceus in relation to mate attraction and territorial defence

Abstract

Variation in the song structure of the great reed warbler Acrocephalus arundinaceus was investigated using a variety of observational, analytical and experimental techniques. Males were found to have two types of song, called long and short songs. Short songs consisted of relatively few, stereo-typed, low-amplitude syllables, and were given by males during territorial encounters with rival males. Males were more reluctant to approach during playback of short songs, and when lured in by long songs retreated when playback was switched to short songs. Long songs consisted of a wide variety of high-amplitude elements added to the basic short song structure. Long songs were only given spontaneously by unpaired males, and ceased when a female had been attracted. In Acrocephalus warblers, monogamous species have evolved long, complex and variable songs for mate attraction largely through intersexual selection. Polygynous species have evolved short, simple and stereotyped songs for territorial defence through intrasexual selection. The great reed warbler is a partial polygynist, and through evolutionary compromise has evolved a variable song structure which can be shortened for territorial defence, and lengthened for mate attraction.