Does complexity of conspecific song influence reproductive decisions and investment in European Common Reed Warblers: an experimental playback approach?

The beginning of reproduction is usually accompanied by a series of decisions including where to establish a territory, attract a mate, to lay eggs or give birth. These decisions might be influenced by the quality of potential partners but also conspecific neighbours. In birds, the quality of an individual can be signaled by song features, like song complexity. Besides choosing the right location for reproduction and mate attraction, we propose here that song may also influence the reproductive investment, in particular early maternal investment, which is known to be a sensitive determinant reflecting different allocation of females in relation to male quality and attractiveness. Here, we examined whether song quality of conspecific neighbours can stimulate various reproductive parameters in European Common Reed Warblers (Acrocephalus scirpaceus). Therefore, we performed field playback experiments advertising song of high and low complexity and examined their influence on settlement decisions, early maternal investment, and breeding success. The number of nests and start of egg laying did not differ between the two playback types but nests were significantly closer to high complex song playbacks. Furthermore, in the high complex song group, a significantly higher proportion of eggs was fully dark pigmented than in the low complex playback group. Nests near high complex playbacks were significantly more successful and significantly more offspring were produced. The results are discussed in relation to whether males use song to stimulate female investment and whether establishing a breeding location near a high-quality neighbour may be an additional aspect in settlement decisions.