The Divergence of Male Reproductive Strategy as the Cause of Nomadism in Wood Warbler

The Wood Warbler Phylloscopus sibilatrix is a nomadic migratory songbird. Males often change territories during breeding season and every year displaying low nest-site fidelity. However, the benefits of frequent change between territories remain unclear. During our research, playback experiments were implemented to test whether male settlement or departure are affected by quality of conspecifics nearby or female presence. High or low rate song broadcasts were used to imitate the presence of males with ‘good’ and ‘poor’ quality, arriving males were subsequently banded with colour rings to track their further movements between plots. The results showed that between 52 and 66,7% of males left the plot during the first week after arrival (labelled as ‘floaters’) but after leaving they did not try to settle on the other plots, where high or low rate songs were broadcasted. We tested the 'hidden lek' hypothesis by tracking male appearances near local nests. The male abundance increased significantly with the start of egg-laying compared to the 10-days prior to it and decreased during the next 10 days after incubation start, assuming that males left the territory after copulation with females. The study suggests that to increase chances of leaving offspring, some floaters move through the territory of other males and copulate with their females rather than settle nearby.