Song degradation in the hole-nesting pied flycatcher Ficedula hypoleuca: Implications for polyterritorial behaviour in contrasting habitat-types

In the hole-nesting pied flycatcher, Ficedula hypoleuca, a male may become polyterritorial after attracting a primary female. However, the female may recognize her mate's song and attack other females that associate with him. Differences in sound degradation amongst different habitats and within nestboxes may, therefore, be important for male and female behaviour since the male may have to move outside female hearing range to avoid harassment, and the female may have to listen for the mate to be able to locate competing females. This may be difficult from inside the nest cavity. We used ten common song elements to test sound degradation with distance in a mixed coniferous and a mixed deciduous forest, measuring broadcast sounds both inside and outside nestboxes. On average, sound degradation increased to a larger extent with distance in the deciduous than the coniferous forest. This is consistent with the shorter polyterritorial distances of flycatchers in the deciduous forest. Furthermore, song degradation was stronger inside the nestboxes. Being inside may, therefore, reduce a female's possibility of detecting and recognizing songs. This may be one reason why female pied flycatchers spend little time within the nest cavity before incubation unlike some other hole nesting species.