Do male birds intercept and use rival courtship calls to adjust paternity protection behaviours?

We tested whether male rock sparrows (Petronia petronia) change behaviours directed at their females when played back courtship display calls simulating a potential cuckolding event in the vicinity of their nests. We compared the behaviour of males before, during and after such playback with the behaviour of males who received a control playback, territorial song. After playback of courtship display calls male rock sparrows increased the frequency of courtship displays directed towards their mate, as predicted, but not mate guarding. These results illustrate the interplay of reproductive and communication strategies, and extend our knowledge of how the social environment can affect within-pair dynamics.