Birdsong is degraded as it propagates through the habitat. This affects its use as a signal in communication networks, depending on song type as well as sender and receiver location. Nest holes constitute special receiver locations to females of many hole-nesting species. Although such locations are frequently used by females during their fertile period, for instance at dawn when information gathering from singing males may be essential, the conditions for receiving sounds inside nest holes are currently unknown. We investigated these conditions with a sound transmission experiment, in which great tit songs were broadcast in a deciduous forest and rerecorded from both outside and inside a nest box. Several aspects of sound degradation encompassing signal attenuation and distortion were quantified.
Attenuation was strongest inside the nest box for both song and background noise. However, the signal-to-noise ratio, which affects song detection and discrimination, was only slightly reduced inside the nest box. Signal distortion, which has implications for both information transfer and ranging, provided conflicting results for the two types of song notes, the highly modulated buzz notes and the less modulated pure notes. These results provide the first evidence that entering nest boxes complicates song reception conditions for female songbirds. We suggest that this may ultimately affect vocally mediated information gathering in the network.