Sound-based species-specific recognition in the blackcap Sylvia atricapilla shows high tolerance to signal modifications

The aim of the present study is to investigate the male blackcap decoding p rocess allowing species-specific recognition in the perspective of possible adaptations for communication in dense vegetation. We played back modified and natural blackcap songs to territorial blackcap males and scored the re action of the territory owners. We examined the response of blackcap males to artificial songs manipulated to reflect a possible environmental degrada tion. Territory owners respond strongly even to crude models of conspecific song. Only when frequency modulation is suppressed or the number of syllab les in the song is drastically reduced do the territory owners cease to res pond. The importance of frequency modulation for species recognition is fur ther emphasised by territory owners' strong response to synthetic sounds, i n which rapid frequency modulation is superimposed by a less rapid and a sl ow frequency modulation within the frequency range of conspecific song. Our results have then put forward the acoustic basis for the initial percep tion of potential conspecifics. It appears that blackcap species-specific d ecoding process seems highly tolerant towards song structure modifications. May be this is an adaptation to the propagation acoustic constraints impos ed by the forest environment.