Learning in advance? Interspecific recognition ability in male Eurasian blackcaps

Interspecific aggression is common in bird communities. It is thought to be a consequence of learned behavior or misdirected intraspecific aggression. In the former case birds acquire the ability to identify individuals of other species by social learning of species-specific traits during interactions with heterospecifics in a shared habitat. I conducted a two-choice song playback experiment to investigate the role of associating signals from two sensory modalities, auditory and visual, in shaping the agonistic response of male Eurasian Blackcaps (Sylvia atricapilla) to simulated male Garden Warbler (S. borin) intruders. I measured focal males’ response to playbacks to the song of a Blackcap or a Garden Warbler while giving them a choice between stuffed male models of both species presented in their territories. The experiments were carried out in early spring, before the arrival of Garden Warblers from Africa. I found that male Blackcaps were able to associate species-specific songs with species-specific plumage types. The ability to associate signals characterized not only experienced after-second-year old males, but also second-year old males that had not had the opportunity to defend breeding territories against heterospecifics. This suggests that second-year old male Blackcaps acquire the ability to associate Garden Warbler song with plumage before they use this skill when defending territory during their first breeding episode. Male Blackcaps do not mistake male Garden Warblers for males of their species, but rather learn these associations during the first months of life. However, the possibility that these associations are innate cannot be excluded.