Birds associate species-specific acoustic and visual cues: recognition of heterospecific rivals by male blackcaps

Abstract

Animals need to be able to identify other species, which is crucial in competition for ecological resources, for using other species as a cue in habitat selection, and for the establishment and maintenance of parasite-host species associations in brood-parasitic species. The ability to discriminate between conspecifics and heterospecifics may be crucially important also in refinement of mating preferences during speciation and for premating isolation of sympatric species. It has long been hypothesized that species identification ability is based on learned associations between multiple features that distinguish species. Here I test this hypothesis using dual-choice song playback experiments with interspecifically territorial male blackcaps (Sylvia atricapilla) that defend territories against male garden warblers (Sylvia borin). I show that male blackcaps can associate species-specific songs with species-specific plumage and also that they retain the memory of this association for an 8-month period without contact with heterospecific rivals. Apparently, yearling male blackcaps achieve this ability several months prior to their first breeding attempt. This is the first time a long-term memory of associations between species-specific signals from two different sensory modalities (visual and auditory) has been shown to be important for distinguishing conspecifics from heterospecifics.