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RESEARCH PRODUCT

Ring species – Do they exist in birds?

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Abstract According to current theory, the splitting of a single species into two is best observed by a ring of intergrading populations which occupy a ring-shaped distribution area and whose terminal populations not only meet but overlap and co-occur without or with only little hybridization. The three most discussed examples in birds are revisited here. The great tit complex ( Parus major s. l.) turned out to be an assemblage of four subspecies groups forming a secondary ring of population. The herring gull/lesser black-backed gull complex ( Larus argentatus s. l.) forms a circumpolar circle of intergrading populations, but lacks the crucial cornerstone, the geographical overlap. The greenish warbler complex ( Phylloscopus trochiloides s. l.) is close to the ideal ring species, but the ring is not complete and the Siberian zone of overlap needs further clarification and characterisation.