Lack of habitat segregation and no interspecific territoriality in three syntopic cryptic species of the golden-spectacled warblers Phylloscopus (Seicercus) burkii complex

It is widely accepted that exploitative competition prevents the coexistence of any two or more closely-related species unless differences exists in their ecological niches and resource use. In sibling bird species, exploitative competition is reduced mainly by spatial segregation of competing species. Spatial segregation can be achieved in two basic ways: by using different habitats or microhabitats that each species is predominately exploiting, or by interspecific territoriality. To our knowledge, either habitat segregation or interspecific territoriality or both have been found in all dyads and groups of sympartic sibling bird species studied so far.  In this study, we investigated the coexistence of three cryptic sibling species of the golden-spectacled warblers Phylloscopus burkii complex in Hunan province, China: Ph. tephrocephalus, Ph. omeiensis and Ph. valentini. We analyzed their habitat preferences, and spatial interrelations between the species. In order to analyze either presence or absence of interspecific territoriality, we additionally performed con- and heterospecific playback experiments. Contrary to expectations, we found no evidences for either habitat segregation or interspecific territoriality in these three species.