This passerine family is endemic on Madagascar. Because of their cryptic lifestyle, not much was known about these birds.
The Short-billed Tetraka (X. zosterops) could be a possible instance of merging lineages. Block et al. (2015) tested this hypothesis by comparing mtDNA and microsatellites, as well as mtDNA from host-specific feather lice in the genus Myrsidae. The Short-billed Tetraka comprises four divergent, broadly sympatric, cryptic mtDNA lineages that diverged around 3.6 million years ago. The microsatellite data, on the other hand, indicate that the mtDNA clades are virtually panmictic. It seems that the previously allopatric lineages are merging by hybridization.
Block, N. L., Goodman, S. M., Hackett, S. J., Bates, J. M. & Raherilalao, M. J. (2015). Potential merger of ancient lineages in a passerine bird discovered based on evidence from host-specific ectoparasites. Ecology and Evolution 5, 3743-3755.