A comprehensive framework for understanding the evolutionary history of forest birds of the Northern Hemisphere

Technological and methodological advances during the past couple of decades in biogeography, paleoecology, phylogenetics and bioinformatics provide a refreshing insight on the evolutionary history of birds. Molecular data of both extinct and extant taxa led to a revolution in reconstructing the phylogenetic history of lineages. These advances shed a new light on the mode, tempo and spatial context of differentiation processes that shaped the composition and structure of extant forest bird communities of the main forest blocks of the Northern Hemisphere. This paper provides an up-to-date insight in this history from a panel of tools deciphering the imprint of the repeated north-south and east-west changes in the geographic configuration of land masses and in climates since the Mesozoic. Differentiation of most extant bird lineages and species have been shown to start in a much deeper past that formerly thought but recent analyses from molecular phylogenies also support the late Pleistocene model of speciation which has long been hotly debated. The combination of dispersive abilities of birds and geographical connections between tropical and temperate regions make north-south flyways important drivers of differentiation for many lineages. The region of origin and the history of differentiation and colonisation of clades including both resident and long-distance migrants is discussed in the framework of two alternative theories, the “southern home theory” and the “northern home theory”. Then, region-specific characters of the bird faunas and differences between the main forest blocks of the Northern Hemisphere are discussed from hypotheses on dispersal processes in relation to the geographical configuration of land masses and from differential dispersal-colonization rates from tropical regions and subsequent diversification in temperate regions. The causes of the observed decline in diversification rates during the Pleistocene and their differences between the main landmasses in response to Neogene climatic pejoration are examined from phylogenetic reconstructions of various clades.