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Tropical islands are renowned as natural laboratories for evolutionary study. Lineage radiations across tropical archipelagos are ideal systems for investigating how colonization, speciation, and extinction processes shape biodiversity patterns. The expansion of the island thrush across the Indo-Pacific represents one of the largest yet most perplexing island radiations of any songbird species. The island thrush exhibits a complex mosaic of pronounced plumage variation across its range and is arguably the world’s most polytypic bird. It is a sedentary species largely restricted to mountain forests, yet it has colonized a vast island region spanning a quarter of the globe. We conducted a comprehensive sampling of island thrush populations and obtained genome-wide SNP data, which we used to reconstruct its phylogeny, population structure, gene flow, and demographic history. The island thrush evolved from migratory Palearctic ancestors and radiated explosively across the Indo-Pacific during the Pleistocene, with numerous instances of gene flow between populations. Its bewildering plumage variation masks a biogeographically intuitive stepping stone colonization path from the Philippines through the Greater Sundas, Wallacea, and New Guinea to Polynesia. The island thrush’s success in colonizing Indo-Pacific mountains can be understood in light of its ancestral mobility and adaptation to cool climates; however, shifts in elevational range, degree of plumage variation and apparent dispersal rates in the eastern part of its range raise further intriguing questions about its biology. 

The presence of two undescribed cisticola warblers in the marshes of the Kilombero floodplain in central Tanzania has been known since the 1980s and these putative new species have been illustrated in field guides on African birds, although with no formal name. Here we name both species, based on two museum specimens collected in 1961 and recently detected in a museum collection. We use these specimens to provide formal descriptions of each form and, using DNA sequence data extracted from these specimens, we place them in a broad phylogenetic framework for the genusCisticola. The phylogenetic placement indicates that one of the new species is nested within a group of plain‐backed duetting cisticolas and the other within the streak‐backed marsh cisticolas. We use our own and public recordings to characterize the vocal repertoire of each of these new species and compare song characteristics with other members of their respective clades. Dating of nodes in the molecular phylogeny suggests that both cisticolas endemic to the Kilombero became isolated and diverged from their sister‐species between 2.5 and 3.5 million years ago, long after the formation of the Eastern Arc Mountains and the Malawi Rift. We propose that both species should be classified as globally endangered, owing to immense anthropogenic pressures on the floodplain, as documented in several publications and by a recent Ramsar Advisory Mission.