The Critically Endangered Sao Tome Grosbeak (Crithagra concolor), endemic to the island of São Tomé in the Gulf of Guinea, is arguably one of the least-known birds in the world.
Large and uniformly coloured, with a massive parrot-like bill in which the upper mandible extends over the lower, it was formerly considered to be an aberrant weaver (Ploceidae) and, later on, placed in a monotypic genus, Neospiza, within the true finches (Fringillidae). A recent genetic study, using mitochondrial and nuclear sequence data, has confirmed that the species is indeed an Old World canary (Fringillidae, subfamily Carduelinae) and that it is very closely related to another endemic species of the Gulf of Guinea, Principe Seedeater (Crithagra rufobrunnea), on Príncipe Island and São Tomé. The molecular data suggest that these two species diverged from a common ancestor between 1·5 and 0·5 million years ago, and, therefore, that both should included in the same genus. The Sao Tome Grosbeak, however, is much larger, with double the body mass and almost double the bill depth, length and width in comparison to the Príncipe Seedeater. The Sao Tome Grosbeak, an island giant, is in fact the world’s largest canary, 50% heavier than the next largest species.