Darwin's finch

Darwin's finch

 or Galápagos finch

Any of 14 species (in three genera) of songbirds (family Fringillidae) whose adaptations to several ecological niches in the Galápagos Islands and Cocos Island gave Charles Darwin evidence for his thesis that “species are not immutable.” All the species are 4–8 in. (10–20 cm) long and brownish or black, but they differ greatly in the configuration of the bill, which is suited to each species' particular feeding habit.