Geographically isolated and without competition from similar species, Darwin's finches developed distinctive anatomy (particularly beak size and shape) and behaviors, with each species exploiting a unique feeding niche. The bill is adapted in the different species for different purposes, such as crushing seeds, pecking wood, and probing flowers for nectar. The woodpecker finch, Camarhynchus pallidus or Cactospiza pallida, an insect-eater, holds twigs and cactus spines in its beak to fish out larvae in tree cavities. Darwin proposed that the Galapagos finches evolved on the islands from a single bird species from mainland South America. Modern methods of DNA (genetic) analysis have confirmed his insight. Darwin's finches are classified in several genera of the phylum Chordata, subphylum Vertebrata, class Aves, order Passeriformes, family Thraupidae, subfamily Geospizinae.
See P. Grant, Ecology and Evolution of Darwin's Finches (1986).
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