Darwin's finches are 13 or 14 different closely related species of finchesCharles Darwin discovered on the Galapagos Islands. Darwin's voyage on HMS Beagle, and the finches in particular, are known to have influenced his thinking so that he would later produce a basic theory of evolution by natural selection. Darwin reasoned that there had to be a common ancestor. Later, much work was done by Peter and Rosemary Grant.
The birds are all about the same size (10–20 cm). The beaks' size and shape compose the largest differences between species, as the beak is highly adapted to food source. The birds are all brownish or black. Their behaviour differs as they have different song melodies.
Different bills and song melodies (http://www.nature.com/nature/journal/v409/n6817/fig_tab/409185a0_F1.html)
Genetics and the Origin of Birds Species, Grant and Grant in PNAS (http://www.pnas.org/cgi/reprint/94/15/7768)
Sato et al Phylogeny of Darwin's finches as revealed by mtDNA sequences in PNAS (http://www.pnas.org/cgi/content/full/96/9/5101?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=Sato&andorexactfulltext=and&searchid=1081449482400_6822&stored_search=&FIRSTINDEX=0&sortspec=relevance&volume=96&firstpage=5101&resourcetype=1)
What makes Darwin's finches so difficult to identify is the variability of their beaks (which can sometimes be exacerbated by interbreeding) and the fact that the beak of one species may overlap into the range of another.
Finch #2 is definitely a large ground finch because I photographed it on Genovesa.
Finch #4 is definitely a small ground finch because I photographed it on Espanola.
All these birds proved to be finches, a cluster of species closely related to one another and all resembling the finches of the South American mainland.
The simplest explaination, Darwin thought, was that a single ancestor species of finch had migrated to the islands in the past, flying across the ocean from South America..
At the base of the tree, the ancestor to all the other finches, is a pointy-beaked warbler finch, Certhidea olivacea, with DNA very similar to warbler finches on Ecuador, 900 km away.
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