Darwin's finches
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Darwin's finches are 13 or 14 different closely related species of finches Charles Darwin discovered on the Galapagos Islands. Darwin's voyage on HMS Beagle, and his observations of the finches in particular, are known to have contributed to the formulation of his theory of evolution by natural selection. Based on his observations, Darwin reasoned that all of the finches shared a common ancestor. Later, Peter and Rosemary Grant conducted extensive research in documenting evolutionary change among the finches. Beginning in 1973, the pair spent many years tracking thousands of individual finches across several generations, showing how individual species changed in response to environmental changes. The Beak of the Finch by Jonathan Weiner is a book on the subject and the Grants' research.
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 and they have different song melodies.
The finch species
- Genus Geospiza
- Large Cactus Finch (Geospiza conirostris)
- Sharp-beaked Ground Finch (Geospiza difficilis)
- Medium Ground Finch (Geospiza fortis)
- Small Ground Finch (Geospiza fuliginosa)
- Large Ground Finch (Geospiza magnirostris)
- Common Cactus Finch (Geospiza scandens)
- ..... (Geospiza parvula)
- Genus Camarhynchus
- Vegetarian Finch (Camarhynchus crassirostris syn. Platyspiza crassirostris)
- Large Tree Finch (Camarhynchus psittacula)
- Medium Tree Finch (Camarhynchus pauper)
- Small Tree Finch (Camarhynchus parvulus)
- Woodpecker Finch (Camarhynchus pallidus)
- Genus Certhidea
- Warbler Finch (Certhidea olivacea)
- Genus Pinaroloxias
- Cocos Island Finch (Pinaroloxias inornata)
Text from the Voyage of the Beagle
The passage in chapter 17 in the Voyage of the Beagle in which Darwin describes the finches and surmises that they may have shared a common ancestor is shown below:
- The remaining land-birds form a most singular group of finches, related to each other in the structure of their beaks, short tails, form of body and plumage: there are thirteen species, which Mr. Gould has divided into four subgroups. All these species are peculiar to this archipelago; and so is the whole group, with the exception of one species of the sub-group Cactornis, lately brought from Bow Island, in the Low Archipelago. Of Cactornis, the two species may be often seen climbing about the flowers of the great cactus- trees; but all the other species of this group of finches, mingled together in flocks, feed on the dry and sterile ground of the lower districts. The males of all, or certainly of the greater number, are jet black; and the females (with perhaps one or two exceptions) are brown. The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in including his sub-group, Certhidea, in the main group) even to that of a warbler. The largest beak in the genus Geospiza is shown in Fig. 1, and the smallest in Fig. 3; but instead of there being only one intermediate species, with a beak of the size shown in Fig. 2, there are no less than six species with insensibly graduated beaks. The beak of the sub-group Certhidea, is shown in Fig. 4. The beak of Cactornis is somewhat like that of a starling, and that of the fourth subgroup, Camarhynchus, is slightly parrot-shaped. Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends. In a like manner it might be fancied that a bird originally a buzzard, had been induced here to undertake the office of the carrion-feeding Polybori of the American continent.
External links
- Darwin, C.R. The Voyage of the Beagle Chapter 17 from Darwin's book The Voyage of the Beagle Chapter 17 in which he discusses the Galapagos islands and the birds (http://www.infidels.org/library/historical/charles_darwin/voyage_of_beagle/Chapter17.html)
- 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)
- http://www.cuencanet.com/ortiz/galfinches.htmde:Darwinfinken