The finches all evolved from a single species called the Blue-Black Grassquit Finch Volatinia jacarina which was found along the Pacific coast of South America. Once they settled on the Galapagos Islands, the finches adapted to their habitat and the size and shape of their beaks reflect their specializations. This is how they are distinguished into their separate groups. Below is an illustration displaying 4 types of finches with 4 diffrent beak shapes.
Click HERE for a larger image which may be printed for educational use. Opens in new window. Over many years, the finches beaks have evolved to suit their eating habits. Small ground finch Geospiza fuliginosa. One of the most common species of finch, found throughout the Islands.
Large cactus finch Geospiza conirostris. This finch is one of the most variable of the finches in appearance and they feed on a range of foods including Opuntia cacti. Common cactus finch Geospiza scandens. As their name suggests, they feed mostly on Opuntia cacti.
When the Opuntia are in flower, the finches feed almost exclusively on pollen and nectar. During other times of the year, they will feed on Opuntia seeds and fruit. They will also feed on a range of other vegetative foods and invertebrates. Sharp-beaked ground finch Geospiza difficilis. Although most populations feed mainly on seeds, those finches found on the small and remote islands of Wolf and Darwin often drink the blood of large seabirds, such as boobies. This has given them an alternative name — vampire finch.
Where to see them: Different finches can be seen on different islands. Its beak is short, pointy and slightly curved. This type of finch mostly eats seeds. It is seen on several of the islands, so you might get to spot this one. The male is a black color with white tips on its undertail, and the female is brown with streaky bits. This Galapagos finch is recognizable as it is the biggest. It also has the largest beak size of any of the Darwin Galapagos finches.
Its beak is big but short which is well suited for eating seeds and nuts, and cracking them open. This particular Darwin Galapagos finch is extremely rare. It is only found on Isabela Island, and only in small area there. It is believed that this finch type is likely to become extinct, as there is insufficient breeding between the two small populations on Isabela.
This bird is found on the islands of Wolf and Darwin, and is also known by the name of vampire finch. This is because it will drink the blood of bigger sea birds. However, it mainly eats seeds. It can also be seen on Pinta and Fernandina. The finch is relatively small. Subsequent studies by the Grants have demonstrated selection on and evolution of bill size in this species in response to other changing conditions on the island.
The evolution has occurred both to larger bills, as in this case, and to smaller bills when large seeds became rare. Learning Objectives Describe how finches provide visible evidence of evolution. Key Points Darwin observed the Galapagos finches had a graded series of beak sizes and shapes and predicted these species were modified from one original mainland species.
Darwin called differences among species natural selection, which is caused by the inheritance of traits, competition between individuals, and the variation of traits. Offspring with inherited characteristics that allow them to best compete will survive and have more offspring than those individuals with variations that are less able to compete.
Large-billed finches feed more efficiently on large, hard seeds, whereas smaller billed finches feed more efficiently on small, soft seeds. When small, soft seeds become rare, large-billed finches will survive better, and there will be more larger-billed birds in the following generation; when large, hard seeds become rare, the opposite will occur.
Key Terms natural selection : a process in which individual organisms or phenotypes that possess favorable traits are more likely to survive and reproduce evolution : the change in the genetic composition of a population over successive generations.
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