Darwin's Finches, also known as the Galápagos finches, are a population are a group of about sixteen species of passerine birds, found on the Galápagos Islands, a set of islands in the Pacific Ocean near South America. The exact number of species is difficult to calculate, as interbreeding between species creates a variety of beak sizes.
They are well known as a prime example of divergent evolution due to their variation of beak sizes, each suited to its own purpose. The finches are believed to have all evolved from the same species, possibly a population of birds from South America blown off course approximately 2 - 3 million years ago. The birds all have different beak shapes, resultant from their different diets. This occurs so there is less competition over food, as well as the fact that different islands have different quantities of different food sources, also making them examples of natural selection and adaption.
History of the Finches
The finches are theorized to have descended from a common ancestor, which is believed to have come from a flock of birds blown off course from South America. As different populations inhabited different islands, gene flow between the populations began to decrease, and many sub-species began to form. Each has adapted to a different diet, and populations of each type of finch vary on the availability of its signature food source.
Types of Finches
The Warbler Finch (Certhidea olivacea and fusca) live in habitats that are subtropical or dry forests or shrublands. The species possesses a thin, probing bill, finer than that of the other species, which is ideal for feeding on small insects
The Vampire Finch (Geospiza difficilis septentrionalis) is most famous for its diet. It often feeds off the blood of other birds, its sharp beak adapted to piercing the flesh of its prey, although insects and prickly pears are not off the menu.
The Ground Finches (Geospiza difficilis, fortis, fuliginosa and magnirostris) have adapted beaks suited to feeding off seeds, flowers, buds, young leaves, and the occasional insect. Its beak, of moderate size, has adapted to suit this diet, being able to process the hardness of seeds.
The Tree Finches (Camarhynchus psittacula, pauper, parvulus) are only found in moist, forested elevated areas. Their diet consists of primarily insects and their becks have evolved accordingly.
The Cactus Finches (Geospiza conirostris and scandens) have one of the most diverse beak dimension ranges. As such, its beak is difficult to specify, as each bird posses a beak shape unique to its dietary requirements. The species generally feeds off cacti and lives in drier climates.
The Woodpecker Finch (Camarhynchus pallidus) is most famous for its ability to use twigs, sticks and cactus spines as tools to extract prey such as grubs and ants from trees. The finches beak shape is not so much suited to its diet as it is to this ability, unique among the finches.
The Mangrove Finch (Camarhynchus heliobates) lives, as its name suggests, in wet areas populated by mangroves. Its diet consists of larvae, spiders and insects. Although it not known to use tools, it shares a beak shape similar to the Woodpecker Finch. The species is also critically endangered and protection measures have been put in place.
The Cocos Finch (Pinaroloxias inornata) is unique in that it is the only one of Darwin's Finches not native to the Galápagos Islands. Its beak is not refined to a specific diet, eating a wide range of plants and insects and is found in every habitat.
The Vegetarian Finch (Platyspiza crassirostris) is one of the largest of Darwin's Finches, measuring up to 16 cm in length. As its name suggests, the finch feeds off plant life, specifically buds, leaves, flowers and fruit, with a short, broad beak.
Interaction Between Species
Although many of the species share similar traits, they mainly keep to themselves as opposed to greatly interacting with each other. Although interbreeding is possible, it is highly uncommon as birds will attract mates through a special mating call. This is because females will be attracted to mates with songs similar to their father's and the fact that the tone, sound and tune of the species is affected by the acoustics of the beak. Research suggests, however, that hybridization between species may contribute to beak size morph.
Impact of the Finches on the Theory of Evolution
While many are lead to believe the finches were the initial inspiration for Darwin's theory of evolution, he did not notice that different islands were inhabited by different finches, who fed off different diets. It was actually ornithologist David Lack who made these connections. The reason for this misconception is Lack published his findings in his book, titled Darwin's Finches, in 1947.
Although the finches were not significant to Darwin's research, the finches have been influencial on many modern experiments on the topic, such as one to have proven that the variation in beak size is from a bone morphogenetic protein known as BMP4 and its differential expression during development of the finches. The circumstances of their theorized origin also helps to prove other related evolutionary theories, such as divergent evolution, natural selection and adaption