In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches. Starting with a single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits. The prototypical example of adaptive radiation is finch speciation on the Galapagos, but examples are known from around the world.
The tanagers comprise the bird family Thraupidae, in the order Passeriformes. The family has a Neotropical distribution and is the second-largest family of birds. It represents about 4% of all avian species and 12% of the Neotropical birds.
Darwin's finches are a group of about 18 species of passerine birds. They are well known for their remarkable diversity in beak form and function. They are often classified as the subfamily Geospizinae or tribe Geospizini. They belong to the tanager family and are not closely related to the true finches. The closest known relative of the Galápagos finches is the South American dull-coloured grassquit. They were first collected when the second voyage of the Beagle visited the Galápagos Islands, with Charles Darwin on board as a gentleman naturalist. Apart from the Cocos finch, which is from Cocos Island, the others are found only on the Galápagos Islands.
Peter Raymond Grant and Barbara Rosemary Grant are a British married couple who are evolutionary biologists at Princeton University. Each currently holds the position of emeritus professor. They are known for their work with Darwin's finches on Daphne Major, one of the Galápagos Islands. Since 1973, the Grants have spent six months of every year capturing, tagging, and taking blood samples from finches on the island. They have worked to show that natural selection can be seen within a single lifetime, or even within a couple of years. Charles Darwin originally thought that natural selection was a long, drawn out process but the Grants have shown that these changes in populations can happen very quickly.
The Galápagos hawk is a large hawk endemic to most of the Galápagos Islands.
The vampire ground finch is a small bird native to the Galápagos Islands. It was considered a very distinct subspecies of the sharp-beaked ground finch endemic to Wolf and Darwin Islands. The International Ornithologists' Union has split the species supported by strong genetic evidence that they are not closely related, and divergences in morphology and song. Other taxonomic authorities still consider it conspecific.
The woodpecker finch is a monomorphic species of bird in the Darwin's finch group of the tanager family, Thraupidae endemic to the Galapagos Islands. The diet of a woodpecker finch revolves mostly around invertebrates, but also encompasses a variety of seeds. Woodpecker finches, like many other species of birds, form breeding pairs and care for young until they have fledged. The most distinctive characteristic of woodpecker finches is their ability to use tools for foraging. This behaviour indicates that they have highly specialized cognitive abilities. Woodpecker finches have also shown the ability to learn new behaviours regarding tool use via social learning. Not all populations of woodpecker finches use tools equally often, as this is influenced by the environment in which they live.
The mangrove finch is a species of bird in the Darwin's finch group of the tanager family Thraupidae. It is endemic to the Galápagos Islands. It was found on the islands of Fernandina and Isabela, but recent surveys have failed to record the species on Fernandina. It has been classified as critically endangered by BirdLife International, with an estimated population of 20–40 mature individuals in 2021, located in two large mangroves on Isabela. A study has shown that the two small populations remaining on Isabela Island have begun undergoing speciation and that one or both populations will eventually become extinct due to a lack of interbreeding.
The Galápagos dove is a species of bird in the family Columbidae. It is endemic to the Galápagos, off Ecuador. It is fairly common and is found in a wide range of open and semi-open habitats, especially in the arid lowlands of the archipelago.
The small tree finch is a bird species belonging to the Darwin's finch group within the tanager family Thraupidae. It has a grasping beak with curved culmens. Its natural habitats are subtropical or tropical dry forests and subtropical or tropical dry shrubland. During the non-breeding season it is known to form large groups with small ground-finches.
The medium tree finch is a critically endangered species of bird in the Darwin's finch group of the tanager family Thraupidae. It is endemic to the Galápagos Islands where it is only found on Floreana Island. Its name is derived from the fact that the bird's beak is intermediate in size between that of the small tree finch and the large tree finch. Because it has a very small range on a single island, and because of the introduction of a parasitic fly which kills the nestlings, the International Union for Conservation of Nature has rated the medium tree finch as "critically endangered".
The sharp-beaked ground finch is a species of bird in the Darwin's finch group of the tanager family Thraupidae. It is classified as a least-concern species by the International Union for Conservation of Nature and it is native to the Galápagos Islands in Ecuador. It has a mass of around 20 grams (0.71 oz) and the males have black plumage, while females have streaked brown plumage. This finch was described by Richard Bowdler Sharpe in 1888.
The medium ground finch is a species of bird in the family Thraupidae. It is endemic to the Galapagos Islands. Its primary natural habitat is tropical shrubland. One of Darwin's finches, the species was the first which scientists have observed evolving in real-time.
The small ground finch is a species of bird in the tanager family Thraupidae. Endemic to the Galápagos Islands, it is common and widespread in shrubland, woodland, and other habitats on most islands in the archipelago. It commonly feeds on small seeds and parasites from the skins of Galápagos land and marine iguanas and Galápagos tortoises.
The Floreana mockingbird or the Charles Island mockingbird, is a species of bird in the family Mimidae. It was endemic to Floreana, one of the Galápagos Islands, but now is found only on two nearby islets, Campeón and Gardner-near-Floreana. The Floreana mockingbird is also known as Darwin's mockingbird, as it was the arguable inspiration for Charles Darwin's work on the origins of species; he noticed distinct differences between them and previous species he had encountered and consequently established the existence of other variants on neighboring islands.
The Inaccessible Island finch, also known as the Inaccessible bunting, is a species of bird in the family Thraupidae.
The vegetarian finch is a species of bird in the Darwin's finch group of the tanager family Thraupidae endemic to the Galápagos Islands. It is the only member of the genus Platyspiza.
The Española cactus finch, is a species of bird in the tanager family Thraupidae. It is one of Darwin's finches, and is endemic to the Galápagos islands, where it is restricted to Española, Genovesa, and the Darwin and Wolf Islands. This rather dark bird resembles the smaller and finer-beaked common cactus finch, but the two species do not co-inhabit any island.
The Daphne Major finches are a group of Darwin's finches that inhabit Daphne Major island of the Galápagos. The common cactus finch and the medium ground finch are the main species; while the large ground finch and the Española cactus finch are regular immigrants. Most extensively studied by Peter and Rosemary Grant of Princeton University since 1973, the birds are one of the sources of the understanding of bird behaviour, adaptation, and evolution.
