Darwin's Finches are a closely related group of 15 species of birds endemic to the Galapagos Islands (1 on Cocos Island). They are at first sight, unremarkable small brown birds that look more alike than they are different.
The species differ in body size, and the shape and proportions of their beak and feet. First described by Darwin, after careful study they were concluded to be an example of adaptive radiation from an original small bird species that arrived in the islands and evolved into different species to occupy a range of different niches.
Darwin's Finches - subfamily Geospizinae
Profile - Animals of the Galapagos
Darwin's finches facts Basics
Weight: 8 to 38 grams for the smallest (warbler finch) and largest (vegetarian finch) species
Length: 10 to 20cm for smallest and largest species
Breeding Season: Like a number of other animals on the Galapagos islands Darwin's Finches will breed at almost any time of the year when conditions are suitable which usually means following rains which stimulates plant growth and therefore food supply. This commonly occurs from January to May.
Estimated world population and conservation status: - The finches are all endemic to the Galapagos Islands other than one species endemic to the Cocos Island which reached there from the Galapagos. Of the Galapagos species, 6 are classed as "least concern" with populations in the thousands or tens of thousands, 6 are "vulnerable" with less than 1,000 individuals and 2 are critically endangered, the medium tree finch, Geospiza pauper has maybe 1000-2000 individuals but with a falling population and is threatened by introduced parasitic flies, the Mangrove finch, G. helibates has less than 100 individuals and is the subject of intensive conservation measures.
Feeding: Between them the finches feed on seeds, vegetation, nectar, insects and other arthropods, it is specialisms in feeding as a result of differing physical size and beak size and shape that caused the separation of the ancestral species into the range of species found today. One sub species, the vampire finch, Geospiza difficilis septentrionalis, occasionally feeds on the blood of Nazca and blue-footed boobies, pecking at the feet until blood is drawn, possibly a development from a similar behaviour whereby the larger birds allow the smaller to peck for parasites.
Distribution: Throughout the Galapagos Islands, one species is found on the Cocos Islands.
Predators: Native predators on the finches include snakes, owls and hawks which don't really threaten numbers in the longer term. Introduced species, cats, rats and dogs are causing more difficulty as is an introduced species of fly which is a nest parasite leading to up to 95% chick mortality in the mangrove finch, G. helibates. Environmental degradation by human inhabitation, pigs, goats and tourism are all taking a toll too.
Evolution, Adaptive Radiation and Speciation
Darwin's Finches form a monophyletic group, this means that they all descended from a common ancestor, an ancestral species of bird that arrived in the Galapagos Archipelago from Central or South America around 2 million years ago.
We now know that this ancestor was not a finch but belonged to the group of birds called Tanagers, the closest modern ancestor to the modern Galapagos Finches is a bird that rejoices in the name of the "Dull-colored Grassquit", Tiaris obscurus. The ancestral birds found their way to the Galapagos, possibly blown off course by winds, established a breeding colony and then over time their descendants colonized the islands of the Archipelago (including some that reached Cocos Island) and underwent a process called adaptive radiation.
Adaptive radiation is the process whereby a group of organisms, in the absence of much competition and given the availability of varied ecological niches evolves to a number of different species each of which have their own specilizations for occupying their own particular niches. Thus the birds that were to become known as Darwin's Finches evolved to occupy a number of niches in the Galapagos based largely on the size and shape of their beaks which allowed them to efficiently eat different types of food, and also their overall body size.
Adaptive radiation with photos or diagrams
Left - a modern Dull-colored Grassquit, Tiaris obscurus, very similar to the ancestor of Darwin's Finches.
Top - Insect eater - Warbler finch,
Middle - Cactus eater - Common cactus finch, Geospiza scandens
Bottom - Nut, large seed eater - Large ground finch, Geospiza magnirostris
Beaks? Is that enough to result in different species?
When the first ancestors of Darwin's Finches arrived on the Galapagos Islands some two million years ago, they will have found a place where there there was perhaps potential food sources going untapped or they were being used by other animals that were not very adept at using that food and so using it inefficiently.
The first colonists would have been able to find enough food to survive and maintain a viable population. Within that population there would have been variability in size, form and function of all body parts in just the way that people differ from each other in endless different ways though are still all people.
The variation in beak size and proportion will have given some of the finches an advantage in eating certain types of food, so enabling them to exist in possibly new areas or to do better than others with the original beak type in the same area. Breeding amongst themselves, those traits that enabled success would have become more established in the new sub-population, at the same time other features that helped deal with the food such as to the digestive system would enhance the benefits of beak shape and size. A phenomenon called "genetic drift" would also be occurring whereby the genes of the breakaway group no longer mix with the original fonder population until such point where interbreeding becomes very rare and the new type can be regarded as a new species. On the Galapagos Islands this separation in breeding is partly related to changes in the birds' song so and mate selection, the birds also prefer mates that look similar to themselves.
The beaks are the tools to do the job of getting enough food, the correct tool enables more efficient food collection of a particular type of food.
Diverse environments produce a greater number of species, the Galapagos Islands can differ quite markedly from each other, with some being very low and arid and others more mountainous with various environments including wetter uplands. The islands are very isolated from other landmasses and it seems that it is very rare for any new animals to arrive there, so when the finches did so, there were a number of assorted environments available for them to adapt to.
Research into the Finches and what they can teach us about evolution is ongoing. Far from evolution being something that happened in the past and moving at a pace that is un-observable as was once assumed, the finches show that evolution can be observed and measured over a time span as short as a few years. (see video below)
In recent years, genome sequencing research has shown that beak morphology in these birds is controlled by just a few genes that explains the changes. here
Galapagos Finch Evolution
Charles Darwin visited the Galapagos Islands in September to October 1835 on board HMS Beagle in his capacity of ships' naturalist. Part of his duties were to collect samples of flora and fauna, this task on the Galapagos was largely left to Syms Covington, his servant who shot, collected and preserved a variety of birds. At the time Darwin paid the finches little attention, and they were not all properly labeled according to where they were collected. Fortunately Darwin was not the only collector of animals on the Beagle and more of what would later be called Darwin's Finches were collected by the ships' captain and doctor/naturalist who did label them correctly according to where they were collected.
In January 1837, Darwin presented the animals he had collected on his voyage to the Zoological Society of London. The finches were given to John Gould, a famous English ornithologist for identification and further study. So intrigued was Gould by the birds that he left his other work and a week later reported to the society that the birds Darwin had collected were "a series of ground Finches which are so peculiar, (as to form) an entirely new group, containing 12 species".
Further study by Gould and Darwin indicated that this group of apparently unremarkable birds were indicative of something quite significant, the beaks were variations on a theme that indicated a common origin.
"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."
Picture credits: Top banner - Medium Tree Finch | Beaks graphics photos - Dull-colored Grassquit, Tiaris obscurus used courtesy of - Dominic Sherony - under CC2 Attribution Share alike Generic license | Warbler finch, Certhidea olivacea used courtesy of - Putney Mark - under CC2 Attribution Share alike Generic license. | Cactus ground finch, Geospiza scandens used courtesy - Nancy ecosense - under CC3 Attribution Unported license. | Large ground finch, Geospiza magnirostris used courtesy - Lip Kee Yap - under CC2 Attribution Share alike Generic license.