Abstract
It was about 150 years ago that Charles Darwin met the thirteen species of finches on the Galapagos Islands. The encounter was to shake the world, but it took twenty-five years for the ideas to germinate into his theory of evolution. Even in 1985 the furious debate continues. Darwin himself said that his new understanding seemed to him like confessing a murder because it challenged the whole framework of the philosophical basis for understanding human life.
The most intense period of controversy came in the 1920s and 1930s, culminating in the confrontation between two lawyers, Clarence Darrow and William Jennings Bryan, in the Scopes "monkey trial," that humankind evolved from a lower form of life rather than being created human by God. The jury found for God in that trial, but the issue continues to split the academic world in many parts of the country. What would Darwin say?
In short, he said that the thirteen species of Galapagos finches apparently had a common ancestry, and that they had become separate species because they spread to different environments that required different feeding skills. Since certain variations would give the possessor an advantage over competing individuals, the ones possessing advantages adaptive to the environment would survive and thus would reproduce better than less fortunate specimens. As the offspring inheriting the advantage increased in the gene pool, a new species eventuated. This came to be referred to as the survival of the fittest. What was his evidence?
Of the thirteen Galapagos finches known to Darwin, all can still be seen on the islands, although some are few and elusive. In 1938 David Lack, the English ornithologist, studied them on the site and said that they were dull to look at and dull to listen to. "Only the variety of their beaks and the number of their species excite attention - small finch-like beaks, huge finch-like beaks, parrot-like beaks, straight wood-boring beaks, decurved flowerprobing beaks, slender warbler-like beaks, species which look very different and species which look very similar." (p. 11; David Lack, Darwin s Finches, New York, Cambridge University Press, Revised, 1983, 208 pp.)
Shapes and relative sizes of the finches' beaks resemble the mandibles of warblers and grosbeaks - and everything between. Heavy beaks are used to crack hard seeds. Long beaks penetrate cactus flowers. Small beaks feed on concealed insects. Roger Tory Peterson watched a large cactus finch use its sturdy beak to toss rocks in search of food. Some of the rocks weighed fifteen times the weight of the bird. That's equivalent to a 130-pound woman moving a ton!
The woodpecker finch has a longish beak but augments this by cutting a cactus spine to force grubs out of holes. As mentioned, the sharp-beaked ground finch snips the fresh feather of a larger bird and drinks the blood. The specialization in food made possible by beak evolution has separated the species remarkably.
Nesting habits of Darwin's finches are interesting. In most species, the single or mated male builds the nest - in fact, may build as many as eight nests. He displays near his nest, and may even display near a nest built by another species. They are so interchangeable that the nest finally chosen by the pair for laying and raising the brood may have been built by the male of another species.
The number of eggs laid is influenced by food supply. If too few eggs are laid, the species cannot be perpetuated, but if so many are laid and hatched that the food supply is inadequate, all babies will starve in the nest. Breeding occurs in the Galapagos only during the rainy season, usually December through March.
Galapagos wildlife is not exported, so the birds are not known to exotic aviculture, but some of the Darwin finches resemble species from the mainland, in particular the blue-black grassquit or jacarini (Volatinia jacarini) or the parrot-billed seedeater (Neoryncbus peruoiensis), two species I have tried to cage-breed for years without success.
In general, Darwin's finches can be described as greyish-brown and shorttailed. Some are monomorphic, some dimorphic. They build large roofed nests, are monogamous and are quite territorial. The main distinction between the species, the factor which caught Darwin's attention, is the beak, as described above by Lack.