Medium ground finch
|Medium ground finch|
The medium ground finch (Geospiza fortis) is a species of bird in the Thraupidae family. It is endemic to the Galapagos Islands. Its natural habitats are subtropical or tropical dry forests and subtropical or tropical dry shrubland. One of Darwin's finches, the species was the first which scientists have observed evolving in real-time.
In 1977, a severe drought reduced the supply of seeds in the Galapagos. The finch, which normally preferred small and soft seeds, was forced to turn to harder larger seeds. Subsequently, there has been a 10% change in the size of beak for these finches in a couple of generations.
Like the other members of its genus, the medium ground finch is strongly sexually dimorphic; the female's plumage is brown and streaky, while male's is solid black, with white tips to the undertail coverts. The bird measures 12.5 cm (4.9 in) in length—which falls between the lengths of the small and large ground finches.[nb 1] The bill of this species is quite variable in size, though the length of the upper mandible is always greater than the depth of the bill at its base.
Habitat and range
The medium ground finch feeds primarily on seeds, although it is also known to eat flowers, buds, young leaves, and the occasional insect. It forages either on the ground or in low vegetation.
- By convention, length is measured from the tip of the bill to the tip of the tail on a dead bird (or skin) laid on its back.
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- BirdLife International (2012). "Geospiza fortis". IUCN Red List of Threatened Species. Version 2012.1. International Union for Conservation of Nature. Retrieved 16 August 2012.
- Scott, Thomas, ed. (1996). Concise Encyclopedia Biology. Berlin, Germany: Walter de Gruyter. p. 510. ISBN 978-3-11-010661-9.
- Swash & Still (2006), p. 102.
- Cramp, Stanley, ed. (1977). Handbook of the Birds of Europe, the Middle East and North Africa: Birds of the Western Palearctic, Volume 1, Ostrich to Ducks. Oxford University Press. p. 3. ISBN 978-0-19-857358-6.
- Swash & Still (2006), p. 32.
- Swash & Still (2006), p. 152.
Swash, Andy; Still, Rob (2006). Birds, Mammals and Reptiles of the Galapagos Islands: An Identification Guide. New Haven, CT, USA: Yale University Press. ISBN 978-0-300-11532-1.
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