Medium ground finch
| Medium ground finch | |
|---|---|
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| Male | |
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| Female | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Thraupidae |
| Genus: | Geospiza |
| Species: | G. fortis |
| Binomial name | |
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Geospiza fortis Gould, 1837 |
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The medium ground finch (Geospiza fortis) is a species of bird in the family Thraupidae. 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.
The population of medium ground finches has been experiencing inbreeding depression due to small population numbers. Inbreeding depression occurs when there is a decrease in fitness due to individuals mating with genetic relatives. Typically, this leads to a loss of genetic diversity and a reduction in heterozygosity.
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. 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. The wing shape, on average, seems to change with ecological shifts. Different selective pressures act on the wing shape of the finches, such as natural and sexual selection. The males have shorter, rounder wings, which help with maneuvering around a female during sexual displays.
Endemic to the Galápagos, the medium ground finch is found on ten islands: Baltra, Floreana, Isabela, Fernandina, Seymour, Pinzón, San Cristóbal, Santa Cruz, Santa Fé, and Santiago.
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Wikipedia