| Small ground finch | |
|---|---|
 | |
| female, Fernandino 976. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Thraupidae |
| Genus: | Geospiza |
| Species: | G. fuliginosa |
| Binomial name | |
| Geospiza fuliginosa Gould, 1837 | |
 | |
Thesmall ground finch (Geospiza fuliginosa) is a species ofbird in thetanagerfamilyThraupidae.Endemic to theGalápagos Islands, it is common and widespread inshrubland, woodland, and other habitats on most islands in the archipelago. It commonly feeds on small seeds andparasites from the skins ofGalápagos land andmarine iguanas andGalápagos tortoises.
The small ground finch is one ofDarwin's finches, a group of closely related birds whichevolved on the Galápagos Islands. The group is related to theTiaris grassquits, which are found in South America and theCaribbean.[2]
WhenCharles Darwin first collected the species in 1835, he thought it was afinch.John Gould, who officially described Darwin's specimens, agreed, placing it in the genusFringilla with theOld World finches. By 1841, Gould had changed his mind, moving this and five other species into the new genusGeospiza — still a genus of finches, but distinct from those of the Old World.[3]DNA research has now shown that all of Darwin's "finches" are actuallytanagers.[4]
The nameGeospiza is a combination of theGreek wordsgeo-, meaning "ground-", andspiza, meaning finch.[5] Thespecific namefuliginosa is lateLatin for "sooty".[6]
It is known tohybridize (rarely) with themedium ground finch.[7]
The small ground finch is the smallest of the ground finches, measuring 11 cm (4.3 in) in length.[8][nb 1] Itsbeak is short and pointed, with a slightly curvedculmen.[8] On average, its beak is smaller than that of themedium ground finch, but there is a significant overlap in size between the two, particularly on islands where only one of the two species exists. On islands where the two species compete directly, the difference between their beaks are greater.[10] The male is black with white-tipped undertail coverts, while the female and young are brown with streaked underparts.[8] There are observable phenotypic differences between finches that live in lowlands and ones that live in highlands, and this change is most likely attributed to adaptation.[11] The finches seen in highlands have larger, more pointed beaks and smaller feet and claws compared to the lowland variety. These finches are on a cline (series of biocommunities on a continuous gradient), and individuals in the hybrid zone have intermediate traits. This is an example of parapatric speciation, where the elevation gradient of 560 meters causes differentiation in traits, but hybrids are well adapted in their “hybrid zone.”[12]
Like all but one of the other Darwin's finches, the small ground finch isendemic to the Galápagos Islands. Abundant and widespread, it is found on every island in the archipelago except for theGenovesa,Wolf andDarwin islands. It is most common in arid coastal and transition areas, though it moves into the highlands following the breeding season.[8]
Like the other Galápagos ground finches, the small ground finch is anomnivore with a preference for vegetable matter.[13] It feeds primarily on the ground or in low vegetation, eating seeds, buds, flowers, leaves and the occasional insect.[14] It formssymbiotic relationships withGalápagos tortoises and bothmarine andGalápagos land iguanas bygleaning parasites from their skins.[8]
The small ground finch's song is rapid and weak and is transcribed as "twichooo-twichooo" or "teur-weee".[8]
Although the population size of the small ground finch has not been quantified, it is described as common across the Galápagos, and theInternational Union for Conservation of Nature lists it as a species ofLeast Concern. Its numbers seem to be stable, and neither its population size nor its range size appear to approach thresholds for concern.[1] However, like all endemic wildlife on the Galápagos Islands, it is impacted by some human activities, including fires, overgrazing by domestic and feral animals, and the introduction of exotic species.[15] It is found in ten of theImportant Bird Areas established on the islands.[1] The species suffers from high mortality rates from the parasitic fly, ranging from 16% to 95% over a four-year period (2002–2006).[16]
