Overview

Brief Summary

Biology

Darwin's finches are distinguished by their highly specialised beaks, which enable each species to occupy a different ecological niche (6). The ground finches (Geospiza sp.) feed mainly on the ground and are generally granivorous, but also feed on arthropods and the fruit of Opuntia cacti (2) (6). In particular, small ground-finch populations in highland areas, such as on Santa Cruz, tend to spend considerably more time foraging in low vegetation (9). With its compact beak, this species is much more efficient at foraging for smaller food items than the other ground-finches, with the very small seeds of Sesuvium edmonstonei and Tiquilia fusca being typical components of its diet (7). Darwin's finches generally breed opportunistically, with egg-laying being most profuse when rainfall is high and food abundant (2). Pairs are typically monogamous and maintain small territories within which they build a small dome-shaped nest in a bush or cactus. On average each clutch comprises three eggs that are incubated for around 12 days before hatching. The nestlings are mostly raised on insects and leave the nest after about two weeks (6). During the breeding season, competition for resources between different species of finch can be extremely intense. In promoting ever increasing levels of specialisation, competition for resources has been the driving force behind the evolution of Darwin's finches. This is exemplified by the widely divergent beak sizes of different finch species co-inhabiting one island, compared with much more convergent beak sizes when the same species are isolated from each other on separate islands (6).
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Description

Motivated by the breadth of morphological variation he witnessed in the Galapagos' thirteen finch species, Darwin mused that “seeing this gradation and diversity 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.” (3) (4). In accordance with their apparent influence on his theory of natural selection, this group of closely related passerines has come to be known as Darwin's finches. One of the commonest species of Darwin's finches is the small ground-finch (3). Like the other ground finches, the adult male plumage of the small ground-finch is completely black while the female is brown and streaked (2) (5). Compared to the other ground finches, the small ground-finch has a reduced beak size, making it adept at foraging for small seeds (6) (7).
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Distribution

Range

Arid scrub of main Galapagos Islands.
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Range

The small ground-finch is endemic to the Galápagos, where it occurs on the islands of Pinta, Marchena, Floreana, San Cristóbal, Santa Fe, Daphne Major, Santa Cruz, Pinzón, Rábida, Santiago, Fernandina, Española, Isabela, Baltra and Seymour (2).
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Ecology

Habitat

Habitat and Ecology

Systems
  • Terrestrial
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Occurs mainly in the arid lowland zones, dominated by cacti, deciduous shrubs and dwarf trees, but on the elevated islands it is also found in the moist highland forest where Scalesia dominates (5) (8) (9).
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s

Justification
Although this species may have a small range, it is not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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Status

Classified as Least Concern (LC) on the IUCN Red List (1).
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Population

Population
The global population size has not been quantified, but this species is described as 'common' (Stotz et al. (1996).

Population Trend
Stable
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Threats

In common with much of the Galapagos' endemic fauna and flora, Darwin's finches are under threat from habitat destruction, introduced diseases, and invasive predatory species such as rats and cats (10). However, the small ground-finch is still relatively abundant and is not thought to be undergoing a significant decline (11).
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Management

Conservation

For their unique biological diversity and significance, the Galapagos Islands are designated both a National Park and a World Heritage Site. As a consequence, conservation of the islands' native fauna and flora is a high priority (12). Furthermore,scientists from the Charles Darwin Foundation continue to conduct further research on Darwin's finches in order to ensure their long-term conservation (10).
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Wikipedia

Small ground finch

The small ground finch (Geospiza fuliginosa) is a species of bird in the tanager family Thraupidae. Endemic to the Galápagos Islands, it is common and widespread in shrubland, woodland, and other habitats on most islands in the archipelago. It commonly feeds on small seeds and parasites from the skins of Galápagos tortoises, and Galápagos land and marine iguanas.

Taxonomy and systematics[edit]

The small ground finch is one of Darwin's finches, a group of closely related birds which evolved on the Galápagos Islands. The group is related to the Tiaris grassquits, which are found in South America and the Caribbean.[2]

When Charles Darwin first collected the species in 1835, he thought it was a finch. John Gould, who officially described Darwin's specimens, agreed, placing it in the genus Fringilla with the Old World finches. By 1841, Gould had changed his mind, moving this and five other species into the new genus Geospiza — still a genus of finches, but distinct from those of the Old World.[3] DNA research has now shown that all Darwin's "finches" are actually tanagers.[4]

The name Geospiza is a combination of the Greek words geo-, meaning "ground-", and spiza, meaning finch.[5] The specific name fuliginosa is late Latin for "sooty".[6]

It is known to hybridize (rarely) with the medium ground finch.[7]

Description[edit]

This is the smallest of the ground finches, measuring 11 cm (4.3 in) in length .[8][nb 1] Its beak is short and pointed, with a slightly curved culmen.[8] On average, its beak is smaller than that of the medium ground finch, though 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 differences 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 have been 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 is causing differentiation in traits, but hybrids are well adapted in their “hybrid zone.” [12]

Habitat and range[edit]

Like all but one of the other Darwin's finches, the small ground finch is endemic to the Galápagos Islands. Abundant and widespread, it is found on every island in the archipelago except Genovesa, Wolf and Darwin. It is most common in arid coastal and transition areas, though it moves into the highlands following the breeding season.[8]

Behavior[edit]

Feeding[edit]

Like the other Galápagos ground finches, the small ground finch is an omnivore 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 forms symbiotic relationships with Galápagos tortoises and both marine and Galápagos land iguanas, gleaning parasites from their skins.[8]

Voice[edit]

The small ground finch's song is rapid and weak, transcribed as "twichooo-twichooo" or "teur-weee".[8]

Conservation and threats[edit]

Although the population size of the small ground finch has not been quantified, it is described as common across the Galápagos, and the International Union for the Conservation of Nature lists it as a species of Least 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 the Important Bird Areas established on the islands.[16] The species suffers from high mortality rates from the parasitic fly, ranging from 16% to 95% over a four year period (2002-2006). [17]

Note[edit]

  1. ^ 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.[9]

References[edit]

  1. ^ a b BirdLife International (2012). "Geospiza fuliginosa". IUCN Red List of Threatened Species. Version 2012.1. International Union for Conservation of Nature. Retrieved 16 July 2012. 
  2. ^ Newton, Ian (2003). Speciation and Biogeography of Birds. San Diego, CA, USA: Academic Press. p. 78. ISBN 978-0-12-517375-9. 
  3. ^ Donahue, Kathleen (2011). Darwin's Finches: Readings in the Evolution of a Scientific Paradigm. Chicago, IL, USA: University of Chicago Press. p. 154. ISBN 978-0-226-15771-9. 
  4. ^ Tudge, Colin (2008). The Bird: A Natural History of Who Birds Are, Where They Came From, and How They Live. New York, NY, USA: Random House. p. 183. ISBN 978-0-307-34205-8. 
  5. ^ Jobling (2010), p. 172
  6. ^ Jobling (2010), p. 165.
  7. ^ Grant (2008), p. xvi.
  8. ^ a b c d e f Swash, Andy; Still, Rob (2005). Birds, Mammals, and Reptiles of the Galapagos Islands: An Identification Guide (2 ed.). London, UK: Christopher Helm. p. 102. ISBN 978-0-300-11532-1. 
  9. ^ 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. 
  10. ^ Rice, Stanley A. (2007). Encyclopedia of Evolution. New York, NY, USA: Facts on File. p. 114. ISBN 978-1-4381-1005-9. 
  11. ^ http://osu.worldcat.org/title/adaptive-divergence-in-darwins-small-ground-finch-igeospiza-fuliginosai-divergent-selection-along-a-cline/oclc/5164006122&referer=brief_results
  12. ^ Sulloway, F, & Kleindorfer, S (2013). Adaptive Divergence in Darwin's Small Ground Finch (Geospiza fuliginosa): Divergent Selection along a Cline. Biological Journal of the Linnean Society, 110, 45-59.
  13. ^ Eibl-Eibesfeldt, Irenäus (1996). Love and Hate: The Natural History of Behavior Patterns. Hawthorne, NY, USA: Aldine de Gruyter. p. 38. ISBN 978-0-202-02038-9. 
  14. ^ Scott, Thomas, ed. (1996). Concise Encyclopedia Biology. Berlin, Germany: Walter de Gruyter. p. 510. ISBN 978-3-11-010661-9. 
  15. ^ Stattersfield, Alison J. (1998). Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. Cambridge, UK: BirdLife International. p. 171. ISBN 978-0-946888-33-7. 
  16. ^ "Small Ground-finch (Geospiza fuliginosa) - BirdLife species factsheet". BirdLife International. Retrieved 21 October 2012. 
  17. ^ O'connor, J, & Robertson, J (2014). Darwin's Finch Begging Intensity Does Not Honestly Signal Need in Parasitised Nests. Ethology, 228, 37.

Cited sources[edit]

  • Jobling, James A. (2010). Helm Dictionary of Scientific Bird Names. London, UK: Christopher Helm. ISBN 978-1-4081-2501-4. 
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