Large cactus-finch (Geospiza conirostris)

Description

Large cactus-finch fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Large cactus-finch description

Ever since they were first collected during the voyage of the Beagle, Darwin’s finches have inspired a plethora of evolutionary research ⁽³⁾. Descending from an ancestral flock that colonised the Galapagos archipelago several millennia ago, each species famously possesses a beak specialised according to its individual dietary niche ^{(2) (4)}. The large cactus-finch is one of the most variable of Darwin’s finches, with individuals in a single population exhibiting a relatively wide array of beak dimensions ⁽⁵⁾. Like the other ground finches (Geospiza sp.), the adult male plumage of the large cactus-finch is completely black while the female is brown and streaked ⁽²⁾.

Weight

28 g ⁽²⁾

Large cactus-finch biology

The large cactus-finch generally feeds on seeds, arthropods and, as its name suggests, various parts of the prickly pear cactus (Opuntia helleri) ^{(5) (7)}. During the dry season when competition for food is most intense, it exercises different skills to obtain four main food items. This includes cracking hard Opuntia seeds, extracting seeds from Opuntia fruit and eating the arils, stripping bark to find arthropods, and opening decomposing Opuntia pads to obtain insect larvae ⁽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 ⁽⁴⁾.

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 ⁽⁴⁾.

Large cactus-finch range

The large ground-finch is endemic to the Galapagos where it occurs on the islands of Española and Genovesa ⁽²⁾.

Large cactus-finch habitat

Occurs mainly in the arid lowland zone ⁽⁶⁾.

Large cactus-finch status

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

Large cactus-finch 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 ⁽⁸⁾. However, there aren’t known to be any substantial threats to the large cactus-finch in particular and its population is thought to be stable ⁽⁹⁾.

Large cactus-finch 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 ⁽¹⁰⁾. Furthermore,scientists from the Charles Darwin Foundation continue to conduct further research on Darwin’s finches in order to ensure their long-term conservation ⁽⁸⁾.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

To find out more about the conservation of Darwin’s finches visit:

• Charles Darwin Foundation:
  http://www.darwinfoundation.org

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org

Authentication

Glossary

Arils

Fleshy coating on some seeds that often functions to attract animals which disperse the seed.

Arthropods

A very diverse phylum (a major grouping of animals) that includes crustaceans, insects and arachnids. All arthropods have paired jointed limbs and a hard external skeleton (exoskeleton).

Endemic

A species or taxonomic group that is only found in one particular country or geographic area.

References

1. IUCN Red List (May, 2009)
   http://www.iucnredlist.org/
2. Grant, P.R. and Grant, B.R. (2007) How and Why Species Multiply: The Radiation of Darwin's Finches. Princeton University Press, Princeton, New Jersey.
3. Sulloway, F.J. (1982) The Beagle collections of Darwin's finches (Geospizinae). Bulletin of the British Museum (Natural History) Historical Series, 43(2): 49 - 94. Available at:
   http://darwin-online.org.uk
4. Hau, M. and Wikelski, M. (2001) Darwin’s Finches. In: Encyclopedia of Life Sciences. John Wiley & Sons, Chichester.
5. Grant, B.R. and Grant, P.R. (1989) Evolutionary dynamics of a natural population: the large cactus finch of the Galápagos. University of Chicago Press, Chicago.
6. Lack, D. (1983) Darwin’s Finches. Cambridge University Press, UK.
7. Grant, B.R. (1985) Selection on bill characters in a population of Darwin's Finches: Geospiza conirostris on Isla Genovesa, Galapagos. Evolution, 3(9): 523 - 532.
8. Charles Darwin Foundation (April, 2009)
   http://www.darwinfoundation.org/en/galapagos/species/birds/native-endemic
9. Birdlife International (April, 2009)
   http://www.birdlife.org
10. UNEP-WCMC (March, 2009)
    http://www.unep-wcmc.org/protected_areas/data/wh/galapago.html