Large ground-finch (Geospiza magnirostris)
|Also known as:||Large ground finch|
|Weight||35 g (2)|
- The largest of the famous Darwin finches - a perfect example of adaptive radiation.
- The large ground-finch is endemic to the Galapagos islands.
- The large ground-finch specialises in eating the big hard seeds on the ground.
- The large ground-finch is generally an opportunist breeder, laying eggs after a period of rainfall when food abundance will be highest.
Classified as Least Concern (LC) on the IUCN Red List (1).
As icons of evolution, no other plant or animal group rivals the fourteen closely related birds known collectively as Darwin’s finches. With the exception of one species, all inhabit the Galapagos Islands where they appear to have evolved from a single ancestral flock that arrived in the archipelago several millennia ago (2) (3) (4). The largest of Darwin’s finches is the appropriately named, large ground-finch (2). Like the other ground finches, the male plumage of the large ground-finch is completely black while the female is brown and streaked (3). In addition to being the largest finch in the Galapagos, it also has the broadest beak; an attribute that enables it to exploit food sources less accessible to the smaller beaked finches (2) (3).
The large ground-finch is endemic to the Galapagos where it occurs on the islands of Wolf, Darwin, Pinta, Marchena, Genovesa, Santa Fe, Daphne Major, Santa Cruz, Pinzón, Rábida, Santiago, Fernandina, Isabela (3).
Occurs mainly in the arid lowland zone on each island (5).
The highly specialised beaks of Darwin’s finches enable each species to occupy a different ecological niche based on different food types (2). 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) (3). Having a large beak, the large ground-finch is able to eat bigger and harder seeds than the other ground finches, with the woody seeds of Tribulus cistoides being its primary food source (6).
Darwin’s finches generally breed opportunistically with egg-laying being most profuse when rainfall is high and food abundant (3). 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 (2).
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 (2).
Like 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 (4). Fortunately, the large ground-finch is still relatively abundant in parts of its range and currently is not thought to be undergoing a significant decline (7).
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 (8). Furthermore,scientists from the Charles Darwin Foundation are continuously involved in research on Darwin’s finches in order to ensure their long-term conservation (4).
To find out more about the conservation of Darwin’s finches visit:
Charles Darwin Foundation:
For more information on this and other bird species please see:
Authenticated (21/04/09) by Professor Peter R. Grant, Department of Ecology and Evolutionary Biology, Princeton University.
- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Granivorous: seed eating.
- Monogamous: having only one mate during a breeding season, or throughout the breeding life of a pair.
IUCN Red List (December, 2008)
- Hau, M. and Wikelski, M. (2001) Darwin’s Finches. In: Encyclopedia of Life Sciences. John Wiley & Sons, Chichester.
- 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.
Charles Darwin Foundation (February, 2009)
- Lack, D. (1983) Darwin’s Finches. Cambridge University Press, UK.
- Grant, P.R. and Grant, B.R. (2006) Evolution of character displacement in Darwin’s Finches. Science, 313: 224 - 226.
Birdlife International (February, 2009)
UNEP-WCMC (February, 2009)