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Darwin's Finches

Last updated over 4 years ago

During his voyage to the Galápagos Islands, Charles Darwin noticed that many of the finches were similar, except for their oddly-shaped beaks. Each species of finch seemed to use its beak for something different. When he formulated his theory of natural selection, Darwin used the finches' beaks as examples of how different environments could shape species.

Additional Darwin's Finches Resources:

BIRRD Finch Problem Space, BioQuest Curriculum Consortium

Charles Darwin's Library Collection, Biodiversity Heritage Library

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    Geospiza scandens

    Cactus Ground Finch

    The foraging behaviour of the common cactus-finch varies with the seasons, but when Opuntia cacti are flowering, the adults use their specialised beaks to feed almost exclusively on the pollen and nectar obtained from the flowers (4) (8). At other times of the year, Opuntia fruits and seeds become important components of its diet, and during the rainy season, this finch will take advantage of various additional sources of food, such as shoots, berries, seeds, caterpillars and budworms.

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    Geospiza magnirostris

    Large Ground Finch

    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).

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    Geospiza fuliginosa

    Small Ground Finch

    With its compact beak, this species is much more efficient at foraging for smaller food items such as seed than the other ground-finches.

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    Geospiza fortis

    Medium Ground Finch

    Having an intermediate sized beak, the medium ground finch is described as a generalist, able to exploit a broader range of seed sizes than the other ground finches.

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    Geospiza difficilis

    Sharp-beaked Ground Finch

    Owing to the availability of different food types, the sharp-beaked ground-finch's diet varies between the high islands and the low islands (2). Although populations on the low, dry islands mainly feed on seeds (7), they are also known to augment their diet from several unusual sources. It is on the small and remote islands of Wolf and Darwin that this species frequently drinks the blood of large seabirds, especially boobies (Sula spp.). Alighting on the backs of the larger birds, it pecks at the feather shafts with its long, pointed beak until blood begins to flow (3) (4) (5) (6) (8). In addition, it likes to feed on the eggs of seabirds, which it cracks open against rocks (5) (8), or alternatively forage for nectar from Opuntia catci (Wolf and Darwin) and the small flowers of Waltheria ovata (Genovesa) (6). In contrast, while populations at high elevations also take seeds, they concentrate most of their foraging efforts in areas of deep ground litter where invertebrate prey is abundant (7).

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    Geospiza conirostris

    Large Cactus Ground Finch

    During the dry season when competition for food is most intense, large cactus-finch 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.

  • Geospiza conirostris darwini

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    Geospiza conirostris propinqua

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    Geospiza conirostris conirostris

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    Geospiza difficilis debilirostris

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    Geospiza scandens scandens

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    Geospiza scandens abingdoni

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    Geospiza scandens intermedia

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    Geospiza scandens rothschildi

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    Geospiza difficilis difficilis

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    Geospiza difficilis septentrionalis

    Vampire Finch