Overview

Brief Summary

Introduction

On Wolf and Darwin, two small, dry, northern islands of the Galápagos, there lives a bird called the vampire finch(1,5,7,9). If you didn’t know its name, you’d probably think it was pretty harmless. This particular subspecies of the sharp-beaked ground finch(1,5,7) (a bird that is found in many different varieties throughout the Galápagos(3,4,5,7,9)) is even more tame and approachable than other Galápagos finches, possibly because, unlike on other islands of the Galápagos, on Wolf and Darwin there are no dangerous hawks or owls to force finches to be cautious(1,6,7). Like other Galápagos ground finches, male vampire finches are black (though they have somewhat more unusual lighter markings under the tail(6)) and females have brown streaked feathers(3,6,9). Yet this seemingly innocent bird has a secret weapon: its beak. The vampire finch’s beak is longer and sharper than that of the other subspecies of the sharp-beaked ground finch(1,5,6,7). This makes it handy for eating the nectar and pollen of Opuntia cactus flowers, and even cracking open and feeding on the eggs of seabirds such as boobies(1,4,5,6,7,9), but that’s not all it’s good for. Vampire finches sometimes drink blood. They will occasionally perch on the feathers of seabirds much larger than themselves, especially certain boobies, and use their special beaks to make a wound at the base of the victim’s wings or tail(1,2,3,4,5,6,7,8,9,10). Then they feast on the blood that flows from the cut, sometimes even gathering in groups to feed off the same wound (8,10). This amazing behavior is believed to have evolved from a habit of the finch’s that was actually beneficial to the seabirds: feeding off of unwanted ticks and flies found on the seabirds’ backs (2,7). The seabirds may not have figured out that the finches aren’t helping keep them clean anymore(2)!

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Comprehensive Description

The vampire finch (Geospiza difficilis septentrionalis) is a subspecies of the sharp-beaked ground finch (Geospiza difficilis)91,5,7), a species which is found in many widely-varying forms throughout the Galápagos Islands(3,4,5,7,9). The vampire finch subspecies lives on Wolf and Darwin, the two small, arid, northern islands of the Galápagos(1,5,7,9). Like the other finches in the genus Geospiza, male vampire finches are black (though they have somewhat more unusual lighter markings under their tails(6)) and females are generally brown with streaks(3,6,9). This subspecies’ relative wing length on average is greater than in the other subspecies of sharp-beaked ground finch(1,7). Another unusual feature is that these finches are even more tame and approachable than other Darwin’s finches, possibly because on Wolf and Darwin, unlike on other islands of the Galápagos, there are no dangerous hawks or owls to threaten small finches(1,6,7). Despite this tameness, though, perhaps the most distinctive physical feature of the vampire finch is its beak, which is longer and sharper than that of the other subspecies(1,5,6,7). This beak is useful for a variety of purposes, from feeding on the nectar and pollen of Opuntia cactus flowers (though sharp-beaked ground finches on Genovesa Island with a shorter beak can do this too(5)) to cracking open and feasting on the eggs of seabirds such as boobies, but it is most famously used for a highly unusual habit: drinking blood (1,4,5,6,7,9). Vampire finches will occasionally perch on the feathers of seabirds much larger than themselves, especially certain boobies (genus Sula), and use their beaks to make a wound at the base of the wing or tail(1,2,3,4,5,6,7,8,9,10). They then feed on the blood that flows out of the cut, sometimes even gathering in groups to feed off the same wound (8,10). This parasitic behavior may have evolved from a habit of the finch’s that was actually beneficial to the seabirds: feeding off of ticks and flies found on their backs (2,7).

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Distribution

Range

Galapagos Islands (Darwin and Wolf Is.).

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Wikipedia

Vampire Finch

The vampire finch (Geospiza difficilis septentrionalis) is a small bird native to the Galápagos Islands. It is a very distinct subspecies of the sharp-beaked ground finch (Geospiza difficilis) endemic to Wolf and Darwin Islands.[1]

The vampire finch is sexually dimorphic as typical for its genus, with the males being primarily black and the females grey with brown streaks. It has the largest and most pointed beak of all G. difficilis subspecies, and overall looks like a miniature common cactus finch rather than, as the other subspecies do, a large small ground finch with a straight bill.[2] It has a lilting song on Wolf, a buzzing song on Darwin, and whistling calls on both islands; only on Wolf, a drawn-out, buzzing call is also uttered.[1]

This bird is most famous for its unusual diet. The vampire finch occasionally feeds by drinking the blood of other birds, chiefly the nazca and blue-footed boobies, pecking at their skin with their sharp beaks until blood is drawn.[2] Curiously, the boobies do not offer much resistance against this. It has been theorized that this behavior evolved from the pecking behavior that the finch used to clean parasites from the plumage of the booby.[3] The finches also feed on eggs, stealing them just after they are laid and rolling them (by pushing with their legs and using their beak as a pivot) into rocks until they break.

More conventionally for birds, but still unusual among Geospiza, they also take nectar from Galápagos prickly pear (Opuntia echios var. gigantea) flowers at least on Wolf (Schluter & Grant 1984). The reason for these peculiar feeding habits is the lack of freshwater on these birds' home islands. Nonetheless, the mainstay of their diet is made up from seeds and invertebrates as in their congeners.[2]

The vampire finch is endangered, being a small-island endemic. The Galápagos finch species collectively form a showcase example of Charles Darwin's theory of natural selection. The 15 species of Galapagos finches are often called "Darwin's finches". They are used as an example of how the descendants of one ancestor can evolve into several species as they adapt to different conditions.

References[edit]

  1. ^ a b Grant, Peter R.; Grant, B. Rosemary & Petren, Kenneth (2000): The allopatric phase of speciation: the sharp-beaked ground finch (Geospiza difficilis) on the Galápagos islands. Biol. J. Linn. Soc. 69(3): 287–317. doi:10.1006/bijl.1999.0382 PDF fulltext
  2. ^ a b c Schluter, Dolph & Grant, Peter R. (1984): Ecological Correlates of Morphological Evolution in a Darwin's Finch, Geospiza difficilis. Evolution 38(4): 856-869. doi:10.2307/2408396 (HTML abstract and first page image)
  3. ^ Galef, Bennett G., Jr. Bekoff, Marc; Jamieson, Dale, eds. Interpretation and Explanation in the Study of Animal Behavior. Volume I: Interpretation, Intentionality, and Communication. BOULDER, SAN FRANCISCO, & OXFORD: Westview Press. p. 78. ISBN 978-0-8133-7979-1. 
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