- 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/
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. 
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. 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.
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. 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. 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.
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 Galápagos finches are often called "Darwin's finches." They are used as an example of how the descendants of one ancestor can evolve through adaptive radiation into several species as they adapt to different conditions on various islands.
- 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
- Rothschild, W. and E. Hartert. 1899. A Review of the Ornithology of the Galapagos Islands. With Notes on the Webster-Harris Expedition. Novitates Zoologicae Vol. VI, No. 2, pp. 85-205, 2 plates.
- 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)
- 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.
- CentralPets.com: Vampire Finch. Retrieved 2006-DEC-19.
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