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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