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)!
Regarding reference 7:
Naish, Darren. “Vampire Finches and the Path to Parasitism.” Tetrapod Zoology. 2007. 2 Sept. 2011. http://scienceblogs.com/tetrapodzoology/2007/02/vampire_finches_and_the_path_t.php
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Regards - I. Ruderfer