Dark Banquet - Bill Schutt [94]
The scientist continued. “As far as human encounters with candirus, I just can’t think of it as anything other than an accident. But how it arrives there—that’s still a mystery.”
I asked Dr. Spotte a final question. “What do you think the odds are that someone submerged in a stream where candiru live, and deciding to take a pee, would get attacked by these creatures?”
Dr. Spotte replied without hesitation. “About the same as being struck by lightning while simultaneously being eaten by a shark.”
What was so thought provoking about all sorts of Galápagos finches to young Charles Darwin…was that they were behaving as best they could like a wide variety of much more specialized birds on the continents. He was still prepared to believe, if it turned out to make sense, that God Almighty had created all the creatures just as Darwin found them on his trip around the world. But his big brain had to wonder why the Creator in the case of the Galápagos Islands would have given every conceivable job for a small land bird to an often ill-adapted finch? What would have prevented the Creator, if he thought that the islands should have a woodpecker-type bird, from creating a real woodpecker? If he thought a vampire was a good idea, why didn’t he give the job to a vampire bat instead of a finch, for heaven’s sake? A vampire finch?
—Kurt Vonnegut
10.
A TOUGH WAY TO MAKE A LIVING
In addition to vampire bats, leeches, bed bugs, ticks, mites, and candirus, there are literally thousands of species that feed on blood. They range from intestinal nematodes called hookworms, that produce iron-deficiency anemia in their hosts,*149 to mosquitoes, one of the eleven families of fly-relatives (dipterans) with blood-feeding members. There are assassin bugs (which may have plagued Charles Darwin) and vampire moths (seven species in the Asian genus Calyptra). These insects use their sharpened mouthparts to pierce the skin of animals like water buffalo, elephants, tapirs, and even humans.
Then there’s Geospiza difficilis, the pint-sized vampire wannabe that so impressed author Kurt Vonnegut. Although dramatic, “vampire finch” is not a terribly accurate name for this bird, which is also known as the sharp-beaked ground finch. Basically, the vampire tag is questionable, because unlike the other sanguivores mentioned thus far, Geospiza difficilis is not an obligate blood feeder.*150 The birds merit mention here, however, because they appear to be giving part-time vampirism a serious shot. In that regard, they occasionally supplement their normal diet of small seeds and nectar by eating eggs and by pecking at the wings, body, and tail regions of another Galápagos resident—the blue-footed booby (Sula nebouxi). Once Geospiza difficilis has inflicted a small wound with its beak, it begins sipping the booby’s blood, hopping out of the way if the larger bird gets annoyed. The finches feed in this manner for several minutes, giving way to other individuals who line up, waiting their turn like customers at a deli counter.
Geospiza difficilis is widely distributed throughout the Galápagos archipelago, but only two populations feed on blood. Researchers have noted differences in feeding behavior, size, and vocalizations in these birds—differences that could indicate that a new finch species is forming before their eyes. For my own part, it’s just as interesting to imagine what might happen if Geospiza difficilis became a bit more adept at obtaining a blood meal, and a bit more dependent on finding one on a daily basis. What if conditions on the tiny islands of Darwin or Wolf changed, and the seeds and flowers these birds needed to survive were no longer available? Would the blood-sipping finches simply relocate to another island? Perhaps, but if they did, they’d certainly run into competition from the well-established finch species already living there. Maybe the vampire wannabes would die out or interbreed with non-blood-feeding members of their own species. Or maybe Geospiza difficilis would accumulate a few more beneficial mutations