Dark Banquet by Bill Schutt Page B

to feed, the kidneys immediately begin producing an extremely dilute form of urine in order to shed excess weight (approximately 25 percent of the blood volume consumed is excreted as urine within the first hour after feeding). Soon, though, the excretory system shifts into a very different gear. The urine produced becomes more and more concentrated as the kidneys work frantically to eliminate the rapidly accumulating urea without causing dehydration in the bat.
    Because of the vampire bat’s need to excrete massive amounts of urea, water loss is a real and constant problem. Dehydration may have been one of the key factors that limited vampire bat ranges to regions that had a high relative humidity and may be one more reason why prehistoric vampire bats disappeared in North America. In a similar vein (sorry, I had to get that out of my system), vampire bats are restricted to relatively short-duration flights each night. *34 Presumably, this limitation is due to the evaporative water loss that typifies bat flight. So, although many bat species are known to migrate or undertake lengthy nocturnal flights, a sanguivorous diet appears to have selected against these behaviors in vampire bats.
    In 1969, Cornell University vampire bat expert William Wimsatt and his coauthor William McFarland put things in perspective: “In a very real sense the vampire bat can be considered to inhabit a desert in the midst of the tropics. But the desert is delimited not by environmental aridity, but rather by the nutrition and behavior of the vampire.”
    In both the vampire bats’ digestive and excretory systems, there have been evolutionary trade-offs related to blood feeding, as speed of food processing has been increased at the expense of nutrient storage. This type of trade-off is a hallmark of biology. Some organisms adapt to the changing environments in which they exist (e.g., vampire bats are able to feed on blood in a humid environment but can’t migrate or fly for extended periods). More often, though, organisms are unable to adapt—like many of the browsing mammals that died off as North American forests transitioned into grasslands. Although it’s certainly more fun to think about the big, sexy mass extinction events (like the one that occurred around sixty-five million years ago), the vast majority of species that have ever lived on this planet apparently disappeared rather gradually. Most extinctions, it seems, were accompanied by a whimper, not a roar.
    Farouk and I moved past the
Desmodus
cage to a smaller unit and peered in. Like their “common” cousins, all of the white-winged vampires were asleep except for one—but that was where the similarities ended. Where
Desmodus
has sharp, hard features (I’ve always maintained that they
looked
the part of vampires),
Diaemus
reminds me of a stuffed-animal version of a vampire bat. Their face is much softer—the sharp angles seem smoothed out and the eyes are huge and gentle looking. Their demeanor reflects these anatomical differences. In three years of handling
Diaemus
in captivity, they never attempted to bite me. Not once.

    Farouk shook his finger at me and then continued his lesson. “Now, if you leave out the same tray of cow blood for newly captured
Diaemus,
you’ll have dead bats in two nights.”
    I soon learned that Farouk’s “secret” for success was that each night he hand fed his newly captured white-winged vampires using a five-cubic-centimeter syringe full of cow blood. If the bats refused to eat, he didn’t force the issue but instead provided them with the opportunity to feed on a live chicken. Over the course of several weeks, even the most finicky of his “babies” got the message and soon enough he had them feeding on cow blood that he’d poured into an ice-cube tray. He supplemented his captive bats’ diet once a week (and probably on holidays) with feeding sessions on live