Dark Banquet (9 page)

In the end, both of these methods are successful because of the low reproductive rate in vampire bats. Like the vast majority of bats, vampires give birth to only one pup per year—a far cry from other mammal pests like rodents, who can crank out babies faster than a baseball player can split sunflower seeds.

Back in the slaughterhouse, Kim and I used the same colander to strain off the strange, woven clots that materialized in the barrel—squeezing out the blood they held, before discarding the sponge-like clumps in a waste bucket. After about fifteen minutes of this fun, the defibrinated blood that remained in the barrel (i.e., the blood minus the clotting factors and proteins making up the clots) was poured, still warm, into the two-gallon plastic containers we'd brought with us. By stimulating clots to form, and then removing them, we were assured that our defibrinated blood would remain liquefied and clot free during storage, and when we placed it out to feed our bats.

Although we didn't realize it at the time, a similar method was employed between the 1820s and 1920s to defibrinate a human donor's blood prior to transfusion. In the days before the medicinal use of anticoagulants, donated blood was collected in a bowl, whisked, and filtered before being transfused into a recipient.

Some researchers use an alternative method to facilitate the storage of blood (for vampire bat meals and other purposes). The technique involves “citrating” the blood by adding the compound trisodium citrate to it. This also prevents the formation of clots, and although we never employed this method, in hindsight it could have provided our captive vampires with a slightly more nutritious meal. This is because, unlike our whisk and filter method, the clotting proteins aren't actually removed from the citrated blood.

After returning to our lab at Cornell's School of Veterinary Medicine, Kim and I transferred the blood into several dozen Snapple bottles we'd collected earlier from the cafeteria (yes, we cleaned them first). We froze the blood-filled bottles, thawing one out each morning so that the liquid would reach room temperature by nightfall. That was when we fed our vampire bat colonies—pouring the blood into an ice-cube tray and elevating it with a wooden block so that the roosting bats wouldn't have to strain themselves while they ate. As Farouk had done in Trinidad, we supplemented the diet of our white-winged vampires with a live chicken (once per week and on holidays). This turned out to be a vital step in maintaining our vampire colony, as I found out three years later.

Shortly after passing the bats off to another Cornell grad student (who had proposed a study on their digestive physiology), I received a rather frantic call from Kim. I discovered that the new researcher had not only relieved my friend of her bat-keeping duties but had decided to suspend the colony's live chicken supplement (basically to save a few bucks each week while eliminating the far from insubstantial hassle of dealing with live chickens). Within ten days, vampire bats began dying at an alarming rate—a trend that stopped immediately after a “talk” with the grad student led to a resumption of weekly chicken dinners for the colony.

During the three years that we maintained our colonies of common and white-winged vampire bats, it's safe to say that we saw some strange stuff, much of it relating to feeding behavior or social interactions between roost-mates. We found out later that Farouk and his Trinidadian bat crew had already noted much of what we were observing at Cornell. Their reluctance to publish, however, made it news to us, and we were grateful that these bat experts had (for some reason) decided to take us on as collaborators and coauthors. There were numerous occasions when something very much like the following exchange took place over a crackling long-distance phone line.

“Yes?” Farouk's Trinidadian accent made it sound more like
yes-ah.

“Farouk?”

“Yes.”

“You're not going to believe what we just saw.”

Silence.

“I think
Diaemus
is mimicking chicks. They're snuggling right up to these hens—then biting them on the chest. It's unfriggin-believable!”

Silence.

“Farouk?”

“Yes.”

“Have you ever seen that before?”

“Yes. The bites are on the brood patch.”

“Oh…Cool. Okay, I'll talk to you soon.”

“Yes.” Click.

I've always considered my friend Farouk Muradali to be one of the most generous and nurturing people I've ever met. But to say that he is a man of few words…well, you get the picture.

My collaborators and I also learned from the start that Arthur Greenhall had been right about the significant differences that existed between vampire bat species (in our case, between
Desmodus rotundus
and
Diaemus youngi
)—and we would discover that most of this variation was related to the bat's preference for either mammalian or avian blood, respectively.

“Diaemus
doesn't jump,” Farouk had said (in what would become his equivalent of the Gettysburg Address). And after a hundred-plus trials on our miniature force platform, we had to agree. But why was this so?

Initially, we tested our system out with the common vampire bat,
Desmodus,
and as in previous studies, we confirmed that these bats could make spectacular, acrobatic jumps, in any direction. Pushing off the ground with their powerful pectoral muscles,
Desmodus
used its elongated thumbs (the last things to leave the ground) to impart precise direction to jumps that could reach three feet in height.

These amazing jumps, along with their ability to run at speeds of up to two meters per second, were adaptations for terrestrial blood feeding. They enabled the common vampire bat to escape predators, avoid being crushed by their relatively enormous prey, and initiate flight after a blood meal. The ability to feed efficiently on large quadrupeds is the primary reason why
Desmodus rotundus
has been so successful in terms of numbers and range, but in all likelihood this success was a rather recent development.

Until about five hundred years ago,
Desmodus rotundus
may have been anything but “common.” In fact, populations would have been severely restricted not only by climate but by the finite number of large mammals that were present in any given area. Quite possibly the vampires would have been compelled (as they sometimes are today) to feed on smaller mammals as well as birds and other vertebrates like snakes and lizards.

Starting in the early 1500s, however, the influx of Europeans and their domestic animals into the Neotropics would have spelled big changes for
Desmodus,
as well as the other two vampire genera. Suddenly, enormous four-footed feeding stations would have sprung up in places where the pickings might have previously been sparse for thousands of years. Additionally, not only would there have been plenty of new animals to prey upon, many of these quadrupedal blood bags would have been penned in, making them super easy to find and ultimately making meal time a whole lot more predictable than it had ever been before. Populations of the opportunistic
Desmodus
would have exploded as more and more land was cleared for cattle farming. The more cows, pigs, and horses, the larger the vampire bat populations that could be sustained by their blood. Human victims weren't necessarily preferred, but they did give the vampires additional opportunities to feed, long before windows, screens, and protective netting would keep them at bay.

From the standpoint of the newly arrived humans, it must have seemed like yet another plague had descended upon them, for with the mysterious nocturnal attacks and the gruesome postbite cleanup came diseases, rabies being the most feared. Soon, stories of vampire bats, their gory attacks, and the horrible diseases that they inflicted, were making the rounds throughout Europe, and from there they spread to the rest of the world. What little scientific knowledge there was on the topic became blurred by misconception and misidentification, turning tales of these creatures into an unreliable blend of vampire fact merged with vampyre fiction.

Unlike
Desmodus, Diaemus youngi
(which resembles a winged teddy bear) has contributed little if anything to vampyre folklore. Perhaps they were once fast and aggressive, and maybe they even initiated flight similarly to their spring-loaded cousins. But now their movements are more deliberately paced and show little sense of urgency. When placed on the surface of our force platform, white-winged vampires would give a little hop or two, then scuttle off to find a dark corner in which to hide.

Watching
Diaemus
feed arboreally, we saw why they didn't need to catapult themselves into the air. Approaching a roosting bird from below the branch, white-winged vampires moved slowly and stealthily—advancing one limb at a time—and always keeping the branch between itself and the underside of its intended prey. Once situated beneath the feathered lunch wagon,
Diaemus
picked a potential bite site, usually on the bird's backward-pointing big toe (i.e., the hallux). This made perfect sense, since feeding from this particular digit kept the bat better hidden from above than if it had chosen to feed on one of the three forward-facing toes. After licking the chosen site for several minutes, an apparently painless bite was inflicted using the razor-sharp teeth that characterize all three vampire bat species. The bite was
never
violent and very often occurred as the bird shifted position slightly on its perch, as if reacting to some slightly uncomfortable irritant. Still hanging below its completely oblivious prey,
Diaemus
began feeding, and within five minutes it began peeing. It did so by extending one hind limb sideways and downward, deftly avoiding the embarrassment of soiling itself while eating. After feeding for between fifteen and twenty minutes, the bat would release its thumbs from a branch, hang briefly by its hind limbs, then drop into flight. Initiating flight in this manner, there was absolutely no need for
Diaemus
to jump, and so it didn't, at least not into flight.

On numerous occasions, we did observe
Diaemus
feeding on birds from the ground. Supporting its body in a low crouch (as compared with the extreme upright stance of
Desmodus
), the white-winged vampire was quite adept at hopping around (rather comically) in pursuit of a feathered blood meal. This behavior had not been reported in the wild and we used it to propose that the white-winged vampire bat had made a relatively recent return to the trees, thus avoiding competition with its ground-feeding cousin,
Desmodus.

During these terrestrial feeding bouts we occasionally recorded behavior that approached chick mimicry on the “weird-o-meter.” This occurred after the bat leaped or climbed onto the chicken's back, then scuttled forward, intent on biting the back of the bird's head or its fleshy comb. Male chickens mounted in this fashion quickly grew agitated and dislodged the bat with a shake and a peck. Hens, however, had an
entirely
different response. Rather than showing annoyance, female chickens quickly assumed a crouching posture that they maintained until after the vampire bat had finished feeding and hopped off. With a little research into poultry behavior, we learned that this was the identical posture taken by a hen while being mounted by a male bird—for a completely different reason.