by Bill Schutt
As the light from my headlamp moved across the glistening surface, something the size of a football catapulted itself through the beam. My reflexes sent me backward onto my butt as the object landed with a loud splash. Three headlamp beams hit the impact point, but by then whatever it was had disappeared below the ink black sludge.
“What the hell was that?” Janet asked, her voice an alarmed whisper.
“I think it was a toad,” I responded. “A big mother.” And as I turned back to Farouk, he nodded in agreement.
“They feed on the bats that fall in from above,” he said. “The babies and the weak ones.”
With that, the Trinidadian directed his light upward, until we could just make out the ceiling of the elevator shaft, twenty feet from where we stood.
As I squinted into the darkness, Farouk moved away, motioning us to follow. “You can see the bats much better from upstairs.”
Our companion stopped before a narrow stairway leading to the second floor. The railings had either collapsed long ago or been carted off by the locals, leaving only small circular holes in the cement. Three separate beams moved across the steps, each of us searching for any indication that the stairs might not be safe.
I was on the verge of saying something about the strong smell of ammonia when I heard Farouk’s voice. His tone had grown more serious. “Janet, maybe you should remain down here.”
“Yeah, that’s gonna happen,” I said with a laugh. My wife had recently spent three hours exploring Caura Cave, the floor of which was slick with guano and crawling with enormous roaches, all without a complaint. Only later did I learn that she had had a migraine the entire time. So it came as no shock when she politely waved off Farouk’s chivalrous suggestion and began climbing the darkened stairs.
One year earlier, at a symposium on bat research, I had gotten up the courage to approach Arthur M. Greenhall, one of the world’s leading authorities on vampire bats. I was in the second year of a Ph.D. program at Cornell and like many grad students I was sniffing around for a dissertation project. (Luckily, the head of my graduate committee, John Hermanson, wasn’t one of those guys who handed you a ready-made project, although I had to admit there were some days when I wished he had.) By this time, Greenhall was in his midseventies but he was still vibrant and inquisitive—as excited about science as anyone I had ever met.
Born and raised in New York City, he’d had a storied career. In 1933 Greenhall and Raymond Ditmars, his mentor at the New York Zoological Park, had collected the first vampire bat ever to be exhibited alive in the United States. It was a female that turned out to be pregnant, delivering a vampire bat pup several months later. The following year, the young scientist arrived in Trinidad during the height of a major rabies outbreak. He studied the deadly virus and its blood-feeding vector with local scientists and collected additional vampire bats. On his return to the United States, he found he had more specimens than his zoo could display or handle. Greenhall solved the problem by keeping twenty of the creatures in his New York City apartment for two years.
During a break between research presentations that day, I had spoken to several noted bat biologists about possible differences in behavior or anatomy between the three vampire bat genera, Desmodus, Diaemus, and Diphylla. From previous studies I had learned that Desmodus, the common vampire bat, exhibited an incredible array of unbatlike behaviors, including a spiderlike agility on the ground. Just as interesting to me was the way Desmodus initiated flight. In virtually all nonvampire bats, takeoff began with a wing beat that accelerated the animal away from the wall, ceiling, or branch from which it hung. Heavily loaded down after a blood meal, Desmodus was renowned for its ability to catapult itself into flight from the ground by doing a sort of super push-up.
“Maybe,” I proposed, “the other vampire bats, Diaemus or Diphylla, did things a little differently.”
“Not likely,” I was told more than once.
“A vampire bat is a vampire bat is a vampire bat,” chanted several bat scientists. I wondered if there might be a secret handshake that went along with this information, one that I had yet to learn.
After introducing myself to Greenhall, I told him what the bat researchers had said, adding that I found their responses puzzling.
“Why’s that?” the vampire maven responded.
“Well, because the rule of competitive exclusion says that if similar animals are competing for the same resource, in this instance blood, then one of three things will happen. One of the animals will relocate. One of them will go extinct. Or one of them will evolve changes, reducing the competition for that resource.”
“And since vampire bat genera have overlapping ranges…?” Greenhall interjected, setting me up beautifully for the punch line.
“They’ve got to be different.”
The old scientist gave me a sly smile. “You’re on to something, kid,” he said. Then he lowered his voice. “Now get on the stick before someone else gets to it first.”
It had taken me six months to “get on the stick,” but by then my fellow Cornell grad students, Young-Hui Chang and Dennis Cullinane, and I had followed our mentor John Bertram’s lead and built a miniature version of a force platform, a device that could measure the forces applied to a flat metal plate as a creature (in this case, a vampire bat) moved across it. By synchronizing the force platform signals with high-speed cinematography, we planned to see if there would be measurable differences in the flight-initiating jumps of Desmodus rotundus and Diaemus youngi, the two vampires I would collect and bring back from Trinidad.
Not long after arriving in Trinidad and Tobago’s capital, Port of Spain, I told Farouk what a pain it had been for us to machine the metal components of our force platform, get the electronics working just right, and then write the data-acquisition software. He stood by patiently as I tooted my own horn, polished it a bit, then tooted some more. Finally, I ran out of intricate gear to describe (or it might have been air).
“It won’t work,” Farouk said, matter-of-factly.
“Excuse me?” I replied, my voice cracking like a twelve-year-old boy’s.
“Your experiment won’t work.”
Now I was getting visibly annoyed. Hadn’t I just told him how much time, effort, and brainpower had gone into this project?
“Of course it’ll work.” I was getting frantic now.
The Trinidadian said nothing.
“Why won’t it work?”
Muradali put his hand on my shoulder and smiled. “Because Diaemus youngi doesn’t jump.”
“Oh,” I replied, sheepishly. “Right.”
The light from Janet’s headlamp swept upward from the bottom of the empty elevator shaft (now below us) to the ceiling. “So where are all the—” Her beam had stopped tracking abruptly.
Illuminated at the top of the chamber were three circular clusters, each composed of a dozen or so black silhouettes, arranged concentrically. They hung silently, reminding me of giant Christmas tree ornaments. Suddenly, one of the fusiform shapes unfurled, revealing wings nearly two feet across.
“Phyllostomus hastatus,” Farouk whispered. “The second-largest bat in Trinidad.”
“Crawling mother of Waldo,” I muttered, and Muradali threw me a confused look.
“Don’t mind him,” Janet explained, keeping her light trained on the bats. “He gets all scientific when he’s excited.”
Muradali nodded politely, then began assembling an object that looked suspiciously like a drawstring-equipped butterfly net at the end of a four-foot pole.
I shot him a quizzical look. “A butterfly net?”
“Swoop net,” Muradali corrected, handing it to Janet.
Farouk nodded toward the net, then shined his light up at a cluster of bats. “To catch the ones closest to the elevator door, you lean out over the edge while someone holds your belt or backpack.”
Janet glanced up at the bats, then quickly shoved the net into my hands. Possibly she’d had the same vision that I�
�d just had, of tumbling down a concrete-lined abyss with nothing except years of rainwater, bat guano, and asbestos to soften the fall.
As I moved into the doorway, it was impossible to chase away the image of that poor woman, stepping off the solid concrete floor and into a bottomless pit of bat-shit soup. “Thanks, hon,” I said.
Janet only smiled.
“We’ll leave these bats alone,” Muradali said, moving away from the shaft.
As we quickly followed him, I let out a breath I hadn’t realized I’d been holding. “Can we catch vampires like this?” I asked, suddenly feeling a bit braver and taking a few swings at some phantom air bats.
“No,” he replied, picking his way through the debris. “Too smart.”
Later, the scientist explained that early efforts to eradicate vampire bats had resulted in the deaths of thousands of non-blood-feeding species. In 1941, Captain Lloyd Gates was placed in charge of protecting the American forces stationed at Wallerfield from the twin threat of mosquitoes and vampire bats. Gates’s less-than-subtle response to the bat problem was to have his men use dynamite and poison gas in caves known to contain bat roosts. Flamethrowers became a popular alternative, but still the vampires persisted, as did their attacks upon the encroaching military men. Also hard hit was the increasing population of locals who had been drawn to the region for the income the base provided. As a result, thousands upon thousands of non-blood-feeding bats were blown up, poisoned, or incinerated. Even worse, these bat eradication techniques were apparently so appealing that over eight thousand caves in post–World War II Brazil were similarly destroyed.*5
Farouk recounted how he and vampire bat expert Rexford Lord had been sent to Brazil to pick up some tips on eradicating Desmodus from the antirabies groups working there.
“These guys took us to a cave. Then they rolled out a big tank of propane and wired it up with an old-fashioned camera flash, running the wires out the cave entrance.”
He described how everyone waited outside the cave entrance while one of the Brazilians opened up the gas-tank valve.
“Must have been the new guy,” I added.
“They used a triggering box to set off the flashbulb and the explosion ripped through the cave like a bomb,” Farouk said. Then he shook his head and continued. “After the smoke cleared, they asked us to go in and identify the dead bats that we found. And there were thousands. All sorts of species—but not one vampire.”
Farouk said that later on the men ventured deeper into the cave and there, lined up above a ledge, was a row of dark shapes.
“They were vampire bats. All of them were looking quite fit and not at all disturbed by the explosion. The bats that died in there were a lot more delicate.”
The Brazilian cave fiasco hadn’t solved the vampire bat problem, but it did serve to illustrate how Desmodus had evolved to become extremely opportunistic, extremely intelligent, and extremely difficult to eliminate.
At this point Farouk got to the heart of the matter. “Feeding on blood is a tough way to make a living.”
Back at Wallerfield, we moved deeper into the building, using our headlamps to avoid tripping over the ceiling, a concept I was just beginning to wrap my mind around. The acrid ammonia smell was getting even stronger and suddenly we were in Bat Central.
The lights and our movements had finally aroused the aerial residents of the icehouse and now there were hundreds of furry bodies flashing past, their barely discernible high-frequency calls set against the parchment flutter of wings.
I turned off my headlamp and took a couple of swings with the swoop net. Almost immediately I felt a slight difference in the weight of the net and tugged the drawstring tight.
I flicked my light back on. Reaching in a gloved hand, I plucked out a tiny struggling form, manipulating it gently so that the wings were folded and pinned against the body. A struggling animal, no matter how large or small, was far more apt to hurt itself, and the person handling it, if it wasn’t fully and comfortably restrained.
Janet and Farouk pulled in close, focusing their headlamp beams on my delicate captive. The bat had an extended snout and a long, protractible tongue that seemed to be equipped with a brushlike tip. Its teeth were tiny and weak and the creature soon gave up trying to bite through my leather batting gloves.*6
“Glossophaga soricina,” Farouk said. “A nectar feeder.”
The bat looked as if it had been assaulted by a powder puff. The “powder” was actually pollen that the creature had inadvertently picked up while feeding. Like hummingbirds, Glossophaga and their relatives were vital components of their ecosystems, in fact, over five hundred species of tropical plants were at least partially dependent on bats to pollinate them.
The nectar-feeding lifestyle was also a great example of convergent evolution, in which organisms (in this case several dozen bat species and over three hundred species of hummingbirds) evolved to resemble one another (anatomically and behaviorally), not because they were closely related but because they existed in similar environments or exploited a similar resource. In this instance, the resource was nectar, the sugar-jacked liquid produced by many plants with an evolutionary ulterior motive. While obtaining its meal, this bat (like hummingbirds or insects like bees and butterflies) had been dusted with pollen, pollen that would now be delivered via airmail to some fertile and, quite possibly, distant flower. It was a coevolutionary relationship that had been going on since the flowering plants first evolved during the reign of the dinosaurs.*7
Additionally, just as in other examples of evolutionary convergence, there were major differences between bat and bird pollinators, and some of these (beyond the obvious daytime-vs. nighttime-feeding habits) were quite significant. For example, hummingbirds, which number around 340 species, are renowned for their ability to hover for extended periods as they feed. Remarkably, they accomplish this maneuver with wing-beat frequencies that can approach ninety beats per second. On the other hand, those relatively few bat species that can hover (certainly fewer than twenty), generally do so for less than a second with wings that max out at around twenty beats per second.
Another difference between bat and bird pollinators concerns the upstroke portion of the wing beat. All bats use the same muscles to raise their wings that humans use to extend their arms out to the side. In both bats and humans, these muscles (i.e., the deltoid and supraspinatus) extend from the back of the shoulder (the scapula) and attach to the upper arm bone (the humerus). When these muscles contract, it’s like pulling the strings on a marionette’s arms—but with the power to lift the wings coming from muscle contraction rather than a puppeteer.
In terms of flight efficiency, though, the important factor is that in bats the upstroke muscles are located above the wing. Since it is more aerodynamically efficient to have as much weight as possible below the wing, this extra weight reduces flight efficiency, giving bats their characteristic flittery flight.*8
Birds have evolved a solution to this problem since both their downstroke and upstroke muscles are located below the wing. Situated on the sternum (deep to the bird’s downstroke-driving pectoral muscles), the supracoracoideus muscle sends its long tendon snaking through a hole in the shoulder joint to an attachment site on the humerus. When the supracoracoideus muscle contracts, its tendon acts like a pulley to raise the wing. The end result is a smoother (less jerky) flight in birds compared to bats.
These performance differences follow a general trend in most flight characteristics in which birds are more aerodynamically efficient than bats. This is almost certainly because birds have been flying (and, in the case of hummingbirds, hovering and feeding on nectar) far longer than their mammalian counterparts.
Back at Wallerfield, Farouk nodded at my tiny captive. “You should release that Glossophaga before we leave,” he said. “If you want it to live.”
“Why’s that?” Janet asked. We’d been bagging bats in Trinidad for several weeks, then taking them back to the PAX Guest House where we were sta
ying in Tunapuna.†9
“Glossophaga has a very high metabolic rate,” Farouk replied. “If that one doesn’t get nectar tonight, it will starve to death.”
“Yikes,” I said, glancing down at the bat with renewed interest.
Janet nudged my arm. “Sounds like those shrews we caught with Deedra and Darrin last year at Arnot Forest.”
Janet had nailed it. Shrews are tiny, insectivorous bundles of energy. Superficially, they resemble rodents (another example of convergent evolution), but they have amped-up, nutrient-burning bodies, that, like the nectar-feeding bats, require a constant and relatively immense intake of energy. The shrews we’d taken during a mammal survey in a forest near Cornell had a resting heart rate of approximately eight hundred beats per minute, and when pressed, they could reach fifteen hundred beats per minute—the highest ever recorded for a mammal. As a consequence, shrews have to eat almost constantly—worms and insects, mostly—but sometimes even other shrews. Their aggressive demeanor and toxic bites also enable them to tackle animals much larger than themselves. During one of our long nights in the field, I’d brought up the topic of a creature feature I recalled seeing as a kid. It was the unintentionally funny, 1959 horror flick, The Killer Shrews, in which dogs outfitted with goofy shrew wigs, terrorized a handful of cocktail-guzzling scientists, a well-endowed young woman, and a testosterone-squirting hero in a captain’s cap. Besides a last line that rivaled Clark Gable’s in Gone with the Wind, what I found most memorable about this mostly forgotten cinema “classic” was the fact that the filmmakers had gotten at least one thing right (two, actually, if you count the alcohol intake by the scientists). If indeed shrews had evolved or, in this case, mutated, to be the size of dogs (even small dogs)—humans would have had a serious and unbelievably vicious predator to contend with. Luckily for those of us collecting real shrews, there was no danger—only the discomfort of late nights during which we had to check over a hundred “live traps” every two hours—to prevent our hyperactive captives from starving to death.
