Dark Banquet - Bill Schutt [30]
Gould cited the panda’s “thumb” as a beautiful example of how evolution doesn’t create; it tinkers with what’s already there (in this case, the panda’s radial sesemoid bone), modifying it for a new function rather than creating a new structure from scratch.
Ailuropoda’s odd little digit also presented some rather daunting questions for those who support a creationist view of how we got here. Basically, if there is an intelligent designer, why did he (or she) give the panda a jury-rigged structure for stripping leaves off branches? Why not just give the Ailuropoda a real thumb?
Back in Ithaca (and several minutes later), I heard scrambling and the sound of the receiver being picked up. “You nailed it, Bill—I’ve got some great shots.”
“Excellent,” I replied. “Do me a favor and send them to me at once.”
Altenbach’s black-and-white photos clearly showed a climbing Diphylla with its calcar tightly wrapped around a wooden dowel. I immediately put together a proposal to record this behavior in the field, setting my sights on a visit to central Brazil. Since Diphylla didn’t live in Trinidad, I contacted Brazilian researcher Wilson Uieda, who had been studying the hairy-legged vampire for years with his colleague, Ivan Sazima.
Outside the capital city of Brasília, at a ranch where the cattle were commonly plagued with Desmodus bites, Wilson and I set up my infrared video camera at sunset. We certainly weren’t interested in the cows or even in Desmodus for that matter. Instead, we aimed our camera upward, into the branches of a fig tree, for it was there that the resident guinea fowl went to roost at dusk.
Several hours after nightfall, as I stared bleary-eyed at the camera’s viewfinder, a pair of dark shapes flew past the sleeping birds.
“Wilson, check this out,” I whispered.
My friend, who had been dozing on the chair next to mine, was instantly alert.
Less than a minute later, the aerial recon was performed for a second time.
Wilson whispered a single word. “Diphylla.”
After that we saw nothing for several minutes—until a tiny pair of glowing spots appeared beneath one of the roosting birds. I hit the zoom on the camera, focusing in on the twin points of reflected light.
They were eyes!
Wilson traced a dark silhouette on the screen and I could just make out Diphylla’s upside-down head peeking out from the guinea fowl’s feathery breast.
“Dinnertime,” he said.
“This is different from Diaemus,” I responded.
Wilson replied with a smile.
Rather than feeding from below the branch, Diphylla was actually hanging from the bird—and photographs taken by Wilson Uieda and his colleagues at another site clearly indicated that Diphylla was using its opposable calcar to get a grip on the body of its avian prey. Unlike the white-winged vampire, which generally fed from bites it inflicted on the toes of perching birds, many of Diphylla’s bites were made around the cloaca (the common opening for the digestive, urinary, and genital tracts found in many nonmammalian vertebrates, like birds).
Several days later, we visited a cave that was home to a small colony of Diphylla. Using the infrared camera again, we recorded three hairy-legged vampires as they moved across the stony ceiling. Not only were the bats walking upside down, they were moving backward (not really strange since bat knees face backward). What was unique was the way that they led with their hind limbs—carefully seeking a secure purchase before taking a step—and using their “sixth digits” like a rock climber would use his thumbs. After scrambling around the cave ceiling for a few minutes, the vampire bats tired of our intrusion and disappeared into a narrow crevice.
I left the cave elated that we’d been able to support my hypothesis with observations