Dark Banquet - Bill Schutt [8]
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 staying 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.
In the icehouse at Wallerfield, Janet and I took a last look at the amazing little pollinator.
“See ya,” I said, gently flipping the bat upward.
The tiny creature disappeared