Nature’s inventiveness knows no bounds. Consider the case of the nectar-drinking bat and the night-flowering vine whose lives intertwine in the lowland tropical forests of Central America.
Glossophaga commissarisi, a tiny, winged mammal with a body no bigger than your thumb, flits among the flowers of Mucuna holtonii, lapping nectar, much as hummingbirds and bumblebees do. In exchange it pollinates the plant. In daylight flowers can flaunt their wares with bright colors such as scarlet and fuchsia, but at night, when even the brightest hues pale to a moonlit silver, Mucuna flowers resort to sound to catch the ear of nectar bats.
At dusk the vine’s buds ready themselves for bats. First the topmost, greenish petal that caps a bud slowly opens vertically, to stand atop the blossom as a glossy beacon. Below the beacon petal, two tiny side petals wing apart, revealing a crack at the top of the pea pod. From this slit wafts a faint, come-hither scent of garlic, a long-distance signal that draws the Mucuna’s winged servants into earshot.
Bats use high-frequency sound as a tool. With their vocal cords, they bang out short, swift bursts through their nostrils or mouths, molding airwaves and interpreting the pattern changes that ricochet back to their sensitive ears. The incoming information is processed fast and continually, allowing bats to adjust their course in mid-flight as they streak through the air after a mosquito or race among flowering trees.
Most bats feed on insects, and they often use powerful, long-range calls, pumped out with every upstroke of their wings. Nectar bats send gentle but very sophisticated calls, which scientists refer to as frequency modulated. These calls trade distance for detail. Most effective within 12 feet, they reflect back pictures that convey precise information about a target’s size, shape, position, texture, angle, depth, and other qualities only a nectar bat can interpret.
Until 1999 no one had any inkling that plants use shapes that reflect sound to streamline bat foraging. That year biologists Dagmar and Otto von Helversen, of the University of Erlangen in Germany, were studying acoustics in bats at La Selva. It occurred to Dagmar that Mucuna’s beacon petal bore a striking resemblance to a sound beacon—a conspicuous acoustic signal, the aural equivalent of a lighthouse’s beam. Field tests with modified Mucuna beacons clinched the theory.