Magazine article Natural History

Sure-Footed Bats

Magazine article Natural History

Sure-Footed Bats

Article excerpt

In the cool of an early Caribbean evening, a group of three bats, each with a two-foot wingspan, glided past me in a line and disappeared into the night over the bay. As I watched from a well-lit dock, the bats returned, speeding just inches above the water, and vanished again into the dark. Then I heard the splash of a small fish leaping out of the water. Seconds later, the line of bats reappeared. The first bat raked its feet over the water near where the fish had splashed; the bats following behind dipped their feet into the water at exactly the same spot. In my excitement at seeing them, I stepped forward for a better view and fell fight off the dock into waist-deep water.

Several species of bats include fish in their diet, but only one has the reputation of being a fish specialist: the fishing bat, Noctilio leporinus (also called the greater bulldog bat because its drooping cheek pouches, pointed ears, and blunt nose give it a doglike appearance). Fishing bats range from Mexico to Argentina, close to lakes, rivers, or the sea. I study them on the small Caribbean island of Culebra.

Fishing bats have unusual physical characteristics that would seem of obvious help in the hunt: large feet, with long, talonlike claws to catch the fish, and long canine teeth to hold the slippery prey. But how the bats are able to detect fish in the first place remained a mystery until researchers using high-frequency sensors showed that the bats' echolocation calls were bouncing off fish fins sticking out of the water and even off the ripples created by a fish swimming just beneath the surface. The returning echolocation pulses enable the bats to determine a fish's speed and direction and thus where to strike.

As a fishing bat strikes, it raises its wings. Once the fish is impaled on its claws, the bat lowers its wings in a powerful downstroke that lifts it up away from the water. In a fraction of a second, a swing of the feet transfers the squirming fish into the mouth, where the bat's canine teeth easily pierce and hold it. With the fish secured, the bat chews it like a hot dog, stuffing it headfirst into its two cheek pouches, which can expand until they resemble small balloons tied beside the bat's chin. Once the fish is safely tucked away, the bat can either finish the job of eating in flight or return to a perch to dine.

On Culebra, sheltered bays are home to enormous schools of sardines, silversides, and needlefish. These small fish are most vulnerable to predation just after sunset, when larger fish, such as barracuda and jacks, chase them into the shallow water near shore to feed on them. With few avenues of escape left, the small fish attempt to flee by jumping into the air and soaring for a few feet before splashing back into the water. Small groups of fishing bats fly back and forth just along the water's edge seeking fish that have been driven to the surface. The bats must be within ten feet or so of a fish in order to detect it. When a fish jumps, the nearest bat maneuvers rapidly to the spot, with the others--perhaps eavesdropping on its echolocation calls--close behind.

During the past year I have made nightly collections of guano and partly eaten prey from beneath fishing bat roosts. After dissecting scats and carefully matching up fish scales, beetle and fly fragments, and moth scales to whole specimens, I have a good idea of what the bats eat. …

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