Panama's Adaptable Bats

• Panama's Adaptable Bats

Winged Victors
Seventy-four species of bats flourish on one small Panamanian island, carving out distinct niches for habitat and forage.
By Jennifer S. Holland
National Geographic staff
Photograph by Christian Ziegler

Sixty million years ago, on a planet crawling with mammals, one tree dweller rose above the crowd on paper-thin wings. So goes the story of ancestral bats, which, equipped with flight and a sixth sense called echolocation, mastered the night sky and flourished.
Having since exploded into more than 1,100 species worldwide, bats are still finding unique ways to evade the masses—and each other. Barro Colorado Island, a Key West–size knob of land in the Panama Canal, is a showplace of bat innovation. This patch of tropical forest is home to at least 74 distinct bat species; the entire United States has only 47, and all of Amazonia, with perhaps the highest bat diversity on Earth, logs about 160. With many thousands of individual bats sharing the island's 3,800 acres (1,500 hectares), it's a wonder their jagged wings don't entangle as they struggle to meet life's basic needs.

How do they all live in peace, skirting competition that would drive some to extinction? By finding their own niches in the forest's many layers. Where they roost, what they eat, when they feed, how they use their senses, where in the forest canopy they fly—each species has its own special how-to list inscribed on its genes, its own ways to exploit the island's endless summer. One bites through the lateral veins of a leaf to fold the sides down—creating a tentlike shelter for up to 15 of its kind to share. Another chews out a home for its harem in the heart of a termite nest, prompting the insects to move over and make room. (These bats choose only occupied nests as roosts; scientists are trying to find out why.) Some species chase down insects in the air, while others lick nectar and pollen from night-blooming flowers. Some use short pulses of sonar-like echolocation to find perched insects amid forest clutter; others send out longer calls to pinpoint airborne bugs, staying high above the tangled canopy.

Physical differences reflect these distinctive habits. Take greater bulldog bats, with their dagger-like claws and cheek pouches, in which they can carry fish they don't eat on the wing. Or herbivorous bats, some equipped with bristled tongues and grooved chins to pick up nectar and pollen as they nuzzle blossoms. Long, thin wings suit the bat that soars on high; broad, compact wings allow quick turns for the one dodging trees down low. Ample ears? Tiny eyes? Flesh-ripping canines? A nose flap? Each feature is a clue to how a species makes its living.

The tropical forest not only supports this immense diversity, it also depends on it. Bats spread seeds and pollen, keep a cap on herbivorous pests that might decimate forest flora, and themselves become meals for other forest animals—monkeys, owls, falcons, other bats, even large spiders. Such a healthy ecosystem can sustain quite a crowd, especially when each species knows its place.

panama bats interactive

http://ngm.nationalgeographic.com/2007/06/panama-bats/christian-ziegler-photography

Equipped with echolocation and gaffing claws, the greater bulldog bat can detect the hair-thin fin of a fish breaking the water's surface, a useful skill in a forest full of competitors.
Noctilio leporinus

An infrared camera turns bat into ghost 120 feet (40 meters) up a fig tree near Panama's Barro Colorado Island. This fruit-eating bat is one of the island's prime movers of tropical fruit seeds. The bat in this photo is visibly pregnant, suggesting she's part of a harem of perhaps six females that roost together with a male. She'll likely bear a single pup.
Artibeus jamaicensis

A great fruit-eating bat grabs a ripe fig. Such frugivores disperse seeds in their waste, helping reforest cleared areas and sowing commercially valuable fruits. Plants and bats have evolved traits that promote alliances: Some figs, for example, ripen en masse with a blast of perfume that attracts bats from a distance. Bats are apt to sow seeds more widely than would birds.
Artibeus lituratus

With claws that knife through water, the greater bulldog bat, Noctilio leporinus, is able to trawl for prey.

A keen sense of smell and a "nose leaf," which tilts to direct the animal's echolocation call, help the chestnut short-tailed bat pinpoint pepper plants in the forest understory.

Leaving its hollow-tree roost after dark, a greater bulldog bat heads to the nearby lake to fish for dinner—a skill known in very few bat species. Using echolocation, it pinpoints small swimmers near the water surface, then trawls with daggerlike claws to capture its prey. Some eat on the wing; others transport the fish in their cheeks to a feeding site nearby. One N. leporinus might down a dozen fish in a night.
Noctilio leporinus

This Tungara frog won't see the light of day: The fringe-lipped bat, Trachops cirrhosus, swoops in and grabs it with a powerful bite. This bat's ears are longer than its head, which helps explain how it can find frogs by the sound of their mating calls, even distinguishing the calls of edible species from those of toxic species. Chemical sensors in its lip fringe give added protection from a toxic meal.
Trachops cirrhosus bat

Working with bat researcher Elisabeth Kalko of the Smithsonian Tropical Research Institute, Sergio Estrada-Villegas studies species—such as this Vampyrodes caraccioli—that inhabit the canal's smaller islands. Says Kalko, "The bats here are so specialized, yet still highly adaptable if they find new resources. That's the key to their success."

With a firm but gentle grip, bat researcher Sergio Estrada-Villegas feeds a little fruit-eating bat, Artibeus watsonii, an energizing mixture of sugar and water prior to releasing it.

Barro Colorado's bats thrive by specializing. At mealtime the fringe-lipped bat, Trachops cirrhosus, ignores blooms, instead listening for frog mating calls. It snatches one with its well-developed canines and may down ten more before the night is out. (Some frogs' calls have changed in response to regular predation by bats.)
rachops cirrhosus bat

A single suction cup on a Spix's disk-winged bat can support the entire weight of the animal. The tiny concave disks, found on these bats' thumbs and ankles, allow them to climb and roost on slick leaves and similarly smooth surfaces—such as the inside of a glass—where other bats couldn't get a grip. Also unusual, Spix's bats roost with their heads up instead of hanging upside down.
Thyroptera tricolor

Spix's disk-winged bats have suction cups that enable them to grip the inside of a smooth furled leaf and scuttle in and out of its protective confines.
Thyroptera tricolor

A chewed-out cavity in an arboreal termite nest houses Lophostoma bats, which may derive warmth from the active insect colony within. Scientists suspect chemical signals between bats and bugs could prompt the termites to wall themselves off from, rather than attack, their unwelcome guests.
Lophostoma silvicolum

Extravagant blossoms rich in nectar invite long-tongued bats to bury their faces in hundreds of flowers a night, pollinating one after another in the process.Glossophaga sp

Strobes capture a greater bulldog bat's success on Lake Gatún. The behavior likely originated when insect-eaters snagged fish by mistake. Trick became tradition, and another specialist took its place in Panama's night skies.
Noctilio leporinus