A-Z Modern Bestiary: Behold the Bat

March 29, 2017 | Posted in: Modern Bestiary

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera

Variety: Teeming
Population: Dwindling

is for the Bats

 

“Flight is not a bonus: flight is all and everything to a bat.”
Simon Barnes, Ten Million Aliens

 

Oh, how we humans dream of flight, have invented our way into the air, but only as visitors. The mammals, you see, did not evolve for flight, leaving that to the birds. Except for one branch of the mammalian family: the bat. And a big branch they are, Chiroptera, as one in five of all mammals are bats and they’re found everywhere minus the freezing poles and a few remote islands. Of the mammals, only humans and rats compete with bats numbers and distribution.

There are an estimated 1,240 species of bats, and these are split into two groups: 1) the larger fruit-eating megabats (also known as flying foxes) and 2) the smaller mainly insect-eating microbats. Due to this variety, the difference in size between species can be staggering. The largest wingspan belongs to the giant golden-crowned flying fox, which has been measured up to 5’6″ (taller than a lot of people). The smallest bat is also the smallest of all mammals, the Kitti’s hog-nosed bat, also known as the bumbleebee bat, which at its largest gets up to 1.3″ long (fits in the palm of your hand).

 Die Fledermaus, Vincent Van Gogh, 1886

Die Fledermaus, Vincent Van Gogh, 1886

Flying foxes aren’t the usual sort of bat we think of: only one genus in this group utilizes a simple form of echolocation, the rest rely on their excellent eyesight to spot their prey. Since they’re frugivorous (the next big diet fad I’m sure) there’s no need for fancy auditory tricks; fruit doesn’t go anywhere fast. Some species can descend in biblical proportions, as happens at the Kasanka National Park in Zambia every October with the return of the straw-colored fruit bat:

“Every year during the dying days of October, at the very beginning of the rainy season, millions of these small creatures swoop down on the forest of Fibwe at the heart of the park and take off again in December for an unknown destination. It is considered the word’s largest mammal migration. Attempts to track them by means of small transmitters have not yielded any answers up to now, because the flight recorders have fallen silent for no apparent reason after a mere few hundred miles of flight.

For a period of almost two months, at dusk the sky above Kasanka regularly turns black as a result of the taking flight of more than five million flying mammals over only two and a half acres…. The invaders main victims are the fruit trees: 330,000 tons of fruit disappear every year during the course of the raid.” Olivier Le Carrer, Atlas of Cursed Places

Microbats are the quintessential bats: small, darting, clicking spots of darkness in the darkness. Most species eat insects, but many include other delicacies in their diet, including frogs, birds, lizards, fish, even smaller bats. Some go in for nectar as well.

Lesser Long-eared bat, detail of the 67th plate from Ernst Haeckel's Kunstformen der Natur (1904)

Lesser Long-eared bat, detail of the 67th plate from Ernst Haeckel’s Kunstformen der Natur, 1904.

Flittermouse: an antiquated English name bestowed on the bats, and a pretty apt description. The flight pattern of a bat is flighty, fitful, all instant changes in direction, jerks and twists. This crazed flight pattern is the bats secret to success: insects, with their own erratic flight, hidden in the dark of night, still can’t escape the bats high frequency chirps. Sound at these higher frequencies (and bats can hear up to 120,000 hertz, six times higher than human hearing achieves) rebound off objects, and bats track the time interval between chirp and returning echo to map the world around them, illuminating auditorily any potential prey nearby.

“For the bat, the world of fast aural vibration is more revealing than the human world of sight. Using a narrow-band, constant-frequency call for detecting objects at a distance, a bat can pick out a tiny insect by the aural glinting on its wings… As it closes in on the insect, the bat switches to a broadband, frequency-modulated (FM) signal. This sweeping acoustical barrage blankets the insect, giving the bat a spectral image of the texture, speed, and direction of its prey. Just before the bat reaches its victim, there is a constant buzz of soundings that guide the animal over the final centimeters to its goal.” William Bryant Logan, Air: The Restless Shaper of the World

It’s hard for a human perspective to grasp sound-as-sight, and yet it’s just so for a bat. In normal flight, bats beat their wings in time with chirps, an average of about 15 per second. But how do they hear the echo coming back without hearing the chirp their currently sending out? This talent to talk (or more accurately, shriek) while simultaneously listening requires the use of a specially developed inner ear muscle which closes in time with the chirps to allow only the echoes to be heard. The bats entire body is perfected for flight guided by sonar:

“Everything in the bat is squeezed in for flight. The lungs and heart are huge, the guts tiny. Every wing beat corresponds to a breath, so the same muscles can work both operations… After it lands, the bat needs about thirty seconds of heavy breathing to take in enough oxygen to make up for the deficit incurred in flight.” Logan

Squelette de chauve-souris, Émile Deyrolle (1838-1917)

Squelette de chauve-souris, Émile Deyrolle (1838-1917)

Bats chirp for more than just hunting of course. As social animals they have a lot to say to one another. Mexican free-tail bats roost in numbers as large as 1.5 million, and at least 15 different calls have been recorded between individuals during feeding times, both to aid communal organization and to claim their own arial territory.  At times these bats will even use a specifically tailored form of echolocation to disrupt another bat’s target on its prey.

And bats sing. Oh yes, the males croon to the females, articulating with lovely chirping who they are, where they are, and to other males where to avoid. Twenty species of bat have been recorded singing, found all across the world. Below is the song of Pipistrellus nathusii:

Usually we humans possess more warm and fuzzy feelings towards our fellow mammals than other forms of life, but bats have suffered a bad repute. Whether it’s their nocturnal lifestyle, or erratic flight movements, or leathery wings, or the stories of vampire bats, there are many people who are disgusted by the mere idea of bats. But I’ve held the small warm body of a bat, felt its incredibly soft and fragile wings glide across my hands, its tiny claws grasping delicately for a secure hold. There is nothing vile in this bat body, nothing sinister or eery or foreign. In your hands, it’s familiar, it’s mammalian.

“[B]ats clear out our skies of mosquitoes and other pesky insects while pollinating the flowers and fruits we enjoy—tasks that have enormous benefits, economic and otherwise, for humans. Yet around the world—and nowhere more relentlessly than in the United States—colony after colony of bats has been destroyed by humans wielding guns, fireworks, dynamite, flames, napalm, poison, tennis rackets, hockey sticks, and other weaponry, simply because we fear these small, nocturnal flying mammals.” Paul Bogard, The End of Night

Vampire bats, C. E. Swan, The Wild Beasts of the World, Frank Finn, 1909

Vampire bats, C. E. Swan, The Wild Beasts of the World, Frank Finn, 1909

Even vampire bats are not the villains many think. In fact, when it comes to sharing, they put many humans to shame. There are three species of vampire bat, ranging from Central and South America, and yes, they live solely on the blood of other mammals and birds. Rarely are humans bite, but cattle are frequent suppliers of fresh blood. With sharp incisors they make a shallow wound, and then lap up the blood. But it’s not easy to find a fresh supply and often these bats go hungry at night. Missing a meal is dangerous, as starvation happens as quickly as three days. Fortunately, they’ve adapted a social welfare program:

“Vampires are social creatures, coming back to the same day-roost at the end of every night…. There are some big colonies, up to 2,000 animals, but most are much smaller, and centre on a core population of females. . . . All members of a roost then, related or not, are likely to know each other well. And so it happens that a bat who has failed to find blood in a night’s flying will beg a meal from a neighbour. From a friend, we would say, if we weren’t so terrified of sounding anthropomorphic. The friend will then regurgitate blood, thus sharing a meal. Under this system females have been known to live for 15 years.” Barnes

Bats benefits humans in so many ways, but we’ve yet to return the favor. We’ve killed them intentionally, destroyed much of their habitat, and transported new diseases and predators to their homes with our own explorations. New Zealand historically had only two species of bat, and one, the greater short-tailed bat, has not been sighted since 1967 and is considered extinct, done in by a combination of the causes above. According to the IUCN, there are currently 26 bat species listed as Critically Endangered, 51 species listed as Endangered, and 954 listed as Vulnerable. Many of the remaining species not listed have yet to be studied enough to have their status known. Basically, it’s not looking good for batkind.

Only known photo of a Greater Short-tailed bat which are now extinct, 1965, Don Merton.

Only known photo of a Greater Short-tailed bat (which are now extinct), 1965, Don Merton.

Perhaps the most bizarre story I’ve heard of humans being horrible to bats comes from WWII, when an American dentist, Lytle S. Adams, managed to get his insane weapon idea approved for experimentation by the U.S. military. He called it Project X-Ray. His idea: bat bombs:

“Gathering thousands of Mexican free-tailed bats from Bracken Cave, where twenty million mom and baby bats roost between March and October, Adams and his team fitted them with small incendiary bombs, and planned to tuck them into individual canisters, each equipped with a parachute, and drop them over Japan. At a thousand feet the canisters would open and the bats fly free to roost under shingles and eaves, where they would soon explode, setting fire to whole cities dotted with wooden and paper houses. President Roosevelt okayed this oddball plan and spent $2 million on it. Then one day armed test bats accidentally escaped and torched a Texas air base, after which Project X-Ray was ditched.” Diane Ackerman, The Human Age

Presently in North America, things are ever more grim for bats. Here, year round species hibernate through the winter, finding safe dark places to settle in upside down, their tiny bodies dropping in temperature to right around freezing, heartbeats slowed, entering a deep state of dormancy. This was a perfect way to handle the winter cold (which is deadly to an active bat) right up until the time a human visitor from some far off continent (many scientists think Europe) visited a New England cave and left behind a guest: the fungus Pseudogymnoascus destructans.

In the winter of 2007, scientists first began receiving reports of dead bats in caves in New York. The bodies were found to have white fungal growth around their noses, and so the cause of death became known as White-Nose Syndrome. This cold-loving fungus grows on its host over the winter, disrupting the bats hibernation and causing its small body to tear through its limited supply of fat reserves. Death is the outcome. By the next winter the fungus had spread to five other states. By winter 2008,  three more states were infected.

Today, the fungus has spread to at least 22 states and 5 Canadian provinces. More than six million bats have died. In human terms, that’s more than the entire population of Colorado. It’s horrific. And it’s still happening every winter, though with less and less bats left to die.

Stainglass sample from a Catalog for the Belcher Mosaic Glass Co. (New York, N.Y.), 1886.

Stain glass sample from a Catalog for the Belcher Mosaic Glass Co. (New York, N.Y.), 1886.

Bats cling on where they can, threatened but still flying against the dying of the light. Their flicking forms should have new meaning for you, if you’re lucky enough to live where the dusk grows fuller with their chirps. So here’s to our fellow mammals who achieved what many of us dream of most: free flight.

“Look up, and you see things flying

Between the day and the night;

Swallows with spools of dark thread sewing the shadows together.
An illustration from Doubt and Other Things by Elihu Vedder, 1922

A twitch, a twitter, an elastic shudder in flight
And serrated wings against the sky,
Like a glove, a black glove thrown up at the light,
And falling back.
Never swallows!

Bats!

Wings like bits of umbrella.
Bats!
Creatures that hang themselves up like an old rag, to sleep;”

—Excerpt from Bat, by D.H. Lawrence

 

The following books informed this post:
Ten Million Aliens, Simon Barnes
Air: The Restless Shaper of the World, William Bryant Logan

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