The Nature Corner, by Ernie Marshall
BATS, FRIEND OR FOE?
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| Photo by Jeff Lewis |
The animals that seem most widely feared are snakes, spiders, and bats. Dread of snakes and spiders makes some sense, since certain snake and spider species are sufficiently venomous to be dangerous to humans. But bats pose no threat to us -- with the possible exception of vampire bats which I will say something about shortly. Bats do not fly into your hair, and the incidence of rabies among them is low, 10 reported cases within the past 50 years.
If Jeff Lewis’s photo of a bat among azalea blossoms at the Elizabethan Gardens outside of Manteo does not make them endearing to you, consider what extraordinary animals bats are. Jeff’s excellent photo reveals several of these traits. They sleep in the daytime, hence are nocturnal or active at night. They “perch” upside down, which requires a specialized circulatory system. (Imagine how you would feel the next morning if you slept hanging by your heels!) They typically have big ears, indicating the importance of hearing to bats. The folded wings tells us that they have the power of flight. Regarding this last point, although there are a few mammals, such as flying squirrels, that can leap and glide from tree to tree, bats are the only mammals, and the only vertebrates besides birds, that can fly.
Roughly 1,240 species strong and world-wide in distribution, bats make up 20% of mammal species. There are 45 to 48 species in the U.S., the little brown bat, big brown bat, and Mexican free-tailed bat being among common species.
Bats compose the order chiroptera. They are not, as some think, “flying rodents”. This term “chiroptera” is from two Greek words meaning “hand wing”, which aptly describes them. Their wings are skin spread between extended of digits (omitting the thumb). This structure makes their wings more flexible than a bird’s, giving a bat more maneuverability in its aerial pursuit of flying insects.
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| Photo by Jeff Lewis |
The main use of echolocation is navigation and finding prey. By its means they can determine whereabouts, direction, and speed of movement of objects around them. (Contrary to common belief bats are not totally blind, but most do have rather poor eyesight. But with echolocation, who needs glasses?)
We are unable to hear all of this bat chatter because their shrieks are ultrasonic, at higher frequencies than we can hear. Otherwise a quiet night might be quite noisy, because their vocalizations are often around 130 decibels. To put that in perspective, a loud rock concert is about 115 decibels, pain begins at about 125 decibels, and permanent hearing damage at about 140 decibels. To deal with this racket, so that they can hear the returning echoes and not deafen themselves, many bats time their calls, adjust their frequencies, and close their ear openings (ear plugs?).
If you still find bats creepy consider how beneficial they are. Most bats eat flying insects, including plenty of mosquitoes. Being nocturnal, they wake up for breakfast just when mosquitoes are most active. It is estimated that a bat eats over 600 mosquitoes per hour. There is a colony of a million and a half bats in Austin, Texas that consumes 10,000 – 30,000 pounds of insects per night.
The huge bat colony living in Carlsbad Caverns in New Mexico is estimated to eat three tons of insects every night. The whole colony exits the cave at sunset making quite a spectacle. Their flight can be seen from miles away as a black streak across the sky and takes from twenty minutes to two hours.
Given their contribution to mosquito and pest control, rather than installing a bug zapper, which attracts mostly moths rather than mosquitoes anyway, a better idea is to put up a bat roosting box in the yard.
Although insects are a typical bat’s nightly staple, some varieties eat fruit, nectar, or pollen, and thus benefit us and nature by spreading fruit seeds and pollinating plants. There is also a bat species that catches and eats fish. But the most interesting exception to a bat’s insectivorous habits is the vampire bat.
There are three species of vampire bats, which range from Mexico to central South America. They prey on livestock, and occasionally on humans. They typically walk up to the cow, using their folded wings as forelegs, climb up the animal’s leg, cut a small gash with it sharp canines, and lap the blood that flows from the cut. They are usually more a pest than real threat to an animal the size of a cow or human, but not a night visitor one would welcome.
A fascinating accompanying adaptation is that their nose includes a heat-sensitive organ similar to that possessed by pit vipers. With a rattlesnake the organ is to help locate warm-blooded prey. Its function for vampire bats is to find blood vessels just under the skin.
The name “vampire bat” is of course borrowed from tales concerning Count Dracula and other human vampires, a genre that is still popular. A chilling image I have from early childhood is from a vampire movie of that era. Count Dracula would transform himself into a bat, fly through some sleeping maiden’s open window, do his evil deed, and return to his castle. Then he changed from bat to the pale, cloaked figure of the diabolical count, and step back into his awaiting coffin.
The bat bit was added to the legendary vampire material by Hollywood, and maybe helped give bats a bad rap. But it makes for a good story, and elements of the natural world are bound to get interwoven with human hopes and fears.
