Originally published in Points West magazine in Winter 2009
Night Travelers Debunked and Demystified
By Philip and Susan McClinton
Former Curatorial Assistant, Draper Natural History Museum
One evening in August 2009, Susan and I watched with awe as yet another rescued bat spread its wings and took flight off our deck from its temporary “prison,” a small ice chest. Barely the length of one of my fingers, she was the seventh “night traveler” in three years rescued from the Buffalo Bill Center of the West. After she’d fed on the grasshopper I offered and lapped water from an eyedropper, she took to the skies, spent a few minutes finding her bearings, and then disappeared from sight.
Just say the word
Just saying the word “bat” conjures up feelings of dread, fear, loathing, and suspicion. We’ve all heard the myths and folklore: Bats get tangled in hair; bats are vampires; bats attack people; bats are blind; bats carry rabies; and bats are flying mice. With one exception, none of these are true.
In fact, the fear generated by all these myths causes far more damage than the species itself. Dr. Merlin D. Tuttle—world renowned bat researcher, aficionado, and founder of Bat Conservation International—writes in his book America’s Neighborhood Bats that people have actually injured themselves while trying to elude bats they thought were rabid; nearly drowned by falling off boat docks trying to escape bats chasing mosquitoes; and in one instance, a homeowner fumigated his house to rid it of bats and destroyed his home in the process!
As curatorial assistant at the Center’s Draper Natural History Museum, I’ve had the opportunity to dispel fears about the small mammals by revealing their natural history and behavior to employees and visitors here. Admittedly, the science of bats is still sketchy at best, adding to their mystique. What we do know is that bats have significant benefits for mankind, but experience a number of challenges.
Bats, bats, bats
Bats belong to the order Chiroptera, which literally means “hand wing.” With extremely elongated fingers and a wing membrane stretched between, the bat’s wing anatomically resembles the human hand. The so-called “New World” species, in particular, exhibit a broad variety of flight habits attributed to different wing morphologies and shoulder structure.
Bats account for nearly one quarter of all mammal species, second only to rodents in ubiquity. They occupy all areas on earth, except the Arctic and the Antarctic and a few islands, and are the only true flying mammal. The smallest bat weighs less than a penny and is about the size of a bumblebee, and the largest—flying foxes of the “Old World” order—can have wingspans of up to six feet. Today’s bats exhibit two remarkable specialties: flight and echolocation.
Originators of sonar
Most smaller bats of the New World navigate by echolocation; that is, they send out a series of clicks or high frequency sounds to “see” everything, even something as fine as human hair! These ultrasonic sounds —beyond the hearing range of most humans—are used to locate prey, avoid obstacles, and navigate, a process researched for navigational aids for the blind.
The sounds are produced in the bat’s larynx, which is similar to humans and other animals. This echolocation is very sophisticated as bats send out high frequency clicks through their mouths and at different wavelengths, depending on the species. The pulses function in much the same way as our modern sonar. A returning echo allows bats to determine distance, direction, presence, and velocity of movement, as well as texture, size, and shape of an object. Many of a bat’s specialized facial and body features have developed to maximize the effectiveness of its echolocation.
Nature’s natural pesticide … and more
With the exception of three species of nectar-feeding bats in the desert southwest, all bat species in the United States feed almost exclusively on twilight-flying insects such as moths, flies, mosquitoes, katydids, cicadas, and the like. Bats worldwide can also eat small animals, fish, fruit, nectar, and pollen.
Three species of bats found primarily in the tropical and subtropical regions of the New World are blood feeders. They land on the ground, climb onto the victim (usually livestock or wild animals), and use their highly modified teeth to make a small v-shaped wound. Then, they lap blood with their specialized tongues—a serious problem since their saliva contains anticoagulant, causing wounds to bleed for a long time, and risking secondary infections. Occasionally, they may feed on humans, but these incidences are rare.
Bats can roost in a variety of shelters such as caves, buildings, bridges, trees, cliff faces, animal burrows, flowers, termite nests, and even large tropical spider webs. Many species adapt to a particular roost and can’t survive elsewhere. Roost selection depends on a narrow set of factors including light intensity, safety from predators, humidity, and temperature.
Many species of bats are colonial while others are solitary, thus adding another element to the importance of roost site selection. Energy use also plays an important role in choosing a beneficial roost site. Bats can modify their roost selection by huddling tightly together to conserve energy and produce an elevated body temperature. The concentration of many small bats functions thermally like that of a large bat.
Hibernacula (where bats hibernate) occur in many locations, too. Temperature is critical to permit the optimum low metabolic rate required for hibernating, and humidity must be high enough to prevent too much moisture loss. Bats can remain in hibernation for up to six months where they live on highly-specialized, stored fat reserves that make the reduction in metabolism possible. Consequently, hibernacula are especially sensitive to human encroachment.
Unnecessary disturbances put bats at risk by making extra demands on this critical energy reserve that cannot be replaced immediately. This may lead to shortages of the fat reserve resulting in death by starvation to individuals and/or the colony. Other species can survive short-term exposure to subfreezing temperatures and can over-winter on cliff faces or outer building walls.
Bats are loyal to birth and hibernaculum sites, but exactly how they find their way to these places over long distances is unknown. Possibilities include identifying landmarks and learned behavior passed from one generation to another. Colonial bats create nursery colonies where pregnant females give birth to their young—usually just one offspring a year, making bats the slowest reproducing mammals for their size. Surprisingly, even among hundreds of thousands of young, mothers recognize their individual baby by smell and voice, and in colonies of Brazilian free-tailed bats, feeding the young may be a communal activity. For unknown reasons, males remain segregated from the young and females in these nursery colonies.
Most bats are nocturnal, flying primarily at twilight. This has distinct advantages, not the least of which is avoiding predators. Next, many of the bat’s prey are also active at night, providing almost unlimited access to food. Moreover, many flowers that open only at night are pollinated solely by bats. Finally, daytime activity carries a higher expenditure of metabolic energy resources because of excessive heat and low humidity. Being active at night allows the bats to expend less energy and conserve water because of lower temperatures and higher humidity.
Bats emerging to forage at night from their roost are an awesome spectacle. Many have been awed by the sight of bats emerging from Carlsbad National Caverns, a seemingly endless “river” flowing from the cavern mouth. These gigantic columns of bats can be visible for up to two miles and may achieve an altitude of more than ten thousand feet. Brazilian free-tailed bats often form colonies of over twenty million individuals (240 metric tons!) in a single cave, specifically Bracken Cave in Texas.
Worth their weight in insecticide and fertilizer
Because many other plant and animal species depend on them for their survival, bats are often called “keystone” species. Bats are the major predators of night-flying insects: One mouse-eared bat can consume up to six hundred mosquitoes in an hour; the twenty million free-tailed bats from Bracken Cave eat 250,000 pounds of insects in a single night. A big brown bat can consume 1,200 insects in one hour.
In addition, many economically valuable plants depend on bats for pollination, and others rely on bats for seed dispersal in reforestation. As well, bat guano (feces) is a source of organic fertilizer and continues to be a beneficial resource in underdeveloped countries.
Debunking myths and superstitions
The large bats of Asia and the Pacific Islands are held in high regard and considered omens of esteem and good luck, but the bats of the New World are persecuted and feared. Ignorance plays an important role in the way individuals view bats, and people often grossly embellish stories of negative encounters.
Many believe that bats are blind and can become tangled in a person’s hair. It’s true that bats may accidentally tangle in the hair but only if the person is flailing about to drive the bat away. And while bats’ eyes are normally small, their vision is quite good at moderate distances. Others believe that most bats are vampires, but as mentioned previously, only three species are “vampires” and pose no serious threat to humans.
Bats are not flying mice, although they may resemble mice to a certain degree. Bats can only transmit two diseases to humans, rabies and histoplasmosis (a fungal disease), and the instances of either are rare and often greatly exaggerated. Bats are actually of great benefit to mankind and the production of food crops because they eliminate insect pests. In basic terms, bats are the only nocturnal predator of great numbers to feed on night-time insect pests.
Rabies and histoplasmosis
Bats do not “carry” rabies; rather, they contract it like other mammals. Only 0.5 percent of bats actually get the disease—comparable to the rate of rabies in other mammals. Unlike dogs, cats, and other wild mammals, they seldom become aggressive after catching rabies. There are only one or two human deaths per year from bat rabies in the U.S., which means one is more likely to catch polio, leprosy, or the plague than to contract rabies from a bat.
Rabies is nearly always transmitted through a bite. According to the Centers for Disease Control, people cannot catch rabies just by seeing a bat in an attic or cave, or from a distance. Rabies can be contracted by an infected bat’s bite, or, rarely, by inhaling dust containing the virus. Contact with urine, guano, or fur of the bat (even though bats should never be handled) does not spread rabies. Finally, the idea that bat colonies in urban settings lead to more cases of rabies is a fallacy. The largest urban bat populations consist almost exclusively of colonial species, and there is no evidence linking them to increased transmission to humans.
The fungus that causes histoplasmosis can be present wherever bat guano accumulates and can infect persons who come in contact with it. Antifungal medications are used to treat severe cases of acute histoplasmosis.
White-nose syndrome: the grim reaper
In winter 2006 – 2007, white-nose syndrome was discovered in eastern New York and is now rapidly spreading to other parts of the northeast. This syndrome is deadly to bats, already killing more than four hundred thousand with a 90 – 100 percent mortality rate at affected sites since the outbreak. Prognosis is grim because so little is known about the syndrome. U.S. Fish and Wildlife Service biologists, along with other federal, state, and local agencies, and university researchers, are working to obtain as much information as possible in order to halt the spread. As Dr. Thomas Kunz, director of the Center for Ecology and Conservation Biology at Boston University recently testified to Congress, “We are witnessing one of the most precipitous declines of wildlife in North America.”
The syndrome appears as a white fungus on the nose and wings of affected bats and is transmitted bat-to-bat. Humans who encroach in caves where bats are hibernating may come in contact with the fungus and spread it from cave to cave. Consequently, the bats are in danger of losing their fat reserves needed for hibernation and may leave the hibernacula in winter and die. Numerous caves in the affected areas have been closed, and cavers are being warned to stay away from other caves in the affected areas to help slow the spread of the syndrome. Currently, officials know of no risk to humans from this syndrome but urge all precautions be taken when entering caves or handling bats.
Species in jeopardy
Yes, bats today face considerable harm from many sources—so much so that six species of bats in the U.S. are endangered, and others may be eventually included. First, destruction and/or disturbance of habitat are contributing to the decline of bats worldwide. Bars or grilles are now placed over mines and caves to protect bats inside from encroaching humans.
Urban sprawl and development are also contributing factors to habitat loss. Moreover, since bats are intensely feared, they are relentlessly persecuted in many areas and are burned, poisoned, or dynamited to extinguish their populations. Unnecessary banding of bats, a means of identification, can put them at risk by stressing them physically and can cause injury if the bands are applied incorrectly.
Likewise, indiscriminate use of pesticides is decimating populations worldwide. The toxic concentrations of pesticide in insects are passed along the food chain (“bio-magnification”) to bats, birds, and other organisms. Finally, chemicals used against wood-boring insects—as well as the chemical chlorophacinone, which is used to eliminate bats in homes—are very dangerous to these species; the latter is also hazardous to humans.
Families can help by building bat houses to help protect bats in their area. Plans are numerous, vary in size and shape, and are adapted to species, climate, and social group. Bat house plans and related information are available on numerous Web sites by entering “bat house” in your Internet browser’s search field.
As one of the most important indicators of a healthy environment, bats act as biological sentinels to warn us of potentially lethal levels of pollution and pesticide use. Their potential and real value to man is undeniable, providing a natural control of many insect pests and pollinating plants. Tuttle puts it best: “…we need bats whether we like them or not; their loss poses serious, potentially irreversible consequences to the environment that we all must share.”
About the authors
Philip L. McClinton is a former curatorial assistant for the Draper Natural History Museum. Susan F. McClinton served as the information and education specialist on grizzly bears for the Shoshone National Forest in Cody, Wyoming, during the summer of 2005. Both have master’s degrees in biology from Sul Ross State University in Alpine, Texas, and each has a keen interest in animal behavior, conservation, and wildlife education. The McClintons have published and presented a number of articles and reports about their work.
All images courtesy Philip and Susan McClinton unless indicated otherwise.