Constructing Nature: Using Artificial Habitats to Save Bats from Fatal Disease

By Lauren Moore • Sciences, Cycle 3, 2012
 

 

 

Introduction

Bats often go unnoticed, retreating into caves and flying in the shadows. Though they may seem sinister, these creatures are vulnerable, and they are under threat. A disease called white nose syndrome, abbreviated as WNS, is wreaking havoc on nine bat species in 19 states across the country. The disease is named for the white fungus (a mold called Geomyces destructans) that grows on bats’ faces. Other physical symptoms include lesions on the wings and ears that provoke severe internal damage by disrupting biological rhythms.

Most current research examining white nose syndrome in North American bats aims to answer the questions of what causes the disease, what environmental factors increase its fatality, and which bats are at risk. Studies conducted in 2010, 2011, and 2012 all confirm that there is a link between cold environmental conditions and fatality from white nose syndrome because cave-roosting bats’ hibernation is disrupted by the disease, causing them to freeze or starve to death in the winter (Frick et al. 681, Foley et al. 225, and Flory et al. 680). With the 73% mortality rate cited by Frick et al., it is clear that WNS is a serious threat that must be ameliorated.

Bats’ situation is not improved by human development. As they lose natural habitat and collide with urban communities, their chances for survival decrease. However, bats can also be adept at blending into the urban world. Stanley D. Gerht and James E. Chelsvig conducted a study in 2004 of bats living in Chicago, and Michael D. Dixon researched bats living in the Minneapolis-St. Paul area in 2012. Both found that bats prefer to live near tree cover and lakes, and as long as those exist in cities, bats are willing to make them their homes (Gehrt and Chelsvig 626, Dixon 695). One species, the big brown bat, even prefers to roost and give birth in attics instead of rock walls, so the urban environment can be appealing for bats (Lausen and Barclay 362). This research shows that bat conservation can coexist with urbanization; the two are not mutually exclusive. Human structures can be repurposed as homes for bats.

Therefore, when we consider both the impact of WNS and the merging of the natural and urban world, it’s clear that the spread of the disease must be slowed and that it will probably have to take a somewhat “unnatural,” human-designed approach. However, few studies measure the efficacy of possible solutions, which is fair, considering the disease was only discovered six years ago. Some scientists have proposed ideas. Justin Boyles and Craig Willis have proposed heating caves in order to prevent bats from freezing to death when they awaken too early from hibernation, and scientists have taken preventive measures like disinfecting spelunking gear and banning people from entering caves to slow the spread of WNS (Zimmerman). Also, there may be hope for finding a treatment for the disease, or using vaccines to help populations survive the disease (Foley et al. 228). However, these are only hypothetical solutions; to date, there is no treatment or cure for the disease. Furthermore, all of these are, in Zimmerman’s words, “stopgap measures.” At best, these solutions can only stave off WNS, but not stop it entirely.

A novel disease requires novel approaches. Our obligation to prevent the spread of WNS can dovetail with urbanization if we work constructively to build artificial habitats. Cleaner, safer artificial caves, which are already being planned and implemented, are the key to uniting the natural and urban world to promote bats’ survival. Research does not exist on such caves because, until September 2012, artificial caves themselves did not exist. A Nature Conservancy project, the artificial cave could potentially save bats by providing them with a temperature-controlled, regularly sterilized area free from natural predators and human trespassing, the best possible environment to survive the disease. It seems promising, which is why I have chosen to research it. The academic community should take notice of this new approach and closely follow this artificial cave to measure its effectiveness in sequestering at-risk bats and protecting them from the disease.

The Disease: Background Information

First, we have to understand exactly how WNS functions. It impairs the crucial process of hibernation by striking bats in the winter and causing them to emerge too early from their dormant states. Once awakened, they freeze or starve to death (Flory et al. 680). According to Bat Conservation International (BCI), more than half of all American bat species hibernate in caves and are, therefore, at risk of infection. WNS targets the thin membranous skin of the bats’ wings, which serve biological functions beyond flight. US Geological Survey pathologist Carol Meteyer wrote in a 2010 survey, “Body temperature, blood pressure, water balance and…circulation” are also integral to wing membranes, which is why the wings’ susceptibility to wounds and lesions is a fatal threat. Bats depend on their stored calories in the winter, and each interruption of their hibernation costs “energy that could fuel 60d of torpor” (Fenton 6794). Bats rely on careful regulation of torpor to ensure their survival when their body temperatures and rates of metabolism slow. It is the interruption of these processes that saps bats of energy. Bats who arise early will need to search for food, which is not only harder to find in the winter but also further exposes them to the elements. Once a bat’s store of nutrients is depleted, it has a slim chance of surviving the winter without contracting an infection, and it has no chance of surviving further cold seasons.

There is some debate over whether the fungus G. destructans actually causes the metabolism-disrupting disease. Robert Zimmerman, a biologist, writes that the fungus, which thrives at cold temperatures, may not be “the primary cause of the deaths” but “simply an opportunistic pathogen.” Regardless of whether G. destructans is the primary pathogen or just a side effect, scientists agree that the effects of the disease are devastating.

Extinction is likely for one of the most common bat species in the country, the little brown bat. As a social species, these bats are at risk because they roost and hibernate close together in high-density colonies. With so many opportunities for contact, a single infected bat can quickly spread the disease throughout the entire population. Winifred Frick et al. predicted the species’ extinction as early as 2026 (681), a grim outcome for a disease that was only discovered six years ago.

Bats are dying in unprecedented numbers: BCI estimates that since 2006, WNS has killed seven billion bats. The biologist Robert Brooks compared two studies of bat activity in New England, one dating back to the discovery of the disease and one that concluded in 2012. After analyzing the frequency with which bats called to other members of their colony, Brooks found “major declines” in the cave-hibernating Myotis species like the little brown bat (2540). In fact, the population had fallen by a precipitous 72%. Disturbingly, Brooks’ data aligns with a 2010 study by Winifred Frick et al., showing a nationwide mortality rate of 73% (680). The results of research are consistent, showing WNS is an undeniable threat.

Our Shared Ecology

Bat survival may seem irrelevant to human interests, but bats are key members of ecosystems across the country. As insectivores, bats keep insect populations in check. They also pollinate flowering plants and contribute fertilizer in the form of guano, making them essential for plant life in North America. Some may argue that since humans are not to blame for WNS, we have no moral incentive to slow its spread and that it would be impossible to eradicate the disease completely given its fast transmission and high mortality rate. Still, we are part of the same ecosystems that bats belong to, and if they disappear, the consequences will be enormous. John R. Platt reported for the Scientific American blog that gray bats in Missouri eat 223 billion insects every year alone. He cites a study from the US Geological Survey that claims the agriculture industry could spend more than $3.7 billion a year in increased expenditure on crop protection and pesticides without bats to balance the insect population. According to the EPA, agribusiness provides “one-eighth of the US GDP and one-sixth of the US civilian labor force.” Our reliance on agricultural revenue requires the survival of bats.

Merging the Natural and Urban Worlds

Unfortunately, natural sanctuary is hard for bats to find. Bat populations were already declining before WNS because, in the words of biologist Cory Holliday, “the biggest threat to bats is the loss of suitable habitat.” Human development has encroached on forests and blocked, destroyed, or contaminated caves. As a result, some bats are finding homes in urban environments. The biologists Cori L. Lausen and Robert M. R. Barclay found that bats gain a survival advantage by moving into urban buildings: they cease to become targets of natural predators and save energy by adjusting their mechanisms of heat regulation. Lausen and Barclay found that bats also gain a reproductive advantage by moving in with humans. Their babies are born earlier and grow faster in the urban “microclimate” than they do in natural roosts (Lausen and Barclay 362).

Nevertheless, urban buildings are not axiomatically good for bats. Once discovered inside, they are usually considered pests and evicted by their human hosts. Integrating bats into developed environments would force us to reexamine our views toward them. The city of Austin, Texas, is famous for being home to the biggest urban bat colony in the country. The annual return of the bats draws crowds of tourists and is a point of pride for the city. It is possible to coexist, not just peacefully but enthusiastically, with bats. But first, most urban dwellers would have to adopt the perspective that bats must be saved at all costs. Bats have to be welcomed by humans in order for them to be integrated in developed areas, as bats often have no choice but to live in cities.

Stanley D. Gehrt and James E. Chelsvig investigated bats living in Chicago from 1997 to 1999, well before the outbreak of WNS. While substantial urbanization is generally unfavorable for bats, their research shows a positive correlation between bat activity and “adjacent urbanization, which may have been a result of favorable microhabitats” (Gehrt and Chelsvig 626). Chicago, with its population of 8 million, is an acceptable last resort for bats because of its proximity to woodland. Moreover, the conservation biologist Michael D. Dixon found in 2011 that six bat species had made their homes in the Minneapolis-St. Paul area because of the “tree cover and proximity to water” (683). Dixon notes that it is lack of trees that drives bats away from cities, not urban development itself. Therefore, as long as “substantial tree cover near urban lakes” is protected, Dixon claims that conservation efforts can coexist with urbanization (695). Clearly, bats can make unnatural areas their homes. Certain conditions must be met, but bats are not unable to live in urbanized land.

This evidence shows that bats are already adapting to urbanization and merging the natural world with the artificial one. The best thing for us to do is to take advantage of that trend and give them the cave environments that they desperately need.

Artificial Caves: A Short-Term Solution

Artificial habitats aren’t necessarily the only option we have to fight back against the spread of WNS. One option is culling infected populations. This is controversial because the removal of infected individuals must be precise and significant enough to reduce transmission for the entire population. Given that bats not only fly but also migrate, this can be difficult to accomplish (Foley et al. 239). A more optimistic option is treatment. However, since the exact cause of the disease is still unknown, no treatment or cure exists. Finally, trapping bats in captivity is an option that may promote population growth, especially for species like the Virginia big-eared bat that were already endangered before the outbreak of WNS (Zimmerman). Nevertheless, none of these possible solutions relate to the habitats of bats.

Given bats’ presence in the urban world, the most effective solution for short-term reduction in the spread of WNS is the creation of artificial habitats. In general, these artificial caves provide a sterile environment where bats can hibernate without risk of infection. The caves can be warmed to keep bats from freezing to death and sanitized every spring, after the hibernation season, to ensure that the fungus cannot take hold in the population. It takes about three years for a cave to reach mass mortality after G. destructans enters the environment (Gorman).

The best artificial caves mimic nature. The first and only artificial cave so far, a Nature Conservancy project led by Cory Holliday, was built in Clarksville, Tennessee, near the natural Bellamy Cave. According to Holliday, it is a “concrete box…almost as long as a basketball court, but only half as wide” with a textured ceiling that bats can hang from (LaCapra). Pop Science reported that the building materials were simply concrete culverts typical in highway construction (Boyle).

In an interview for the Nature Conservancy, Cory Holliday said that the ideal cave has multiple entrances and levels to recreate a natural cave’s many layers. NPR reported on September 20, 2012 that the cost of the cave was $300,000. Species that could benefit include the gray bat, Indiana bat, and Eastern small-footed bat. Holliday estimates that the initial population of the cave colony will number in the hundreds but could reach up to 200,000. Not all of those bats will necessarily survive: although the cave will be safe from infection, individuals could still become infected outside. But the cave will undoubtedly save tens of thousands of bats.

Therefore, cities across the country should start to invest in these caves. They will have to be built in places like Clarksville: small cities close to both metropolitan areas and woodland. That way, the artificial caves will attract both bats drawn to infected natural caves and bats drawn to cities.

The caves will be most necessary in the Northeast, where the disease is concentrated. This makes sense given that G. destructans flourishes in the cold. Abigail R. Flory et al. found that “WNS mortality is more likely to occur in landscapes that are higher in elevation…drier and colder during winter, and more seasonally variable” (1365). This points to a continual spread of the disease through the drier, colder Northeast. However, other regions are not immune. According to Jeremy Coleman of the US Fish and Wildlife Service, quoted in an April 2012 NPR article, WNS has crossed the Mississippi River and is likely to spread to the South and Midwest, especially now that is has been discovered in Alabama. The entire Eastern half of the United States harbors the disease, and the South will no longer be a safe haven.

To extrapolate from the Clarksville numbers, if these caves are constructed in the outskirts of just 24 Eastern cities, millions and millions of bats could find disease-free sanctuary. Making the Clarksville plan happen on a national scale would certainly be cost-effective, given the billions that the agricultural industry stands to lose from bats’ extinction. And it provides the best possible bulwark against WNS.

If I had access to a database of bat caves across the country, I would use it to locate potential sites for artificial caves in the Eastern U.S., especially the Northeast. While there are substantial cave systems in New York, Pennsylvania, North Carolina, Tennessee, and Virginia, it is unclear whether such caves are used by bats or, instead, too heavily frequented by tourists to be useful in conservation efforts.

Although I lack the resources to compile a list of new locations for artificial caves, it seems likely that BCI, the Nature Conservancy, or a similar group does have access to a list of American bat caves. I have established the criteria for a good location and shown how the Clarksville cave can be effective. With this in mind, many more artificial caves can be constructed. Though I am unable to formulate a more specific plan for the future, this is an issue of expertise rather than feasibility. To make progress in fighting the spread of WNS, artificial caves must be part of the solution.

Conclusion

White nose syndrome remains a powerful threat against the long-term survival of American bats. Since we cannot afford their loss, and cannot cure the disease, we have to find ways to prevent it. Building artificial caves can work by providing a stable, temperature-controlled microhabitat for bats: an environment free from natural predators and regularly inspected by humans to clear it of the fungus. The disease is so new that artificial caves have just recently emerged as an option, and only one has been constructed. A full picture of its advantages and disadvantages has yet to emerge, but it seems able to attract a significant colony of at least 10,000 bats. If the cave is successful, it will serve as a model for the rest of the nation to reproduce. More importantly, it will provide a safe haven for critically endangered species, give them greater chances of survival, and put off ecological collapse resulting from unchecked disease.

Urbanization has moved people closer to the natural world and reduced bats’ habitats, their potential refuge from infection, but ironically, cities can also provide safe homes for bats that are better for them than those in nature. Also, cities with trees continue to draw bats. Bats are adept at blending into the urban world, so we must blend artifice with nature to create artificial sanctuaries for them. We must acknowledge the reality of urbanization and use it for the good of our collective ecology.